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3D concrete printing – a structural engineering perspective

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... • Deposition of medium-fine filaments with cross-sectional dimensions up to several cm. Contour Crafting at University of Southern California [8,[41][42][43] and 3DCP at Eindhoven University of Technology [10,44] belong to this group. In both cases, the printing head is part of a 3-axis gantry robot. ...
... Further tests and standardizations are essential to enable engineers to derive reliable product properties depending on the chosen feedstock material, printing process, and process parameters. To this end, it is also necessary to develop and validate simulation models for different AM processes [44]. Moreover, a widely automated digital planning workflow is needed, allowing to represent and store complex geometric and material data, to consider manufacturing constraints, as well as to perform numerical simulations efficiently for any printable geometry. ...
... Along with various measurement results, the FE computations are used for the structural verification of the 3D-printed metal bridge [101]. Overall, however, there is a significant lack of experimental data and validated models for printed building components [44,98,184]. This is a major obstacle for establishing computation-based proofs of stability and serviceability. ...
Article
Full-text available
The application of additive manufacturing (AM) in construction has been increasingly studied in recent years. Large robotic arm- and gantry-systems have been created to print building parts using aggregate-based materials, metals, or polymers. Significant benefits of AM are the automation of the production process, a high degree of design freedom, and the resulting potential for optimization. However, the building components and 3D-printing processes need to be modeled appropriately. In this paper, the current state of AM in construction is reviewed. AM processes and systems as well as their application in research and construction projects are presented. Moreover, digital methods for planning 3D-printed building parts and AM processes are described.
... ? permanent shuttering where the shutter is printed and the structural element is cast conventionally (a and b). The orientation of manufacture also varies and is either predominantly vertical (Figure 2 b, c, d and f) 25 or horizontal ( Figure 2 a and e). Components can be predominately planar (Figure 2 a, b, d, e and f) or volumetric ( Figure 2c). ...
... Tall structures which must be manufactured in a vertical orientation (Figure 2: d, for example) are par- ticularly affected and early-age mechanical behavior [24] and modelling [25] are of interest. Two approaches to alleviate build up rate problems have been suggested: the dynamic adjustment of the nozzle height during 155 printing [23]; and the careful control of build up rate, which may include the addition of accelerators injected prior to extrusion to speed up the hardening of lower layers such that they are capable of maintaining the progressively increasing load [12,26]. ...
... Hatching patterns developed for conventional additive manufacturing are often not appropriate for 3DCP because they do not account for these process constraints [11,21]. Work is needed to develop these codes, as well as the development of geometry capture, both during build and for conformity verification [42,25]. ...
Article
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Large-scale additive manufacturing processes for construction utilise computer-controlled placement of extruded cement-based mortar to create physical objects layer-by-layer. Demonstrated applications include component manufacture and placement of in-situ walls for buildings. These applications vary the constraints on design parameters and present different technical issues for the production process. In this paper, published and new work are utilised to explore the relationship between fresh and hardened paste, mortar, and concrete material properties and how they influence the geometry of the created object. Findings are classified by construction application to create a matrix of issues that identifies the spectrum of future research exploration in this emerging field.
... Though the increases of concern have improved the literature in this field, it introduces objections for investigators to obtain an outline of the study improvement [6]. ...
... Figure 2 provides an overview of areas that have houses built by using 3DP technologies as well as Indonesia and Malaysia were not one of these countries using C3DP in future house projects. C3DP could modify its settings to conform to the speed rate, amount, and kind of printing material being consumed in printing a three-room house [6]. Several benefits of C3DP techniques, for instance reducing time and cost savings, decreasing the contamination of ecosystem and reduction of damages and accidents on construction sites might be refer to death. ...
