Thermographic stress analysis in cortical bone.

Under adiabatic (or near adiabatic) conditions a volumetric change in an elastic material will produce a corresponding change in temperature. Based upon this principle, thermographic stress analysis (TSA) measures changes in surface heat flux (which are related to changes in surface temperature) and relates them to a coupled form of strains or stresses. To demonstrate the feasibility of using this technique for biomechanical applications, we thermographically measured heat flux from loaded specimens of cortical bone and correlated the results with strain gage data. Regular parallelepipeds were cut from the cortex of bovine femora and loaded sinusoidally at 20 Hz. At this rate of loading, mechanically induced changes in surface temperature could be sampled (via heat flux) prior to a measureable attenuation of the thermoelastic effect. Correlation coefficients demonstrated a significant linear relationship between TSA and measured and computed mechanical parameters (stress, strain, first strain invariant, and strain energy density). TSA therefore appears to be a promising technology for experimental stress analysis in cortical bone.