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Bond Interface Design for Single Lap Joints using Polymeric Additive Manufacturing
Abstract
In this paper, the use of polymer additive manufacturing technology, also called 3D printing, for imparting texture to bond regions in adhesively bonded joints is explored. An improvement in the apparent shear strength values of adhesively bonded single lap joints is achieved by fusing structural reinforcements to the adherents through fused deposition modeling (FDM) additive technique. Towards that, computational models were first developed to simulate stress distribution along the overlap region of single lap shear joints, and four models that performed the best were chosen for physical testing. Pure adhesive (PA) joints were manufactured first, followed by the fabrication of 3D-printed adhesive (3D-PA) joints. Peak loads, shear stresses, and failure types were compared between these models. PA joints failed mainly adhesively, resulting in low peak loads and shear strength, whereas, 3D-PA joints registered higher average peak loads and shear strengths (increased by up to 832 %) with predominantly cohesive failure. 3D printed reinforcements appear to have imparted higher shear resistance against failure at the bond regions. Overall, using a combined computational and experimental approach, it is established that the 3D printed reinforcements have the potential to drastically improve the apparent shear strength of adhesively bonded single lap joints.
... History of bonding and adhesives. [5][6][7][8][9][10][11][12][13] bending stiffness delays damage but does not cause failure. The joint injury's progression determines the eventual load. ...
... Because of real-time applications, the various failure mechanisms are illustrated in Figure 8, which were obtained under shear loading in single-lap joints by previous researchers. 13 Adhesive failure was a failure of the interfacial bond between the adhesive and the adherend. Cohesive failure is the term used to describe a fracture that permits an adhesive layer to remain on both surfaces. ...
... A 3D-printed polymer pin was used in this method, and it was embedded in the adhesive along a transverse direction to the adherend. Garcia et al. 13 have prepared the FRP composites single lap joint by inserting 3D-printed adhesive interface reinforcement using pure adhesive material to improve average peak loads and shear strengths. The laminates were made of carbon fibre, an adhesive LOCTITE Hysol EÀ120HP epoxy, and 3D-printed reinforcements using the ABS-M30 polymer. ...
... [148,149] The free shape of the AM substrate allows the creation of various complex and simple structured surface textures to study the influence of surface texture on the strength of bonded joints. [148][149][150][151][152][153] Despite the strong development of the AM process, the interactions between the structured surface texture of AM parts and structural adhesives have not yet been studied in depth. ...
... However, the depth had little effect on the shear strength of structured surfaces. Similarly, Garcia and Prabhakar [152] developed a new methodology by 3D printing (FDM) trapezoidal texture reinforcement over the carbon-fibre substrate, as illustrated in Figure 44. They reported that the surface pattern modified the stress distribution in the bonded region, which improved the shear strength and the absorbed energy of adhesively bonded joints. ...
... PA (Epoxy/microspheres): bonded FRPC substrates with mass epoxy/microsphere ratio and without texturing. [152] . that the tube texture increased the contact area, allowed to manually adjust the adhesive thickness and created mechanical keying, which significantly improved the tensile shear strength. ...
Surface treatment before adhesive bonding is vital for improving both strength and durability of adhesively bonded joints by modifying surface characteristics. This article reviews the effect of surface texture on the strength of adhesive-bonded joints. It starts with a presentation of different adhesion mechanisms. Afterwards, the surface texture is classified into stochastic and structured surfaces, the effect of these textures on the wettability is then discussed. The influence of surface texture on quasi-static strength and fatigue behaviour of adhesively bonded joints is reviewed with a focus on the effect of structured surface parameters. This paper provides also an overview of the manufacturing process of structured surface texture for adhesive bonding applications. Finally, future trends in this research direction are highlighted and fundamental conclusions are drawn.
... Those two intensity levels were significantly decreased with 120 min irradiation time, as shown in Figure 8. The continued decomposition of the PA6 matrix on the surface deteriorates the mechanical properties of the CFRTP itself [39]. The damaged CFRTP surfaces are easily delaminated or fail, and consequently, the joint shear strength is also reduced when the irradiation time is longer than 120 min. ...
... Those two intensity levels were significantly decreased with 120 irradiation time, as shown in Figure 8. The continued decomposition of the PA6 matri the surface deteriorates the mechanical properties of the CFRTP itself [39]. The dama CFRTP surfaces are easily delaminated or fail, and consequently, the joint shear stren is also reduced when the irradiation time is longer than 120 min. ...
Adhesive bonding is a suitable joining method to satisfy the increasing industrial demand for carbon fiber-reinforced polymers without the need for a machining process. However, thermoplastic-based carbon fiber-reinforced polymers have small adhesive strength with structural thermoset adhesives. In this study, an ultraviolet irradiation surface treatment was developed to improve the adhesive bonding strength for polyamide-based carbon fiber-reinforced polymer. The type of ultraviolet wavelength, irradiation distance and irradiation time were optimized. Surface treatment with simultaneous UV irradiation of 185 nm and 254 nm wavelength generated unbound N-H stretching that was capable of chemical bonding with epoxy adhesives through a photo-scission reaction of the amide bond of polyamide matrix. Therefore, ultraviolet irradiation treatment improved the wettability and functional groups of the polyamide-based carbon fiber-reinforced polymers for adhesive bonding. As a result, the adhesive strength of the polyamide-based carbon fiber-reinforced polymers was increased by more than 230%.
... However, the mechanical performance of adhesive joints in 3D-printed parts can raise concerns. The intrinsic variability in material properties and surface roughness, attributed to the nature of 3D printing, can culminate in diminished bond strength [10], [13]- [15]. Therefore, strategies to enhance the mechanical performance of adhesive joints within 3D-printed components garner importance, proving the reliability and longevity of the final product. ...
... Garcia & Prabhakar [10] used FDM to modify the joint surface of carbon fibre composite adherends with layers of ABS-M30. They altered the bonded interface 20 VOLUME 34 (YEAR XXXIV) 2023 geometry by creating different patterns and tested the peak loads, shear stress, and failure types of each specimen. ...
The use of additive manufacturing (AM) has revolutionized the production of polymer-based materials, offering a wide range of design possibilities and geometric complexity. However, due to the limitations of 3D printers to produce large parts, the parts often must be printed in several separate components and further joined together to obtain the final 3D-printed part. 3D printing can be used to produce only the most complex parts, which can be further combined with simple, non-printed parts from other materials to make the final product. One way to join 3D-printed part is an adhesive-bonded method. This paper focuses on the recent advances in adhesive bonding techniques for 3D-printed parts and explores various methods to enhance their mechanical performance. The benefits and limitations of each technique were discussed, and highlighted promising paths for future research. Finally, this paper provides a comprehensive overview of the current strategies to improve the mechanical performance of adhesive joints with AM-based adherents, offering guidance for the design and fabrication of high-performance structures in a range of applications. It was concluded that the configuration of the bonding area represents an essential parameter that directly influences the bonding strength and overall structural integrity of AM adhesive joints, and that the implementation of customized joint geometries can lead to a substantial enhancement in the joint strength of 3D-printed parts. The incorporation of reinforcing materials, optimization of the printing parameters of adherents, pre and post-treatment methods show potential in enhancing the bonding strength of the 3D-printed joints. The synergistic integration of these cutting-edge technologies can yield mutual advantages that complement each other, ultimately resulting in an enhanced overall performance for AM parts.
... The results revealed that the adherend and adhesive design parameters can play a quite crucial role in the mechanical behavior of the adhesively bonded 3D-printed joints. Garcia and Prabhakar [24] used a combined computational and experimental approach to examine the shear strength of adhesively bonded joints by adding fusing structural reinforcements. The interfacial adhesion of 3D printed acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) using commercially available epoxy and elastomeric bonding agents was evaluated by Delta et al. [25]. ...
... First, the adherends were designed in dimensions of 25.4 × 101.6 × 2 mm similar to Refs. [21,24] and STL files were exported by using Solidworks software [43]. Next, G-code files were generated via the 3D printing software Cura [44]. ...
... A smart designing method is always desired to minimise the damage and failure incurred by weak bond interfaces. Garcia and Prabhakar [85] implemented 3D printing technology for imparting texture to bond regions in ABJs. ...
... Images of the substrate surface with printed reinforcements for Model 1, 2, 3, and 4, respectively; (e)-(h) Digital microscopy of 3D printed substrates with visible gaps in side view of lap joint[85]. ...
... Additionally, the application of AM in joining two polymeric parts has also been extensively studied [53]. However, in these studies, both adherents and adhesives are produced in a single print job [54][55][56][57], or epoxy is used to join different parts [58,59]. When the epoxy is used, the bonding strength between adherents and adhesives can be improved by changing the geometry of the adherents (pieces being joined) [58,59] or by changing the printing parameters during AM [56,57]. ...
... However, in these studies, both adherents and adhesives are produced in a single print job [54][55][56][57], or epoxy is used to join different parts [58,59]. When the epoxy is used, the bonding strength between adherents and adhesives can be improved by changing the geometry of the adherents (pieces being joined) [58,59] or by changing the printing parameters during AM [56,57]. These factors improve the surface area and its properties, leading to a better adhesion to the epoxy. ...
