Response of fiber reinforced ceramic matrix composites through computational modeling of damage

Uni-axial tension experiments with a uni-directional ceramic matrix composite have indicated which damage mechanisms are active during the deformation history. A finite element model has been developed to investigate the onset and evolution of these experimentally observed damage mechanisms in a unit cell. This computational model is based on an axisymmetric unit cell which is discretized into cohesive interface elements and linearly elastic elements. As cohesive elements fail according to critical stress and energy release rate criteria, cracks form and propagate. To obtain converged solutions during crack propagation the full dynamic equations were solved implicitly using the Newmark method. The unit cell response was determined as a function of the fiber/matrix interface strength and toughness and as a function of the matrix toughness. Details of matrix crack propagation and the subsequent debond initiation were observed, and the implications for material toughening are discussed. The simplest unit cell response was averaged using the experimentally determined evolution of matrix crack density. The averaged response of the unit cell corresponds very well to the experimentally measured macroscopic composite response.