Effect of tensile strain rate on spall fracture in 20 steel

Using a gas gun, a set of plate impact experiments were performed for 20 steel by measuring the rear free-surface velocity profiles with a velocity interferometer system for any reflector (VISAR). Experiments were arranged by adjusting the thicknesses of flyer and sample to change the tensile strain rate, in order to investigate the effect of the tensile strain rate on the spall strength. The maximum tensile strain rate approximately reaches 106 s-1, and approachs to the value determined by the laser irradiation. Compared with laser irradiation, the thin flyer technique is easy to satisfy the one-dimensional strain condition for spall fracture. The measured results show that an apparent increase of spall strength with tensile strain rate is evidenced, and 70% increase of spall strength is determined in the present tensile strain rate range of 104-106 s-1. Based on the numerical simulation results, the influence of the loading conditions on the spall strength was discussed.