Polymer-based engineering materials (plastics, polymer matrix composites, and similar) are becoming more widely used for the design and construction of consumer products and systems. While providing a host of design benefits, these materials also can have a large detrimental effect on the environment when not handled properly. One of the best ways to increase the sustainability of systems created using these materials is to extend their operating life as much as possible. Additive manufacturing (AM) technologies offer a powerful tool for this, as they allow easy repair of damaged or worn components in an automated or semi-automated way. This article explores the use of the fused filament fabrication (FFF) process as a tool for repairing high-value (i.e., difficult or expensive to replace) thermoplastic parts. The major design opportunities and restrictions are presented, as well as an evaluation of the types of repair jobs for which this process could be suitable and effective. Advice and ideas for future implementations and improvements are provided as well. A detailed case study is presented, where cracked ABS bars were repaired using FFF-deposited patches while varying the print parameters using a factorial designed experiment. The repaired bars were tested against the baseline and in most cases were found to be as good as or better than the original bars under a bending load. This case study demonstrates the concepts and explores how this repair approach could be realistically employed in practice.
... The lap shear joint performance can also be enhanced by introducing foreign material into 69 the adhesive or adherend surface [1,[15][16][17][18][19][20] found that hybrid CFRP/stainless steel wire mesh composite produced higher initial stiffness, 82 tensile strength, and ultimate strain than pure CFRP. Enhanced interlocking between steel wire 83 and carbon fibre was observed, which limited the crack propagation and increased the failure 84 strain. ...
... Secondly, the metal mesh acts as a stress reliever and effectively enhances the bonding strength. This type of mechanism was before reported by Garcia et al.[20], who introduced 3D printed structural reinforcement made of polymer material into the lap shear joint. Their polymer reinforcements lowered the peak stress near the bonding boundary and imparted higher shear resistance to the bond regions. ...
Effects of surface modifications on the adhesive joint of carbon fibre reinforced polymer (CFRP) were investigated. CFRP surfaces were treated with traditional methods, such as acetone cleaning, sanding, grit blasting and peel ply. As a novel type of surface modification, stainless steel 316 wire mesh was co-cured on the CFRP laminate during the manufacturing stage. The surface topography of CFRP adherends was analysed through microscopic imaging. Surface roughness values were measured using a surface roughness tester. Contact angle measurements of probe liquids were performed to calculate surface energy. All adherends were bonded with a low viscosity epoxy adhesive. The single lap shear tests were used to measure the bonding strength of the CFRP joints. The experimental results showed that the highest average shear strength (24.2 MPa) was achieved for metal mesh modified joints. This amounted to a 101.7% increase compared with acetone-cleaned specimens. There was no statistically significant difference in shear strength among joints subjected to traditional surface treatments. Fracture surface images were analysed and correlation between surface treatment and lap shear strength was critically discussed.
... When the displacement exceeds 2.5 mm, the specimen bends sufficiently so that the grips align, and thereafter, the load-displacement curve becomes nearly linear. Such nonlinearity has also been reported in existing studies [15][16][17] for single lap shear tests. The load drop to zero occurs immediately after failure. ...
... Figure 9 presents the calculated shear strengths for all specimens. The magnitudes of these calculated values, as well as for the energy absorption of the adhesive joints (Fig. 10), are very close to what has been reported in the literature [15]. The shear strengths of the four specimens presented in Figure 9 do not show a clear correlation with the lightning strike current levels. ...
Adhesive bonding to join fiber reinforced polymer matrix composites holds great promise to replace conventional mechanical attachment techniques for joining composite components. Understanding the behavior of these adhesive joints when subjected to various environmental loads, such as lightning strike, represents an important concern in the safe design of adhesively bonded composite aircraft and spacecraft structures. In the current work, simulated lightning strike tests are performed at four elevated discharge impulse current levels (71.4, 100.2, 141, and 217.8 kA) to evaluate the effects of lightning strike on the mechanical behavior of single lap joints. After documentation of the visually observed lightning strike induced damage, single lap shear tests are conducted to determine the residual bond strength. Post-test visual observation and cross-sectional microscopy are conducted to document the failure modes of the adhesive region. Although the current work was performed on a limited number of specimens, it identified important trends and directions for future more comprehensive studies on lightning strike effects in adhesively bonded composites. It is found that the lightning strike induced damage (extent of the surface vaporization area and the delamination depth) increases as the lightning current increases. The stiffness of the adhesive joints and shear bond strength did not show a clear correlation with the lightning current levels, which could be due to many competing factors, including the temperature rise caused by the lightning strike and the surface conditions of the adherends prior to bonding. The failure modes of the adhesive regions for all specimens demonstrate a mixed mode of adhesive and cohesive failure, which may be due to inconsistent surface characteristics of the adherends before bonding. The energy absorbed during the lap shear tests generally increases as the lightning current increases.
... These findings underscore the importance of tailoring adherend geometry to optimize stress distribution and bonding efficiency. Garcia et al. 12 utilized 3D printing to introduce textured surfaces on bonded joints, achieving an average strength increase of up to 832% compared to unmodified joints. Finally, Khosravani et al. 13 identified an optimal adhesive thickness of 0.2 mm for PLA adherends, which maximized joint strength compared to other thicknesses. ...
The scope of 3D printing is limited by its maximum printing area, necessitating
joints for assembling larger structural elements. Natural fibers have been
employed to reinforce printed materials, enhance their mechanical properties,
and reduce polymer usage. However, the effects of these fibers on bonded
joints, particularly in the context of continuous natural yarns, remain underexplored
in the literature. This study investigates the mechanical behavior of
3D-printed single-lap joints (SLJ) with biocomposite adherends, using Fused
Filament Fabrication (FFF). Continuous Jute Fiber Reinforced Polymer
(JFRP) and Polylactic Acid (PLA) were used to fabricate the adherends.
Mechanical characterization, including surface roughness analysis and singlelap
shear tests, was performed on PLA-PLA, JFRP-JFRP, JFRP-steel, and
JFRP-wood joints. Results show that the addition of continuous jute fibers in
mono-material joints increased the failure load by 66.53% compared to neat
PLA-PLA joints, due to a 47.20% increase in surface roughness. Jute Fiber
Reinforced Polymer-wood joints demonstrated the best performance, achieving
a failure load of 2543.76N, 56.85% higher than JFRP-JFRP joints, indicating
their potential for mixed-material, sustainable structures. Analytical models
were applied to assess the load distribution along the adhesive.
... The insert was made of thermoplastic (polyamide-6) with a wavy microstructure 0.8 mm thick using an additive manufacturing (AM) technique, i.e., a 3D printer (BCN3D Sigma). AM technique has been increasingly used to fabricate a complex part [29] for enhancing joint strength [30,31], toughness [32], and fatigue response [33]. We additive manufactured the insert and weft separately and manually weaved them to provide a 'wavy' microstructure; see the details in Ref. [12]. ...
... In the literature, friction stir welding [9][10][11] and adhesive bonding applications [12][13][14][15][16] are frequently reported for joining plastics produced using 3D printers. However, joining multi-material parts has not received sufficient attention from researchers. ...
In the industry sector, it is very common to have different types of dissimilar materials on the same construction rather than products made from a single type of material. Traditional methods (welding, mechanical fastening, and adhesive bonding) and hybrid techniques (friction stir welding, weld bonding, and laser welding) are used in the assembly or joining of these materials. However, while joining similar types of materials is relatively easy, the process becomes more challenging when joining dissimilar materials due to the structure and properties of the materials involved. In recent years, additive manufacturing and 3D printing have revolutionized the manufacturing landscape and have provided great opportunities for the production of polymer-based multi-materials. However, developments in the joining of multi-material parts are limited, and their limits are not yet clear. This study focuses on the joining of 3D-printed products made from PLA-based multiple materials (PLA and PLA Wood) using friction stir welding. Single-material and multi-material parts (with 100% infill ratio and three different combinations of 50% PLA/50% PLA Wood) were welded at a feed rate of 20 mm/min and three different tool rotational speeds (1750, 2000, and 2250 rpm). Tensile and bending tests were conducted on the welded samples, and temperature measurements were taken. The fractured surfaces of the samples were examined to perform a damage analysis. It is determined that the weld strength of multi-materials changes depending on the combination of the material (material design). For multi-materials, a welding efficiency of 74.3% was achieved for tensile strength and 142.68% for bending load.
... Athan et al. 27 found that increasing the loading rate of tensile and flexural has improved the performance of 3D-printed adhesive joints. Garcia et al. 28 indicated that the use of 3D-printed reinforcements in the bonding area significantly increased joint strength by providing higher shear resistance. Öztürk et al. 29 found that 3D-printed lap joints using polycarbonate with a 0 orientation and a 25.4 mm overlap length demonstrated higher load resistance compared to other combinations. ...
