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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.

Accelerated ageing experiments have been conducted to address durability issues of carbon/epoxy composites to be used for emerging facilities and infrastructure, such as, bridges and buildings, in different climatic zones. The degradation of carbon/epoxy composites under UV, hygrothermal exposure, and applied tensile stress has been investigated. The tests were designed to capture the synergistic effects of field exposure and extreme temperatures, viz., hot/dry, hot/wet, cold/dry, and cold/wet conditions. Short beam shear tests (SBST) were performed for the determination of interlaminar shear strength (ILSS) of conditioned composite specimens. The hot/dry samples showed increased strength, while the hot/wet ones showed a decrease in strength. It is conjectured that conditioning at 90 °C possibly contributed to an increase in the ILSS from post curing. For the hot/wet samples (90 °C, immersed in water) the results indicate that strength degradation due to moisture-induced hydrolysis overshadowed the post-curing effect. The samples subjected to shear stress under hot conditions (90 °C) showed a higher ILSS, possibly due to improved crosslink density arising from post-cure. There is insignificant variation in the ILSS of UV treated and the UV untreated control samples. All the SBST test data reported in this work are from tests performed at room temperature and ambient humidity after environmental ageing. A two-dimensional cohesive layer constitutive model with a prescribed traction-separation law constructed from the basic principles of continuum mechanics, taking into account hygrothermal mechanisms that are likely to occur within a cohesive bi-material interface, such as between adjacent plies in a laminate, was applied to simulate interlaminar failure in the SBST specimens, using Finite Element Analysis (FEA). A phenomenological predictive model was developed using the finite element results.

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