Microcracking in dog bone under load. A biomechanical study of bone visco-elasticity.

Entire diaphyseal bones from adult dogs were repeatedly loaded in torsion. The residual deformation after unloading from the non-linear deformation range was found to decrease with time. Acoustic-emission signals typical for micro-cracking were registered not only during loading in the non-linear deformation range but also during the initial phase of the following unloading. The initial torque and twist required for further micro-cracking decreased for every subsequent load-cycle, i.e. with the amount of cracking already formed. These observations are indications of visco-elastic properties of bone material.