Adhesively bonded joints play a vital role in improving the structural performance of 3D‐printed components. This research aims to examine the effect of graphene inclusion on the failure load and vibrational behavior of polylactic acid flat‐joggle‐flat (FJF) joints prepared using fused deposition modeling. The present research focused on the effect of print directions (0°, 45°, 90°) and the inclusion of graphene nanofiller (0.25, 0.50, 0.75, and 1.00 wt%) on the performance of FJF joints. The effect of raster direction on mechanical properties was examined by tensile testing of dog‐bone samples. Results showed that 0° print orientation had higher tensile strength compared to other printing directions. Shear testing of FJF joints indicated that the inclusion of graphene has enhanced the strength of 3D‐printed FJF joints by 61.18%. Fractography results showed that the formation of the shear band with the inclusion of 0.50 wt% graphene helps to distribute the stress more evenly and prevent catastrophic failure of the FJF joint. The free vibrational test revealed that the inclusion of 0.50 wt% graphene had improved the natural frequencies, as the presence of graphene‐enhanced the interfacial bonding between FJF adherend and adhesive.
Highlights
0° print orientation had higher tensile strength than other printing directions.
Inclusion of graphene‐enhanced the shear strength of flat‐joggle‐flat (FJF) joints by 61.18%.
Shear band formation delayed the failure of graphene‐reinforced FJF joints.
FJF reinforced with 0.50 wt% graphene had adherend failure.
FJF joint added with 1.0 wt% graphene had lower natural frequencies.
... The failure mode of the SLJ significantly impacts the loadcarrying capacity and behavior of the joint. In the literature, damage modes in SLJ parts have been studied as an indication of the structural behavior of SLJs (Garcia and Prabhakar, 2017;Öz and Özer, 2017;Singh et al., 2022). Figure 11 represents the damage modes seen in this study; 14 different groups of SLJs were subjected to the tensile test. ...
Purpose
Adhesive bonding is critical to the effectiveness and structural integrity of 3D printed components. The purpose of this study is to investigate the effect of joint configuration on failure loads to improve the design and performance of single lap joints (SLJs) in 3D printed parts.
Design/methodology/approach
In this study, adherends were fabricated using material extrusion 3D printing technology with polyethylene terephthalate glycol (PETG). A toughened methacrylate adhesive was chosen to bond the SLJs after adherend printing. In this study, response surface methodology (RSM) was used to examine the effect of the independent variables of failure load, manufacturing time and mass on the dependent variable of joint configuration; adherend thickness (3.2, 4.0, 4.8, 5.6, 6.4, and 7.2 mm) and overlap lengths (12.7, 25.4, 38.1, and 50.8 mm) of 3D printed PETG SLJs.
Findings
The strength of the joints improved significantly with the increase in overlap length and adherend thickness, although the relationship was not linear. The maximum failure load occurred with a thickness of 7.2 mm and an overlap of 50.8 mm, whilst the minimum failure load was determined with a thickness of 3.2 mm and an overlap of 12.7 mm. The RSM findings show that the optimum failure load was achieved with an adherend thickness of 3.6 mm and an overlap length of 37.9 mm for SLJ.
Originality/value
This study provides insight into the optimum failure load for 3D printed SLJs, reducing SLJ production time and mass, producing lightweight structures due to the nature of 3D printing, and increasing the use of these parts in load-bearing applications.
... As a result of the average of the measurements, the thickness of the composite sample is 2.78 mm, while the thickness of the aluminum sample is 3.15mm. As a result of the experiment, it was found that the maximum failure load that the adhesive could withstand was 10.75 kN, and the maximum stress it reached was 16.5MPa as shown in Fig. 16a. Furthermore, Figure 16b shows that the fiber reinforcement of the composite sticks in the fractured region. ...
... It was noted that the polyurethane performs better than epoxy following the joint deformation during testing; this prevents the substrate from delamination and reduces stress concentration. Garcia et al. [14] worked on the bond interface design for adhesively bonded single-lap joints fabricated using the additively manufacturing technique. Improvements in the shear strength of adhesively bonded lap joints were noticed for the samples fabricated by fusing structural reinforcements to the adherents through the FDM technique. ...
This study focuses on evaluating the fatigue life performance of 3D-printed polymer composites produced through the fused deposition modelling (FDM) technique. Fatigue life assessment is essential in designing components for industries like aerospace, medical, and automotive, as it provides an estimate of the component’s safe service life during operation. While there is a lack of detailed research on the fatigue behaviour of 3D-printed polymer composites, this paper aims to fill that gap. Fatigue tests were conducted on the 3D-printed polymer composites under various loading conditions, and static (tensile) tests were performed to determine their ultimate tensile strength. The fatigue testing load ranged from 80% to 98% of the total static load. The results showed that the fatigue life of the pressed samples using a platen press was significantly better than that of the non-pressed samples. Samples subjected to fatigue testing at 80% of the ultimate tensile strength (UTS) did not experience failure even after 1 million cycles, while samples tested at 90% of UTS failed after 50,000 cycles, with the failure being characterized as splitting and clamp area failure. This study also included a lap shear analysis of the 3D-printed samples, comparing those that were bonded using a two-part Araldite glue to those that were fabricated as a single piece using the Markforged Mark Two 3D printer. In summary, this study sheds light on the fatigue life performance of 3D-printed polymer composites fabricated using the FDM technique. The results suggest that the use of post-printing platen press improved the fatigue life of 3D-printed samples, and that single printed samples have better strength of about 265 MPa than adhesively bonded samples in which the strength was 56 MPa.
... The research discovered that the edgewise orientation had the maximum bonding strength in lower layer thicknesses, but the flatwise orientation had the highest bonding strength in higher layer thicknesses. Garcia and Prabhakar (2017) used the polymer AM technology to impart texture to bond regions in adhesively bonded joints. By fusing structural reinforcements to adherends, the researchers enhanced the shear strength of adhesively bonded SLJs. ...
Purpose
Adhesively bonded joints are used in many fields, especially in the automotive, marine, aviation, defense and outdoor industries. Adhesive bonding offers advantages over traditional mechanical methods, including the ability to join diverse materials, even load distribution and efficient thermal-electrical insulation. This study aims to investigate the mechanical properties of adhesively bonded joints, focusing on adherends produced with auxetic and flat surfaces adhered with varying adhesive thicknesses.
Design/methodology/approach
The research uses three-dimensional (3D)-printed materials, polyethylene terephthalate glycol and polylactic acid, and two adhesive types with ductile and brittle properties for single lap joints, analyzing their mechanical performance through tensile testing. The adhesion region of one of these adherends was formed with a flat surface and the other with an auxetic surface. Adhesively bonded joints were produced with 0.2, 0.3 and 0.4 mm bonding thickness.
Findings
Results reveal that auxetic adherends exhibit higher strength compared to flat surfaces. Interestingly, the strength of ductile adhesives in auxetic bonded joints increases with adhesive thickness, while brittle adhesive strength decreases with thicker auxetic bonds. Moreover, the auxetic structure displays reduced elongation under comparable force.
Originality/value
The findings emphasize the intricate interplay between adhesive type, bonded surface configuration of adherend and bonding thickness, crucial for understanding the mechanical behavior of adhesively bonded joints in the context of 3D-printed materials.
... We chose ABS material because it is inexpensive and one of the most studied and used FFF/FDM materials combined with adhesives (Espalin et al., 2010;Arenas et al., 2012;Garcia and Prabhakar, 2017;Xu et al., 2018;Spaggiari and Denti, 2019;Kariž et al., 2021); therefore, sufficient information is available to contrast the results. ...
Purpose
Additive manufacturing has disadvantages, such as the maximum part size being limited by the machine’s working volume. Therefore, if a part more considerable than the working volume is required, the part is produced in parts and joined together. Among the many methods of joining thermoplastic parts, adhesives and mechanical interlocking are considered. This study aims to characterize and optimize mechanically stressed adhesive joints combined with female and male mechanical interlocking on acrylonitrile butadiene styrene (ABS) specimens made with fused filament fabrication (FFF) so that the joint strength is as close as possible to the strength of the base material.
Design/methodology/approach
This study characterized the subject’s state of the art to justify the decisions regarding the experimental design planned in this research. Subsequently, this study designed, executed and analyzed the experiment using a statistical analysis of variance. The output variables were yield strength and tensile strength. The input variables were two different cyanoacrylate adhesives, two different types of mechanical interlock (truncated pyramid and cylindrical pin) and the dimensions of each type of mechanical interlock. This study used simple and factorial experiments to select the best adhesive and interlocking to be optimized using the response surface and the steep ascent method.
Findings
The two adhesives have no statistical difference, but they show different data dispersion. The design or yield stress was a determining factor for selecting the optimal specimen, with cylindrical geometry exhibiting higher resistance at initial failure. Geometry type is crucial due to the presence of stress concentrators. The cylindrical geometry with fewer stress concentrators demonstrated better tensile strength. Ultimately, the specimen with a mechanically reinforced joint featuring a cylindrical pin of radius 5.45 mm and height of 4.6 mm exhibited the maximum tensile and yield strength.
Originality/value
Previous research suggests that a research opportunity is the combination of bonding methods in FFF or fused deposition modeling, which is not a frequent topic, and this research to enrich that topic combines the adhesive with mechanically interlocked joints and studies it experimentally for FFF materials, to provide unpublished information of the performance of the adhesive joint with mechanical interlocking, to designers and manufacturers of this technology.
