Effect of fatigue damage on the shock and spall behavior of α Fe and 4340 steel

Accumulation of microplastic defects generated through high cycle elastic fatigue loading results in microstructure, especially porosity, states that vary significantly from the pristine materials typically investigated in shock studies. In order to probe the effects of these microstructural changes, specimens of α Fe and 4340 steel are loaded under high cycle fatigue to differing percentages of their anticipated fatigue life followed by shock loading at pressures below and above the phase transformation stress. Results indicate that fatigue generated damage has little effect on the Hugoniot elastic limit (HEL) of α Fe, the phase transformation stress of either material, or the spall strength of 4340 steel. However, preliminary, crude data suggests the possibility of an effect of fatigue damage on the spall strength of α Fe and the HEL of 4340 steel, though for now, that effect remains unclear.