Off-Diagonal Elastic Constants and Anisotropic Damage

Various anisotropic damage models are investigated to take into account the nonlinear behavior of a ceramic matrix composite. A critical analysis of classical strain metrology results proves that it is unfeasible to evaluate the damage in a direction orthogonal to the stress one, because the nine elasticity constants of an orthotropic material are independent and Poisson’s ratios are strain’s second order, whereas Young’s modulus are first-order ones. An ultrasonic method provides the necessary stiffness variations, inaccessible by classical strain measurements, required to identify the anisotropic damage.