... Manufacturing micro-scale structures on adherend surfaces is usually an effective way to improve bonding strength. Garcia et al. [8] created submicronscale structural reinforcements on the adherend surface through fused deposition modeling and claimed that the apparent shear strength values of adhesively bonded single-lap joints could be significantly improved. Feng et al. [9] manufactured dimple, groove, and grid patterns on a steel substrate by a nanosecond fiber laser and examined the effect of micron-scale patterns on bonding strength. ...
... Single-lap joints are one of the most widely used geometries due to the simplicity of fabrication [23,24]. Based on the literature search, it is understood that single-lap joints have been investigated in different materials, but there is a lack of research on the failure modes of single-lap joints bolted and bolted/bonded of polymeric plates. ...
In this study, the joint strengths of single-lap bolted and bolted/bonded (hybrid) joints formed by using four different engineering plastics were experimentally investigated. High-density polyethylene (HDPE), ultra-high molecular weight polyethylene, Delrin (POM), and Teflon were used as plate materials in single-lap connections. Standard M6 bolts were used in bolt connections. The specimens were prepared as single bolted, double bolted, single bolted/bonded, and double bolted/bonded in 20, 40, and 60 mm single-lap lengths. Weicon company’s RK-7100 two-component adhesive was used as the adhesive. Tensile tests were carried out with the displacement control of 2 mm/min. After the tensile tests, load–extension graphs were created for each connection type, and the strengths of the connections were compared with each other. Three parameters were used to evaluate the strength of the additional lap joints. These are effect of the bolt numbers, effect of the adhesive, and effect of single-lap length. Depending on the plate material, double-bolt connections performed 20–56% better than single-bolt connections. The adhesive had no effect on ultimate joint strength. As the overlap length increased, an increase was generally observed in the joint strength of the specimens. Depending on the overlap length increase from 20 to 60 mm, the strength of the single-bolt configurations of HDPE-B specimens was found to be approximately two times that of the best results. When polymeric plates are compared among themselves, double-bolted Delrin (POM) specimens exhibited the highest joint strength in all single-lap lengths.
... However, the shear stress/strain fields of this test were impossible to verify. Garcia and Prabhakar [19] and Kuncius et al. [21] employed a lap-joint shear test, which is often used in composite laminate tests. Although it is easy to operate, its shear stress is largely nonuniform, and its alignment often becomes a problem. ...
Shear strength measurement becomes increasingly important because three-dimensional (3D) printing materials are used in load-bearing structures subjected to a combined normal and shear stress state. Hence, this paper presents a combined experimental and numerical investigation of the interlayer shear strength measurement approach, and its application to four kinds of 3D printing polymers including acrylonitrile butadiene styrene (ABS), polycarbonate (PC), and polylactic acid (PLA) made with fused deposition modeling (FDM), and polyamide 12 (PA12) made with selective laser sintering (SLS). First, a traditional Iosipescu shear specimen was employed to validate the uniform shear strain field using digital image correlation. Second, a new necking-shaped shear specimen was proposed to measure the shear strength efficiently with the aid of an effective alignment assistant beam. Third, 3D finite element analysis was conducted to highlight the stress comparisons of the Iosipescu shear specimen and the necking-shaped shear specimen. In order to quantify the anisotropic strengths, three kinds of shear specimens with different build directions were designed and tested. The results demonstrated that the minimum shear strength of a 3D printing polymer specimen was the interlayer shear strength when the shear force was acting along the printing surface. Our measurement was consistent with the shear strength measurements of the same type of 3D printing PA reported by other researchers. Moreover, our measurement was more conservative and accurate due to the pure shear stress state of all specimens.
... Examining the studies in the literature reveals that various designs and techniques are used to modify the adhesive thickness. Some methods for regulating adhesive thickness [1][2][3][4] include incorporating micro glass beads, and applying wires, tape or pressure. ...
... The free shape of the 3D-printed parts allows the manufacturing of various simple and complex structured surfaces to investigate the effect of surface texturing on the resistance of bonded joints. [22][23][24][25] Despite the strong development of the AM process, the relationship between structural adhesives and structured surface texturing of AM components has not yet been fully understood. Furthermore, the intelligent combination of adhesive bonding and AM technology can be very useful for overcoming one of the major limitations of AM (the limited bed size of AM machines), improving the joint strength by exploiting the capacity of the AM to tailor a suitable surface texture of a part, and manufacturing parts with structured surfaces in one step. ...
Surface preparation before adhesive bonding is crucial to improve the resistance and durability of the joint by altering the surface properties of the adherend. The purpose of surface treatment is to clean the surface from contaminants, activate the adherend surface and create an optimal surface structure to promote adhesion mechanisms. In that context, this work aims to investigate the influence of substrate surface texturing on the resistance of adhesive joints. Two bio-inspired surface textures were investigated, Fish scale (FS) and Tree frog (TF). Polycarbonate (PC) specimens with different surface patterns were manufactured using the fused deposition modelling process. Surface morphology, such as pattern dimension (shape and depth), surface roughness (Ra), and wettability, were used to characterise the substrates. The influence of these texture patterns on the shear strength of adhesively bonded joints was evaluated through the standardised block shear test method ASTM D4501-01. Moreover, the shear strength of the structured joints was compared to the results from bonding with polished surfaces (surfaces abraded with 80, 600 and 1000 grit paper), and with as-printed surfaces. The results revealed that the FS and TF surface textures enhanced the shear strength by 242% and 283% compared to the adhesive joints with polished surfaces. It was also shown that the variation in depth of the bio-inspired surface texture has no significant impact on the joint strength. Failure analysis demonstrated that the fracture mode of bonded joints with polished surfaces was the adhesive failure while mixed failure (cohesive and adhesive) characterises the as-printed, TF and FS surfaces. Worthy results are obtained rising the effectiveness of surface texture for the PC's bonded joints.
Graphical Abstract [Formula: see text] This is a graphical representation of the abstract.
... Of course, the actual shear failure process in this study was extremely complicated; so, our purpose was to promote immediate interest from interdisciplinary researchers. Specifically, not many studies have focused on the shear failure of 3D printing polymers [11][12][13]. Our future work will be focused on the shear crack propagation of the same PA12 material, but the specimens will be made with SLS and FDM. ...
Because additively manufactured materials are increasingly being used in load-bearing structures, strength research has become critical. Surprisingly, numerous studies have reported the tensile strength measurements, but only a few studies have presented meaningful results for the shear strength measurements of additively manufactured polymers. Hence, this paper proposes a combined experimental and numerical investigation of a new interlayer shear strength measurement approach, and it targeted the applications of the same polyamide (PA12) specimens made with fused deposition modeling (FDM) and selective laser sintering (SLS). A necking-shaped shear specimen was developed to measure the pure shear strengths with the aid of a three-dimensional (3D) finite element analysis. The results showed that the specimens made with FDM and SLS exhibited totally different shear failure behaviors. The ultimate shear strength of the FDM-PA specimens had more than a 32% increase over that of the SLS-PA specimens. An interface mechanics assumption was employed to explore the different shear failure mechanisms with the support of a fractography analysis.
... Ayrıca, vida-civata-somun bağlantılarında termal bir gereksinim duyulmaz [13]. Bu bağlantıların en büyük dezavanjı delikler sebebiyle gerilme yığılmalarına yol açmalarıdır [9,14,15] 2. Tiwary, V.K., P., A. and Malik, V.R., "An overview on joining/welding as post-processing ...
Üç boyutlu (3B) yazıcı teknolojisi, günümüzde sıklıkla tercih edilmeye başlayan, önemli ve popüler teknolojidir. Bu teknoloji gelecekte üretimin farklı alanlarında kullanılabilir olması ile tasarımdaki kısıtlılıklar tamamen ortadan kalkacaktır. Bununla birlikte, 3B yazıcı teknolojisi sınırlı yapı hacmine sahiptir. Bu sebeple, oluşturulan hacim parçalı tasarlanır ve bu parçalar gövdeyi oluşturmak için birbirine bağlanır. Hacimce büyük bir modelin 3B yazıcılardan çıktısını alırken bölümlendirilmiş parçaların bağlantısı çeşitli bağlantı tipleri ile yapılabilmektedir. Bu çalışmanın amacı, 3B yazıcı ile imal edilen parçalı bir üründe kullanılan bağlantı tiplerinin mukavemet açısından değerlendirmek ve en uygun bağlantı tipini belirlemektir. Bu çalışmada, parçaları birbirine bağlamak için dört farklı bağlantı tipi oluşturulmuştur. Bu bağlantı tiplerinin mukavemetini değerlendirmek için standart çekme numunesi tasarımı yapılmış ve bu tasarım ortadan ikiye ayrılarak üretilmiştir. İki parça olarak üretilen çekme numunesi japon yapıştırıcısı (siyanoakrilat), pim, kaynak ve hem kaynak hem de yapıştırıcı (siyanoakrilat) ile birbirine bağlanmıştır. Çekme numunesinin parçalanmamış tek parçalı hali referans numune olarak üretilmiştir. Her grup için yedişer adet üretilen parçalar, üniversal çekme test cihazı ile çekme testine tabi tutulmuştur. Çekme testi sonunda, maksimum çekme kuvveti ve yer değiştirme değerleri elde edilmiş ve bu değerlere göre gerilme, gerinim ve elastik modülleri hesaplanmıştır. Sonuç olarak, 3B kalem kullanılarak yapılan kaynakta en yüksek gerilme ve elastik modül değerleri hesaplanmıştır. Pim ile birbirine bağlanan parçaların en düşük mukavemete sahip olduğu belirlenmiştir. Referans model ile karşılaştırıldığında, tüm bağlantı tipleri parça mukavemetinde minimum %37 azalmaya yol açmıştır. Elde edilen sonuçlara göre, mukavemeti en iyi sağlayan bağlantı tipi 3B yazıcı kalemi kullanılarak yapılan kaynak bağlantı tipidir.
