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Modeling the fracture behavior of 3D-printed PLA as a laminate composite: Influence of printing parameters on failure and mechanical properties
Abstract
Additively Manufactured parts are known to be heavily affected by the 3D-printing parameters, and their layered morphology represents a challenge in the mechanical design analysis for engineering applications. In this work, the fracture mechanics of 3D-printed polylactic acid (PLA) samples along different printing directions was simulated as a laminate composite analysis using different numerical approaches, i.e. extended Finite Element (XFEM) and cohesive method. Tensile specimens were 3D-printed via Fused Filament Fabrication in different directions and tested to build the stiffness matrix needed to define the constitutive behavior of the 3D-printed material. Moreover, the influence of different printing parameters (i.e. printing direction, infill, nozzle temperature and perimeter) on the mechanical response was investigated using the statistical approach analysis of variance (Anova). The statistical analysis has shown a strong influence of the printing direction and the perimeters on the resulting mechanical properties, with tensile strength ranging from 52 MPa in the best case to 4 MPa in the worst. The performed FEM analysis correctly predicts the fracture behavior of the 3D-printed samples, with an error on the predicted failure load well below 7%. The investigated model, thus, represents a useful analysis approach to broader the use of 3D printing in engineering applications.
... It is known that a number of parameters may influence on the quality of printed specimens, such as: nozzle and bed temperature, printing direction, infill type and percentage, number of perimeters, layer height and width, nozzle speed, cooling, supports, etc. These may have an impact on the interlayer adhesion, mechanical properties, waste of material, surface quality, warping, etc [11,[23][24][25][26][27][28]. Because AM is highly sensitive to environmental conditions and equipment setup, a series of tests/attempts were carried out in order to find an appropriate balance between printing time and mechanical/dimensional quality of the part. ...
... After these trial-and-error tests, the parameters described in Table 1 were defined for all prototypes and specimens printed during this study. One important feature to mention is that the cooling fan was disabled during printing, in order to minimise the thermal gradient between layers, increase the residual thermal energy and, thus, improve interlayer adhesion which was empirically verified and is known by literature [23]. ...
... The printing direction should, also, be highlighted, as it plays a major role on mechanical behaviour of the printed part [23][24][25]. So, for the geometry to be developed in this work, the three feasible printing directions are depicted in Fig. 8 and it is clear that the third option is the most appropriate. ...
The aim of this work is to develop a novel alternative for boltless moment connections for pultruded profiles. To accomplish this task, the current study takes advantage from the benefits of Additive Manufacturing (AM), which include the fabrication of complex geometries without high cost of time. This feature of AM enabled the pro-totyping and, further, the experimental investigation of optimised and non-optimised joints, which were compared in terms of stiffness, strength and other parameters. All connection components were fabricated using commercial printers and slicers designed for Fused Deposition Modelling (FDM or FFF) technique. Acrylonitrile Butadiene Styrene (ABS) polymer was chosen to fabricate the samples, which were, in some cases, externally strengthened through the manual application of glass fibres at tension regions. To evaluate these components, reduced-scale moment-rotation tests have been carried out on beam-to-column connection systems. The results showed that the group of fibre-reinforced light joints exhibited the greatest stiffness and load bearing capacity. In this context, the interlayer and interbead failure of the 3D printed prototypes seems to play an important role on ultimate strength. Also, the mechanical behaviour was compared with results reported in previous studies, confirming the potential of the proposed joints.
... Thus, interface zones of adjacent filaments were defined differently from the rest of the model, considering debonding responses in the meso-scale. The debonding behaviour was modelled by the cohesive model introduced in the numerical model [37], given as: ...
... While considered biodegradable, PLA requires specific conditions, such as industrial composting, for efficient decomposition, and it can take a significant amount of time to fully degrade under natural conditions [26]. PLA melts at a temperature range of 185-210 • C [17,27]. While PLA degrades under invasive weather and environmental conditions, it maintains its properties for an extended period if stored appropriately [28]. ...
This study explores the application of materials used in 3D printing to manufacture the housings of non-invasive sensors employed in measurements using a TDR (Time Domain Reflectometry) meter. The research investigates whether sensors designed with 3D printing technology can serve as viable alternatives to conventional invasive and non-invasive sensors. This study focuses on innovative approaches to designing humidity sensors, utilizing Fused Deposition Modeling (FDM) technology to create housings for non-invasive sensors compatible with TDR devices. The paper discusses the use of 3D modeling technology in sensor design, with particular emphasis on materials used in 3D printing, notably polylactic acid (PLA). Environmental factors, such as moisture in building materials, are characterized, and the need for dedicated sensor designs is highlighted. The software utilized in the 3D modeling and printing processes is also described. The Materials and Methods Section provides a detailed account of the construction process for the non-invasive sensor housing and the preparation for moisture measurement in silicate materials using the designed sensor. A prototype sensor was successfully fabricated through 3D printing. Using the designed sensor, measurements were conducted on silicate samples soaked in aqueous solutions with water absorption levels ranging from 0% to 10%. Experimental validation involved testing silicate samples with the prototype sensor to evaluate its effectiveness. The electrical permittivity of the material was calculated, and the root-mean-square error (RMSE) was determined using classical computational methods and machine learning techniques. The RMSE obtained using the classical method was 0.70. The results obtained were further analyzed using machine learning models, including Gaussian Process Regression (GPR) and Support Vector Machine (SVM). The GPR model achieved an RMSE of 0.15, while the SVM model yielded an RMSE of 0.25. These findings confirm the sensor’s effectiveness and its potential for further research and practical applications.
... A combination of experiments and numerical methods has been used to evaluate the influence of printing parameters on the overall mechanical properties widely. Finite-element models explicitly account for the layer pattern with the filament orientation, thickness, and void density [24][25][26][27][28]. ...
In this study, eight infill strategies with multiple infilling modes (line, grid, and honeycomb) were used in manufacturing 3D printing of a polylactic acid (PLA) by fused deposition modeling (FDM) process, and the resulting surface topographies and tensile properties were reported. The results showed that the grid/line/grid and honeycomb/line/ honeycomb samples with sandwich structures had the best tensile fracture resistance, which depended directly on the degree of quality of the interlayer. Based on the analysis of the scanning electron microscopy (SEM) of the fracture surface, the improving tensile properties of 3D samples in sandwich structures with line in core were attributed to effective raster, layer bonding, and fewer voids. The finite element (FE) simulation was performed on 3D‐printed parts to predict von Mises stress and tensile strength, which made it possible to reduce the design time to improve the tensile behavior of 3D‐printed structures.
... Guessasma et al. (2022) stated that vertical building orientation reduced the tensile strength and elasticity of the polymers, and the printing direction, along with the sample, provided higher strength for 3D-printed polymers. Bragaglia et al. (2023) concluded that the tensile strength of the 3D-printed PLA decreased by 70 to 75% with changing raster orientations from 0º to 90º due to the interaction between printing direction and the layerwise nature of the printed polymers. Lares Carrillo et al. (2023) compared the tensile strength of the PLA and PLA/wood and concluded that 3D-printed PLA with raster orientations 0º, 45º, and 90º had 28% to 34% higher strength than those comprising PLA/wood. ...
Thermal, morphological, and mechanical properties were studied for 3D-printed biocomposites prepared from polylactic acid (PLA) and hemp fibers. For this purpose, the neat PLA, PLA/Hemp fiber (3 wt%), PLA/Hemp fiber/Maleic anhydride (3 wt% and 0.6 wt%), and PLA/Hemp fiber/Maleic anhydride/Glycerol (3 wt% and 0.6 wt% + Glycerol added in 10% of PLA) biocomposites were extruded to obtain filaments for fused filament fabrication (FFF). Thermogravimetric analysis (TGA) provided temperatures corresponding to 5%, 10%, and 90% mass losses for materials before and after 3D printing. During 3D printing, filaments were extruded with a nozzle temperature of 220 ºC; consequently, their thermal properties worsened after 3D printing. In thermal analysis, Tg increased by adding hemp fiber and maleic anhydride but was decreased with glycerol addition. The tensile and flexural strengths of neat PLA and biocomposites were not statically different, but flexural strength was slightly increased by adding ingredients one by one. Regarding modulus of elasticity (MOE) of materials, the sample group of the PLA/hemp fiber/maleic anhydride had the highest value. However, glycerol addition decreased MOE by 17%. These results showed that material performance of the PLA could be improved or remain statistically identical by adding hemp fiber, maleic anhydride, and glycerol.
... Moreover, the use of FDM is applicable for AFO due to its results of the porosity and density measurement [12]. Besides, it has demonstrated its capability to produce parts with complex geometrical features which makes FDM attractive for AFO manufacturing [13]. ...
