Development of damage in a 2D woven C/SiC composite under mechanical loading: II. Ultrasonic characterization

The non-linear mechanical behavior of a CVI-processed 2D woven C/SiC composite has been investigated by means of an ultrasonic method. This method provided the complete variation of the stiffness tensor of the material required to fully identify anisotropic damage, which was otherwise inaccessible by classical strain measurements. The various damage mechanisms induced by mechanical loading and their influence on the tensile behavior were determined and analyzed by comparing the variations of the components of the stiffness tensor obtained from the ultrasonic measurements with the prediction of microcracks by a system of slit cracks derived from a micromechanical model. Two damage modes were thus emphasized: transverse microcracking characterized by a deterministic accumulation and a random development of longitudinal microcracking, i.e. fiber/matrix and bundle/matrix debonding. Comparisons with the results obtained in Part I from both classical strain measurements and microstructural observations are also made and discussed, whenever possible.