MICRO-MECHANICAL MODELING OF THE PRESSURE DEPENDENT FAILURE OF HIGHLY CROSSLINKED EPOXY RESIN

In order to improve the modelling and the prediction of the mechanical behaviour of fibre reinforced polymers, a more detailed description of the constitutive behaviour of their constituents is necessary. A new fracture criterion of the industrial grade epoxy resin RTM 6, widely used in aerospace applications as a matrix of fiber reinforced composites, is presented. The fracture criterion explains the brittle fracture of the resin both in uniaxial tension and compression, despite a much larger ductility in the later case, by the existence of internal small size defects which induce local tensile stresses in their vicinity. Therefore, finite element analyses were carried out in order to compute the stress levels under different loading conditions at the instant and the location corresponding to the onset of failure. The comparison of the stress levels computed in uniaxial tension of notched and unnotched specimens and in pure compression enables an estimation of the aspect ratio of the critical microdefects and of the critical principal tensile stress. Fracture mechanics allows a determination of an upper bound of the size of defect, whose nature remains to be determined.