Article
Full-text available
Global construction industry for construction 3D printing(3DP) is a novel technique that has started since 3DP innovation in 1981 while still, this technique has undergone a challenge in Indonesia and Malaysia's construction industry. Applying 3DP in the construction industry has given various benefits more than the conventional construction way. The most witnessed challenges in this technology are printing material, print equipment, stakeholders, and suppliers. Moreover, the absence of standard codes and policies, structural solidity, and extensibility have been over and over referred to as the most critical issues facing the designers. This research introduces the qualitative analysis based on a questionnaire to evaluate the environmental aspects and then analyze it by applying the strategic planning technique SWOT matrix to help identify strengths, weaknesses, opportunities, and threats related to this aspect. This research attempted to investigate the environmental aspects of Construction by 3D Printing (C3DP) will be the trending technology in the next 10 years. The research also offers some future research ideas, insights, and recommendations.
... All rights reserved. crete additive manufacturing (AM) state of the art can be found elsewhere [1,2,4,9,10]. AM methods regarding selective binder jetting [11,12] will not be covered in this study. ...
... This effect becomes increasingly significant as new layers are built, since the distance between the nozzle and the material increases, and it can ultimately cause the filament to move laterally before being placed, causing instability (buckling) of the whole structure [7]. This phenomenon is relevant when printing tall structures [9,34]. Two approaches to address this problem have been studied: a real-time adjustment of the height of the nozzle while printing based on the real-time deformability of the structure [34], and the control of the structuration rate by using accelerators sprayed at the nozzle and reducing the printing speed (set on-demand solution) [22,35]. ...
Article
Additive manufacturing relies on the deposition of layers of material upon existing ones. The nature of this method disadvantages materials such as concrete due to the rheological changes of the material over time, the lack of standardization of the printing process, and the nature of the deposition process. This paper examines the significance of infill printing patterns on the anisotropic properties of 3D printed concrete. The rheological properties, the compressive strength, and the interlayer and interfilamentous bond strength of the 3D printed concrete were characterized. We show that there is a directional dependency on all the infill patterns. The specimens show lower compressive strength, and modulus of elasticity in the Z (extrusion) direction compared with the X and Y directions but insignificant difference of the strength and modulus between the X and Y directions. However, no directional dependency was found for the strain at failure. On the other hand, no significant difference in the mechanical properties of 3D printed concrete was observed or can be attributed to the infill printing patterns. The results also show that the 3D printed concrete shows higher compressive strength, for two out of the three testing directions (X and Y) than conventionally cast concrete. This is due to the compactness associated with the printing process that is strongly dependent on the printing parameters.
... Since then, AM technologies have made incredible progresses allowing the use of different materials, e.g. polymers [3,4], metals [5,6], cementitious [7,8] and bio materials [9] at different scales. A review of terminology related to AM can be found in [1]. ...
... The above printing process should result in a material with orthotropic/anisotropic behavior, as with other binder jet printers [7]. ...
Article
Full-text available
Additive manufacturing can be used for the construction of small-scale specimens that are useful for the understanding of the seismic behavior of conventionally constructed masonry structures. In fact, it can provide useful information for the validation of the global level assumptions that numerical models of structures have to make, but are hard to validate as large-scale tests are very expensive. To this end, this paper suggests the use of a Binder Jet printer to manufacture small-scale masonry models. The first step for such a validation procedure is the determination of the mechanical properties of the bulk material printed with a Binder Jet printer. Compression and bending tests on a sand based printer that uses furan binder shows that the bulk material presents anisotropy in compression, but to a lesser degree than other powder based printers. In tension, the anisotropy is found to be statistically insignificant-in stark contrast with values reported in the literature for powder based printers. Aging is found to be crucial for the mechanical properties: They are found to reach a plateau after 15 days of curing time. No scale phenomena were observed for length scales between 50 and 100 mm.
... First experiences with 3D concrete printing by the authors [5,13] and other research institutes [14,15] have shown that both the print- ability (i.e. the structural integrity of the object during printing) and the post-print properties (e.g. interface strength) are highly dependent on print process parameters, such as time, temperature, kinematics etc. ...
Article
A numerical model was developed to analyse the mechanical behaviour of fresh, 3D printed concrete, in the range of 0 to 90 min after material deposition. The model was based on a time-dependent Mohr-Coulomb failure criterion and linear stress-strain behaviour up to failure. An experimental program, consisting of unconfined uniaxial compression tests and direct shear tests, was set-up and performed to obtain the required material properties. The material tests showed that the Young's modulus and cohesion linearly increase with fresh concrete age, as do the compressive and shear strength. The Poisson's ratio and angle of internal friction, on the other hand, remain constant. Subsequently, the model was validated by comparison to printing experiments. Modelling of the printed samples reproduced the experimental results qualitatively, but the quantitative agreement with the print experiments could be improved. However, the deviations can well be explained and the type of failure-deformation mode was predicted accurately.
