Stress Concentrations and Notch Sensitivity in Woven Ceramic Matrix Composites Containing a Circular Hole—An Experimental, Analytical, and Finite Element Study

Abstract

In this paper, the stress concentrations associated with a circular hole and subjected to uniform tensile loading in woven ceramic matrix composites (CMCs) have been determined experimentally through strain gauge measurements. The stress concentrations were calculated from the measured strain distributions surrounding the holes during the initial loading period. Then, the load‐carrying capacity of notched CMCs with various hole radius to width ratios (a/w) has been determined. The objective is to study the stress concentrations due to circular notch, and then evaluate the notch sensitivity in woven CMCs. Both quasi‐isotropic [0/90/+45/−45]s and cross‐ply [0/90/0/90]s laminates of woven SiC/SiNC composites were considered. The experimental data of stress concentrations were compared with the results obtained from a complex variable method and finite element analysis. The notched strength data were also analyzed on the basis of some existing theories. The results show significant stress concentrations in the range of 3.75–4.75 near the notch edges during the early stage of loading. But in most cases, the notched strength data show notch insensitivity in CMCs, particularly with small hole diameters. This occurs mostly due to stress redistribution effects during inelastic deformation in ceramic matrix composites. The degree of notch insensitivity in CMCs is observed to decrease with comparatively larger diameter holes. For notch insensitivity, the limiting value of a dimensionless parameter n, comprising of fracture toughness, un‐notched strength, and width of the specimen, has been determined on the basis of existing notch sensitivity theories. The stress concentration factors are seen not to be influenced by the lay‐up sequence of the laminate. Reasonable agreement was observed between the theory and experimentally determined stress concentration factors, particularly for small hole diameters.