... Therefore, as reported in recent technical literature (Spaggiari and Denti, 2019), combining the adhesive bonding and the AM manufacturing presents several advantages: Firstly, it exploits fully the AM device capability; secondly, it increases the dimensional range of AM applications and third, it brings the mechanical resistance of the adhesively bonded AM joint to the same level of the base polymeric material. To date, the mechanical characterization of the AM components or adhesive joints can be traced in the literature, but the interactions of AM parts bonded with structural adhesives has not been deeply investigated yet, with only partial studies about the bonding of AM plastic components being available (Garcia and Prabhakar, 2017;Kariz et al., 2017). The possibility to add mechanical interlocking is an additional feature, which improves the adhesion, with the typical substrates used in AM, either metallic or polymeric, as studied in Dugbenoo et al. (2018) for composite parts. ...
Purpose
The purpose of this paper is to evaluate and exploit the combination of additive manufacturing polymeric technology and structural adhesives. The main advantage is to expand the maximum dimension of the 3D printed parts, which is typically limited, by joining the parts with structural adhesive, without losing strength and stiffness and keeping the major asset of polymeric 3 D printing: freedom of shape of the system and low cost of parts.
Design/methodology/approach
The materials used in the paper are the following. The adhesive considered is a commercial inexpensive acrylic, quite similar to superglue, applicable with almost no surface preparation and fast curing, as time constraint is one of the key problems that affects industrial adhesive applications. The 3D printed parts were in acrylonitrile butadiene styrene (ABS), obtained with a Fortus 250mc FDM machine, from Stratasys. The work first compares flat overlap joint with joints designed to permit mechanical interlocking of the adherends and then to a monolithic component with the same geometry. Single lap, joggle lap and double lap joints are the configurations experimentally characterized following a design of experiment approach.
Findings
The results show a failure in the substrate, due to the low strength of the polymeric adherends for the first batch of typical bonded configurations, single lap, joggle lap and double lap. The central bonded area, with an increased global thickness, never does fail, and the adhesive is able to transfer the load both with and without mechanical interlocking. An additional set of scarf joints was also tested to promote adhesive failure as well as to retrieve the adhesive strength in this application. The results shows that bonding of polymeric AM parts is able to express its full potential compared with a monolithic solution even though the joint fails prematurely in the adherend due to the bending stresses and the notches present in the lap joints.
Research limitations/implications
Because of the 3D printed polymeric material adopted, the results may be generalized only when the elastic properties of the adherends and of the adhesive are similar, so it is not possible to extend the findings of the work to metallic additive manufactured components.
Practical implications
The paper shows that the adhesives are feasible way to expand the potentiality of 3 D printed equipment to obtain larger parts with equivalent mechanical properties. The paper also shows that the scarf joint, which fails in the adhesive first, can be used to extract information about the adhesive strength, useful for the designers which have to combine adhesive and additive manufactured polymeric parts.
Originality/value
To the best of the researchers’ knowledge, there are scarce quantitative information in technical literature about the performance of additive manufactured parts in combination with structural adhesives and this work provides an insight on this interesting subject. This manuscript provides a feasible way of using rapid prototyping techniques in combination with adhesive bonding to fully exploit the additive manufacturing capability and to create large and cost-effective 3 D printed parts.
... Even the studies in which end milling parameters are examined for various polymers are quite limited in the literature (Kalla et al., 2010;Karpat and Polat, 2013;Zemann, 2016). The literature on polyamide materials produced by AM is limited to the production of biocomposites and examination of their mechanical properties (Abdullah et al., 2017;Garcia and Prabhakar, 2017;Justo et al., 2018;Le Duigou et al., 2019). In this study, the surface qualities obtained by end milling PA6 produced by FDM and PA6G blocks produced by casting were investigated in various conditions. ...
Fused deposition modeling (FDM) is an additive manufacturing (AM) technique that has emerged as a suitable application in different areas, including machine design and manufacturing. The main advantages of this method over conventional methods include that it is faster and produces less material waste. Besides, AM offers computer-aided design and manufacturing but does not include any limitations on the product's geometry and does not require any extra tools. End milling is a conventional manufacturing process used for profiling, slotting, and facing. In this study, at the point of overcoming the weaknesses of AM surface quality, it was investigated whether the cast polymer's surface quality could be reached with hybrid manufacturing (AM + milling). For this reason, the parts produced by FDM were subjected to end milling, and the effect of cutting depth, feed rate, and rotation speed on surface quality and chip type were investigated. The results obtained are compared with the results of the milling operation of cast polyamide. For all results, surface quality increases with a rising feed rate. In general, the surface quality obtained by milling parts produced using FDM is low, but each manufacturing technique is affected differently by the end milling conditions. Low rotation speed and high feed rates should be preferred to obtain the desired surface quality from FDM printed polyamide parts.
Interfaces play a critical role in modern structures, where integrating multiple materials and components is essential to achieve specific functions. Enhancing the mechanical performance of these interfaces, particularly their resistance to delamination, is essential to enable extremely lightweight designs and improve energy efficiency. Improving toughness (or increasing energy dissipation during delamination) has traditionally involved modifying materials to navigate the well‐known strength‐toughness trade‐off. However, a more effective strategy involves promoting non‐local or extrinsic energy dissipation. This approach encompasses complex degradation phenomena that extend beyond the crack tip, such as long‐range bridging, crack fragmentation, and ligament formation. This work explores this innovative strategy within the arena of laminated structures, with a particular focus on fiber‐reinforced polymers. This review highlights the substantial potential for improvement by presenting various strategies, from basic principles to proof‐of‐concept applications. This approach represents a significant design direction for integrating materials and structures, especially relevant in the emerging era of additive manufacturing. However, it also comes with new challenges in predictive modeling of such mechanisms at the structural scale, and here the latest development in this direction is highlighted. Through this perspective, greater durability and performance in advanced structural applications can be achieved.
Delamination is a critical concern in laminated composites, affecting their structural integrity and overall performance. This study investigates the enhancement of Mode-I and Mode-II fracture toughness in carbon fiber/epoxy (CF/EP) composites through the incorporation of 3D-printed polyamide (PA) interlayers. Vacuum-assisted resin transfer molding was utilized to fabricate composite laminates with and without 3D-printed PA interlayers. Comprehensive testing was conducted to assess the effect of 3D-printed PA interlayers on the Mode-I and Mode-II fracture toughness, interlaminar shear strength, and flexural properties, as well as thermomechanical response using dynamic mechanical analysis. The results revealed a significant improvement in critical energy release rates for both Mode-I and Mode-II (G Ic and G IIc ), increasing by 43.5% and 81.2% respectively, compared to the reference composites. This enhancement was primarily attributed to crack bridging and plastic deformation of PA filaments in the interlaminar region. Additionally, interlaminar shear strength increased by 17.4%. While the reference composites had a glass transition temperature of 117.3 °C, the PA-reinforced composites showed a slightly higher value at 119.6 °C, with no significant change in the glass transition temperature. tanδ max values increased from 0.321 to 0.576, suggesting better energy dissipation in PA-reinforced composites. However, flexural properties were adversely affected by the increased thickness and reduced fiber volume fraction due to the introduction of 3D-printed PA interlayers, with the flexural modulus decreasing by approximately 28% and the flexural strength by around 50%. These findings offer promising opportunities to enhance the performance of CF/EP composites under specific loading scenarios, thus expanding their potential applications across diverse industries.
Fused deposition modeling is preferred to fabricate the biodegradable poly lactic acid (PLA) parts, owing to its impeccable characteristics, such as, customization, waste minimization and scalability. However, limited printing volume constraint restricts the ubiquitous applications of this technique. The current experimental investigation is focused on the employment of ultrasonic welding technique to address the printing volume challenge. The effect of infill density, type of energy directors (triangular (TED), semicircular (SCED) and cross energy directors (CED)) and different levels of welding parameters have been investigated on the mechanical and thermal behavior of welded joints. Presence of rasters and gap between them plays a pivotal role in overall heat generation at weld interface. The joint performance of 3D printed parts has also been compared with injection molded specimens of same material. All printed/molded welded specimens with CED recorded higher tensile strength than equivalent specimens with TED and SCED. Moreover, These specimens also performed better than specimens without energy directors and recorded higher tensile strength, that is, 317, 73.5, 59.7 and 42% higher for injection molded (IM), 80%, 90% and 100% infill density (IF) specimens without energy directors at lower level of welding parameters (LLWP). These specimens also exhibited higher tensile strength at optimal levels of welding parameters. Although, at medium and higher levels of welding parameters, both printed/molded specimens with CED observed comparatively more degradation of joints due to higher concentration of energy at weld interface. The dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), derivative thermogravimetry (DTG) and field emission scanning electron microscopy (FESEM) analysis have been performed to substantiate the experimental results.
