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Description
Residual stresses strongly influence the mechanical performance of metallic components and require reliable non-destructive characterization techniques. In this work, modal vibrations of cuboidal aluminum and copper samples with and without residual stresses are investigated using Laser Ultrasound (LUS) and compared to finite element simulations in Ansys Mechanical. LUS provides contact-free excitation and detection, making it particularly suitable for the investigation of modal behavior.The experiments were performed using a pulsed, non-focused excitation laser positioned at the center of the underside of the sample, while a continuous-wave detection laser was scanned across the topside to measure the out-of-plane displacement with a stabilized Michelson Interferometer. Modal frequencies were extracted from long time-domain signals (~20 ms) using Fourier analysis.The measured modal frequencies of the aluminum sample are compared with numerical simulations and show good agreement. The copper samples are cut from a cold-rolled block along both the rolling and transverse directions in order to investigate the influence of residual stress orientation on the modal response. The measurements reveal mode-dependent shifts in the modal frequencies that correlate with the direction of the residual stress.The results demonstrate the sensitivity of modal LUS measurements to residual stress and highlight the potential of the method for non-destructive testing. Future work will focus on the inverse problem of extracting elastic material parameters and residual stress states from the measured frequency spectra.