Elastic and failure response of imperfect three-dimensional metallic lattices: the role of geometric defects induced by Selective Laser Melting
TL;DR: In this paper, the authors examined three-dimensional metallic lattices with regular octet and rhombicuboctahedron units fabricated with geometric imperfections via Selective Laser Sintering and found that each lattice exhibits a distinct failure mechanism that is governed not only by cell topology but also by geometric defects induced by additive manufacturing.
Abstract: This paper examines three-dimensional metallic lattices with regular octet and rhombicuboctahedron units fabricated with geometric imperfections via Selective Laser Sintering. We use X-ray computed tomography to capture morphology, location, and distribution of process-induced defects with the aim of studying their role in the elastic response, damage initiation, and failure evolution under quasi-static compression. Testing results from in-situ compression tomography show that each lattice exhibits a distinct failure mechanism that is governed not only by cell topology but also by geometric defects induced by additive manufacturing. Extracted from X-ray tomography images, the statistical distributions of three sets of defects, namely strut waviness, strut thickness variation, and strut oversizing, are used to develop numerical models of statistically representative lattices with imperfect geometry. Elastic and failure responses are predicted within 10% agreement from the experimental data. In addition, a computational study is presented to shed light into the relationship between the amplitude of selected defects and the reduction of elastic properties compared to their nominal values. The evolution of failure mechanisms is also explained with respect to strut oversizing, a parameter that can critically cause failure mode transitions that are not visible in defect-free lattices.
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TL;DR: A comprehensive summary of the experimental data reported on the mechanical response of Selective Laser Melting (SLM) lattice structures can be found in this paper, where the design, fabrication and performance of SLM lattice structure are reviewed and the quality of data reported to inform best-practice for future studies.
580 citations
TL;DR: In this paper, powder bed fusion technology was employed to fabricate the cellular structures of various relative densities out of Maraging steel, and compressive testing was performed to deduce the mechanical properties of the considered cellular structures.
Abstract: Recent advances in additive manufacturing facilitated the fabrication of parts with great geometrical complexity and relatively small size, and allowed for the fabrication of topologies that could not have been achieved using traditional fabrication techniques. In this work, we explore the topology-property relationship of several classes of periodic cellular materials; the first class is strut-based structures, while the second and third classes are derived from the mathematically created triply periodic minimal surfaces, namely; the skeletal-TPMS and sheet-TPMS cellular structures. Powder bed fusion technology was employed to fabricate the cellular structures of various relative densities out of Maraging steel. Scanning electron microscope (SEM) was also employed to assess the quality of the printed parts. Compressive testing was performed to deduce the mechanical properties of the considered cellular structures. Results showed that the sheet-TPMS based cellular structures exhibited a near stretching-dominated deformation behavior, while skeletal-TPMS showed a bending-dominated behavior. On the other hand, the Kelvin and Gibson-Ashby strut-based topologies exhibited a mixed mode of deformation while the Octet-truss showed a stretching-dominated behavior. Overall the sheet-TPMS based cellular structures showed superior mechanical properties among all the tested structures. The most interesting observation is that sheet-based Diamond TPMS structure showed the best mechanical performance with nearly independence of relative density. It was also observed that at decreased volume fractions the effect of geometry on the mechanical properties is more pronounced.
426 citations
TL;DR: In this paper, the authors investigated the mechanical properties and energy absorption abilities of three types of TPMS sheet structures (Primitive, Diamond, and Gyroid) fabricated by selective laser melting (SLM) with 316 L stainless steel under compression loading and classified their failure mechanisms and printing accuracy with the help of numerical analysis.
Abstract: Designing metallic cellular structures with triply periodic minimal surface (TPMS) sheet cores is a novel approach for lightweight and multi-functional structural applications. Different from current honeycombs and lattices, TPMS sheet structures are composed of continuous and smooth shells, allowing for large surface areas and continuous internal channels. In this paper, we investigate the mechanical properties and energy absorption abilities of three types of TPMS sheet structures (Primitive, Diamond, and Gyroid) fabricated by selective laser melting (SLM) with 316 L stainless steel under compression loading and classify their failure mechanisms and printing accuracy with the help of numerical analysis. Experimental results reveal the superior stiffness, plateau stress and energy absorption ability of TPMS sheet structures compared to body-centred cubic lattices, with Diamond-type sheet structures performing best. Nonlinear finite element simulation results also show that Diamond and Gyroid sheet structures display relatively uniform stress distributions across all lattice cells under compression, leading to stable collapse mechanisms and desired energy absorption performance. In contrast, Primitive-type structures display rapid diagonal shear band development followed by localized wall buckling. Lastly, an energy absorption diagram is developed to facilitate a systematic way to select optimal densities of TPMS structures for energy absorbing applications.