Orthotics are the body support devices used for correction, immobilization, fixation, and prevention of paralysis. The greatest number of orthotics utilized by people suffering from plantarflexion and dorsiflexion disability, especially in Indonesia, is ankle foot orthotic (AFO). However, the duration associated with fabricating AFO through conventional methods is considered time-consuming. This paper aims to fabricate ankle foot orthotics (AFO) using innovative combinations of 3D scanning and 3D printing. The method begins with 3D scanning of the patient’s lower limb using photogrammetry (3DF Zephyr). The design is generated and adjusted, afterwards, the orthotic prototype is produced by fused deposition modeling (FDM) 3D printing using polypropylene (PP) material. This choice is attributed to the material's advantages, such as being lightweight, rigid, durable, and cost-effective. The 3D mesh model scanned using 3DF Zephyr shows good quality and more precise results. In addition, the prototype produced using 3D printing was tested by walking based on normal gait analysis’s angle of foot and calf measurement, which shows a maximum range of motion (ROM) of 16.1˚. The proposed methods of fabricating orthotic prototypes can successfully reduce the processing time by approximately 70% compared to the conventional method.
... As FDM is affordable and easyto-use, it has been used in diverse applications, and relatively growing number of scientific research works have been performed over the last ten years [9][10][11][12]. Considering applications of 3D-printed parts, the mechanical performance and structural integrity of 3D-printed components have become of great importance [13][14][15]. Although FDM-printed components have been used in different applications (as prototypes or final products), these parts have showed poor mechanical strength. ...
... Polylactic acid (PLA), a bio-based polymer, has increasingly become the focus of attention in recent years, primarily due to its advantageous properties and environmentally friendly profile [12]. Moreover, PLA is highly compatible with additive manufacturing techniques, making it an ideal candidate for 3D printing [13][14][15][16][17][18]. ...
This article investigates the thermal, mechanical, and shape memory performances of 3D-printed polylactic acid (PLA), polyethylene terephthalate glycol (PETG), and their blends for potential applications in 4D printing. Differential Scanning Calorimetry reveals distinct glass transition temperatures for PLA-PETG blends, confirming their immiscibility. The integration of PETG alters the crystalline structure of PLA, shifting its behavior from brittle to ductile. This confirms PETG’s function as an effective plasticizer. The tensile strength and Young’s modulus are influenced by material composition and printing orientation. The results show that 75% PLA and 25% PETG blend demonstrated enhanced mechanical properties compared to other polymer blends. Shape memory experiments demonstrate exceptional fixity and recovery rates, reaching 100%, with the 75% PLA blend exhibiting outstanding performance across 15 cycles. These findings, coupled with insights into the impact of programming temperature, offer valuable perspectives for designing 4D-printed structures with shape memory attributes, unlocking innovative applications across diverse fields.
Graphical abstract
... Each technology offers different possibilities for 3D printing of polymeric materials based on its unique working principle, and the choice of technology mainly depends on the performance requirements of the target products and the properties of the selected polymers. 46,47 2.1 | Material extrusion ME is the most widely used 3D printing technology and can be subdivided into two categories. The first category is filament-based extrusion, also known as fused deposition modeling (FDM) 48 or fused filament fabrication (FFF). ...
The potential of three‐dimensional (3D) printing technology in the fabrication of advanced polymer composites is becoming increasingly evident. This review discusses the latest research developments and applications of 3D printing in polymer composites. First, it focuses on the optimization of 3D printing technology, that is, by upgrading the equipment or components or adjusting the printing parameters, to make them more adaptable to the processing characteristics of polymer composites and to improve the comprehensive performance of the products. Second, it focuses on the 3D printable novel consumables for polymer composites, which mainly include the new printing filaments, printing inks, photosensitive resins, and printing powders, introducing the unique properties of the new consumables and different ways to apply them to 3D printing. Finally, the applications of 3D printing technology in the preparation of functional polymer composites (such as thermal conductivity, electromagnetic interference shielding, biomedicine, self‐healing, and environmental responsiveness) are explored, with a focus on the distribution of the functional fillers and the influence of the topological shapes on the properties and functional characteristics of the 3D printed products. The aim of this review is to deepen the understanding of the convergence between 3D printing technology and polymer composites and to anticipate future trends and applications.
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... Fracture mechanics research should become the priority as demonstrated in recent publications [21,[27][28][29]. Usually, materials are subjected to applied normal and shear stresses, therefore, mixed-mode fracture research of 3D printing materials [28][29] is more important than the common mode-I fracture research. ...
... The additive manufacturing (AM) process, also referred to as 3D printing, is being used these days extensively not just for prototyping of industrial parts but also to create functioning components for numerous purposes in everyday life using a variety of materials, including metals, composite materials, polymers and ceramics [1,2]. Fused deposition modelling (FDM) is extensively employed in industrial applications, including automotive and aerospace with the application of sandwich structures with excellent mechanical properties [3]. ...
The 3D printing parameters are known to have a significant impact on manufactured
parts, and the layered morphology of these parts makes mechanical design analysis for
engineering applications difficult. In this work, the tensile strengths and microhardness
of 3D printed polylactic acid (PLA) specimens with different orientations and numbers
of individual layers of mesh material (polyvinyl chloride – PVC) were investigated as a
laminate composite. Composite specimens were obtained using 3D printing via fused
deposition modelling (FDM). Moreover, the influence of printing parameters (i.e. infill
density and layer height) and the number and orientation of reinforced meshes on the
mechanical response was investigated. Fracture strength of PLA/PVC laminate
composites ranges from 31.30 MPa (3 PVC mesh layers; mesh height position:
25 % │ 50 % │ 75 %; infill density: 60 %; PVC mesh orientation: 90° │ 45° │ 90°; layer
height: 0.2 mm) to 18.62 MPa (without PVC mesh; infill density: 30 %; layer height: 0.1
mm) demonstrating a significant impact of the number of the PVC mesh layers, infill
density of PLA and layer height on the final mechanical parameters of printing
PLA/PVC elements. The surface hardness at the micro load level showed that the
number of reinforcement layers affects the microhardness value, as well as material
filling and mesh orientation. The specimen with the following parameters gave the
best results: layer height: 0.2 mm; 3 PVC mesh layers; infill density: 60 %; PVC mesh
orientation: 90° │ 45° │ 90°. The average hardness values for one layer and three layers
of mesh were in accordance with tensile test results.
... A clear trend of increasing fracture strength with the number of density fraction zones is observed. To describe the failure, it must be understood that 3D-printed materials exhibit a characteristic failure depending on their configuration, printing parameters, and the stress to which they are subjected [32][33][34][35][36]. In this context, Benamira et al. [34] investigated the effects of printing parameters on failures in 3D-printed PLA. ...
The objective of this paper is to determine the impact of density fraction on the mechanical properties of 3D printed thermoplastic materials to maximize the mechanical strength of parts through a combination of topology optimization and tailored density fraction. The results obtained reveal a significant finding of the applicability of the strategy for improving additive manufacturing processes, design automation, and manufacturing of high-strength components. The effect of infill density and print orientation on the mechanical properties of PLA-based 3D-printed parts are quantified by ultimate strength and Young’s modulus in two material orientations (in the printing direction and out of the printing plane), employing both experimental and simulated uniaxial tensile tests, a polynomial relationship as a function of density fraction is determined. These data are then used in a series of successive topological optimizations of a part subjected to operational loads that maximize strength with a targeted reduction in the overall mass. The resulting optimized part exhibits a discrete density fraction distribution from the overlapped topologies that allows the total mass of the original part to be maintained with a 258% increase in load-carrying capacity before failure and a mere 23% increase in fabrication time by fused deposition modeling. These findings underscore the promise of leveraging advanced 3D printing methods and topology optimization to enhance the strength and efficiency of manufactured components.
... The stress parameters of utmost interest, namely, the principal stresses, maximum shear stress, and von Mises stress, were meticulously estimated along the central line of the specimen for the intact sample. Additionally, for the flawed sample with the central crack, the stress distribution was thoroughly assessed in the vicinity of the crack [72]. These data points offered invaluable insights into how the presence of the crack influenced the stress patterns and potential failure regions within the material. ...
This investigation aimed to comprehensively investigate the integrity and failure characteristics of deteriorated polymeric components produced through Fused Filament Fabrication (FFF) technology. The primary focus was to examine the performance of flawed 3D-printed samples, which were purposely designed and 3D-printed to incorporate a range of crack types and geometric features that were initially designed through CAD. This study adopted two main approaches to deal with the cracks by producing the flaws through design and laser processes. These specimens were subjected to destructive testing to gain valuable insights into the FFF-printed components’ performance and failure characteristics under the tensile mode, a significant concern in engineering applications. A Finite Element Analysis (FEA) was employed on the flawed and intact specimens to compare and correlate the experimental results with the simulation results. This study reveals the tested samples’ structural response and failure mechanisms under tensile loading conditions. Exceptionally, it was found that the faulty 3D-printed parts made by the laser process demonstrated less resistance to failure due to disturbing the 3D-printed extruded filament streams. In contrast, the flaws initially produced solely by the 3D printing process showed better resistance to mechanical failure due to the crack-bridging effect. It was observed that there were reductions of 11% and 32% in the failure load of the 3D-printed cracked sample and the laser-cracked samples, respectively, in comparison with the intact one. Additionally, the stress intensity factor showed a decrease of 20% in the laser-cracked sample compared to the 3D-printed one.
