Experimental Investigation of Fatigue Damage in Composite Structures Considering Second Harmonic Lamb Waves
Abstract
To detect microstructural damages like fiber / matrix cracks and delaminations in composite materials accurately new methods are developed. Previous works have investigated and shown that the acoustical nonlinearity parameter is an appropriate tool to detect micro-structural damages like plasticity and fatigue in metal as well as thermal fatigue and impact damages in composites. In this work the second harmonic generation is used to analyze unidirectional composite specimens for fatigue damage caused by cyclic tensile load. Therefore, Lamb waves are launched and detected by piezoelectric actuator and sensor, respectively, at a certain frequency to generate cumulative second harmonic modes. The excitation frequency has to meet special conditions. The signal processing is done by using the wavelet transform. The correlation of the results of the nonlinear wave propagation to the damage state is investigated. It is shown that the relative acoustical nonlinearity parameter is sensitive to the damage state.
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