In this study, a plasticity-induced crack closure model, FASTRAN, was used to predict the fatigue life of Inconel 718, 17-4 precipitation hardening (PH) stainless steel (SS), and Ti-6Al-4V alloys fabricated via additive manufacturing (AM) systems. Results indicated that in the presence of large defects (e.g., lack-of-fusion defects), the total fatigue life of AM specimens is dominated by crack growth. Results indicated that variations in the fatigue lives of specimens in machined and as-build surface conditions can be predicted based on the characteristics of AM process-induced defects and surface profile. Effect of build orientation on fatigue life was also captured based on the size of defects projected on a plane perpendicular to the loading direction. In addition, maximum valley depth of the surface profile can be used as an appropriate parameter for the fatigue-life prediction of AM specimens in their as‐built surface condition.
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Themes: Fatigue and Fracture of Additively Manufactured Materials
ANALYSIS OF POROSITY EFFECTS ON SPALL FAILURE OF ADDITIVELY MANUFACTURED 316L SS
Additive manufacturing (AM) allows for tuning of mechanical properties for unique functionalities, and stainless steel is a prime candidate for use in many applications due to its high strength, ductility, and corrosion resistance. AM fabricated 316L stainless steel samples with intentionally random pore placement are compared to samples with known pore placement to study the interaction of the shock wave with individual and grouped pores. Velocity profiles were obtained using photon doppler velocimetry (PDV) probes placed strategically along the location of the known pores to understand the limits of local influence for the known pores. Post-mortem characterization of soft-recovered samples using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) was performed to investigate the strain accommodation around pores. It was observed that shock wave fronts are highly dispersed and slow as they propagate through the pore due to strain accommodation around individual pores. As a result, there is shifting of the spall plane away from the impact face. This slow wave front propagation also results in slow rise time and lack of velocity plateau in the collected velocity profiles when areas with pores were probed.
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