Acoustic emission monitoring of thin ply hybrid composites under repeated quasi-static tensile loading

This paper investigates the applicability of the acoustic emission (AE) technique for identification of the damage onset and accumulation in S-Glass/TR30-Carbon hybrid laminates under repeated quasi-static tensile loading. The samples were made of 2 layers of unidirectional thin carbon prepreg plies which were sandwiched between 2 standard thickness S-glass prepreg plies. Analysis of the AE results shows that there are two types of events regarding energy and amplitude ranges of the AE signals. The signals with low values are found to be related to the delamination of the carbon/glass interface whereas the signals with high values are linked with the carbon layer fragmentation. There are more friction related AE signals during the unloading stage than the loading stage due to collision and rubbing between existing crack faces. Increasing the strain level increases the number of fragmentations and the AE technique is able to quantify this. It is concluded that the AE technique can be used to evaluate the number of fragmentations and can identify the damage evolution of the hybrid laminate under repeated quasi-static tensile loading.