Identification of fatigue damage modes for carbon fiber/epoxy composites using acoustic emission monitoring under fully reversed loading

In this study, the fatigue damage modes of carbon fiber/epoxy composite laminates with symmetrical architecture were investigated by acoustic emission (AE) technique under fully reversed loading. The principal component analysis and the K-means cluster analysis using correlation AE characteristic parameters, including the energy, the amplitude, and the duration time, were performed to identify various damage modes during the fatigue test process. The analysis results of the AE signals indicated that the high-intensity AE signals were generated by the compressive load and the low-intensity AE signals were generated by the tensile load. The maximum energy and duration time generated by the compression load are approximately 20 and 10 times that of the tensile load, respectively, which was consistent with the force-controlled static test results under tension and compression loadings. Therefore, the fatigue damage caused by the compressive load is much greater than that of tensile load under fully reversed loading. The results of the multi-AE parametric clustering analysis combined with scanning electron microscope micromorphology revealed that the damage modes of the laminate specimens were classified into five types, namely matrix cracks, fiber/epoxy interface debonding, shear, delamination, and fiber breakage. In addition, the damage modes at different stages during the fatigue test process were also analyzed and discussed.