... With digitally fabricated concrete (DFC) quickly outgrow- ing the laboratory phase, as showcased by recent examples such as a pedestrian bridge in Spain (3ders 2017a), a bicycle bridge in the Netherlands ( Salet et al. 2018), an office hotel in Denmark (3dprinthuset 2017), and a workshop in Dubai (3ders 2017b), the quest for tensile capacity and ductility has become a major issue ( Salet et al. 2017;) because conven- tional reinforcement techniques are either incompatible with DFC, or largely cancel out its potential benefits. Several innovative concepts have been presented that provide ductility and tensile capacity to printed concrete in an automated fashion, including robotised placement of mesh-reinforcement and automatically entrained cable reinforcement (Hack and Lauer 2014;Hack et al. 2015;Bos et al. 2017). ...
Article
Full-text available
With the number of 3D printed concrete structures rapidly increasing, the demand for concepts that allow for robust and ductile printed objects becomes increasingly pressing. An obvious solution strategy is the inclusion of fibers in the printed material. In this study, the effect of adding short straight steel fibers on the failure behaviour of Weber 3D 115-1 print mortar has been studied through several CMOD tests on cast and printed concrete, on different scales. The experiments have also been simulated numerically. The research has shown that the fibers cause an important increase in flexural strength, and eliminate the strength difference between cast and printed concrete that exists without fibers. The post-peak behaviour, nevertheless, has to be characterised as strongly strain-softening. In the printed specimens, a strong fiber orientation in the direction of the filament occurs. However, this has no notable effect on the performance in the tested direction: cast and printed concrete with fibers behave similarly in the CMOD test. For the key parameters, no scale effect was found for the specimens with fibers, contrary to the ones without. Numerical modelling of the test by using the Concrete Damage Plasticity material model of Abaqus, with a Thorenfeldt-based constitutive law in compression and a customised constitutive law in tension, results in a reasonable fit with the experimental results.
... The use of cable reinforcement as a more advanced concept is illustrated by Salet et al. [2018], Bos et al. [2017], and Bos et al. [2018]. At TU/e, an entrainment device that can embed various types of cables has been developed. ...
Preprint
Full-text available
Concrete is by volume the most widely used building material all over the world. The concrete industry emits large quantities of greenhouse gases. Therefore, developing low CO2 concrete becomes an urgent issue for those countries with significant concrete production and consumption. In recent years, 3D concrete printing (3DCP) which is a new concrete construction method, is being developed by many research institutions and enterprises throughout the world. The primary advantages of 3DCP include increasing architecture flexibility, reducing labor usage, as well as saving in-situ construction time and cost. According to the statements by Tay et al. [2017], Wolfs et al. [2018], and Bos et al. [2016], 3DCP as a future construction trend may be a potential low CO2 approach. Thus, the objective of this paper is to critically explore the possible low CO2 strategies for 3DCP which have not been systematically conducted so far. Initially, this study introduces an overview of 3DCP by reviewing the relevant publications over last 20 years. Moreover, the potential low CO2 aspects of 3DCP are illustrated and discussed. Finally, the challenges and opportunities of developing 3DCP are analyzed and summarized. Overall, 3DCP is exploring possibilities of a low CO2 concrete approach, since it might consume less concrete materials and does not need formwork. On the other hand, to maximize CO2 reduction and accelerate the development of this technique, the future routes of 3DCP can be identified such as developing low CO2 printable concrete, seeking the proper reinforcement methods, improving print quality and capability.
... The speed and frequency of the pump were reduced around corners of the structure. The nozzle standoff distance [76] (height of the print head above the print surface or distance between the nozzle and the print surface) was identified as an important parameter to control the shape and properties of the printed structures [78]. Reducing the nozzle standoff distance to slightly less than the nozzle opening may facilitate compaction and interface adhesion [30]. ...
