Dynamic indentation hardness and rate sensitivity in metals

An experimental technique for determining the dynamic indentation hardness of materials is described. Unlike the traditional static hardness measurements, the dynamic hardness measurements can capture the inherent rate dependent material response that is germane to high strain rate processes such as high speed machining and impact. The dynamic Vickers hardness (DHV) of several commonly used engineering materials is found to be greater than the static Vickers hardness (HV). The relationship between the hardness and yield stress under static conditions, i.e., HV = 3 sigma(y), is also found to be valid under dynamic conditions. It is suggested that this simpler technique can be used to assess the rate sensitive nature of engineering materials at moderate strain rates in the range of around 2000/s.