School of Engineering and Materials Science
Research Student Awards
PhD Thesis: Elastic and anelastic deformation of human compact bone
Author: DABESTANI, Minoo
Supervisor(s): Bill Bonfield
The tensile deformation properties of human compact bone have been investigated as a function of applied stress, strain rate, age and temperature. A microstrain measuring technique employing rosette strain gauges and in-house data logging system was developed. The advantage of this system was that the entire deformation cycle, as well as the anisotropic components could be studied using a single specimen together with one mode of testing.
The tensile properties of human compact bone were characterised in terms of elastic and anelastic deformation. At stress levels < 20 MNm-2, limited elastic deformation was observed, manifested by a straight line load-unload cycle, followed by a transition to anelastic deformation, at stress levels 20 < < 50 MNm-2, resulting in the formation of closed hysteresis loops during loading and unloading without any residual strain at zero stress.
The cortical bone was assumed to behave in a transverse isotropic manner, and four independent elastic constants were determined to define the behaviour in the straight line portion of the stress-total strain curve.
At higher stress levels the formation of hysteresis loops indicated that the deformation was non-elastic. However, the non-elastic strain was fully recoverable and was defined as anelastic deformation. The deformation was characterised by the area of the hysteresis loops which indicated the energy absorption of the bone specimen. The anelastic deformation was further characterised by the concept of a friction stress for the directions, along perpendicular, and at 45 degrees to the long axis of the specimen.
The effect of increasing strain rate on the elastic constants was small. It was further shown that the formation of hysteresis loops was not only dependent on the applied stress, but also on the strain rate. The area of the loops significantly increased with increasing strain rates in the range from 100 -2500 micro strain per second.
It was demonstrated that there is no systematic relationship between age and the deformation properties of human compact bone.