Article
Additive manufacturing (AM) has had an enormous impact on the manufacturing sector. Its role has evolved from printing prototypes to manufacturing functional parts for a variety of applications in the automotive, aerospace, and medical industries. Recently, AM processes have also been applied in the infrastructure construction industry. Applications of AM processes could bring in significant improvements in infrastructure construction, specifically in the areas of productivity and safety. It is desirable to have a review on the current state of emerging AM processes for infrastructure construction and existing gaps in this field. This paper reviews the AM processes in infrastructure construction. It discusses the process principle, application examples, and gaps for each of the AM processes.
... Finally, the material has to yield appropriate mechanical properties, e.g. compressive strength [7,[18][19][20]. Conventional foam concrete features good workability and flowability, which are promising with respect to the process parameters extrudability and pumpability as required for 3Dprinting. ...
Preprint
Full-text available
3D-printing with foam concrete, which is known for its distinct physical and mechanical properties, has not yet been purposefully investigated. The article at hand presents a methodological approach for the mixture design of 3D-printable foam concretes and a systematic investigation of the potential application of this type of material in digital construction. Three different foam concrete compositions with water-to-binder ratios between 0.33 and 0.36 and having densities of 1100 to 1580 kg/m³ in the fresh state were produced with a pre-foaming technique using a protein-based foaming agent. Based on the fresh-state tests, including 3D-printing as such, an optimum composition was identified and its compressive and flexural strengths were characterised. The printable foam concrete showed compressive strength above 10 MPa and low thermal conductivity, which make it suitable for 3D-printing applications, while fulfilling both load-carrying and insulating functions.
... However, till now it is not clear to what extent those structures are applied structurally, and what strategies have been applied to achieve structural safety. Alternatively, for the first time, researchers at TU/e demonstrated the ability to print concrete in combination with steel reinforcement and fiber Salet et al., 2018). Significant post-cracking deformations and post-cracking strength is achieved by printing reinforcement with concrete. ...
... The last decade has seen an increase in research topics related to concrete 3d printing [4] as well as in the apparitions of its commercial applications at a large scale. Houses, columns inspired by organic shapes, walls with specific insulation properties [5], even bridges [6] have been printed, extending each time the design space associated with the technology. ...
Article
3d printing of cementitious material is a relatively new additive manufacturing process whose growing interest and fast development is mainly due to the digitalised manufacturing, allowing the disposition of material where it pleases. Yet, due to the properties of the fresh material and the difficulty to generate paths for the robots, the printed geometries have remained simple. In this regard, this papers longs to broaden the range of printable shapes by proposing a process-aware exploration of the 3d printing design space. This is done by looking at historic strategies that have been developed to build cantilevers, vaults and domes in masonry - a more ancient additive manufacturing process. Similarities and main differences between the two processes are pointed out, at the scale of the component, the layer and the global structure. From that a classification of masonry strategies to build cantilevers is proposed, facilitating the identification of parameters for 3d printing that will allow to reproduce such structures. Later, some guidelines for the design of printable geometries and the generation of robotic toolpaths are given, in the light of previous findings.
... Since previous work showed that this reinforcement approach is not suitable as the main reinforcement, this reinforcement strategy is used to provide shear reinforcement. For comparison, steel cables are used as shear reinforcement, which is derived from previous work [5,6]. For the longitudinal reinforcement, this study investigates the use of post-tensioning or conventional reinforcement, similar as in previous studies [7]. ...
Conference Paper
Full-text available
This study investigates the structural behaviour of different reinforcement concepts for extrusion-based 3D concrete printed beams. As longitudinal reinforcement, unbonded post-tensioning and passive bonded reinforcement are explored. As shear reinforcement, fibres and cables placed between the layers of concrete are analysed. The results of four-point bending tests show that unbonded reinforcement leads to highly brittle failure without a proper activation of the shear reinforcement. The beams with conventional bonded reinforcement behave monolithically, with little influence of the concrete layer-ing. Cables, as well as fibres, increase the shear resistance significantly. While cables have higher efficiency, fibres lead to finer and more closely spaced cracks.
