Microscopic analysis of failure in woven carbon fabric laminates coupled with digital image correlation and acoustic emission

This study focuses on the failure analysis of woven fabric carbon-reinforced polymeric composites under tensile and flexural loading. To conduct a detailed investigation acoustic emission is used to attain damage evolution under flexural loading conditions. For the first time, the GAP function is suggested to find the optimal number of clusters for acoustic emission data. The advantage of this function is its suitability for classifying elongated data points in the vector space of acoustic data. Three clusters of data are determined with this new approach, indicating various failure types in composite laminates which show that simultaneous occurrence of all failures results in a major change of material stiffness. These failures are also substantiated by scanning electron microscope studies of fracture surfaces. Further studies on tensile behavior of the same laminates are conducted with the help of scanning electron micrographs and 3D-digital image correlation technique. Remarkably, the presence of the shear and transverse strain fields at the surface of the tensile specimen obtained through the digital image correlation technique can be correlated to shear dominant and high energy failure (interlaminar delamination and fiber pull-outs), respectively, which are also confirmed by microscopic images of the same fracture regions.