Effect of the Opening/Closure of Microcracks on the Nonlinear Behavior of a 2D C-SiC Composite under Cyclic Loading

The nonlinear mechanical behavior of a 2D ceramic matrix composite is investigated under cyclic loading by combined use of an ultrasonic method and strain measurements. This method allows the accurate determination of the loss of stiffness of the material under tensile stress and which part of the global strain is either elastic or inelastic. It appears that the loss of stiffness during monotonic loading is mainly due to transverse microcracks density and that the variation of the elastic response of the composite during cyclic loading is the result of the opening/closure of these cracks. In order to take this effect into account, an internal variable that represents the damage accumulated along the loading is introduced. By using the analytical expressions of the effective properties of a cracked solid, the nonlinear behavior of a 2D C-SiC is fully predicted under both monotonic and cyclic loading. The constitutive laws of the crack density and the opening/closure variable describe the three dimensional changes in elasticity under cyclic loading as well as the inelastic strains along the whole test.