309 citations
TL;DR: This strategy may be applied to create the next generation of intelligent infrastructure, able to perform a variety of structural and functional tasks, including simultaneous impact absorption and monitoring, three-dimensional pressure mapping and directionality detection.
Abstract: Piezoelectric coefficients are constrained by the intrinsic crystal structure of the constituent material. Here we describe design and manufacturing routes to previously inaccessible classes of piezoelectric materials that have arbitrary piezoelectric coefficient tensors. Our scheme is based on the manipulation of electric displacement maps from families of structural cell patterns. We implement our designs by additively manufacturing free-form, perovskite-based piezoelectric nanocomposites with complex three-dimensional architectures. The resulting voltage response of the activated piezoelectric metamaterials at a given mode can be selectively suppressed, reversed or enhanced with applied stress. Additionally, these electromechanical metamaterials achieve high specific piezoelectric constants and tailorable flexibility using only a fraction of their parent materials. This strategy may be applied to create the next generation of intelligent infrastructure, able to perform a variety of structural and functional tasks, including simultaneous impact absorption and monitoring, three-dimensional pressure mapping and directionality detection. Piezoelectrics convert force into electrical charge, and vice versa, but the coefficients that determine piezoelectric behaviour are constrained by crystal structure. Here, metamaterials are 3D printed that show arbitrary piezoelectric coefficients.
274 citations
TL;DR: In this article, the authors discuss the progress to date in the improvement of the fatigue performance of cellular structures manufactured by additive manufacturing, especially metal-based, providing insights and a glimpse to the future for fatigue-tolerant additively manufactured architected cellular materials.
Abstract: Additive manufacturing of industrially-relevant high-performance parts and products is today a reality, especially for metal additive manufacturing technologies. The design complexity that is now possible makes it particularly useful to improve product performance in a variety of applications. Metal additive manufacturing is especially well matured and is being used for production of end-use mission-critical parts. The next level of this development includes the use of intentionally designed porous metals - architected cellular or lattice structures. Cellular structures can be designed or tailored for specific mechanical or other performance characteristics and have numerous advantages due to their large surface area, low mass, regular repeated structure and open interconnected pore spaces. This is considered particularly useful for medical implants and for lightweight automotive and aerospace components, which are the main industry drivers at present. Architected cellular structures behave similar to open cell foams, which have found many other industrial applications to date, such as sandwich panels for impact absorption, radiators for thermal management, filters or catalyst materials, sound insulation, amongst others. The advantage of additively manufactured cellular structures is the precise control of the micro-architecture which becomes possible. The huge potential of these porous architected cellular materials manufactured by additive manufacturing is currently limited by concerns over their structural integrity. This is a valid concern, when considering the complexity of the manufacturing process, and the only recent maturation of metal additive manufacturing technologies. Many potential manufacturing errors can occur, which have so far resulted in a widely disparate set of results in the literature for these types of structures, with especially poor fatigue properties often found. These have improved over the years, matching the maturation and improvement of the metal additive manufacturing processes. As the causes of errors and effects of these on mechanical properties are now better understood, many of the underlying issues can be removed or mitigated. This makes additively manufactured cellular structures a highly valid option for disruptive new and improved industrial products. This review paper discusses the progress to date in the improvement of the fatigue performance of cellular structures manufactured by additive manufacturing, especially metal-based, providing insights and a glimpse to the future for fatigue-tolerant additively manufactured architected cellular materials.
238 citations
References
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TL;DR: The methods and software engineering philosophy behind this new tool, ITK-SNAP, are described and the results of validation experiments performed in the context of an ongoing child autism neuroimaging study are provided, finding that SNAP is a highly reliable and efficient alternative to manual tracing.
