Cyclic Deformation Behaviour and Damage Development on Different Hierarchical Levels in Cortical Bone

Abstract

Bone is a complex natural composite material built of organic and anorganic components and very well adapted to the in vivo loading conditions. The material exhibits an excellent damage resistance under static and fatigue loading conditions. This is partially due to self-healing processes, but to a great extent also to its hierarchical microstructure. The investigation of the deformation behaviour and the damage mechanisms on different length scales gives valuable insight into which level(s) of hierarchy influence the fatigue resistance in which way. In the present work, cyclic deformation tests have been performed on cortical bone specimens. On one hand, stress-strain-hysteresis measurements in different types of tests, such as constant amplitude tests, load increase tests, and combined static and cyclic tests, give information on the active damage mechanisms. For example, changes in the development of the stiffness, non-elastic strain amplitude and non-elastic mean strain as a result of different loading velocities and stress levels allow the discrimination between time and cycle dependent damage mechanisms. These results were correlated with microstructural investigations of the damage development on different hierarchical levels by light and scanning electron microscopy.