Nonlinear Phased Array System for Detection/Imaging of fatigue damage precursors and assessment of remaining useful life

Despite decades of experimental and theoretical studies cyclic fatigue failure remains one of the most critical challenges for engineering as it can occur without any indication of impending failure. More than half of mechanical in service failures are due to cyclic fatigue resulting in unanticipated and significant costs. Metallurgical Acoustic Research Solutions, LLC (MARS, LLC) in collaboration with Murray State University propose to use the recent development of a nonlinear ultrasonic phased array (NLPA) system based on diffuse field analysis with the major objectives of imaging the accumulation of fatigue damage precursors and quantifying the remaining useful life for inspected metallic and other solid materials by using degradation models. Our procedure is based on the later portion of the ultrasonic waveforms, referred to as diffuse field, which contains information of microstructural features within the bulk of the material that scatter the propagating ultrasound. We observed that nonlinear nano- and micro-scale features such as crystal dislocations, plastic shear bands, and microvoids shift spectral energy into subharmonics and higher harmonics and we optimized empirically nonlinear metrics that are highly sensitive to this energy transfer.