The present paper is concerned with the investigation of the inelastic behaviour observed in load-unload cyclic tests performed at 50°C in single lap joints composed of a polyurethane based composite reinforced with fibreglass bonded to an ASTM A1020 steel substrate using an epoxy adhesive. The experiments presented in this research show that the inelastic behaviour of the joint is strongly dependent on the load frequency, eventually leading the structure to exhibit a progressive deformation when submitted to load-unload cyclic loading. The main goal of this study was to propose a preliminary rate-dependent mechanical model capable to describe the cyclic inelastic behaviour for an arbitrary load-unload history at low frequencies and a reasonable agreement was obtained between the experimental results and the model predictions.
Son yıllarda 3B yazıcı teknolojileri, bu teknolojilerde kullanılan baskı materyalleri ve yazılımları giderek yaygınlaşmaya başlamıştır. Üretilen parçaların boyutlarındaki sınırlılık sebebiyle 3B yazıcı ile üretilen parçaların birleştirilmesi konusunda çalışmalar yapılmaktadır. Bu çalışmalarda, diğer birleştirme yöntemlerinden daha ekonomik ve pratik olmasından dolayı yapıştırma tekniği öne çıkmaktadır. Fakat yazıcı ile üretilen parçaların düşük yüzey enerjilerine sahip olmalarından dolayı ekstra yüzey işlemleri yapılmadan birleştirilmeleri zordur. Yapıştırma işleminin etkili olabilmesi için yapıştırıcı tipi, yüzeyin hazırlanması, yapıştırma kalınlığı ve yapıştırma işlemi boyunca uygulanan basıncın optimizasyonu gereklidir. Bu çalışmada 3B yazıcı ile PLA Plus filamentten üretilen farklı doluluk oranlarındaki parçalar (%20 ve %100) JB Kwick Weld yapıştırıcı kullanılarak birleştirilmiştir. Yapıştırma bağlantılarında sıkıştırma için yaygın olarak kullanılan metal klips uygulaması ve tasarım/imalatı yapılan bir kalıp kullanılmıştır. Yapıştırma yüzeyinin hazırlanmasında mekanik aşındırma yöntemi (240 SiC ve 600 SiC zımparalama) tercih edilmiştir. Yapıştırma işlemi sonrasında bağlantı mekanik özellikleri çekme testi ile belirlenmiştir. Yapılan deneysel çalışmalar sonucunda doluluk oranının artmasıyla, parçanın mukavemet değerinde artış olduğu görülmüştür. Yüzey hazırlık işlemlerinin ve baskı/basınç tipi seçiminin bağlantı mukavemetini doğrudan etkilediği görülmüştür. En yüksek bağlantı dayanımı, iki farklı doluluk oranında da 240 SiC zımpara yüzey hazırlığı ve metal klips uygulaması kullanıldığında elde edilmiştir.
3D printing, considered as a revolutionary manufacturing process of industry 4.0 has a fundamental hurdle of the maximum physical size of parts it can print. Sectioning the CAD model and later joining/welding them can be a meaningful solution to circumvent this issue. This article explores the joining of micro-particle enhanced dissimilar 3D-printed parts fabricated from generally preferred materials (PLA/ABS) by the Friction Stir Welding (FSW) technique. The aim being 2-fold; to circumvent the bed size limitation of the commercially offered 3D printers and secondly to analyze the effect of Nylon micro-particles on the joint strength of FSWed parts. Critical parameters related to the process were identified, while their significance and mutual interactions were established and validated using DOE/ANOVA statistical tools. The reliable findings showed that adding Nylon micro-particles resulted in the joint strength reaching up to 76% in the case of PLA while it had a detrimental effect on ABS. Further, statistical results revealed that the material combination played a significant role (with a contributing factor of 95.78%) affecting the joint’s strength and its geometric properties (flatness). The revamped results when applied to assemble a Clark-Y wing having a span of 400 mm, displayed good strength as well as a metrological acceptable flatness value of 0.68 µ/m. With the proposed technique, it is anticipated that joining/welding techniques will become a more accepted method in the future, increasing the acceptability of smaller 3D printers.
Carbon fiber-reinforced polymer (CFRP) is an engineering composites with excellent performance. The adhesion strength of nickel layer on CFRP composite was enhanced by pretreatment processes, including sandblasting and activation. The surface roughness, wettability, phase and microstructure of the CRFP and the layer were determined by surface profile-meter, goniometer, X-ray diffraction and scanning electronic microscopy, respectively. The adhesion force of nickel layer on CFRP composite was estimated by 3 M tape and pull-out test. The results showed that electroless nickel layer was composed of crystalline phase with small grain size, which belonged to medium-phosphorus deposits. The sandblasting improved the surface roughness and wettability of CFRP surface and rendered hydrophobic surface hydrophilic. The surface roughness of CFRP composites after sandblasting was enhanced by about 60.2%, at the same time the adhesion strength of the layer metalized CFRP composites after sandblasting was improved by 131%. After 3 M tape test, the adhesion state of nickel-CFRP composites with and without sandblasting could be qualitatively classified as grade 5B and 1B, respectively. The good adhesion of nickel layer on CFRP composite was generated from the increase in the surface roughness of CFRP composites after sandblasting and chemical activation, resulting in hydrogen bonds and covalent bonds. The lightning strike test showed that electroless nickel layer did not provide sufficient protection for the sandblasted CFRP composite when subjected to an big impulse current of up to 40 kA current peak and 8–20 μs duration due to the high electrical resistivity.
Three-dimensional printing (3D), a vital technological pillar of industry 4.0 suffers from an important bed size limitation, wherein it cannot print any part larger than its bed size. Unfortunately, research in this domain has not kept pace with the other limitations hindering the acceptability of fused deposition modeling (FDM)-3D printers. This paper investigates the adhesive joining of dissimilar 3D-printed parts made from usually preferred materials (Acrylonitrile Butadiene Styrene (ABS), Polylactic Acid (PLA)) having different geometric joint designs (lap, scarf, stepped) employing diverse adhesives (epoxy, cyanoacrylate, polyurathane-based) subjected to different surface treatments (sanding, vapor, plasma). The aim is two-fold: to enhance the joint strength making adhesive bonding a suitable solution for complex structural application, as well as to overcome the bed size limitation of commercially available 3D printers. The individual and combined effect of the parameters, prediction, and validation for tensile strength were realized by statistical tools (DOE and ANOVA). The results revealed the significance of the process parameters in the following order: material type, joint configuration, adhesive types, and surface pre-treatments. The preferred material turned out to be ABS + ABS, with stepped configuration, subjected to plasma treatment and bonded with Loctite adhesives giving a strong improvement in terms of performance. Finally, the model summary with R2 value of 95.6% implied that the experimentation was successful and could be easily reproduced on an industrial scale helping to attain high strength-less weight components even with smaller FDM-3D printers.
Full factorial designs are conducted to identify the effects of the incorporation of microparticles of silica, Portland cement and carbon laminate wastes (carbon microfibres (CMF)), at 3, 6 and 9 wt% levels, on the mechanical performance of epoxy polymers and single carbon fibre joints at two grammage levels (200 and 600 g/m²). Particulate reinforced polymers (PRP) are characterised in tensile, compression, three-point bending and impact tests to better assess the influence of particles in the interlaminar region of hybrid composites composed of fibres and particles. The single joint test is performed to verify the presence of shear locking effect using particles between laminae. Compressive strength and modulus of PRPs increase when 3 wt% CMFs are added, revealing the most efficient level. The apparent shear strength is higher in composite joints made with 600 g/m² grammage and CMF particles, promising reinforcement mechanisms for hybrid composites.
This paper presents the results of an experimental study into single-lap joints. One part of the joint was made as a 3D printed polymer and had cylindrical tenons, while the other part was made of an aluminium flat bar having mortises whose diameter and distribution corresponded to the polymer tenons. In addition to the mechanical joint, a layer of double-sided VHB (Very High Bond) adhesive tape was also placed in the lap, thus creating a hybrid joint. In total, 80 specimens were made, which were divided into four groups: A—specimens with one tenon of different diameters, B—specimens with different number of tenons of the same diameter, C—specimens characterised by multi-stage operation and R—reference specimens, connected only by double-sided adhesive tape. The joints were subjected to uniaxial tensile tests. The force–displacement characteristics obtained and the energy required, up to the point of the failure of the joints, have been analysed in this paper. The four and six-stage joints designed can significantly increase the safety of the structures in which they will be used.