One of the primary limitations of fiber‐reinforced polymer composites, particularly carbon fiber, is their low impact resistance. Helicoidal structures, inspired by natural biological materials, are created by rotating each layer at a small angle through the thickness, forming a staircase pattern. These structures have been used as microstructure models to improve impact resistance in composite laminates. This paper provides a comprehensive review of recent progress in the impact resistance of bio‐inspired helicoidal laminates (BIHL). The review begins with an introduction to typical microstructural characteristics of helicoidal architectures, including single‐ and double‐twisted Bouligand structures. The impact damage mechanisms specific to BIHL are then elucidated, particular emphasis is placed on key parameters that affect impact performance, including different forms of helicoidal structures, constituent materials and impact factors. Furthermore, a critical discussion is conducted to highlight the advantages and limitations of manufacturing processes tailored for high‐volume production of BIHL. Finally, after identifying research gaps in the current literature, future directions for BIHL in design, fabrication and application are presented. This review may serve as a practical guide for engineers and researchers interested in developing polymer composite laminates that are highly resistant to impact loads.
Highlights
Helicoidal structures significantly enhance the impact resistance of composites.
The damage pattern and mechanisms of BIHL are identified and summarized.
Key parameters influencing the impact behavior of BIHL are discussed in detailed.
The advantages and limitations of manufacturing processes for BIHL are examined
Contemporary challenges and future research directions for BIHL are outlined.
In this work, we shall implement a novel modeling approach to simulate interface debonding and bulk cracking in realistic 3D printed ffber reinforced composites. The materials are ffrstly manufactured with the Selective Laser Sintering of PA12 polymer powder embedding glass ffbers and additive particles. An in-situ compression test on a cylindrical sample is conducted. X-Ray Computed Tomography (XRCT) technique is employed to obtain experimental fracture images and to provide a complete 3D description of the morphology of each component for constructing a
completely Realistic 3D microstructure mesh Model (R3M) . Meanwhile, an Extended Phase Field Model (EPFM) is presented considering gradient plasticity and interfacial debonding mechanisms. Following that, numerical simulations are conducted, by using the EPFM and R3M, to investigate the fracture behavior in the ffber reinforced composite. In contrast to existing works, a qualitative comparison of fracture phenomena in experiments and simulations is conducted. Anisotropic behavior of the 3D printed ffber reinforced composite is observed both in the experiments and
simulations. Our results reveal that the EPFM can well capture the experimental damage phenomena, including ffber/matrix debonding, ffber breaking and pore connecting in 3D printed ffber reinforced composites, by employing the R3M where the microstructure directly arises from the experimental XRCT.
The progression of manufacturing technology has significantly benefited from the adoption of 3D printing techniques, which enable the production of parts with intricate geometries. However, it is important to acknowledge that components fabricated through this additive manufacturing method frequently manifest defects and exhibit a propensity for failure under severe conditions. Therefore, a thorough examination of the mechanical properties of these parts is essential to effectively reduce the failure. This study aimed to explore the mechanical properties of two prevalently used 3D-printed polymers, specifically Onyx and ABS, by integrating computational and experimental analyses. The experimental study utilized a material testing system and digital image correlation (DIC) technology, while the computational analysis covered the finite element (FE) modeling of the 3D-printed samples. The research focused on evaluating the tensile strength and fatigue resistance of the specimens printed in various orientations, alongside a detailed investigation of their fracture behavior. The crack propagation analysis was carried out using the DIC system and the Separating Morphing and Adaptive Re-meshing Technology (SMART) scheme in ANSYS. It was observed that upright build orientation produced the weakest samples for axial loading and specimens with notches failed earlier than those without. Moreover, Onyx was found to have a higher resistance to fracture or failure compared to ABS. The FE modeling results demonstrated strong agreement with the experimental results, validating their accuracy and reliability in characterizing the critical mechanical response of 3D-printed parts rapidly and cost-effectively.
It is well known that printing parameters strongly affect the mechanical performance of 3D printed parts. This work explores the role of i) extruder temperature, ii) print speed, and iii) layer height on the interlaminar strength of 3D-printed continuous fibre-reinforced composites. The carbon fibre-reinforced thermoset filament is printed concomitantly with polyethylene terephthalate glycol (PETG) thermoplastic filament in a single nozzle, characterising a continuous fibre co-extrusion (CFC) process. There is a significant variation in the short beam strength for composites printed with different parameters. The load–displacement curves have a similar pattern, with clear load peaks followed by a plastic zone. Optical micrographs and computed tomography (CT) scans reveal that the microstructure is dependent on the printing parameters. Image analysis elucidates the various mechanisms of void formation. Following the application of a three-way ANOVA and statistical tests to quantify the effects and interactions among variables, the analysis concludes that the extruder temperature has the highest influence, followed by print speed and layer height. When considering all possible interactions between the factors, the interaction between print speed and layer height is the most impactful.
Three-dimensional printing is widely used in many fields, including engineering, architecture and even medical purposes. The focus of the study is to obtain the ideal weight-to-performance ratio for making a 3D-printed part. The end products of the 3D-printed part are hugely affected by not only the material but also the printing parameters. The printing parameters to be highlighted for this study are the infill density, wall perimeter and layer height, which are the commonly adjusted parameters in 3D printing. The study will be divided into two parts, the simulation analysis and the experimental analysis, to confirm both results toward the trend of Young’s modulus for the material. It will then be analyzed and discussed toward any differences between the two results. The results showed that increasing the value of all three parameters will increase the tensile elasticity of the part.
In this paper, poly-ether-ether-ketone (PEEK) carbon-nanotube (CNT) self-monitoring composites at different levels of filler loading (i.e., 3, 5 and 10% by weight) have been extruded as 3D-printable filaments, showing gauge factor values of 14.5, 3.36 and 1.99, respectively. CNT composite filaments of 3 and 5 wt% were 3D-printed into tensile samples, while the PEEK 10CNT filament was found to be barely printable. The 3D-printed PEEK 3CNT and PEEK 5CNT composites presented piezo-resistive behavior, with an increase in electrical resistance under mechanical stress, and showed an average gauge factor of 4.46 and 2.03, respectively. Mechanical tests highlighted that 3D-printed samples have a laminate-like behavior, presenting ultimate tensile strength that is always higher than 60 MPa, hence they offer the possibility to detect damages in an orthogonal direction to the applied load wit high sensitivity.
Mechanical properties and fracture morphologies of Poly-Lactic acid (PLA) neat and composites (PLA reinforced with Aluminium, Copper, Carbon fibres and Brass) developed by Material Extrusion based Additive Manufacturing technique were studied to consolidate the comprehensive data for various applications. In the current study, printing parameters viz., layer height, print angle and print speed were varied to form the arrays of experimental trials to estimate the Tensile (Ultimate Tensile strength, young's moduli) and Flexural (Maximum bending strength) properties. Further, the study emphasized on fracture morphologies and categorized the types of fractures within the PLA neat and composite samples via Field Emission Scanning Electron Microscope (FESEM). An analytical model was adopted for a qualitative validation of results of micrographs for estimating the tensile and bending strengths.
Results
showed that the percentage improvement in the young's modulus was relatively higher for carbon fibre and brass reinforced composites in comparison to the other counterparts. It was conclusive from fracture morphology that the Intra-laminar type of fracture was prominent. However, PLA + Carbon Fibre (CF) samples exhibited Trans-laminar type of fracture, owing to their higher aspect ratio. Also, the composite samples exhibited better strengths during flexural test, in comparison to the tensile test. Optimization plots showed that the print angle was the most dominant factor influencing the strength values.
The extrusion-based additive manufacturing (AM) is currently the most common there-dimensional (3D) printing for the fabrication of polymer components. In this study, the fracture behavior of 3D-printed polymer parts is investigated. To this aim, polylactic acid material (PLA) was used to print intact and defected specimens based on the fused deposition modeling (FDM) process. The specimens were printed with three different raster directions to determine their effect on the fracture behavior of the parts. Moreover, wood-reinforced PLA material was used to print another group of test coupons. All specimens were subjected to a series of tensile tests and their fracture behaviors are investigated. Based on the comparison of the results, the influence of reinforcement is determined. In addition, parallel to the experiments, a series of finite element analyses were conducted utilizing the anisotropic phase-field fracture model. For an efficient calculation, we treated the whole specimen as a homogenized solid where the anisotropic property of the layered material is considered in the formulation. By calibrating the model based on the experimental measurement, one can predict the anisotropic fracture behavior of the 3D-printed part with high precision. Since applications of 3D-printed composites have been significantly increased, the results of this study can be used for optimization, further numerical analysis, and next development.
