The effect of static and dynamic loading and temperature on the yield stress of iron and mild steel in compression

Cylindrical test samples were compressed statically and dynamically at temperatures ranging from +100 to -195°C and the yield stress, form of yield and surface markings observed. A Hopkinson bar and throw -off rod and electric resistance strain gauges were used for stress determinations under dynamic loads. The stress necessary to in intiate yield rises steeply with fall in temperature and is accompanied by a change in mechanism of deformation from normal slip to the formation of Neumann lamellae at a critical temperature. The critical temperature is higher under dynamic loading, but there appears to be a critical stress for the formation of Neumann lamellae, whether caused by high rates of loading or low temperatures.