Analysis of Spall Damage Mechanisms in LPBF SS316L with Manufactured Porosity

This presentation will describe spall and alternative strain accommodation mechanisms present in Stainless Steel 316L (SS316L) fabricated with intentional porosity using Laser Powder Bed Fabrication (LBPF). Spall failure is locally altered through the interaction of powder filled pores with reflected shock waves. LPBF manufactured cylinders were impacted at velocities of 250 m/s in a series of symmetric plate impact experiments. Randomly distributed pores were either 200 350, or 500 microns in size and were present in up to 1, 2, and 5 vol.% of the printed material. For each selected pore volume and size, one instrumented sample backed with PDV probes was used to capture free surface velocity profiles, while a second sample was soft recovered in the catch tank for postmortem microstructure characterization. Electron Backscatter Diffraction (EBSD) in combination with Scanning Electron Microscopy (SEM), and optical microscopy is used to determine the role of porosity on spall initiation and strain accommodation. Effects of porosity on shock and elastic wave arrival time and resulting spall response were clearly observed through slope analysis of velocity profiles.