... The structural performance of 3D-printed construction is related to both printing parameters and overall print quality. Consequently, strict process control is required to ensure predictable, repeatable results [93]. Reliability and repeatability are particularly important in remote environments, when material, labor, and time constraints require guaranteed success on the first printing attempt. ...
Article
Full-text available
3D-printed construction is an additive, layer-by-layer construction method with the potential to reduce material consumption, optimize design, decrease construction time, lower labor requirements, minimize logistical demand, improve sustainability, and reduce costs as compared to conventional construction. This paper presents the results of a systematic review of 4491 publications spanning from 1998 through 2019. The review presents the viability of 3D-printed construction as a replacement for conventional construction methods, specifically in remote, isolated, or expeditionary environments, where conventional construction capability may be limited. The paper includes an analysis and characterization of the existing body of 3D-printed construction literature before evaluating seven viability factors of the method: materials, structural design, process efficiency, logistics, labor, environmental impact, and cost. In addition, the paper highlights three case studies of 3D-printed construction in remote, isolated, and expeditionary environments. The paper concludes by suggesting areas of future research to ensure the viability of this technology, such as printing full-scale structures and components with locally sourced materials in uncontrolled environments, defining standards for 3D printing, automating additional construction processes, and performing both environmental impact and cost life-cycle analyses. With continued investment in research and development, 3D printing could become a more viable and accepted method of construction, transforming the way the industry is managed in remote, isolated, and expeditionary environments.
Article
The hardened-state mechanical characteristics of 3D printable concrete (3DPC) mixtures exhibit a strong dependence on the employed extrusion-based process, material, and design parameters and are predominantly anisotropic by nature. It has been shown that at the heart of the observed mechanical anisotropy lies the microstructural morphology of the manufactured component. Additionally, it is hypothesised that a linear Coulomb friction assumption misrepresents the interfacial compression-shear constitutive behaviour exhibited in 3DPC. Thus, additional calibration of the shear model parameters is sought, forming the basis for the current investigation. In this regard, the present contribution offers a comprehensive investigation of the constant compression-shear performance of a fibre-reinforced printable concrete (FRPC) mixture via a direct shear test (DST) methodology for concrete samples additively manufactured by extrusion-based 3D concrete printing (3DCP). The anisotropic material strength is studied in the three orthogonal material planes, then suitable failure criteria are considered, and a novel modified Mohr-Griffith criterion is proposed. X-ray computed tomography (CT) is employed to explore the microstructural morphology (pore size, shape, orientation, and total porosity content), fracture surface angle, and fracture surface area of 3DCP inter and intralayers compared to specimens cast from the same FRPC mixture. A mechanistic evaluation of the constant compression-shear performances relates the ensuing shear strength to the microstructural morphology observed in the experimentally assessed samples. Thereby, this contribution provides the basis for a fundamentally more detailed understanding of the hardened-state mechanical capacity of 3DPC, which is supported by a novel failure criterion and solid theoretical explanations of the influential microstructural features affecting the mechanical characteristics. Finally, it is postulated that improved mechanical performance and reduced anisotropy, conjuring less material complexity and uncertainty, is permitted by stabilising the microstructural morphology in 3DPC.
Chapter
Additive manufacturing (AM) or 3D printing is a rapid prototyping process that has captured the attention of architects and designers worldwide in the last few years. Multiple research groups and commercial entities are exploring different areas of 3D concrete printing (3DCP) with one of the main topics being the potential to improve the design freedom, while simultaneously achieving sufficient structural ductility. Based on the target design impression of a free form 3DCP structure, this study presents a number of 3DCP strategies to print arbitrary double-curved geometries with improved concrete ductility. A digital design-to-fabrication workflow was applied, consisting of defining parameters at various stages of the process. Two case study objects have been printed, both featuring double-curved surfaces achieved through cantilevered printing with support material, and by printing on a curved support surface, respectively. The former object acted as support for the latter. Entrained cables and secondarily added glass fibres were used to obtain ductility. The result is a double-curved 1 \(\times \) 1 m panel with fibre-reinforced printed concrete, as well as a double curved print bed, reinforced with high strength steel cables.