The purpose of this work is to study the mechanical behavior of microstructured materials, in particular porous media. We consider a detailed description of the material through a discrete model, considered as the benchmark of the problem. Two continuous models, one micropolar and one classic, obtained through a homogenization procedure of the material, are studied both in static and dynamic conditions. Furthermore, the internal characteristics of the material, such as the internal scale of the microstructure and the percentage of the voids, are made to vary in order to investigate the mechanical response and to have an exhaustive comparison among the models.
This research focuses on the thermal characterization of 3D-printed parts obtained via fused filament fabrication (FFF) technology, which uses a poly(lactic acid) (PLA)-based filament filled with milled carbon fibers (MCF) from pyrolysis at different percentages by weight (10, 20, 30 wt%). Differential scanning calorimetry (DSC) and thermal conductivity measurements were used to evaluate the thermal characteristics, morphological features, and heat transport behavior of the printed specimens. The experimental results showed that the addition of MCF to the PLA matrix improved the conductive properties. Scanning electron microscopy (SEM) micrographs were used to obtain further information about the porosity of the systems.
For the purpose of fabricating electrically conductive composites via the fused filament fabrication (FFF) technique whose properties were compared with injection-moulded properties, poly(lactic acid) (PLA) and polycaprolactone (PCL) were mixed with different contents of graphene nanoplatelets (GNP). The wettability, morphological, rheological, thermal, mechanical, and electrical properties of the 3D-printed samples were investigated. The microstructural images showed the selective localization of the GNPs in the PCL nodules that are dispersed in the PLA phase. The electrical resistivity results using the four-probes method revealed that the injection-moulded samples are insulators, whereas the 3D-printed samples featuring the same graphene content are semiconductors. Varying the printing raster angles also exerted an influence on the electrical conductivity results. The electrical percolation threshold was found to be lower than 15 wt.%, whereas the rheological percolation threshold was found to be lower than 10 wt.%. Furthermore, the 20 wt.% and 25 wt.% GNP composites were able to connect an electrical circuit. An increase in the Young’s modulus was shown with the percentage of graphene. As a result, this work exhibited the potential of the FFF technique to fabricate biodegradable electrically conductive PLA-PCL-GNP composites that can be applicable in the electronic domain.
Fused Deposition Modeling (FDM) can be used to manufacture any complex geometry and internal structures, and it has been widely applied in many industries, such as the biomedical, manufacturing, aerospace, automobile, industrial, and building industries. The purpose of this research is to characterize the polylactic acid (PLA) and polyethylene terephthalate glycol (PETG) materials of FDM under four loading conditions (tension, compression, bending, and thermal deformation), in order to obtain data regarding different printing temperatures and speeds. The results indicated that PLA and PETG materials exhibit an obvious tensile and compression asymmetry. It was observed that the mechanical properties (tension, compression, and bending) of PLA and PETG are increased at higher printing temperatures, and that the effect of speed on PLA and PETG shows different results. In addition, the mechanical properties of PLA are greater than those of PETG, but the thermal deformation is the opposite. The above results will be a great help for researchers who are working with polymers and FDM technology to achieve sustainability.
We propose a new phase-field damage formulation which takes into account anisotropic damage evolution in solids. Such anisotropy projects itself in fracture energy values which depend on the direction of the crack surface. Therefore, instead of one constant scalar parameter for the fracture energy value, we use a direction-dependent fracture energy function. By incorporating a direction-dependent fracture energy function, only a single damage variable as well as a first order damage gradient need to be used within the standard phase-field damage model. This is in contrast to other available anisotropic phase-field models which typically use multiple variables or higher order gradient terms. To obtain values for the fracture energy function, atomistic calculations are performed. Here, molecular static simulations are utilized to calculate the energy of free surfaces within an Aluminum crystal. As a result, we report the fracture energy value as a function of the surface orientation. The obtained fracture energy function is passed directly to the phase-field damage formulation to investigate transgranular fracture within a single crystalline. Moreover, the grain boundary is represented via a cohesive zone model to take into account intergranular fracture in a bi-crystalline structure. The predicted crack path is in good agreement with obtained results from molecular dynamics simulations. Finally, by calibrating the length scale parameter in the phase-field damage model, it is possible to compare the reaction forces from finite element calculations with atomistic ones.
Permanent Rare Earth magnets are becoming more and more important in efficient motors and generators with high energy density. Among them NdFeB magnets are the most employed, with NdFeB having higher remanence, high coercivity and energy product. Nevertheless,their poor corrosion resistance makes them susceptible to degradation of the magnetic properties. One possible solution is the development of innovative polymeric composite magnetic materials. The preparation of NdFeB powders filled polymeric matrix (PEEK), with a double goal of protecting the magnetic alloy is proposed, thus preventing it from corrosion, and to realize a new material that can be shaped in the form of filaments. This material was used as feedstock in the 3D printing process to produce high performance magnets with customized and optimized design. The PEEK-NdFeB filaments were produced with three percentages of filler amount(i.e. 25, 50 and 75 wt%). PEEK neat filaments were produced as reference. The influence of the filler on the main thermomechanical properties of the resulting composites, as well as its effect onthe 3D printing process were evaluated by means of different investigation techniques (DSC, DMTA, XRD, tensile testing). The magnetic properties exhibited by Fused Filament Fabrication (FFF) printed parts confirmed the feasibility of employing such a combination of an innovative manufacturing technique and high-performance PEEK-NdFeB compounds.
The characterization carried out on both neat and composite filaments evidenced that the presence of the filler slightly decreased the thermal stability, increased the elastic modulus while decreasing ductility and maximum tensile strength. By means of DSC analysis, it was confirmed that the crystallinity is influenced by the presence of the filler. Magnetic measurement performed on the 3D printed parts demonstrate that interesting magnetic properties were achieved, confirming the feasibility of the magnetic 3D printed composite with PEEK.
Fused deposition modelling (FDM™) is one of the most promising additive manufacturing technologies and its application in industrial practice is increasingly spreading. Among its successful applications, FDM™ is used in structural applications thanks to the mechanical performances guaranteed by the printed parts. Currently, a shared international standard specifically developed for the testing of FDM™ printed parts is not available. To overcome this limit, we have considered three different tests aimed at characterizing the mechanical properties of technological materials: tensile test (ASTM D638), flexural test (ISO 178) and short-beam shear test (ASTM D2344M). Two aerospace qualified ULTEMTM 9085 resins (i.e., tan and black grades) have been used for printing all specimens by means of an industrial printer (Fortus 400mc). The aim of this research was to improve the understanding of the efficiency of different mechanical tests to characterize materials used for FDM™. For each type of test, the influence on the mechanical properties of the specimen’s materials and geometry was studied using experimental designs. For each test, 22 screening factorial designs were considered and analyzed. The obtained results demonstrated that the use of statistical analysis is recommended to ascertain the real pivotal effects and that specific test standards for FDM™ components are needed to support the development of materials in the additive manufacturing field.
Fused filament fabrication (FFF), a much-appreciated three-dimensional printing (3DP)
technology, has triggered the industrial innovations by providing viable and cost-effective
solutions for design validations, product prototyping, and the production of high-performance functional components. Indeed, the main credit of its successful career goes to material and printing flexibilities. However, the technology still faces various downsides, including poor finish, geometrical fits and tolerances, anisotropy, in-printing errors, and limited mechanical strength, that cannot be easily outweighed as these suppress its practical implications. As of utmost necessity, this review paper discusses the various abilities and inabilities of this technology to generate a roadmap of futuristic tasks for better outcomes. The review paper will act as a first-hand reference, through the well-defined possible directions, to the young researchers and senior scientist.
It is discovered in this investigation that there exist two different failure modes and a special separation angle which is the demarcation point of the two different failure modes when FDM (Fused Deposition Modelling) 3D printing materials fail under a tensile load. In order to further understand the mechanical properties of FDM 3D printing materials and promote the use of FDM 3D printing materials, their tensile failure strengths at different printing angles and separation angles are measured and analysed theoretically. A new separate-modes of transversely isotropic theoretical failure model is established to predict the tensile failure strength and separation angle of FDM 3D printing PLA (polylactic acid) material based on the hypothesis of transverse isotropy and the classical separate-modes failure criterion. During this research, the tensile specimens designed according to the current test standard ISO (527-2-2012) for plastic-multi-purpose specimens are fabricated in 7 different printing angles (0∘, 15∘, 30∘, 45∘, 60∘, 75∘, 90∘) and three levels of printing layer thickness (0.1 mm, 0.2 mm, 0.3 mm). Experimental results show that the tensile failure strength increases with the increase of the printing angle or the decrease of the layer thickness. Meanwhile, inter-layer failure tends to occur when the printing angle is small and in-layer failure tends to occur when the printing angle is big. In comparison with the results predicted by the established theoretical model, all values of the Generalized-Relative-Root-Mean-Square Error are close to zero and the experimental separation angles are also between 45∘ and 60∘. So the predictive capacity of the theoretical model is affirmed by experimental results.