6,669 citations
TL;DR: The possibilities for manufacturing metal foams or other porous metallic structures are reviewed in this article, where various manufacturing processes are classified according to the state of matter in which the metal is processed, such as solid, liquid, gaseous or ionised.
3,294 citations
Additional excerpts
...All rights reserved. lar metals ( Banhart, 2001 ; Wadley, 2002 ; Dong et al., 2015 ; Wadley et al., 2003 )....
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TL;DR: In this paper, a simple theoretical model is developed to predict residual stress distributions in selective laser sintering (SLS) and selective laser melting (SLM), aiming at a better understanding of this phenomenon.
Abstract: Purpose – This paper presents an investigation into residual stresses in selective laser sintering (SLS) and selective laser melting (SLM), aiming at a better understanding of this phenomenon.Design/methodology/approach – First, the origin of residual stresses is explored and a simple theoretical model is developed to predict residual stress distributions. Next, experimental methods are used to measure the residual stress profiles in a set of test samples produced with different process parameters.Findings – Residual stresses are found to be very large in SLM parts. In general, the residual stress profile consists of two zones of large tensile stresses at the top and bottom of the part, and a large zone of intermediate compressive stress in between. The most important parameters determining the magnitude and shape of the residual stress profiles are the material properties, the sample and substrate height, the laser scanning strategy and the heating conditions.Research limitations/implications – All exper...
1,415 citations
"Elastic and failure response of imp..." refers background in this paper
...These processes, however, generally fabricate lattices with geometries that depart from their as-designed counterparts; as a result, their geometry is far from being defect-free ( Vayre et al., 2012 ; Zaeh and Branner, 2009 ; Mercelis and Kruth, 2006 ; Bagheri et al., 2016 )....
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TL;DR: A route is developed for fabricating extremely low-density, hollow-strut metallic lattices that exhibit complete recovery after compression exceeding 50% strain, and energy absorption similar to elastomers and attribute these properties to structural hierarchy at the nanometer, micrometer, and millimeter scales.
Abstract: Ultralight (<10 milligrams per cubic centimeter) cellular materials are desirable for thermal insulation; battery electrodes; catalyst supports; and acoustic, vibration, or shock energy damping. We present ultralight materials based on periodic hollow-tube microlattices. These materials are fabricated by starting with a template formed by self-propagating photopolymer waveguide prototyping, coating the template by electroless nickel plating, and subsequently etching away the template. The resulting metallic microlattices exhibit densities ρ ≥ 0.9 milligram per cubic centimeter, complete recovery after compression exceeding 50% strain, and energy absorption similar to elastomers. Young’s modulus E scales with density as E ~ ρ^2, in contrast to the E ~ ρ^3 scaling observed for ultralight aerogels and carbon nanotube foams with stochastic architecture. We attribute these properties to structural hierarchy at the nanometer, micrometer, and millimeter scales.
1,412 citations
"Elastic and failure response of imp..." refers background in this paper
...They are exploited in a wide range of multifunctional applications, such as energy absorbers ( McKown et al., 2008 ; Tancogne-Dejean et al., 2016 ; Schaedler et al., 2011 ; Evans et al., 2010 ), vibration and sound control devices ( Delpero et al., 2016 ; Wu et al., 2015 ; Nolde et al., 2011 ),…...
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TL;DR: In this article, the effective mechanical properties of the octet-truss lattice structured material have been investigated both experimentally and theoretically, and the intervention of elastic buckling of the struts is also analysed in an approximate manner.
Abstract: The effective mechanical properties of the octet-truss lattice structured material have been investigated both experimentally and theoretically. Analytical and FE calculations of the elastic properties and plastic yielding collapse surfaces are reported. The intervention of elastic buckling of the struts is also analysed in an approximate manner. Good agreement is found between the predictions of the strength and experimental observations from tests on the octet-truss material made from a casting aluminium alloy. Moreover, the strength and stiffness of the octet-truss material are stretching-dominated and compare favourably with the corresponding properties of metallic foams. Thus, the octet-truss lattice material can be considered as a promising alternative to metallic foams in lightweight structures.
1,260 citations