Tension-compression asymmetric mechanical behaviour of lattice cellular structures produced by selective laser melting

2020 ◽  
Vol 234 (16) ◽  
pp. 3241-3256 ◽  
Author(s):  
Sunil Raghavendra ◽  
Alberto Molinari ◽  
Vigilio Fontanari ◽  
Michele Dallago ◽  
Valerio Luchin ◽  
...  
Keyword(s):  
Selective Laser Melting ◽  
Stress Shielding ◽  
Tensile Tests ◽  
Porous Titanium ◽  
Cellular Structures ◽  
Compression Tests ◽  
Laser Melting ◽  
Broad Array ◽  
Cell Topology ◽  
Titanium Alloy Ti6al4v

Additive manufacturing is an evolving technology for fabricating porous structures used in a broad array of applications, ranging from the aerospace industry to biomedical engineering. Porous titanium alloy (Ti6Al4V) structures play a major role in biomedical implants and are preferred over conventional solid implants because their properties can be tailored to obtain the stiffness required to avoid stress shielding and improve osteointegration. The mechanical properties of these structures are dependent on unit cell topology and overall porosity. In the present work, three open cellular configurations were studied, namely regular (square), irregular (skewed square) and fully random structures, at three different porosity levels. The samples were manufactured using the selective laser melting of spherical Ti6Al4V powder. The deviations of manufactured samples from as designed were assessed using morphological characterisations and porosity analyses. The mechanical characterisations of the samples included monotonic and cyclic tensile tests, along with conventional compression tests under monotonic and cyclic conditions. The results from the study indicate a clear deviation of thickness values from as-designed values. The effect of inclination of the strut with respect to the loading axis has been studied in compression samples. The off-axis loading in compression led to the asymmetry in the Young's modulus in compression and tension. These led to finite element modelling of structures in the elastic regime and its validation using Gibson–Ashby model for cellular structures.

Effects of the unit cell topology on the compression properties of porous Co-Cr scaffolds fabricated via selective laser melting

2017 ◽  
Vol 23 (1) ◽  
pp. 16-27 ◽  
Author(s):  
Changjun Han ◽  
Chunze Yan ◽  
Shifeng Wen ◽  
Tian Xu ◽  
Shuai Li ◽  
...  
Keyword(s):  
Cell Size ◽  
Selective Laser Melting ◽  
Unit Cell ◽  
Porous Scaffolds ◽  
Compression Tests ◽  
Laser Melting ◽  
Content Type ◽  
Compression Properties ◽  
Fe Simulations ◽  
Cell Topology

Purpose Selective laser melting (SLM) is an additive manufacturing process suitable for fabricating metal porous scaffolds. The unit cell topology is a significant factor that determines the mechanical property of porous scaffolds. Therefore, the purpose of this paper is to evaluate the effects of unit cell topology on the compression properties of porous Cobalt–chromium (Co-Cr) scaffolds fabricated by SLM using finite element (FE) and experimental measurement methods. Design/methodology/approach The Co-Cr alloy porous scaffolds constructed in four different topologies, i.e. cubic close packed (CCP), face-centered cubic (FCC), body-centered cubic (BCC) and spherical hollow cubic (SHC), were designed and fabricated via SLM process. FE simulations and compression tests were performed to evaluate the effects of unit cell topology on the compression properties of SLM-processed porous scaffolds. Findings The Mises stress predicted by FE simulations showed that different unit cell topologies resulted in distinct stress distributions on the bearing struts of scaffolds, whereas the unit cell size directly determined the stress value. Comparisons on the stress results for four topologies showed that the FCC unit cell has the minimum stress concentration due to its inclined bearing struts and horizontal arms. Simulations and experiments both indicated that the compression modulus and strengths of FCC, BCC, SHC, CCP scaffolds with the same cell size presented in a descending order. These distinct compression behaviors were correlated with the corresponding mechanics response on bearing struts. Two failure mechanisms, cracking and collapse, were found through the results of compression tests, and the influence of topological designs on the failure was analyzed and discussed. Finally, the cell initial response of the SLM-processed Co-Cr scaffold was tested through the in vitro cell culture experiment. Originality/value A focus and concern on the compression properties of SLM-processed porous scaffolds was presented from a new perspective of unit cell topology. It provides some new knowledge to the structure optimization of porous scaffolds for load-bearing bone implants.

scholarly journals High Strain Rate Yielding of Additive Manufacturing Inconel 625 by Selective Laser Melting

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5408
Author(s):  
Kang Du ◽  
Laixia Yang ◽  
Chao Xu ◽  
Bin Wang ◽  
Yang Gao
Keyword(s):  
Ambient Temperature ◽  
Strain Rate ◽  
Yield Stress ◽  
Selective Laser Melting ◽  
Mechanical Performance ◽  
Rate Sensitivity ◽  
Tensile Tests ◽  
Inconel 625 ◽  
Compression Tests ◽  
Laser Melting

