Non-destructive and non-contacting stress-strain characterization of aerospace metallic alloys using photo-thermo-mechanical radiometry

A photo-thermo-mechanical non-destructive inspection methodology was developed theoretically and experimentally for non-contact, non-destructive evaluation of mechanical stress-strain relations in metallic materials. A one-dimensional thermal-wave model modified to include mechanical stress explicitly was used to fit experimental data from both frequency scan and stress scan tests and determine the thermal effusivity and diffusivity of an aerospace-industry-relevant aluminum 6061 alloy. Within the elastic regime the thermal conductivity values measured from both photothermal radiometry (PTR) amplitude and phase showed very good agreement, thereby establishing the self-consistency of the new photo-thermo-mechanical radiometry (PTMR) method. Furthermore, a linear conductivity-stress dependence was found, thus establishing the dominant role this property plays in the ability of PTMR to monitor mechanical changes in the aluminum alloy. It was demonstrated that PTMR can be used as a non-contact “strain gauge” within and far beyond the operational strain range of commercial strain gauges, up to the fracture point.