Spall Behavior of AF9628 Steel as a Function of Local Microstructural Variations

A high-throughput protocol was developed employing plate-on-plate impact experiments using multiplexed PDV diagnostics and high-fidelity analysis to correlate effects of local microstructural variations on the dynamic tensile response (spallation) and fragmentation in a forged AF9628 steel cylinder. The high-throughput protocol employed gas gun plate-on-plate impact experiments utilized multi-sample target configuration with simultaneous impact on three target samples sectioned from different orientations of the same steel cylinder. Multi-probe PDV interferometry was used to measure the sample free-surface velocity profiles and identify spall failure signatures, and post mortem-microscopy is used to determine the characteristics of incipient spall damage in soft-recovered samples. Signatures captured in PDV velocity profiles show characteristics representative of elastic-to-plastic loading, variations in decompression and recompression, and velocity pullback due to spall failure and resulting free surface generation. These spall signatures are correlated with the spall damage characteristics based on morphology of incipient spall induced voids observed in soft-recovered samples. The results illustrate a decrease in spall strength with increase in impact velocity, typical of high-strength steels. Additionally, the spall strength and transition from dominance of void nucleation and growth also appears to be affected by orientation dependent microstructural heterogeneity and/or texture.