Analysis of Spall Damage Mechanisms in LPBF SS316L with Manufactured Porosity

The spall and alternative strain accommodation mechanisms associated with shock compression of Stainless Steel 316L (SS316L) fabricated with intentional porosity using Laser Powder Bed Fabrication (LBPF) will be described in this presentation. 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, 3, and 5 vol.% of the printed material. For each selected pore volume and size, one sample backed with PDV probes was used to capture free surface velocity profiles, while a second similar 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 was used to determine the role of porosity on spall initiation and strain accommodation. Effects of porosity on shock and elastic wave transit time, and locally altered spall failure response due to presence of powder-filled pores were clearly observed through analysis of velocity risetime, pull-back and recompression signatures captured by the PDV profiles.