Is mechanical anisotropy in extrusion-based 3D-printed parts caused by weak inter-filament bonding, as is widely accepted? This study demonstrates that filament-scale geometric features may be a more important factor than filament bonding. Specially designed 3D-printed compact tension specimens were tested normal to, and along, the direction of extruded filaments. Higher strength and toughness were found in the filament direction. These differences disappeared when small grooves, comparable to micro-features, were introduced in specimens tested along the former direction to replicate grooves that naturally occur between filaments/layers. Mechanical testing and fractography demonstrate that filament-scale geometric stress raisers are critically important and cause anisotropy in 3D-printed materials.
The evolution of fused filament fabrication (FFF) technology, initially restricted to the manufacturing of prototypes, has led to its application in the manufacture of finished functional products with excellent mechanical properties. However, FFF technology entails drawbacks in aspects, such as dimensional and geometric precision, and surface finish. These aspects are crucial for the assembly and service life of functional parts, with geometric qualities lagging far behind the optimum levels obtained by conventional manufacturing processes. A further shortcoming is the proliferation of low cost FFF 3D printers with low quality mechanical components, and malfunctions that have a critical impact on the quality of finished products. FFF product quality is directly influenced by printer settings, material properties in terms of cured layers, and the functional mechanical efficiency of the 3D printer. This paper analyzes the effect of the build orientation (Bo), layer thickness (Lt), feed rate (Fr) parameters, and plate-extruder movements on the dimensional accuracy, flatness error, and surface texture of polylactic acid (PLA) using a low cost open-source FFF 3D printer. The mathematical modelling of geometric properties was performed using artificial neural networks (ANN). The results showed that thinner layer thickness generated lower dimensional deviations, and feed rate had a minor influence on dimensional accuracy. The flatness error and surface texture showed a quasi-linear behavior correlated to layer thickness and feed rate, with alterations produced by 3D printer malfunctions. The mathematical models provide a comprehensive analysis of the geometric behavior of PLA processing by FFF, in order to identify optimum print settings for the processing of functional components.
This paper experimentally observed at a small level the influence of nozzle temperature change on warping deformation (WD), dimensional Accuracy (DA) and density. The materials chosen are pure PLA and advanced PLA+ specimens of rectangular shape of 63.5 mm × 9.53 mm × 3.2 mm produced by the end-user 3D printer based on fused deposition modeling (FDM). During the printing work, the nozzle temperature was conducted at twelve different values 195°C to 250°C with 5°C increments. Additionally, the infill density was set at 20% along with infill line direction of 0°, 90°, 45° and ±45°. After the fabrication, the FDM 3D printed parts naturally cooled down to room temperature at T = 23±2°C. As a result, the higher the nozzle temperature, the lower the deformed shape errors (with low uncertainty) of the specimens were. Experimental results show that the measured dimensions are always more than the original CAD file dimension along the height but less than the original CAD file dimensions along the width and length. The density measurements of both materials at 90° infill line direction have higher values compared with other directions (0°, 45°, ±45°), which have very similar results. The data and knowledge obtained from this investigation can be helpful for both an academic and an industrial perspective to set optimum nozzle temperature at small scale level and also it can be used to fabricate low-cost functional objects. Furthermore, it will also allow us to redesign the original CAD file in order to compensate the warping deformation encountered when using end-user FDM 3D additive manufacturing.
The increase in accessibility of fused filament fabrication (FFF) machines has inspired the scientific community to work towards the understanding of the structural performance of components fabricated with this technology. Numerous attempts to characterize and to estimate the mechanical properties of structures fabricated with FFF have been reported in the literature. Experimental characterization of printed components has been reported extensively. However, few attempts have been made to predict properties of printed structures with computational models, and a lot less work with analytical approximations. As a result, a thorough review of reported experimental characterization and predictive models is presented with the aim of summarizing applicability and limitations of those approaches. Finally, recommendations on practices for characterizing printed materials are given and areas that deserve further research are proposed.
In the present study, the mesostructure of a fused deposition modeling (FDM) processed part is considered for the investigation of its mechanical behavior. The layers of FDM printed part behave as a unidirectional fiber reinforced laminae, which are treated as an orthotropic material. The finite element (FE) procedure to find elastic moduli of a layer of the FDM processed part is presented. The mesostructure of the part that would be obtained from the process is replicated in FE models in order to find stiffness matrix of a layer. Two distinctive architectures of mesostructure are considered in the study to predict the mechanical behavior of the parts. Also, influences of layer thickness, road shape and air gap on the elastic properties of a material are investigated. Further, the parts fabricated with FDM process are treated as laminate structures. From the numerical results, it is seen that the elastic moduli are governed by mesostructures. Our laminate results are validated with experimental to demonstrate the use of classical laminate theory (CLT) for FDM parts. The elastic moduli (E1, E2, G12, ν12) of a layer used in the analysis are calculated from FE simulations. This study establishes relationship between mesostructure and macro mechanical properties of the part.
The Additive Manufacturing (AM) technology initially was developed as a rapid prototyping tool for visualization and validation of designs. The recent development of AM technologies, such as Fused Deposition Modelling (FDM), is driving it from rapid prototyping to rapid manufacturing. However, building end-user functional parts using FDM proved to be a challenging task. The difficulty arises from the large number of processing parameters that affect the final part design such as: building direction, extrusion temperature, layer height, infill pattern and more. The processing parameters of FDM influence the quality of the parts and their functionality. In addition, a more systemic understanding is required to elaborate on the impact of the FDM processing parameters on the final part's mechanical properties, dimensional accuracy and building time. The presented paper provides an experimental study to investigate the independent effect of each processing parameter on the mechanical properties and dimensional accuracy repeatability of FDM parts. A total of 18 test specimen samples were printed using varying processing parameters. In order to investigate the repeatability and resulted tolerances, the dimensions of these specimens were measured and compared with a 3D CAD model. The presented work utilizes a tensile test per ASTM D638 standards to obtain the mechanical properties of each fabricated sample. In addition, the work provides a Finite Element Analysis (FEA) model for AM parts. The work suggested to simulate their behavior under mechanical loads for future investigation on the coupled effects of processing parameters.
Polyetheretherketone (PEEK) is a polyaromatic semi-crystalline thermoplastic polymer with mechanical properties favorable for bio-medical applications. Polyetheretherketone forms: PEEK-LT1, PEEK-LT2, and PEEK-LT3 have already been applied in different surgical fields: spine surgery, orthopedic surgery, maxillo-facial surgery etc. Synthesis of PEEK composites broadens the physicochemical and mechanical properties of PEEK materials. To improve their osteoinductive and antimicrobial capabilities, different types of functionalization of PEEK surfaces and changes in PEEK structure were proposed. PEEK based materials are becoming an important group of biomaterials used for bone and cartilage replacement as well as in a large number of diverse medical fields. The current paper describes the structural changes and the surface functionalization of PEEK materials and their most common biomedical applications. The possibility to use these materials in 3D printing process could increase the scientific interest and their future development as well.
In contrast to conventional subtractive manufacturing methods which involve removing material to reach the desired shape, additive manufacturing is the technology of making objects directly from a computer-aided design model by adding a layer of material at a time. In this study, a comprehensive effort was undertaken to represent the strength of a 3D printed object as a function of layer thickness by investigating the correlation between the mechanical properties of parts manufactured out of acrylonitrile butadiene styrene (ABS) using fused deposition modeling and layer thickness and orientation. Furthermore, a case study on a typical support frame is done to generalize the findings of the extensive experimental work done on tensile samples. Finally, fractography was performed on tensile samples via a scanning digital microscope to determine the effects of layer thickness on failure modes. Statistical analyses proved that layer thickness and raster orientation have significant effect on the mechanical properties. Tensile test results showed that samples printed with 0.2 mm layer thickness exhibit higher elastic modulus and ultimate strength compared with 0.4 mm layer thickness. These results have direct influence on decision making and future use of 3D printing and functional load bearing parts.
We have developed a method for the three-dimensional (3D) printing of continuous fiber-reinforced thermoplastics based on fused-deposition modeling. The technique enables direct 3D fabrication without the use of molds and may become the standard next-generation composite fabrication methodology. A thermoplastic filament and continuous fibers were separately supplied to the 3D printer and the fibers were impregnated with the filament within the heated nozzle of the printer immediately before printing. Polylactic acid was used as the matrix while carbon fibers, or twisted yarns of natural jute fibers, were used as the reinforcements. The thermoplastics reinforced with unidirectional jute fibers were examples of plant-sourced composites; those reinforced with unidirectional carbon fiber showed mechanical properties superior to those of both the jute-reinforced and unreinforced thermoplastics. Continuous fiber reinforcement improved the tensile strength of the printed composites relative to the values shown by conventional 3D-printed polymer-based composites.