Article
Full-text available
Concrete is by volume the most widely used building material all over the world. The concrete industry emits large quantities of greenhouse gases. Therefore, developing low CO2 concrete becomes an urgent issue for those countries with significant concrete production and consumption. In recent years, 3D concrete printing (3DCP) which is a new concrete construction method, is being developed by many research institutions and enterprises throughout the world. The primary advantages of 3DCP include increasing architecture flexibility, reducing labor usage, as well as saving in-situ construction time and cost. According to the statements by Tay et al. [2017], Wolfs et al. [2018], and Bos et al. [2016], 3DCP as a future construction trend may be a potential low CO2 approach. Thus, the objective of this paper is to critically explore the possible low CO2 strategies for 3DCP which have not been systematically conducted so far. Initially, this study introduces an overview of 3DCP by reviewing the relevant publications over last 20 years. Moreover, the potential low CO2 aspects of 3DCP are illustrated and discussed. Finally, the challenges and opportunities of developing 3DCP are analyzed and summarized. Overall, 3DCP is exploring possibilities of a low CO2 concrete approach, since it might consume less concrete materials and does not need formwork. On the other hand, to maximize CO2 reduction and accelerate the development of this technique, the future routes of 3DCP can be identified such as developing low CO2 printable concrete, seeking the proper reinforcement methods, improving print quality and capability.
Chapter
Full-text available
Extrusion-based additive manufacturing (AM), or three-dimensional (3D) printing, has matured into a set of advanced methods to automate the construction of large-scale concrete structures, while minimizing cost and material waste. However, current AM data models are inadequate for 3D concrete printing due to insufficient incorporation of information on the relationships between process, material, and geometry, which may cause redundancy, information loss, and inconsistencies. Aiming at improving AM data modeling for concrete printing, this paper proposes a metamodeling approach for AM of concrete structures, referred to as “printing information modeling”, which takes advantage of building information modeling (BIM). As will be shown in this paper, the BIM-based printing information model, serving as a metamodel, incorporates the digital data triplet of process, material, and geometry parameters to generate computer numerical control (CNC) commands that may readily be used for concrete printing. A validation test is performed, which instantiates the printing information model, using a BIM model, for generating CNC commands, enabling optimal digital data exchange from BIM models to concrete printers. As a result of this study, it is demonstrated that printing information modeling adequately defines the information required for AM of concrete structures using a BIM-based approach, showing promising potential to improve current AM data modeling efforts.
Article
Conventional cement-based concrete is widely used as a construction material due to its ability to flow before hardening and to adopt the shape of the formwork as it is placed. Contrarily, in layered extrusion additive manufacturing, commonly known as three-dimensional (3D) printing, concrete is shaped without formwork. This imposes stringent time-dependent rheological requirements of materials used for 3D printing. Polymer concrete (PC) is a material extensively used in the precast industry. This paper reports on the potential use of PC for 3D printing applications. The influence of mixture design parameters—specifically rheology modifier content, filler-polymer ratio, and aggregate-polymer ratio—on the rheological properties of a 3D-printable PC are investigated. The rheological properties of seven PC mixtures are tested and characterized. PC can be described as a Bingham pseudoplastic material, and a Herschel-Bulkley model can accurately describe its rheological behavior (dynamic shear stress) over time. The evolution of static yield stress over time was found to follow an exponential trend. The use of these models to predict the dynamic and static yield stress of PC shall enable the design of efficient and stable 3D printing. Finally, 3D-printed PC shows good mechanical performance with compressive strength above 30 MPa (4351 psi) at 7 days of age. Automation of the PC precast industry using 3D printing will create new opportunities for the use of PC in civil infrastructure.
