Microscopical observations of interface cracks from inter-fibre failure under compression in composite laminates

Matrix/inter-fibre failure is characterized by the appearance at the fibre matrix interfaces of small debonds that can progress along them until reaching a certain extension, then changing their orientation to kink towards the matrix and, finally, growing through it. The particular case of compressive loading is specially interesting, given the morphology of the interface cracks and the specific angle that the macro-cracks form in the matrix. To date, the analysis of this problem at micro-mechanical level has been carried out mainly by means of Finite Element or Boundary Element models. In this work, the problem is approached from the experimental point of view, observing under optical microscope those coupons previously tested at different loading levels. Several aspects such as the identification of the stages of the failure mechanism, the kinking angle, the extension of the interface cracks and the presence of damage as a function of the loading level are studied.