Lay-up effect on the open-hole shear strength of composite laminates

The effect of lay-up on the open-hole shear (OHS) strength of quasi-isotropic carbon fibre/epoxy composite laminates was investigated. It was found that laminates with equivalent specific stiffness but different laminate lay-up, i.e. with different arrangements of plies and ply thicknesses, exhibit significant differences in ultimate OHS strength of up to 16.3% and 27.9% for the prepreg material systems IM7/8552 and T800/epoxy, respectively. Using Digital Image Correlation (DIC), X-ray Computed Tomography (CT), and Finite Element Analysis (FEA), it is shown that the lay-up dependent OHS strengths were associated with distinctly different failure modes. These lay-up dependent failure modes are challenging to predict. It is therefore proposed that the OHS test could be used for material screening, and as a new benchmark case for the development and validation of advanced progressive damage modelling frameworks for laminated composites, complementing the commonly used open-hole tensile (OHT) test.