Nonlinear Resonant Ultrasound Spectroscopy (NRUS) applied to damage assessment in bone

This study shows for the first time the feasibility of Nonlinear Resonant Ultrasound Spectroscopy (NRUS) techniques for damage characterization in bone. Two diaphysis of bovine bone were subjected to a progressive damage experiment. Fatigue damage was progressively induced in the samples by mechanical testing in 11 steps. At each damage step, the nonlinear elastic parameter was measured using NRUS. For independent assessment of damage, high energy X-ray CT imaging was performed, but only helped in the detection of the prominent cracks. As the amount of damage accumulation increased, a corresponding increase in the nonlinear response was observed. The measured nonlinear response is much more sensitive than the change in modulus. The results suggest that NRUS could be a potential tool for micro-damage assessment in bone. Further work has to be carried out for a better understanding of the physical nature of damaged bone, and for the ultimate goal of in vivo implementation of the technique.