Nickel-based alloy Inconel 625, produced by the selective laser melting method, was studied experimentally for its mechanical performance under strain rate loading using Hopkinson bars. Both compression and tensile tests were carried out, with the former also being conducted at 500 °C. The strain rate was in the range of 300 to 3500 s−1 at ambient temperature, and 1200 to 3500 s−1 at the elevated temperature, respectively, for compression tests, and 900 to 2400 s−1 for tensile tests. Results show that the alloy has a strong rate sensitivity with the dynamic yield stress at 3500 s−1, almost doubling the quasistatic value. The test results also show that, even though the temperature elevation leads to material softening, the strain rate effect is still evidential with the dynamic compressive yield stress at the rate 103 s−1 and 500 °C still being higher than the quasistatic one at ambient temperature. It is also observed that dynamic tensile strengths are generally higher than those of compressive ones at room temperature.

Study on Cellular Structures as the Core Architectures of Parts Based on Selective Laser Melting

2012 ◽  
Vol 538-541 ◽  
pp. 1904-1907 ◽  
Author(s):  
Dong Ming Xiao ◽  
Yong Qiang Yang ◽  
Xu Bin Su ◽  
Man Hui Zhang ◽  
Di Wang
Keyword(s):  
Mechanical Properties ◽  
Relative Density ◽  
Selective Laser Melting ◽  
High Heat ◽  
Unit Cell ◽  
Cellular Structures ◽  
Compression Tests ◽  
Laser Melting ◽  
The Core ◽  
Cell Architecture

Cellular structures exhibit favorable properties for multifunctional applications, such as light weight, high load-bearing combined with high heat exchange capability. This paper is to seek optimal cellular structures as the core architectures of parts manufactured by selective laser melting (SLM) technology, which provides required mechanical properties. Design features for characterizing optimal structural performance are discussed. Some preliminary design rules are developed to improve the manufacturability and the quality of cellular structures, the orientation of strut is designed as ±45° or 90°. Compression tests are also carried out to seek cellular structures of synthetically optimal mechanical properties. Comparing the effects of the unit cell architecture and the relative density on mechanical properties, it reveals that unit cell architecture is dominant rather than the relative density, and the truss lattice with [90°,±45°] structure is the overall best performing among the selected cellular structures.

scholarly journals Multi-axial fatigue behaviour of titanium periodic cellular structures produced by Selective Laser Melting (SLM)

2019 ◽  
Vol 300 ◽  
pp. 03004
Author(s):  
Khalil Refai ◽  
Charles Brugger ◽  
Marco Montemurro ◽  
Nicolas Saintier
Keyword(s):  
Selective Laser Melting ◽  
Complex Geometry ◽  
Axial Loading ◽  
Numerical Approach ◽  
Fatigue Behaviour ◽  
Porous Titanium ◽  
Elementary Cell ◽  
Cellular Structures ◽  
Laser Melting ◽  
Manufacturing Techniques

Additive manufacturing techniques such as selective laser melting (SLM) allow for manufacturing periodic porous titanium structures having complex geometry. The mechanical properties of these structures with different elementary cell (ECs) designs have been already studied in literature. However, their fatigue behaviour is not yet well understood. This work aims at proposing a numerical approach to predict the periodic cellular structures fatigue behaviour under multiaxial loadings. The approach is based on an explicit description of the EC combined to an extreme statistical analysis making use of a fatigue indicator parameter to investigate (and compare) different EC configurations. On the other hand, the numerical model relies on the use of a general numerical homogenisation scheme to properly apply the multi-axial loading conditions to the EC at the mesoscopic scale. Results show that lattice fatigue strength is strongly affected by the relative density as well as by the geometrical features of the EC.

scholarly journals Design of Customize Interbody Fusion Cages of Ti64ELI with Gradient Porosity by Selective Laser Melting Process

Micromachines ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 307
Author(s):  
Cheng-Tang Pan ◽  
Che-Hsin Lin ◽  
Ya-Kang Huang ◽  
Jason S. C. Jang ◽  
Hsuan-Kai Lin ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Selective Laser Melting ◽  
Stress Shielding ◽  
Simulation Software ◽  
Surrounding Tissue ◽  
Shielding Effect ◽  
Stress And Strain ◽  
Laser Melting ◽  
Flexion Extension ◽  
Intervertebral Cage

