Elastic waves can travel across relatively large distances in thin metallic plates,and can be affected by discontinuities such as cracks. This paper presents aninvestigation of the interaction of Lamb waves with both open and closed low-cyclefatigue cracks in aluminum plates using a three-dimensional laser Doppler vibrometer(3D-LDV). The 3D-LDV provides measurements of both in- and out-of-planevelocity components over a uniform grid of up to ～27,000 points with approximately0.7 mm spacing in the x- and y-directions. Images created from the 3D-LDVmeasurements clearly show the interaction of the elastic wave energy with the cracks.Comparisons between in- and out-of-plane components provide insight into whetherand how the propagation behaviors of symmetric and antisymmetric Lamb wavemodes differ upon encountering fatigue cracks.
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