Constant strain rate compression of bovine cortical bone on the Split-Hopkinson Pressure Bar

Abstract

Cortical bone is a visco-elastic material which implies that strain rate will affect its response. Although the Split-Hopkinson Pressure Bar is an accepted technique for determining the dynamic compressive properties of cortical bone it has been shown that the strain rate of compression does not remain constant throughout the duration of a classical experiment with a uniform striker. This raises concerns as to the measurement of smeared responses. This paper presents a shaped striker technique whereby the incident pulse can be shaped to attain a constant strain rate experiment for bovine bone. Shaped strikers offer benefits such as re-usability and increased test repeatability. A comparison of the stress-strain-strain rate responses attained through classical and constant strain rate experiments shows that the shape of the stress-strain curves from conventional experiments is adversely affected in the portion where the strain rate varies. The dynamic response corridors for the two tests are similar, however the ultimate properties are affected. It is concluded that the strain rate history should be presented with dynamic stress-strain responses since the instantaneous strain rate is a likely contributor to potential constitutive models.