Effect of transverse cracks on lamb wave velocity in CFRP cross-ply laminates

Abstract

In the case of cross-ply laminates subjected to uniaxial loading, transverse cracks initiate in the 90◦ plies at the specimen edge and extend across the laminates. As the applied load increases, the crack density increases, resulting in stiffness reduction until it reaches to a limiting value. Therefore, it has been a subject of considerable interest to analyze the effect of the crack density on the stiffness reduction [1] and to monitor the cracks nondestructively, For example, with acoustic emission [2] and embedded fiber Bragg grating sensors [3]. Among the various techniques available, ultrasonic Lamb waves offer a convenient approach for evaluating the damaged composite laminates. As the Lamb were velocity depends on the in-plane stiffness of the laminate, the transverse cracks that cause the stiffness reduction can be monitored by the measurements of the velocity [4]. The acoustic emission method is also useful due to its ability of sensitive detection and source location for damages and impacts [5]. For the accurate AE source location, the in-situ wave velocity should be used in the calculation if the laminate is damaged. So combining the active sensing of measuring the in-situ Lamb wave velocity and the passive sensing of detecting acoustic emission is ideal to monitor the transverse cracks. However, as far as we know, there have been no studies considering the reduced wave velocity for the AE source location. In the present letter, the stiffness and the velocity of the lowest order symmetric (S0) mode for CFRP crossply laminates with various transverse crack densities were measured. The reduction of the stiffness and the S0 mode velocity as a function of the crack density were calculated theoretically and then the predicted values were compared with the experimental results. Furthermore, linear AE source locations were conducted on the damaged specimen and the effect of the reduction of S0 mode velocity on the accuracy of the source location was investigated. The materials studied were CFRP (T300/F593) cross-ply with two stacking sequences of [0/906/0] and