Stiffness evaluation and damage identification in composite beam under tension using Lamb waves

This paper precisely investigated stiffness changes in cross-ply CFRP laminates loaded in tension using Lamb waves. Young’s modulus was obtained as a function of applied strain by in situ measurement of the velocity of the extensional mode during the tensile test. The modulus exhibited a complicated behavior due to stiffening of the 0° plies and transverse cracks. The effect of the stiffening on the modulus was evaluated by the rule of mixtures and the effect of the cracks alone was successfully deduced. The experimental modulus reduction due to the cracks was predicted by a shear-lag analysis including the stiffening effect. Consequently, this study demonstrated that in situ measurement of the wave velocity can quantitatively evaluate damage in the loaded laminates. Furthermore, a new linear location method using the calculated in situ wave velocity was proposed. A dramatic improvement in location accuracy was obtained compared with the conventional method.