The advent of the Three-Dimensional (3D) printing technique, as an Additive Manufacturing technology, made the manufacture of complex porous scaffolds plausible in the tissue engineering field. In Fused Deposition Modeling based 3D printing, layer upon layer deposition of filaments produces voids and gaps, leading to a crack generation and loose bonding. Cohesive zone model (CZM), a fracture mechanics concept, is a promising theory to study the layers bond behavior. In this paper, a combination of experimental and computational investigations was proposed to obtain bond parameters and evaluate the effect of porosity and microstructure on these parameters. First, we considered two different designs for scaffolds beside a non-porous Bulk design. Then, we performed Double cantilever beam and Singe Lap Shear tests on the 3D printed samples for Modes I and II, respectively. Afterward, we developed the numerical simulations of these tests using the Finite element method (FEM) to obtain CZM bond parameters. Results demonstrate that the initial stiffness and cohesive strength were pretty similar for all designs in Mode I. However, the cohesive energy for the Bulk sample was approximately four times of porous samples. Furthermore, for Mode II, the initial stiffness and cohesive energy of the Bulk model were five and four times of porous designs while their cohesive strengths were almost the same. Also, using cohesive parameters was significantly enhanced the accuracy of FEM predictions in comparison with fully bonded assumption. It can be concluded that for the numerical analysis of 3D printed parts mechanical behavior, it is necessary to obtain and suppose the cohesive parameters. The present work illustrates the effectiveness of CZM and FEM combination to obtain the layer adhesive parameters of the 3D printed scaffold.
Purpose
There are many investigations in design methodologies, but there are also divergences and convergences as there are so many points of view. This study aims to evaluate to corroborate and deepen other researchers’ findings, dissipate divergences and provide directing to future work on the subject from a methodological and convergent perspective.
Design/methodology/approach
This study analyzes the previous reviews (about 15 reviews) and based on the consensus and the classifications provided by these authors, a significant sample of research is analyzed in the design for additive manufacturing (DFAM) theme (approximately 80 articles until June of 2017 and approximately 280–300 articles until February of 2019) through descriptive statistics, to corroborate and deepen the findings of other researchers.
Findings
Throughout this work, this paper found statistics indicating that the main areas studied are: multiple objective optimizations, execution of the design, general DFAM and DFAM for functional performance. Among the main conclusions: there is a lack of innovation in the products developed with the methodologies, there is a lack of exhaustivity in the methodologies, there are few efforts to include environmental aspects in the methodologies, many of the methods include economic and cost evaluation, but are not very explicit and broad (sustainability evaluation), it is necessary to consider a greater variety of functions, among other conclusions
Originality/value
The novelty in this study is the methodology. It is very objective, comprehensive and quantitative. The starting point is not the case studies nor the qualitative criteria, but the figures and quantities of methodologies. The main contribution of this review article is to guide future work on the subject from a methodological and convergent perspective and this article provides a broad database with articles containing information on many issues to make decisions: design methodology; optimization; processes, selection of parts and materials; cost and product management; mechanical, electrical and thermal properties; health and environmental impact, etc.
Additive manufacturing provides the production of many machine parts and components with complex geometries. The adhesive bonding technique can be alternative method for joining parts produced with additive manufacturing. This experimental study investigates the applicability of the adhesive bonding technique for PLA (polylactic acid) adherends produced with additive manufacturing and especially the effects of loading rate on the strength of 3D-printed PLA adhesive single-lap joints under tensile, three-point bending (with shear) and four-point bending (no shear effect) loadings. Both PLA and adhesive tensile test specimens exhibited a better strength but lower failure strain with increasing loading rate. PLA had better mechanical behaviour in the raster orientation than those in the layer-build direction. The strength of adhesive single-lap joints improved slightly with increasing loading rate for the tensile and three-point bending tests whilst a decrease of strength and an improvement of bending stiffness were observed for the four-point bending test. Failure initiated at the free edge of the top adherend-adhesive interface for all tests, and propagated along this interface for both bending tests whilst a sudden through-the-thickness failure of top adherend occurred for tensile load after a small interfacial damage propagation. The failure propagation appeared in a wavy form for the three-point bending test whilst it was along the top adherend-adhesive interface for the four-point bending test. Digital Image Correlation (DIC) method for tensile tests showed that the peeling and shear strains were more critical and concentrated around both free edges of adherend-adhesive interfaces; thus, at the right free edge of the top adherend-adhesive interface and at the left free edge of the bottom adherend-adhesive interface.
Adhesive joints exhibit very high toughness and good fatigue resistance. This technique is a serious candidate to replace rivets or welding in primary structural components. Nevertheless, there is hesitation on the part of the industry to replace traditional fasteners in primary structural applications, mainly due to the limited understanding of joint performance over the life of structures. In the present research, we focus on the static strength of adhesive bonded aluminium alloys for the automotive industry. So, the aim of this work is to carry out and quantify the various variables affecting the strength of single lap joints, especially the effect of the surface preparation. Aluminium single lap joints (SLJs) were fabricated and tested to assess the adhesive (structural one-component polyurethane adhesive) performance in a joint. We found that the decrease in surface roughness was found to increase the shear strength of single lap joints. Furthermore, it has been possible, qualitatively, to identify the relative sensitivity of the effects of various surface roughnesses on the behaviour of spreading kinetics. Experimental results show that rougher surfaces have less wettability which is in coherent with shear strength tests.
Procedures for the preliminary design of composite adhesive joints are described. Typical joints, their respective free body diagrams and approximate equations for estimating the stresses in each of these typical joints are summarized. Equations are also presented to check the critical conditions of the joint, such as: minimum length, max imum adhesive shear stress and peel-off stress. To illustrate the procedure, sample designs are described in step-by-step fashion for a butt joint with single doubler subjected to static loads, cyclic loads and environmental effects. The results show that (1) unsymmetric adhe sive joints are inefficient and should be avoided, and (2) hygrothermal environments and cyclic loads dramatically reduce the structural integrity of the joint and require several joint lengths compared to those for static load with no environmental effects.
A review of the investigations that have been made on adhesively bonded joints of fibre-reinforced plastic (FRP) composite structures (single skin and sandwich construction) is presented. The effects of surface preparation, joint configuration, adhesive properties, and environmental factors on the joint behaviour are described briefly for adhesively bonded FRP composite structures. The analytical and numerical methods of stress analysis required before failure prediction are discussed. The numerical approaches cover both linear and non-linear models. Several methods that have been used to predict failure in bonded joints are described. There is no general agreement about the method that should be used to predict failure since the failure strength and modes are different according to the various bonding methods and parameters, but progressive damage models are quite promising since important aspects of the joint behaviour can be modelled by using this approach. However, a lack of reliable failure criteria still exists, limiting in this way a more widespread application of adhesively bonded joints in principal load-bearing structural applications. An accurate strength prediction of the adhesively bonded joints is essential to decrease the amount of expensive testing at the design stage.
The uniaxial compression behavior of adhesively bonded composite scarf-joints was studied and the role of scarf-angle on joint strength and failure mechanism was investigated. Adhesively bonded scarf-joints made of carbon-fibre reinforced polymer laminates and ‘AF-163-2’ structural film adhesive were compressed to final failure and the responses of the joints to the compressive loads were measured. The results showed that the compressive strength of the joints decreased monotonically as the scarf-angle (with respect to the loading axis) increased. The studies on post-fractured specimens revealed that the failure mechanism switched from predominantly fiber microbuckling for joints with scarf-angles below 3°, to cohesive shear deformation of the adhesive layer (with attendant fiber microbuckling), for joints with scarf-angles above 3°. These findings are useful for assessing the knockdown of compressive-joint strengths of adhesively bonded composite joints for less than ideal scarf-angles.
Adhesives with functionally graded material properties are being considered for use in adhesively bonded joints to reduce the peel stress concentrations located near adherend discontinuities. Several practical concerns impede the actual use of such adhesives. These include increased manufacturing complications, alterations to the grading due to adhesive flow during manufacturing, and whether changing the loading conditions significantly impact the effectiveness of the grading. An analytical study is conducted to address these three concerns. An enhanced joint finite element, which uses an analytical formulation to obtain exact shape functions, is used to model the joint. Furthermore, proof-of-concept testing is conducted to show the potential advantages of functionally graded adhesives. In this study, grading is achieved by strategically placing glass beads within the adhesive layer at different densities along the joint.
An alternative technique of bonding single-lap joints was investigated by removing portions of the adhesive from the interior of the overlap. This technique is termed as recessed bonding. Recessed bonded joints were analyzed using the finite element method. A linear, two-dimensional, plane strain analysis with isotropic materials was conducted. The stress distributions at the adhesive mid-thickness and interface were determined for joints with various levels of recessing, and compared to the stress distributions in continuous single-lap joints. In continuous single-lap joints, maximum stresses occur near the adhesive spew terminus. In recessed single-lap joints, maximum stresses remain near the adhesive spew terminus, and increase only slightly with increased level of recessing. At the recess ends steep stress gradients occur, which should be accounted for.
Adhesive bonding has been used for a number of decades for construction of aircraft components. Light weight sandwich construction and structural bonded joints form a major proportion of modern aircraft. Bonded patches are also used for repair of sandwich panels, cracks in metallic structure or reinforcement of deficient structures. The in-service durability of bonded structures and repairs has varied dramatically, with some structures and repairs providing life-of-type service and others failing in a very short time, leading to a poor acceptance by aircraft operators of adhesive bonded structures and repairs. A corresponding reluctance has occurred amongst manufacturers and repair authorities to accept the superior performance of adhesive bonding which has been demonstrated in laboratory and field trials over a number of decades. The variability of bonded joints can occasionally be traced to deficient bonded joint design, but usually the deficiency lies in a lack of understanding of the adhesive bonding processes. If some basic principles are applied (and preferably embodied in some form of design and processing standard for airworthiness certification) reliable adhesive bonded structures and repairs would achieve a significantly superior performance over conventional mechanically fastened systems. This paper details basic principles required for the production of strong, durable adhesive bonds.
