Prediction of delamination onset in ±θs angle-ply carbon-fiber/epoxy-resin laminates is proposed by means of two approaches. Both are based on a preliminary analysis of the boundary effects. In the first, more classical, case, an 'average stress' criterion retaining only the interface shear component of the stress field is used. Layer-thickness influence is taken into account to estimate the averaging length. The second case takes advantage of the stress concentrations caused by singularities to put to work an incremental Griffith-like criterion. Initiation is considered to be a locally unstable process. It requires us to account for the existence of surface flaws to explain the influence of layer thickness on the critical delamination stress.

A damage model based on a micromechanical approach was studied in order to predict damage development in ceramic-matrix composites under thermomechanical loading conditions. Complex damage phenomena like matrix microcracking, fibre or bundle debonding and fibre breakage can occur. All these mechanisms can be modelled at the microscopic scale. Thus, correlation between the different scales and reliable homogenization procedures have been developed. This micro-macro model is applied to various SiC/SiC and a C/SiC composites. By the use of this model, the intrinsic mechanical properties of the classical CVI SiC matrix have been identified. Implementation of this model was done by means of the finite-element code ABAQUS. An application was carried out on a notched specimen made of Cerasep® N3-1 composite.

This paper shows the results of a theoretical and experimental study of the free edge delamination on carbon-epoxy laminates. Edge delamination tests have been made on different stacking sequences to make specimens delaminate under various modes (interlaminar tension, shear or combinations of the two). The tests give results which are necessary to validate a criterion. The thickness influence on the delamination onset stress is used to identify the parameter of the criterion. This method provides good results for the shear delamination. One set of parameters is sufficient to predict the onset delamination stress for [±θ]s, with θ= 10, 20 and 30°.

The non-linear stress-strain curve obtains under tensile loading, is related to a multi-scale development of damage phenomena like matrix microcracking, fibre or bundle debonding and fibre breakage. To describe this damage evolution and its consequences on the industrial components mechanical behaviour, correlation between the different scales and reliable homogenization procedure have been studied. This micro-macro model is applied to various SiC-SiC (CVI) and a C-SiC (CVI) made by S.E.P (Société Européenne de Propulsion, France).