Experimental and Numerical Investigation of the Damage Response of Ceramic Matrix Composites.

Ceramic matrix composites (CMCs) are of interest in the aerospace industry due to their ability to retain high stiffness at elevated temperatures. CMC materials are slated to replace metal alloys currently used in the combustion section of aerospace jet engines, leading to weight savings due to the lower density. In this work monotonic tensile tests at room and high temperature are conducted. Three different composite layups are investigated. Mechanics based numerical models based on finite element analyses are developed to predict the damage behavior of CMCs. The energy based crack band model implemented in Abaqus' user subroutines is used to enforce mesh objectivity. Crack densities are predicted with microstructural FEM models including hundreds of fibers. Geometrical inhomogeneities are included in the model in order to represent the microstructure accurately. Crack-paths and stress-strain responses are compared to experimental results. Component level numerical predictions are developed using a multiscale approach referred to as the integrated finite element method (IFEM). In the IFEM, a representative volume element, which includes nonlinear response due to constituent level damage, is embedded within Abaqus user subroutine UMAT. This allows the user to capture the influence of constituent stress-strain relation at the RVE level. Energy based fracture mechanics models are implemented in the constitutive relations of the RVE model. Damage of each constituent within the RVE is predicted. Macroscopic crack paths are predicted and compared to experimental results. In support of IFEM, micromechanics based models are developed to study the effect of fiber packing and other geometrical features on the transverse response of CMC plies. Experiments on CMCs at elevated temperature revealed the existence of fiber debonding and subsequent sliding and pullout of the fibers. A numerical model is developed to predict the fiber debonding using discrete cohesive zone elements (DCZM).PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111477/1/pasmey_1.pd