In this paper self-sensing nanocomposite formulations made of acrylonitrile butadiene styrene and different loading (3, 5 and 10 wt%) of multi-walled carbon nanotubes have been produced and 3D printed via fused filament fabrication. The nanocomposites have been characterized from a rheological, mechanical, thermal and electrical point of view to assess the strain-sensing properties. All the samples show a piezoresistive behaviour and the electrical resistance changes when a stress is applied. The gauge factor, measure of the sensitivity, for ABS 3CNT, ABS 5CNT and ABS 10CNT are 11.36, 3.21 and 1.62, respectively. The ABS 3CNT samples have shown the best self-sensing performances with high sensitivity and this formulation has been used for producing a health-monitoring 3D-printed smart structure where the active material is placed locally in the structure. The 3D-printed structure itself is able to monitor the strain and hence the stress level to which is subjected with a gauge factor of 1.5. A finite element analysis helps to explain the reason for reduced sensitivity namely the placement of the sensing layer.
Polyether-ether-ketone (PEEK) nanocomposites with different amount of CNT (i.e. 3%, 5%, 10% by weight) have been produced in the form of filaments and successively 3D printed via fused filament fabrication. Different analytical models, based on rule of mixture and mechanical percolation have been applied to evaluate the elastic modulus and the ultimate tensile strength of PEEK-CNT composites. From the comparison of the predicted mechanical properties with those obtained experimentally the combination of Takayanagi I and Takayanagi II models, based on mechanical percolation, allows to compute the elastic modulus trend of the composites with an error less than 10%. The ultimate tensile strength Takayanagi model well represents the behaviour found experimentally, with predicted values being slightly higher than the measured ones (error < 11%). The analytical models cannot be applied to predict the mechanical behaviour of 3D printed parts because it is shown that mechanical properties of additive manufactured composites are deeply influenced by the sum of mechanical percolative behaviour and the interphase strength among 3D printed layers.
The fracture toughness of Polylactic acid (PLA) parts printed using the Fused deposition modeling (FDM) additive manufacturing process is experimentally investigated in this study. The compact tension (CT) specimens were printed with 0°/90° and −45°/45° filament orientations at different printing speeds varying from 20 mm/s to 60 mm/s. Fracture toughness values for each process parameter were estimated using the linear elastic fracture mechanics (LEFM) approach. It is observed that the CT specimen printed at the highest speed showed the lowest value of fracture toughness; however, the energy absorbed before failure is the highest. The −45°/45° CT specimen showed higher value of fracture toughness compared to the 0°/90° specimen. Tensile tests were also conducted on PLA filament and part level coupons to estimate the mechanical behavior. The FDM printed tensile coupon showed a brittle failure. However, the PLA filament showed ductile behavior with a clear plastic zone.
Objectives
To compare the marginal gap and fracture resistance of implant-supported 3-dimensional (3D) printed definitive composite crowns with those fabricated by using 3 different millable materials.
Material and Methods
A prefabricated abutment was digitized by using a laboratory scanner (E4 Lab Scanner) and a complete-coverage maxillary first premolar crown was designed (Dental Designer). Forty crowns were fabricated either by 3D printing (Saremco Print Crowntec, SP) or milling (Brilliant Crios, BC; Vita Enamic, VE; Cerasmart 270, CS) (n=10). Baseline marginal gap values were evaluated by measuring 60 predetermined points on an abutment (15 points for each side) with a stereomicroscope at ×40 magnification. Marginal gap values were reevaluated after adhesive cementation. Load-to-fracture test was performed by using a universal testing machine. Two-way analysis of variance (ANOVA) was used to evaluate the effect of material type and cementation on marginal gap values. While Tukey HSD tests were used to compare the materials’ marginal gap values before and after cementation, the effect of cementation on marginal gap values within each material was analyzed by using paired samples t-tests. Fracture resistance data were analyzed by using 1-way ANOVA (α=.05).
Results
Material type and cementation significantly affected marginal gap values (P<.001). Regardless of cementation, SP had the lowest marginal gap values (P<.001), while the differences among milled crowns were nonsignificant (P≥.14). Cementation significantly increased the marginal gap values (P<.001). Material type did not affect fracture resistance values (F=1.589, P=.209).
Conclusion
Implant-supported 3D-printed composite crowns showed higher marginal adaptation compared with the milled crowns before and after cementation. In addition, all crowns endured similar forces before fracture.
Additive Manufacturing (AM), typically known as three-dimensional (3D) printing has paved the way for fabrication of individualized products. Since 3D-printed composites show a superior strength to weight ratio, their applications have significantly increased. In the current study, fracture behavior of 3D-printed fiber-reinforced composites and steel specimens was determined and compared. Particularly, the Fused Filament Fabrication (FFF) process was used to print Semi-Circular Bending (SCB) composite specimens. In this context, nylon and glass fibers were used as matrix and fiber reinforced materials, respectively. Moreover, steel SCB specimens were fabricated and examined for comparison. All specimens were subjected to three-point bending and their mechanical behavior was examined. In this study, Digital Image Correlation (DIC) technique was utilized to measure strain on the surface of the specimen. In addition, a numerical simulation was performed to study fracture load of SCB steel specimens and verify experimental observations. The outcome of this study indicates that structural integrity of SCB specimens increases with fiber volume fraction. The documented results can be used for design, optimization, development, and simulation of 3D-printed continuous glass fiber-reinforced composites.
Additive manufacturing (AM) (also known as 3D printing) has enabled the customized fabrication of objects with complex geometries and functionalities in mechanical and electrical properties. AM technologies commonly use polymers and composites and have been advancing in a variety of industrial and emerging applications. Despite recent progress in 3D printing of polymer composites, many challenges, such as the suboptimal quality of manufactured products and limited material available for 3D printing, need to be addressed for the broad adoption of additively manufactured polymer composites. This review first provides a brief history of AM technologies along with 3D printing polymers. Subsequently, we discuss the state-of-the-art for the design of polymers and filling materials, the principles of AM processes, and emerging applications of 3D printed polymer and composites. Finally, we share our outlook of potential problems and challenges presented in AM of polymer composites, which might lead to future research directions.
Commercially available FFF machines have limitations in process reliability and quality of the products. The live monitoring of the 3D printing process could improve quality and the produced part performance. In the present work, a print-head integrated system, based on optical and thermal sensors, for live monitoring of a FFF 3D printing process was developed. A Design of Experiments (DoE) campaign has been set in order to optimise the printing process parameters for polyamide 6 (PA6), starting from the analysis of the acquired data. Experimental results show that optical and thermal cameras allow to detect invisible to naked eye defects, such as warping, incorrect filament deposition, stringing and oozing. Moreover, the thermal data have been successfully used to calculate the cooling kinetics of the different layers of a job, providing direct information related to degree of crystallinity. From DoE campaign the bed temperature has been found to be the most influential process parameter affecting morphology and mechanical properties of 3D printed samples. Optimized samples show an increase of young modulus and tensile strength up to 70% and 79% respectively compared to not optimized samples.
The mechanical behaviour of structural elements made of 3D-printed materials is numerically investigated. With this aim a multiscale approach that allows to determine the macroscopic response, as depending on the material heterogeneity at the microscale level, is conceived. A non-linear laminate finite element that employs a reduced homogenization technique at each integration Gauss point is developed. In detail, the Piecewise Uniform Transformation Field Analysis is implemented. In order to validate the procedure, some numerical applications are developed. The obtained results are compared with evidence of experimental tensile and bending tests, available in literature. The application of a multiscale strategy, employing a reduced order method at the Gauss point level for the analysis of 3D-printed structural elements, could represent a good compromise in terms of accuracy of the results and computational efficiency.
Neodymium-Iron-Boron (NdFeB) permanent magnets are essential components in many mechanical, electric and electronic devices, providing large magnetic fields with no energy consumption. Nevertheless, their poor corrosion resistance is an important issue that makes them susceptible to degradation of the magnetic properties. In this paper, the authors propose the preparation of NdFeB-Poly-ether-ether-ketone (PEEK) composites, with the dual target of protecting the magnetic alloy, preventing it from corrosion, while realizing a new 3D printable material , to produce high performance magnets with customized and optimized design. PEEK-NdFeB filaments were produced with different filler amount (15, 34 and 41 vol%). 3D printed bonded magnets were successfully produced, resulting in magnetic remanence of 82, 218, and 226 mT respectively, as well as intrinsic coercivity of 627, 684 and 672 kA/m. The influence of the filler on the thermal and mechanical properties of the resulting composites were evaluated by means of several investigation techniques.
