FINITE ELEMENT MODELING OF TRANSVERSE DEFORMATION IN REPRESENTATIVE VOLUME ELEMENTS OF CERAMIC MATRIX COMPOSITES (CMCs)

The paper reports the use of the finite element method to model longitudinal and transverse deformation of representative volume elements (RVE) of ceramic matrix composites subjected to uniaxial loading parallel to fibers. Cohesive elements have been used to model two forms of damage: fracture initiation and propagation both within the matrix, and along the fiber–matrix interface. From the knowledge of the constituent materials behavior, the FE technique has been used to predict the stress–strain behavior and the variation of Poisson's ratio of the RVE due to these two damage forms; but the model does not cater for fiber failure. The RVE predictions have been benchmarked against experimental results for Nicalon-CAS material and good agreement has been obtained. Comparison of the predicted behavior of the single Nicalon-CAS RVE with experimental data for unidirectional tows indicates that the stress–strain curve is predominantly controlled by the Weibull distribution of fiber failure stress, while the degradation of Poisson's ratio is determined by the Weibull distribution of interfacial strength. The same approach has been used for a HITCO C/C material for which transverse deformation behavior is unknown. The results for the HITCO C/C material, as for the Nicalon-CAS, show that the fiber behavior determines the ultimate failure of the RVE, and that interface debonding is the controlling mechanism for the variation of the Poisson ratio with axial strain.