<p>During the non-destructive testing (NDT) and/or structural health monitoring (SHM) of any material or structural component, detecting defects such as fatigue cracks at their early stages is critically important to avoid catastrophic failures. However, detection of micro-scale defects poses a challenge to conventional linear ultrasonic techniques such as absolute time of flight and attenuation. On the other hand, nonlinear ultrasonic techniques have been proven to be more reliable and sensitive to micro-scale defects. This study uses the nonlinear Sideband Peak Count Index (SPC-I) technique to evaluate the nonlinearity of the material. The problem is simulated using the finite element method (FEM). Fatigue cracks are simulated as breathing cracks which exhibit a breathing behavior. The problem is modeled as an infinite aluminum plate to minimize the geometrical effects such as reflections from the boundaries. A narrow band signal is excited and propagated through the material in a single sided excitation/detection setup. The degree of nonlinearity in a material caused by breathing cracks is investigated at multiple configurations. First, the problem is modeled with no cracks to be taken as a reference condition. Then open and closed breathing cracks are modeled, analyzed, and compared. Finally, problems with different number of breathing cracks are simulated and analyzed. All simulated results are compared to investigate the dependence of the degree of nonlinearity on the density and orientation of the cracks.</p>

Evaluating the Degree of Nonlinearity by Applying the Nonlinear Spc-I Technique in the Fem Simulation of Materials With Breathing Cracks

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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