Failure process, mode and strength of unidirectional composite single lap bonded joints were investigated experimentally with respect to bonding methods, that is, co-curing with or without adhesive and secondary bonding. The co-cured joint specimen without adhesive had the highest failure strength. Progressive failures along an adhesive layer occurred in the secondary bonded specimen. In the co-cured specimen with adhesive film, delamination failure occurred and the joint strength was lower than that of secondary bonded specimens. Delamination failure did not occur in the secondary bonded specimen because of early crack growth and progressive failure in the adhesive layer. Therefore, The failure strength of composite bonded joint is not always proportionate to adhesion strength of adhesive due to the weakness of delamination in composite materials. The influences of surface roughness, bondline thickness and fillets in the secondary bonded specimens were also studied.
The tapered composite laminates are optimized by a patchwise layup design method. In this approach, the weight of tapered composite laminates under the strength constraints was minimized. For this purpose, stacking sequences and the number of plies were optimized. The design variables were the discrete ply angles such as 0°, ±45°, and 90° and the number of plies in each patch. The design results are compared with the uniform thickness laminates. It showed that the optimized layup could considerably reduce total weight of the composite laminates. Also, a new design concept – manufacturing cost – for the expenditure of manufacturing such as time and labor is proposed. The composite laminates designed by the consideration of manufacturing cost were more practical than those designed by only strength constraints.
In the present paper, the following topics are reviewed in detail: (a) the available adhesives, as well as their recent advances, (b) thermodynamic factors affecting the surface pretreatments including adhesion theories, wettability, surface energy, (c) bonding mechanisms in the adhesive joints, (d) surface pretreatment methods for the adhesively bonded joints, and as well as their recent advances, and (e) combined effects of surface pretreatments and environmental conditions on the joint durability and performance. Surface pretreatment is, perhaps, the most important process step governing the quality of an adhesively bonded joint. An adhesive is defined as a polymeric substance with viscoelastic behavior, capable of holding adherends together by surface attachment to produce a joint with a high shear strength. Adhesive bonding is the most suitable method of joining both for metallic and non-metallic structures where strength, stiffness and fatigue life must be maximized at a minimum weight. Polymeric adhesives may be used to join a large variety of materials combinations including metal-metal, metal-plastic, metal-composite, composite-composite, plastic-plastic, metal-ceramic systems. Wetting and adhesion are also studied in some detail in the present paper since the successful surface pretreatments of the adherends for the short- and long-term durability and performance of the adhesive joints mostly depend on these factors. Wetting of the adherends by the adhesive is critical to the formation of secondary bonds in the adsorption theory. It has been theoretically verified that for complete wetting (i.e., for a contact angle equal to zero), the surface energy of the adhesive must be lower than the surface energy of the adherend. Therefore, the primary objective of a surface pretreatment is to increase the surface energy of the adherend as much as possible. The influence of surface pretreatment and aging conditions on the short- and long-term strength of adhesive bonds should be taken into account for durability design. Some form of substrate pretreatment is always necessary to achieve a satisfactory level of long-term bond strength. In order to improve the performance of adhesive bonds, the adherends surfaces (i.e., metallic or non-metallic) are generally pretretead using the (a) physical, (b) mechanical, (c) chemical, (d) photochemical, (e) thermal, or (e) plasma method. Almost all pretreatment methods do bring some degree of change in surface roughness but mechanical surface pretreatment such as grit-blasting is usually considered as one of the most effective methods to control the desired level of surface roughness and joint strength. Moreover, the overall effect of mechanical surface treatment is not limited to the removal of contamination or to an increase in surface area. This also relates to changes in the surface chemistry of adherends and to inherent drawbacks of surface roughness, such as void formations and reduced wetting. Suitable surface pretreatment increases the bond strength by altering the substrate surface in a number of ways including (a) increasing surface tension by producing a surface free from contaminants (i.e., surface contamination may cause insufficient wetting by the adhesive in the liquid state for the creating of a durable bond) or removal of the weak cohesion layer or of the pollution present at the surface, (b) increasing surface roughness on changing surface chemistry and producing of a macro/microscopically rough surface, (c) production of a fresh stable oxide layer, and (d) introducing suitable chemical composition of the oxide, and (e) introduction of new or an increased number of chemical functions. All these parameters can contribute to an improvement of the wettability and/or of the adhesive properties of the surface.
Arbitrarily nonlinear stress-strain behaviour in both shear and peel for adhesive are utilised to formulate two coupled nonlinear governing equations for an adhesive-adherend sandwich of single-lap type. For a balanced adhesive-adherend sandwich, the two equations can be integrated, and simple formulas for bond strength are developed for characterising pure shear, peel and mixed failure in adhesive. These formulas define the bond strength in terms of the maximum strain energy density in the adhesive. It is shown that the product of the adhesive strain energy density and the adhesive thickness is equal to the energy release rateJ of mode I, mode II and mixed fracture.
It is well known that geometric nonlinear effects have to be taken into account when the ultimate strength of single lap composite joints are studied. In the present paper we investigate for which level of loads or prescribed end displacements nonlinear effects become significant and how they appear. These aspects are studied by comparing finite element results obtained from geometric nonlinear models with the results from the linear ones. The well-known software package ANSYS is applied in the numerical analysis together with a self-implemented module in the C++ library Diffpack. Some of the results are also compared with classical analytical theories of idealized joints showing significant differences.The joints examined are made of cross-ply laminates having 0 or 90° surface layers. A combined cross-ply/steel joint and an isotropic joint made of steel are also studied. All the models except the all-steel one are assembled with adhesives, while the latter is welded.Through the investigation a considerable departure from linear behavior has been detected for a large regime of prescribed end displacements or external loads. Geometric nonlinear effects begin to develop for external loads that produces stresses which are far below ultimate strength limits and for average longitudinal strains that are less than 0.5%. It has also been detected that the distribution of materials within the joint has some influence on the nonlinear behavior. Thus, geometric nonlinear methods should always be applied when single lap (or other non-symmetric) composite joints are analyzed.
For realistic applications, the design of bonded repairs and lap-joints, has often been undertaken through trial and error finite element analyses, or experiment. Recent experience indicates that for more complex practical applications, unacceptably high adhesive stresses can occur in the adhesive layer. In the present work, an automated sensitivity-based shape optimisation procedure has been developed for the optimal design of free-form bonded repairs and lap-joints, with the aim of achieving reduced adhesive stresses. The approach has been demonstrated through application to a number of single and double-sided configurations where both the shapes of the adhesive layer and the outer adherend are allowed to vary. Significant improvements over conventional designs are obtained, as assessed by the reduction in peak adhesive stresses. These results indicate that the numerical shape optimisation procedures presented can provide designs that offer substantial improvements over standard designs.
Adhesively bonded joints with cross-ply adherends having a 0° or 90° surface layer have been manufactured and tested. The stresses in the joint were determined using a continuum method of analysis and large displacement finite element analysis was also undertaken. A numerical crack simulation was used to determine approximately stress/strain redistribution after initial cracking. Numerical predictions are compared with joint experimental performance and failure modes.
Published work, mostly theoretical, relating to all aspects of adhesively bonded joints in composite materials is reviewed. The theoretical work is subdivided into classical and finite element methods. General principles and design guidelines are also presented.
The effect of cracks embedded in strap adherend on the lap shear joints is presented in this paper. The failure loads and failure modes of specimens with different length of cracks are determined in the experimental study. A non-linear finite element analysis (FEA) is conducted to illustrate the effect of crack and adhesive spew fillet on the stress distribution in the adhesive layer and the energy release rates at both crack tips. An analytical solution is also developed for the lap shear joints with embedded crack. Failure loads of the joints are predicted using the critical energy release rate based and the maximum stress criteria. A good correlation is found between the measured failure loads and those predicted using FEA and analytical models.
This paper discusses the static and fatigue behavior of adhesively bonded single lap joints in SMC-SMC composites. Effects of lap length and adhesive thickness on the static and fatigue strength of SMC-SMC adhesive joints are studied. Effects of SMC surface preparation and test speed on the joint performance are evaluated. Finally, the effect of water exposure on the joint durability is also investigated. Results show that the static behavior of adhesive joints in SMC-SMC composites is significantly influenced by the lap length and adhesive thickness. With an increase in lap length from 12.7 mm to 38.1 mm, the joint failure load increases by 37%. The joint failure load also increases with the adhesive thickness, but it reaches a maximum at an adhesive thickness of 0.33 mm and then decreases. However, lap length and adhesive thickness have negligible effect on the ratio of fatigue strength to static strength. The fatigue strength at 10 6 cycles is approximately 50% to 54% of the static strength for various adhesive thicknesses and lap lengths investigated in this study. Adhesive failure, fiber tear or combination of these two failure modes are observed during both static and fatigue tests. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/34827/1/10084_ftp.pdf