Browsing by Subject "fatigue behavior"

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An Automated Method for Geometrical Surface Characterization for Fatigue Analysis of Additive Manufactured Parts
(University of Texas at Austin, 2019) Rasoolian, Behnam; Pegues, Jonathan; Shamsaei, Nima; Silva, Daniel
Recent interest to implement additive manufactured parts into structural applications has created a critical need to better understand the fatigue behavior of these parts. Alloys such as Ti-6Al-4V are popular in the aerospace and biomedical industries due to their superior strength to weight ratio and biocompatibility. Previous works have associated fatigue behavior with surface roughness, especially radius of curvature of notches. It is therefore important to develop a fast, reliable and consistent methodology for extracting such curvatures. The contribution of this paper is in providing an automated method for extracting radius of curvature using image processing techniques and optimization. Results on fatigue life prediction indicates similar results between the automated method and manually extracted radii in a significantly shorter period of time.
Fatigue Behavior of Selective Laser Melted 17-4 PH Stainless Steel
(University of Texas at Austin, 2015) Yadollahi, Aref; Shamsaei, Nima; Thompson, Scott M.; Elwany, Alaa; Bian, Linkan; Mahmoudi, Mohamad
In this investigation, fully-reversed strain-controlled fatigue tests were conducted on Selective Laser Melted (SLM) 17-4 PH stainless steel (SS). Cylindrical 17-4 PH rods were fabricated vertically-upward using optimized process parameters to ensure a dense product. Post-fabrication heat treatments (solution annealing and aging) were applied on half of the as-built samples. Fatigue behavior and tensile properties of the as-built and heat treated samples were investigated and compared with available data from the literature. The microstructure analysis and fractography were performed to discern the failure initiation sites, crack propagation path, and fracture surface morphology. Fatigue lives of SLM 17-4 PH SS specimens were found to be significantly shorter than their wrought counterparts. It was also found that heat treatment hardens the SLM 17-4 PH SS specimens while also shortens their fatigue life in the high cycle regime. The presence of defects, which serve as crack initiation sites, and more sensitivity of heat treated specimens to impurities, due to higher hardness, were the main reasons for these observations.
Laser-Assisted Surface Defects and Pore Reduction of Additive Manufactured Titanium Parts
(University of Texas at Austin, 2019) Ahmadi, Zabihollah; Lee, Seungjong; Shamsaei, Nima; Mahjouri-Samani, Masoud
Laser surface treatment of additively manufactured parts has attracted considerable interest in the past few years due to its flexibility, operation speed, and capability for polishing complex surfaces as compared to conventional mechanical based methods. This study presents the role of laser surface processing in minimizing the surface roughness and pores that have detrimental effects on the fatigue behavior of additively manufactured specimens. This study is performed by a precise laser melting and recrystallization process to close the pores within 70 μm of the surface in order to enhance the fatigue life of these specimens. A continuous-wave fiber laser is employed to investigate the effect of various processing parameters for controlled laser surface treatments in this study.
Volume Effects on the Fatigue Behavior of Additively Manufactured Ti-6Al-4V Parts
(University of Texas at Austin, 2018) Pegues, Jonathan; Roach, Michael; Williamson, R. Scott; Shamsaei, Nima
Recent interest to implement additive manufactured parts into structural applications has created a critical need to better understand the fatigue behavior of these parts. Alloys such as Ti-6Al-4V are popular in the aerospace and biomedical industries due to their superior strength to weight ratio and biocompatibility. In these two industries, part sizes can range from very small surgical implants to large structural components, all of which are subjected to cyclic loading conditions. The fatigue behavior of additively manufactured parts may show more sensitivity to part size than their wrought counterparts due to the defects that are inherent to the fabrication process. This research investigates the sensitivity of additively manufactured Ti-6Al-4V parts to volume size by comparing the stress-life fatigue curves of three geometries with increasing gage volumes. Results indicate that additive Ti-6Al-4V parts show reduced fatigue lives because of an increase in surface or near-surface defects.