A correlation of quasistatic and ultrasonic measurements of the elastic properties of cortical bone
Description
Bovine haversian femora were assumed to possess transversely isotropic material symmetry and the elastic properties of this tissue were determined from tests on machined specimens (taken from the cortex of femoral mid-sections) using two different testing techniques; namely, ultrasonic and standard (quasistatic) test machine methods Quasistatic machine testing consisted of performing uniaxial tension and simple torsion tests at a strain rate of approximately 3.5 x 10('-4)(s('-1)). Tensile specimens were tested while having an axial and a diametral extensometer attached concurrently to record axial strain and diametral change in their gage region. Ultrasonic testing consisted of measuring the velocity of longitudinal and transverse waves propagating in various directions in a 5mm bone cube. This technique utilized two transducers located on opposite sides of the specimen to transmit (at a resonance frequency of 2.25 MHz) and receive a continuous ultrasonic sine wave The test data were examined to develop empirical correlations between the quasistatic (test machine) values and ultrasonic measurements. Correlations were also examined for quasistatic elastic properties and the density and mineral content of bone. The results indicate that adequate estimates of the Young's moduli can be made from linear first order regression equations on the appropriate longitudinal velocity of ultrasound. Poisson's ratio can be adequately estimated from linear regression equation involving density. However, adequate estimates of the two independent moduli of rigidity can only be made using linear regression equations on three variables: wave speed, density, and mineral content The stress-strain curves produced during mechanical testing had regions that were slightly nonlinear. These curves also exhibited a sizeable amount of residual (anelastic) strain which was completely recovered in a fairly short period of time (less than thirty seconds). The stress-strain curves produced during torsional tests had a peculiar 'hump' that was characteristic of all specimens of this type