Deformation Criterion of Low Carbon Steel Subjected to High Speed Impacts

A study has been carried out to examine effects of blast loading on the microstructure deformation response of A572 Grade 50 low carbon structural steel. Symmetrical planar impact experiments have been carried out using a single stage gas gun to drive projectiles to velocities between 200 and 500 m/sec resulting in low to moderate shock loading of disc type steel specimens. Longitudinal stress histories of the impacted specimens were captured at the back face of the loaded specimens with the use of manganin gages. A constitutive model was employed to numerically simulate the particle velocity at the impact surface as well the pressure distribution across the specimens as a function of impact duration. An analytical approach utilizing a deformation model was used to link twin volume fraction to blast severity. Post-mortem analysis was carried out on the impacted specimens with the use of optical and scanning microscopy in order to correlate the severity of the impacts with development of twinning within the microstructure. A comparison between the analytically calculated and experimentally measured twin volume fraction was used to optimize the material and deformation models and establish a correlation between impact pressure and deformation response of the steel under examination.