Characterization of Fracture Process in Bovine Bones under Static and Cyclic Loading

Abstract

Static and cyclic compression tests of bovine cortical bone were carried out. For both tests, compressive stress was applied along longitudinal axis of bones and fracture surfaces were parallel to the loading direction. Damage accumulation during tests was monitored by the measurements of acoustic emission (AE) signals and ultrasonic wave velocity. For the static compression test, specimens fractured catastrophically and the most of AE signals were detected close to final fracture, i.e. few damage accumulation was detected. On the other hand, AE events increased and wave velocity decreased gradually during fatigue fracture of bone. A majority of AE signals were detected during unloading and they formed characteristic ‘AE bands’. AE wavelet analysis demonstrated that the peak frequencies of unloading AE, as well as loading AE, were equivalent to the resonant frequency of the specimen thickness. Finally, it was strongly suggested that microcrack extension due to wedging effect of debris took place during unloading in the fatigue process of cortical bone under cyclic compression.