Wu Shengchuan
Southwest Jiaotong University, China
Title: Defect induced fatigue damage behaviors of additively manufactured components via in situ 3D X-ray microtomography
Biography
Biography: Wu Shengchuan
Abstract
Selective laser melting (SLM), as a metalworking additive manufacturing technology, has received considerable attention from both academic and industry fields due to unprecedented design freedom, high surface quality and balanced material property. Titanium alloys and in particular Ti6Al4V are well suitable to be processed by SLM. It is believed that the mechanical performance of SLM Ti6Al4V alloys can satisfy the design standard typically based on wrought material properties. However, the fatigue behavior of SLM components often suffer from local imperfections including micronized pores and Lack of Fusion (LOF), presenting a defect dominated failure where cracks are prone to initiate from pre-existing defects. In order to promote the robust design of SLM parts used into aerospace and high-speed railway industries, this paper performs a detailed investigation about the process-induced defect and its effect on the fatigue damage behavior of selective laser melting Ti6Al4V alloys. With high brightness and resolution synchrotron radiation source, the accurate characterization and statistics of defects in terms of population, size, location and morphology have been realized. Most micropores tend to be a sphericity of 0.40-0.65 and have the equivalent diameter less than 50 μm. Extreme value statistical method was applied to predict the maxima defect in larger volume. To detect and identify the coupling effect between defects and cracks, an in situ fatigue testing rig was developed to well work at the synchrotron radiation tomography system. It was found that the fatigue failure occurred at a smaller irregular defect near the specimen surface rather than the largest defect, showing a typical I mode semi-elliptical crack profile. Finite element simulation was further employed to elucidate the interaction between the pore and cracking behavior in terms of stress concentration factor and extended pore volume. Finally, by using high cycle fatigue experiment and fatigue crack growth rate testing as well as the fractography-based measurement, a modifi ed Kitagawa-Takahashi (KT) diagram was tentatively established
for the defect tolerance assessment. A critical defect size of 54 μm was assumed inside SLM Ti6Al4V alloys in terms of the KT diagram.