Mechanical Properties Testing for Database and Constitutive Modeling of CMC Composites

摘要

A constitutive model of the deformation behavior of a “weak matrix” oxide-oxide ceramic matrixcomposite has been developed. The model employs triaxial deflection measurements taken fromspecifically oriented test tensile samples machined from CMC laminate plate to calculate thegeneralized elastic constants for the orthotropically symmetric material. It was tested by comparingits predictions with wall-plane deformation measurements taken from multiaxially loaded filamentwound cylinders. A discrepancy between the predictions of the initial model and the behavior ofpressurized hoop specimens was associated with the underestimation of the stiffness and strength ofmaterial resulting from testing insufficiently wide material samples when the load axis was at 45° tothe fiber directions in the composite. Use of wider test samples produced constitutive equationconstants that better correlated with the behavior of multiaxially loaded cylinders. The origins of thespecimen width effect in the 45° specimens are proposed to be related to the “weak matrix” nature ofthe composite and the mechanisms by which axial load must be transferred between terminatingfibers at the edges of finite width specimens.