Article
3D Printing of Concrete is gaining more attention with time as an alternative method for construction for its high degree of freedom. Until now, most of 3D printed elements are pre-printed then moved to their designated locations. The most practical method for moving printed elements is lifting them by means of implemented anchors. However, due to the nature of this construction method, it does not allow for any type of vibration, also due to the use of a special type of concrete mix, that do not flow by itself, there are still a lot of queries concerning the adherence of concrete with steel bars. The objective of this paper is to characterize the bond between steel and printed mortars as a function of mortar’s workability and printing method. Pull-out tests of an 8 mm steel bar embedded in either printed or non-printed mortars of varying workability have been performed after 3 days of casting. It is found that the workability of the ink does not affect the pull-out strength, neither the printing method nor layers direction affect the pull-out strength in respect to the steel bar.
Article
Experimental measurements are a critical component of model development, as they are needed to validate the accuracy of the model predictions. Currently, there is a deficiency in the availability of experimental data for laser powder bed fusion made parts. Here, two experimental builds of cylindrical geometry, one using a rotating scan pattern and the other using a constant scan pattern, are designed to provide post-build distortion measurements. Measurements are made using a coordinate-measuring machine providing distortion profiles along the height of the part at four separate locations. Measurements show that for these cylindrical thin wall builds, there is no discernable effect on distortion from using the rotating versus constant scan patterns. Project Pan finite element modeling software is used to model each of the experimental builds. The simulation results show good agreement with experimental measurements of post-build deformation, within a 12% percent error as compared to experimental measurements. Using the FE model, the effect of a flexible versus a rigid substrate on distortion profile are examined. The FE model is validated against in situ experimental measurements of substrate distortion. The simulated results are used to study stress and distortion evolution during the build process. Internal stresses calculated by the model throughout the part are used in explaining the final part distortion. The combination of experimental and simulation results from this study show that the distortion of the top layer is relatively small (less than 30%) throughout the duration of the build process compared to the peak distortion, which occurs several layers below the most recently deposited layer. For these geometries once the part is built to a sufficient height, the peak distortion magnitude does not change.
Article
A method for modeling the effect of stress relaxation at high temperatures during Laser Direct Energy Deposition processes is experimentally validated for Ti-6Al-4V samples subject to different inter-layer dwell times. The predicted mechanical responses are compared to those of Inconel® 625 samples, which experience no allotropic phase transformation, deposited under identical process conditions. The thermal response of workpieces in additive manufacturing is known to be strongly dependent on dwell time. In this work the dwell times used vary from 0 to 40 s. Based on past research on ferretic steels and the additive manufacturing of titanium alloys it is assumed that the effect of transformation strain in Ti-6Al-4V acts to oppose all other strain components, effectively eliminating all residual stress at temperatures above 690°C. The model predicts that Inconel® 625 exhibits increasing distortion with decreasing dwell times but that Ti-6Al-4V displays the opposite behavior, with distortion dramatically decreasing with lowering dwell time. These predictions are accurate when compared with experimental in situ and post-process measurements.
Additive manufacturing of concrete in construction: potentials and challenges of 3D concrete printing
  • F P Bos
  • R J M Wolfs
  • Z Y Ahmed
  • T A M Salet
Bos, F.P., Wolfs, R.J.M., Ahmed, Z.Y., Salet, T.A.M.: Additive manufacturing of concrete in construction: potentials and challenges of 3D concrete printing. Virtual Phys. Prototyp. (2016). doi:10.1080/17452759.2016.1209867
Properties of 3D-printed fiber-reinforced portland cement paste
  • M Hambach
  • D Volkmer
Hambach, M., Volkmer, D.: Properties of 3D-printed fiber-reinforced portland cement paste. Cement Concrete Composites (2017). doi:10.1016/j.cenconcomp/2017.02.001
A real-time height measurement and feedback system for 3D concrete printing
  • R J M Wolfs
  • F P Bos
  • C F Emiel
  • E C F Van Strien
  • T A M Van Salet
Wolfs, R.J.M., Bos, F.P., Emiel, C.F., van Strien, E.C.F., van Salet, T.A.M.: A real-time height measurement and feedback system for 3D concrete printing. In: fib Symposium, Maastricht, the Netherlands (2017a, this conference)
Early age mechanical behaviour of 3D printed concrete
  • R Wolfs
  • F Bos
  • T A M Salet
Wolfs, R., Bos, F., Salet, T.A.M.: Early age mechanical behaviour of 3D printed concrete (2017b, in preparation)