• Chinese Journal of Lasers
  • Vol. 48, Issue 18, 1802016 (2021)
Xiongmian Wei1, Di Wang1、*, Yongqiang Yang1, Changjun Han1, Jie Chen1, Yunmian Xiao1, Xin Zhou2, Xinglong Wang2, Cheng Deng1, and Yingjun Wang1
Author Affiliations
  • 1School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, Guangdong 510641, China
  • 2Science and Technology on Plasma Dynamics Laboratory, Air Force Engineering University, Xi'an, Shaanxi 710038, China
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    DOI: 10.3788/CJL202148.1802016 Cite this Article Set citation alerts
    Xiongmian Wei, Di Wang, Yongqiang Yang, Changjun Han, Jie Chen, Yunmian Xiao, Xin Zhou, Xinglong Wang, Cheng Deng, Yingjun Wang. Study on Tensile Properties of Titanium Alloy Porous Structure Using Selective Laser Melting[J]. Chinese Journal of Lasers, 2021, 48(18): 1802016 Copy Citation Text show less

    Abstract

    Objective The titanium alloy porous structure has great application prospects in medical implants and lightweight aerospace parts. Studies have shown that human bones suffer from more microdamage in tension than in compression. Currently, researchers have conducted several studies on the mechanical properties and failure mechanism of porous structures using static compression, static tension, and fatigue tests. However, few studies have been conducted on the comparative analysis of tensile properties between lattice porous structures, the relationship between porosity and tensile properties, and numerical simulation. In this study, the tensile specimens of three representative porous structures, namely, body-centered cubic (BCC), BCC with Z-struts (BCCZ), and honeycomb, each with five porosity values are designed. The porous tensile specimens are fabricated using laser selective melting (SLM). The tensile test and finite element analysis of porous structures with different types and porosity are conducted. The findings of this study indicate the influence of the structure type and porosity on the tensile properties of Ti-6Al-4V porous structure and provide a reference for the design and application of porous structures.

    Methods First, the cell bodies of BCC, BCCZ, and honeycomb structures with different porosities and their tensile specimens are designed using Rhino software. Then, ABAQUS software is used to perform static simulation analysis on the porous tensile specimens. Porous tensile specimens are prepared using the Ti-6Al-4V powder in Dimetal-100 equipment independently developed by the South China University of Technology. Next, tensile tests are conducted according to GB/T 228.1—2010 tensile test method. The fracture morphology of the porous tensile specimens is observed using environmental scanning electron microscopy, and the fracture mechanism is analyzed. The three-dimensional (3D) super depth-of-field microscope VHX-5000 is used to observe the forming condition of the porous structure struts and measure the dimensions of the struts. Finally, the effects of structure type and porosity on the tensile properties of the titanium alloy porous structure are analyzed based on simulation and experimental results.

    Results and Discussions The tensile mechanical properties of the three types of porous structures (i.e., BCC, BCCZ, and honeycomb) are linearly negatively correlated with porosity, and their elongations are extremely low compared with those of the solid structures (Figs. 7 and 8). Moreover, the study shows that the minimum cross-sectional area of the porous unit body exhibits a linear relationship with porosity (Fig. 12 (c)). This implies that the minimum cross-section of the porous structure decreases linearly with an increase in the porosity, resulting in a linear decrease in the tensile properties. Owing to the small cross-sectional area of the porous structure, the fracture of each porous unit will cause a larger load to be distributed over a smaller cross-sectional area. Therefore, the porous tensile specimens suddenly break after entering a short plastic stage, and their elongations are considerably lower than those of the solid structures. The low elongation of porous tensile specimens can be attributed to the brittle martensite structure (Fig. 4 (b)), powder-sticking phenomenon, and the formation of brittle fracture caused by void defects in the pillar (Fig. 10). The tensile properties of honeycomb porous structures are clearly higher than those of BCC and BCCZ porous structures. This phenomenon can be explained by two reasons. First, the minimum cross-sectional area of the honeycomb structures is larger than those of BCC and BCCZ structures (Fig. 12 (c)). Second, according to stability of Maxwell, honeycomb structures are tensile-dominated structures, whereas BCC and BCCZ structures are bending-dominated structures. Despite the influence of the experimental errors and external conditions, the finite element analysis and experimental results are highly consistent in the regular and elastic stages (Figs. 5 and 11), which can provide an effective reference for the structural design of porous implants in the medical field.

    Conclusions This study investigates the influence of structure type and porosity on the tensile properties of Ti-6Al-4V porous structures fabricated using SLM based on a combination of finite element analysis and experiments. Simulation and experimental results show that the ultimate tensile strengths of BCC, BCCZ, and honeycomb structures linearly decreased by 348.81, 375.45, and 217.20 MPa, respectively, with an increase in the porosity from 10.91% to 33.84%. This is attributed to a linear decrease in the minimum cross-sectional area of the structures as the porosity increased. All the printed Ti-6Al-4V porous structures exhibited brittle fractures because of the formation of brittle martensite microstructure, powder adhesion to struts, and pore defects inside the struts. Additionally, brittle fractures and the reduction of the cross-sectional area significantly decreased the elongation of the porous structures compared with those of solid structures. The honeycomb structure achieved the best tensile properties among the three, and its specific strength increased with an increase in its porosity. The simulation results are consistent with the experimental results in the regular and elastic stages. The deviation in the plastic stage is relatively large owing to the surface adhesive powder of the inner pillar, internal hole defects, and processing errors.

    Xiongmian Wei, Di Wang, Yongqiang Yang, Changjun Han, Jie Chen, Yunmian Xiao, Xin Zhou, Xinglong Wang, Cheng Deng, Yingjun Wang. Study on Tensile Properties of Titanium Alloy Porous Structure Using Selective Laser Melting[J]. Chinese Journal of Lasers, 2021, 48(18): 1802016
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