A Combined NDE/Finite Element Technique to Study the Effects of Matrix Porosity on the Behavior of Ceramic Matrix Composites

摘要

Ceramic matrix composites are being considered as candidate materials for high temperature aircraft engine components to replace the current high density metal alloys. Ceramic Matrix Composites (CMC) are engineered material composed of coated 2D woven high strength fiber tows and melt infiltrated ceramic matrix. Matrix voids are common defects generated during the melt infiltration process. The effects of these matrix voids are usually associated with a reduction in the initial overall composite stiffness, and a decrease in the thermal conductivity of the component. Furthermore, the role of the matrix as well as the coating is to protect the fibers from the harsh engine environment. Hence, the current design approach is to limit the design stress level of CMC components to be always below the first matrix cracking stress. In this study, the stress concentrations around observed macroscopic matrix voids are calculated using a combined NDE/Finite-Element Scheme. The Computed Tomography (CT) is utilized as the NDE method to characterize the initial macroscopic matrix void's locations and sizes in a CMC tensile test specimen. The Finite Element is utilized to calculate the localized stress field around these voids based on the 2D CT images. The same specimen was also scanned after tensile testing to a maximum nominal stress of 150 MPa to depict any growth of the previous observed voids. The post test CT scans depicted an enlargement and some coalescence of the existing voids.