THE RESPONSE OF EQUINE CORTICAL BONE TO LOADING AT STRAIN RATES EXPERIENCED INVIVO BY THE GALLOPING HORSE

The behaviour of cortical bone under load is strain rate-dependent, i. e. it is dependent on the rate at which the load is applied. This is p articularly relevant in the galloping horse since the strain rates exp erienced by the bone are far in excess of those recorded for any other species. In this study the effect of strain rates between 0.0001 and 1 sec-1 on the mechanical properties of equine cortical bone were asse ssed. Initially, increasing strain rates resulted in increased mechani cal properties. Beyond a critical value, however, further increases in strain rate resulted in lower strain to failure and energy absorbing capacity. This critical rate occurred around 0.1 sec-1 which is within the in vivo range for a galloping racehorse. Analysis of the stress-s train curves revealed a transition in the type of deformation at this point from pseudo-ductile to brittle. Bones undergoing brittle deforma tion are more likely to fail under load, leading to catastrophic fract ure and destruction of the animal.