Thermally conductive but electrically insulating polymer matrix composites are of great interest in many engineering applications such as thermal management applications (i.e. heat sinks in microelectronic packaging, cooling of mechatronic components and mechanisms). Among possible functional fillers, hexagonal boron nitride seems to be one of the most promising choice due to its high thermal conductivity, and in this work it was used as filler of polyamide 6 matrix. The resulting composites were firstly prepared in form of pellets, extruded into filaments and successively 3D printed, with the aim to study and compare the thermal performances of the 3D printed samples to the ones manufactured using traditional compression moulding technique. The thermal conductivity of 25% wt and 45% wt loaded compression moulded samples was 1 and 2.5 W/mK respectively, while the neat polymer showed a thermal conductivity of 0.29 W/mK. 3D printed samples showed the same trend, namely increasing thermal conductivity with filler amount, despite a great influence of the 3D printing processing parameters (i.e melt rheology and printing temperature) which lower the resulting thermal conductivity. 3D printed 25% and 45% by weight loaded samples showed a through plane thermal conductivity of 0.67 W/mK and 0.92 W/mK respectively, and in-plane thermal conductivity of 0.96 W/mK and 1.52 W/mK due to the presence of porosity and filler alignment along the printing direction.
The present paper studies the effect of in-plane raster orientation on the tensile and fracture strengths of poly-lactic acid (PLA) samples made by fused deposition modeling technique. Four different raster angles of 0/90°, 15/-75°, 30/-60°, and 45/-45° are selected for the dog-bone and the semi-circular bending (SCB) specimens to investigate the tensile and mode I fracture behavior of the 3D-printed PLAs. The results demonstrate anisotropic behavior in the both tensile and fracture properties of the material. Additionally, due to the plastic deformations of the material prior to the fracture initiation load, the J-integral is selected as the fracture characterizing parameter. To do so, some elastic-plastic finite element simulations were performed to obtain the critical values of J-integral. The raster orientation of 45/-45° exhibits the best performance with maximum percent elongation and fracture resistance compared with the three other raster angles. While the critical J-integral of 45/-45° sample is 6815 J/m², this value is 1839 J/m² for 0/90° sample. In addition, in the samples used for fracture tests, the crack growth path is investigated to analyze the effect of raster orientation on the fracture trajectories of the SCB specimens. Based on the observed crack growth trajectories, the difference between the fracture loads and the amounts of plastic deformation in the SCB samples with different raster orientations are justified. Finally, the scanning electron microscopy (SEM) is utilized to explore the failure mechanism in the dog-bone samples.
Permanent Rare Earth magnets are becoming more and more important in efficient motors and generator for space applications. One of the magnet most diffused composition for space application is Neodymium Iron Boron (NdFeB). These magnets are characterized by high remanence, higher coercivity and energy product, but due to their poor corrosion resistance, they are susceptible to degradation of magnetic properties. This paper offers a possible solution to the corrosion issue developing innovative 3D printed magnetic PEEK-NdFeB composite material, characterized by enhanced corrosion resistance and space environment compatibility and demonstrate the processability by means of Additive Manufacturing (AM) technologies. Peek matrix and NdFeB fillers (melt spun powders) were characterized prior to use in terms of microstructure (SEM/ EDX) and phase analysis (XRD). As part of the research activity, PEEK-NdFeB composite were extruded in feedstock filaments for FDM (fused deposition modeling) printing using different percentages of filler (i.e. 25% 50% 75% wt) as well as PEEK neat used as reference. The influence of filler on the thermomechanical properties of the composite, as well as the criticalities and effect of the 3D printing process were evaluated by means of different investigation technique. The magnetic performance of all 3D printed composite samples was then assessed.. Tensile test showed a lower tensile strength but an enhancement of the elastic module with the increase of NdFeB particles. Magnetic characterization was also performed, demonstrating the feasibility of the magnetic 3D printed composite with PEEK. The magnetic properties exhibited by FDM printed parts confirmed the feasibility of employing such a combination of an innovative manufacturing technique and high-performance PEEK-NdFeB compounds. Nomenclature (BH)max = Maximum Energy Product ∆H m = Enthalpy of Fusion at Melting ∆H c =Enthalpy of Crystallization ∆H f = Enthalpy of Fusion Tc = Crystallization Temperatures Tg = Glass Transition Temperature Tm = Melting Temperature Xc = Amount of Cristallinity (during cooling cycle) Xm = Amount of Cristallinity (during melting cycle)
The research presented in this article discusses the subject of poly(lactic acid) (PLA) modification via reactive mixing with poly(butylene adipate-co-terephthalate) (PBAT) copolymer for 3D printing applications. Filaments suitable for fused deposition modeling (FDM) were prepared from blends of PLA containing 10, 20 and 30% by weight of PBAT. Mechanical testing clearly indicated that the blending with PBAT effectively increases the impact strength of PLA, from an initial value of approximately 30 J/m, to more than 700 J/m for the optimized PLA/PBAT (30%) chain extender modified blend. The addition of the multifunctional chain extender (ESA) also has a positive effect on the rheological profile of the PLA/PBAT materials, which facilitates both the production process of the extruded filament and the maintenance of a stable width of the printed material path. Despite the use of a significant PBAT content, analysis of thermo-mechanical properties did not show any significant deterioration in the thermal resistance of the materials, while a detailed differential scanning calorimetry (DSC) analysis indicates a small tendency to nucleate the PLA structure by PBAT inclusions. The structural analysis of scanning electron microscopy (SEM) clearly indicates a change in the mechanism of deformation from brittle fracture for pure PLA, to more favorable shear yielding for PBAT rich blends. The comparison of the properties of printed and injected PLA/PBAT blends indicates the possibility of obtaining similar or in some respects better mechanical properties, especially for ESA modified samples.
Purpose
Lightweighting of components in the automotive industry is a prevailing trend influenced by both consumer demand and government regulations. As the viability of additively manufactured designs continues to increase, traditionally manufactured components are continually being replaced with 3D-printed parts. The purpose of this paper is to present experimental results and design considerations for 3D-printed acrylonitrile butadiene styrene (ABS) components with non-solid infill sections, addressing a large gap in the literature. Information published in this paper will guide engineers when designing fused deposition modeling (FDM) ABS parts with infill regions.
Design/methodology/approach
Uniaxial tensile tests and three-point bend tests were performed on 12 different build configurations of 20 samples. FDM with ABS was used as the manufacturing method for the samples. Failure strength and elastic modulus were normalized on print time and specimen mass to quantify variance between configurations. Optimal infill configurations were selected and used in two automotive case study examples.
Findings
Results obtained from the uniaxial tensile tests and three-point bend tests distinctly showed that component strength is highly influenced by the infill choice selected. Normalized results indicate that solid, double dense and triangular infill, all with eight contour layers, are optimal configurations for component regions experiencing high stress, moderate stress and low stress, respectively. Implementation of the optimal infill configurations in automotive examples yielded equivalent failure strength without normalization and significantly improved failure strength on a print time and mass normalized index.
Originality/value
To the best of the authors’ knowledge, this is the first paper to experimentally determine and quantify optimal infill configurations for FDM ABS printed parts. Published data in this paper are also of value to engineers requiring quantitative material properties for common infill configurations.
A mixture design of experiment (DoE) was used to guide the fabrication and analysis of sustainable poly (lactic acid) (PLA) and biobased poly (butylene succinate) (BioPBS) 3D printing filaments. The statistical DoE approach was employed to investigate the correlation between the mechanical properties of the PLA/BioPBS blends at different PLA and BioPBS loadings and to obtain linear regression models of the mechanical properties of the blends. The statistical models help to design PLA/BioPBS blends with the desired mechanical properties. The PLA/BioPBS blends with different composition ratios were 3D printed via fused deposition modelling (FDM). The 3D printability of the polymer blends was determined by the flowability and dimensional stability of the filaments, provided by fundamental rheological and coefficient of linear thermal expansion (CLTE) studies. Preliminary research found that the printability of PLA/BioPBS filament with BioPBS content higher than 50% was unsuccessful due to high viscosity and low thermal stability. These findings were verified with rheological tests for ranges of PLA/BioPBS blend ratios and thermomechanical studies. Rheological results show a significant increase of the blend viscosity when BioPBS content in the blend was higher than 50%. Additionally, the CLTE drastically increased with higher levels of BioPBS, making the PLA/BioPBS filament thermally unstable during FDM processing. These results confirmed that the printability of PLA/BioPBS filament is greatly influenced by the blend viscosity and the printing temperature. Rheological studies revealed that the viscosity range of a 3D printable PLA/BioPBS filament lies within 1000 – 100 Pa.s. scanning electron microscopy (SEM) and polarized optical microscopy (POM) images confirmed that PLA and BioPBS are immiscible. However, the addition of BioPBS improved the ductility and the crystallinity of PLA., PLA/BioPBS (90/10) showed an interesting result in that it obtained higher tensile and impact strengths than the neat PLA, which was attributed to crystallinity and morphological factors.
