Extended proof of fibre-reinforced laminates with holes

Purpose: A calculation method for the strength prediction of tensioned laminated plates with circular notches is presented.Design/methodology/approach: An extensive basis of experimental data from tensile fracture tests on carbon fibre reinforced specimens with circular notches was used to analyse factors determining the notched strength. The proposed extension of the known Whitney-Nuismer and Karlak Point Stress Criteria improves the strength prediction accuracy through introduction of a special coefficient function that takes into account the dependence between stress gradients in the notch near-field and the distance of the outer boundary.Findings: It was found that the theoretical, notch size and outer boundary independent stress concentration factor is not sufficient for a reliable prediction of the notched strength. The presented results show that calculation procedure based on fundamental mechanical relations of the elasticity theory with few experimentally determined factors delivers results which good agree with experiments.Research limitations/implications: The calculation procedure was verified on the representative population of tensile specimens made of several types of carbon fibre reinforced laminates used in the aerospace industry.Practical implications: As openings represent relevant sites of failure in the construction, an accurate calculation of the notched strength is essential for the lightweight-oriented design of fibre-reinforced elements. The presented procedure is relevant for construction of practically important tensioned elements with circular holes.Originality/value: The presented formulation of the phenomenological “characteristic distance” concept and its thorough experimental verification is original.