Nonlinear ultrasound monitoring of single microcrack propagation in cortical bone
Résumé
Accumulation of bone microdamage is suspected to lead to severe impairment of mechanical properties with an increase in skeletal fragility and fracture risk. The objective of the study was to evaluate the sensitivity of nonlinear resonant ultrasound spectroscopy (NRUS) measurements to the propagation in cortical bone of a single microcrack induced by 4-point bending mechanical loading. Twelve human cortical bone specimens were machined as parallelepiped beams (50*2*2mm) to unambiguously identify resonant modes for NRUS measurements. A central notch of 600 µm was made to control crack initiation and propagation during four-point bending loading. During stable crack propagation, load and displacement curves were recorded to extract mechanical parameters (J-integral J and stress intensity toughness K). Before and after toughness experiments, the nonlinear ultrasonic elastic coefficient (\alphaf) was monitored by NRUS for all notched samples. Despite substantial between-sample variability, \alphaf increased significantly (up to 50-fold) while no significant variation was observed for linear resonant frequency. Moreover, the crack length, assessed under epifluorescence microscope, was found to be significantly correlated to the nonlinear elastic parameter αf (r2=0.7, p=0.01). These results strongly suggest that NRUS measurements are sensitive to damage accumulation and can be used as a marker of microcrack length.
Domaines
Acoustique [physics.class-ph]
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