In the present study additive manufacturing of Polylactic acid by fused deposition modeling were investigated based on statistical analysis. The honeycomb internal pattern was employed to build inside of specimens due to its remarkable capability to resist mechanical loads. Simplify 3D was utilized to slice the 3D model and to adjust fixed parameters. Layer thickness, infill percentage, and extruder temperature were considered as controlled variables, while maximum failure load (N), elongation at break (mm), part weight (g), and build time (min) were selected as output responses and analysed by response surface method. Analysis of variance results identified layer thickness as the major controlled variable for all responses. Interaction of infill percentage and extruder temperature had a significant influence on elongation at break and therefore, tough fracture of printed parts. The input parameters were optimized to materialize tow criteria; the first one was to rise maximum failure load and the second was to attain tough fracture and lessen build time and part weight at a time. Optimal solutions were examined by experimental fabrication to evaluate the efficiency of the optimization method. There was a good agreement between empirical results and response surface method predictions which confirmed the reliability of predictive models. The optimal setting to fulfill the first criterion could bring on a specimen with more than 1500 (N) maximum failure load and less than 9 (g) weight.
The present paper concerns the additive layer manufacturing of polyether-ether–ketone (PEEK) by means of fused deposition modelling (FDM). PEEK is a high-performance polymer (outstanding mechanical properties, high thermal stability and chemical resistance), suitable for space applications, that, however, due to its semicrystalline nature is difficult to process; moreover, only very few FDM printers suitable for PEEK are currently available on the market. In this paper the results of mechanical (tensile tests), thermal (DSC), microstructural (XRD) and morphological (OM and CT-scans) testing of FDM printed PEEK samples are reported, and some of them compared with that of the extruded filament prior to printing. The results evidence the effect of the process on the printed parts in terms of thermal and mechanical properties including fracture mechanism. Moreover, the impact of printing parameters (as infill and filament deposition pattern) on the final mechanical performance is evidenced too, as it is linked to the resisting cross section.
Purpose
This study aims to investigate issues of quality and quality control (QC) in three-dimensional (3D) printing by reviewing past work and current practices. Possible future developments are also discussed.
Design/methodology/approach
After a discussion of the major quality dimensions of 3D-printed objects, the applications of some QC techniques at various stages of the product life cycle (including product design, process planning, incoming QC, in-process QC and outgoing QC) are introduced.
Findings
The application of QC techniques to 3D printing is not uncommon. Some techniques (e.g. cause-and-effect analysis) have been applied extensively; others, such as design of experiments, have not been used accurately and completely and therefore cannot optimize quality. Taguchi’s method and control charts can enhance the quality of 3D-printed objects; however, these techniques require repetitive experimentation, which may not fit the work flow of 3D printing.
Originality/value
Because quality issues may discourage customers from buying 3D-printed products, enhancing 3D printing quality is imperative. In addition, 3D printing can be used to manufacture diverse products with a reduced investment in machines, tools, assembly and materials. Production economics issues can be addressed by successfully implementing QC.
In the food packaging sector many efforts have been (and are) devoted to the development of new materials in order to reply to an urgent market demand for green and eco-sustainable products. Particularly a lot of attention is currently devoted both to the use of compostable and biobased polymers as innovative and promising alternative to the currently used petrochemical derived polymers, and to the re-use of waste materials coming from agriculture and food industry. In this work, multifunctional eco-sustainable systems, based on poly(lactic acid) (PLA) as biopolymeric matrix, diatomaceous earth as reinforcing filler and spent coffee ground extract as oxygen scavenger, were produced for the first time, in order to provide a simultaneous improvement of mechanical and gas barrier properties. The influence of the diatomite and the spent coffee ground extract on the microstructural, mechanical and oxygen barrier properties of the produced films was deeply investigated by means of X-Ray diffraction (XRD), infrared spectroscopy (FT-IR, ATR), scanning electron microscopy (SEM), uniaxial tensile tests, O2 permeabilimetry measurements. An improvement of both mechanical and oxygen barrier properties was recorded for systems characterised by the co-presence of diatomite and coffee grounds extracts, suggesting a possible synergic effect of the two additives.
Purpose
This paper aims to present the methodology and results of the experimental characterization of three-dimensional (3D) printed ABS and polycarbonate (PC) parts utilizing digital image correlation (DIC).
Design/methodology/approach
Tensile and shear characterization of acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) 3D-printed parts was performed to determine the extent of anisotropy present in 3D-printed materials. Specimens were printed with varying raster ([+45/-45], [+30/-60], [+15/-75], and [0/90]) and build orientations (flat, on-edge, and up-right) to determine the directional properties of the materials. Tensile and Isopescu shear specimens were printed and loaded in a universal testing machine utilizing 2D digital image correlation (DIC) to measure strain. The Poisson’s ratio, Young’s modulus, offset yield strength, tensile strength at yield, elongation at break, tensile stress at break, and strain energy density were gathered for each tensile orientation combination. Shear modulus, offset yield strength, and shear strength at yield values were collected for each shear combination.
Findings
Results indicated that raster and build orientation had a negligible effect on the Young’s modulus or Poisson’s ratio in ABS tensile specimens. Shear modulus and shear offset yield strength varied by up to 33% in ABS specimens signifying that tensile properties are not indicative of shear properties. Raster orientation in the flat build samples reveals anisotropic behavior in PC specimens as the moduli and strengths varied by up to 20%. Similar variations were also observed in shear for PC. Changing the build orientation of PC specimens appeared to reveal a similar magnitude of variation in material properties.
Originality/value
This article tests tensile and shear specimens utilizing DIC, which has not been employed previously with 3D-printed specimens. The extensive shear testing conducted in this paper has not been previously attempted, and the results indicate the need for shear testing to understand the 3D-printed material behavior fully.
This article explores the influence of production technique on the strength of nylon parts. Identical specimens were manufactured by various techniques. The material of specimens was nylon PA6. 3D printing and injection molding were used, with various orientations of printed layers, and various orientations of specimens in the working space of the 3D printer. The variants are described in detail. A special mold was used for the injection molding process in order to make specimens with and without a weld line. The effect of this weld line was evaluated. All specimens were tested using the standard tensile test configuration. The strength was compared. It was found that the same plastic material has very different mechanical properties depending on the production process.
Fused deposition modelling is a rapidly growing additive manufacturing technology due to its ability to build functional parts having complex geometries. The mechanical properties of a built part depend on several process parameters. The aim of this study is to characterize the effect of build orientation, layer thickness and feed rate on the mechanical performance of PLA samples manufactured with a low cost 3D printer. Tensile and three-point bending tests are carried out to determine the mechanical response of the printed specimens.
Fully dense PLA blocks were manufactured by 3D-printing, depositing a polymer filament in a single direction via the fusion deposition method (FDM). Specimens were cut from printed blocks using conventional machining and were used to perform tension, compression and fracture experiments along different material directions. The elasto-plastic material response was found to be orthotropic and characterised by a strong tension-compression asymmetry; the material was tougher when loaded in the extrusion direction than in the transverse direction. The response of the unidirectional, 3D-printed material was compared to that of homogeneous injection-moulded PLA, showing that manufacturing by 3D-printing improves toughness; the effects of an annealing thermal cycle on the molecular structure and the mechanical response of the material were assessed.
Global awareness of material sustainability has increased the demand for bio-based polymers like poly(lactic acid) (PLA), which are seen as a desirable alternative to fossil-based polymers because they have less environmental impact. PLA is an aliphatic polyester, primarily produced by industrial polycondensation of lactic acid and/or ring-opening polymerization of lactide. Melt processing is the main technique used for mass production of PLA products for the medical, textile, plasticulture, and packaging industries. To fulfill additional desirable product properties and extend product use, PLA has been blended with other resins or compounded with different fillers such as fibers, and micro and nanoparticles. This paper presents a review of the current status of PLA mass production, processing techniques and current applications, and also covers the methods to tailor PLA properties, the main PLA degradation reactions, PLA products' end-of-life scenarios and the environmental footprint of this unique polymer.
Most desktop 3D printers designed for the consumer market utilize a plastic filament extrusion and deposition process to fabricate solid objects. Previous research has shown that the operation of extrusion-based desktop 3D printers can emit large numbers of ultrafine particles (UFPs: particles less than 100 nm) and some hazardous volatile organic compounds (VOCs), although very few filament and printer combinations have been tested to date. Here we quantify emissions of UFPs and speciated VOCs from five commercially available desktop 3D printers utilizing up to nine different filaments using controlled experiments in a test chamber. Median estimates of time-varying UFP emission rates ranged from ~108 to ~1011 #/min across all tested combinations, varying primarily by filament material and, to a lesser extent, bed temperature. The individual VOCs emitted in the largest quantities included caprolactam from nylon-based and imitation wood and brick filaments (ranging from ~2 to ~180 μg/min), styrene from acrylonitrile butadiene styrene (ABS) and high-impact polystyrene (HIPS) filaments (~10 to ~110 μg/min), and lactide from polylactic acid (PLA) filaments (~4 to ~5 μg/min). Results from a screening analysis of the potential exposures to these products in a typical small office environment suggest caution should be used when operating many of the printer and filament combinations in enclosed or poorly ventilated spaces or without the aid of a combined gas and particle filtration system.