Intervertebral fusion surgery for spinal trauma, degeneration, and deformity correction is a major vertebral reconstruction operation. For most cages, the stiffness of the cage is high enough to cause stress concentration, leading to a stress shielding effect between the vertebral bones and the cages. The stress shielding effect affects the outcome after the reconstruction surgery, easily causing damage and leading to a higher risk of reoperation. A porous structure for the spinal fusion cage can effectively reduce the stiffness to obtain more comparative strength for the surrounding tissue. In this study, an intervertebral cage with a porous gradation structure was designed for Ti64ELI alloy powders bonded by the selective laser melting (SLM) process. The medical imaging software InVesalius and 3D surface reconstruction software Geomagic Studio 12 (Raindrop Geomagic Inc., Morrisville, NC, USA) were utilized to establish the vertebra model, and ANSYS Workbench 16 (Ansys Inc, Canonsburg, PA, USA) simulation software was used to simulate the stress and strain of the motions including vertical body-weighted compression, flexion, extension, lateral bending, and rotation. The intervertebral cage with a hollow cylinder had porosity values of 80–70–60–70–80% (from center to both top side and bottom side) and had porosity values of 60–70–80 (from outside to inside). In addition, according to the contact areas between the vertebras and cages, the shape of the cages can be custom-designed. The cages underwent fatigue tests by following ASTM F2077-17. Then, mechanical property simulations of the cages were conducted for a comparison with the commercially available cages from three companies: Zimmer (Zimmer Biomet Holdings, Inc., Warsaw, IN, USA), Ulrich (Germany), and B. Braun (Germany). The results show that the stress and strain distribution of the cages are consistent with the ones of human bone, and show a uniform stress distribution, which can reduce stress concentration.

Influence of Heat Treatment on Microstructure and Mechanical Properties of Selective Laser Melted TiAl6V4 Alloy

2018 ◽  
Vol 284 ◽  
pp. 615-620 ◽  
Author(s):  
R.M. Baitimerov ◽  
P.A. Lykov ◽  
L.V. Radionova
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Selective Laser Melting ◽  
Room Temperature ◽  
Base Alloy ◽  
Tensile Tests ◽  
Heat Treatments ◽  
Laser Melting ◽  
Microstructure And Mechanical Properties ◽  
Treatment Procedures

TiAl6V4 titanium base alloy is widely used in aerospace and medical industries. Specimens for tensile tests from TiAl6V4 with porosity less than 0.5% was fabricated by selective laser melting (SLM). Specimens were treated using two heat treatment procedures, third batch of specimens was tested in as-fabricated statement after machining. Tensile tests were carried out at room temperature. Microstructure and mechanical properties of SLM fabricated TiAl6V4 after different heat treatments were investigated.

scholarly journals Fracture behavior of cellular structures obtained by selective laser melting

2020 ◽  
pp. 35-47
Author(s):  
I. S. Kamantsev ◽  
◽  
Yu. N. Loginov ◽  
S. V. Belikov ◽  
S. I. Stepanov ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Selective Laser Melting ◽  
Fatigue Fracture ◽  
Fracture Resistance ◽  
Cellular Structure ◽  
Fracture Behavior ◽  
Cellular Structures ◽  
Laser Melting ◽  
Cellular Architecture ◽  
Fatigue Fracture Resistance

An example of samples with a cellular architecture, obtained by selective laser melting, is used to study the influence of the building direction of cellular objects on the characteristics of fracture under cyclic loading. The origin of their fracture has been revealed. The mechanism providing increased fatigue fracture resistance of objects which, along with the cellular structure, have anisotropy of properties due to the technological features of their production has been determined.

scholarly journals Hydrogen Embrittlement Behavior of 18Ni 300 Maraging Steel Produced by Selective Laser Melting

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2360 ◽  
Author(s):  
Young Jin Kwon ◽  
Riccardo Casati ◽  
Mauro Coduri ◽  
Maurizio Vedani ◽  
Chong Soo Lee
Keyword(s):  
Hydrogen Embrittlement ◽  
Maraging Steel ◽  
Selective Laser Melting ◽  
Solution Treatment ◽  
Tensile Tests ◽  
Constant Current ◽  
Hydrogen Atoms ◽  
Laser Melting ◽  
Constant Current Density ◽  
Hydrogen Charging

A study was performed to investigate the hydrogen embrittlement behavior of 18-Ni 300 maraging steel produced by selective laser melting and subjected to different heat treatment strategies. Hydrogen was pre-charged into the tensile samples by an electro-chemical method at the constant current density of 1 A m−2 and 50 A m−2 for 48 h at room temperature. Charged and uncharged specimens were subjected to tensile tests and the hydrogen concentration was eventually analysed using quadrupole mass spectroscopy. After tensile tests, uncharged maraging samples showed fracture surfaces with dimples. Conversely, in H-charged alloys, quasi-cleavage mode fractures occurred. A lower concentration of trapped hydrogen atoms and higher elongation at fracture were measured in the H-charged samples that were subjected to solution treatment prior to hydrogen charging, compared to the as-built counterparts. Isothermal aging treatment performed at 460 °C for 8 h before hydrogen charging increased the concentration of trapped hydrogen, giving rise to higher hydrogen embrittlement susceptibility.

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