Non-contact stress-strain characterization of aluminum alloy by laser-induced thermal-wave radar (LTR) imaging

Abstract

Evaluation of the stress/strain state in alloys is usually performed by direct mechanical measurements, contact ultrasound or ionizing-radiation nondestructive testing (NDT). Safe and totally non-contact methods have considerable advantages and are worthy of further development. In this work, a novel active infrared NDT framework with a linear-frequency-modulated laser-induced thermal-wave radar (LFM-LTR) imaging modality was proposed to quantitatively analyze thermo-mechanical properties as a function of the changing external loading. Chirp-modulated laser emission generates a depth-resolved diffusion-wave field which is analyzed with a modified anisotropic LTR theory. Features of stress-induced thermal anisotropy within uniaxial loaded materials were parametrized and extracted from simulated LTR signals which form the basis for solving the inverse problem of determining tensorized thermo-mechanical properties. An LTR experimental setup was built and used to validate the foregoing theoretical model and numerical analysis. Experimental thermo-mechanical property variation throughout the tensile test was eventually determined in terms of the nominal conductivity tensor without using any contacting sensors. The proposed active infrared testing scheme is promising to facilitate remote and indirect sensing of residual stresses in materials.