Stress concentration factors in a plain woven ceramic textile composite with the flexible graphite matrix

Abstract

The paper aims at solving a problem of determining the stress concentration factor in the plain square (1/1 twill, i.e. equal warp and weft orders) woven composite layer caused by the texture complex geometry and local technological defects (internal pores and local fiber breakages). Also, the paper examines the mechanisms that predetermine the main damage scenario based on the earlier developed two-level model of the woven textile composite with reinforcement coefficients equal to 0.14, curved ceramic fibers and FG matrix. Plain weaves provide such benefits as the shortest overlaps, maximum strength, density and increased stiffness of a homogeneous textile surface (geometrically identical both from the front and back sides), but cause internal technological pores. Modeling macrohomogeneous deformations of a woven composite layer in its plane was carried out on the basis of numerical solutions of the boundary-value problems by FEM using an open integrable platform SALOME-MECA. Ceramic fibers and FG matrix were assumed to be isotropic, linearly elastic, not changing their geometry, relative position and type of elastic symmetry under loading. Under the macroscopically homogeneous pure shape change of the woven composite layer, we determined values of the stress concentration factors caused by local technological defects in the presence of a guaranteed FG matrix interlayer around the ceramic fiber of the reinforcing frame, as well as in the presence of a friction contact between them. So, to increase of a woven composite capability to oppose the external action (when closed internal pores are revealed), we need to carry out operations that provide the FG matrix penetration into the local technological caverns. Otherwise, the FG matrix can be damaged by shear and breaking mechanisms.