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Mode II fracture energy, G IIC , is a critical parameter for determining the propagation of delamination in composite laminates. Its value can be affected by Through-Thickness Compression (TTC) stress acting on the crack tip and here this effect has been studied using IM7/8552 carbon/epoxy laminates with cut central plies. External TTC loads were applied through bi-axial testing. Unidirectional (UD) cut-ply specimens were used to determine the TTC enhancement factor, η G , for G IIC . A similar enhancement effect was also found in Quasi-isotropic (QI) specimens with 2 extra cut central 0° plies inserted into the layup. The TTC enhancement factor was implemented in a Finite Element Analysis (FEA) framework using cohesive interface elements, showing that the determined η G can be successfully used to model the effect of TTC on delamination. [ABSTRACT FROM AUTHOR]

In this paper, a set of initial R-curves were measured for three different in-plane sizes using scaled Over-height Compact Tension (OCT) specimens and two different stacking sequences. The data reduction scheme was based on a Virtual Crack Closure Technique which is informed by the measured failure load and effective crack length. The R-curve effects were studied by using X-ray Computed Tomography to measure the crack length throughout fracture propagation. It was found that the initial R-curves measured from all three specimen sizes follow the same linearly increasing trend, with similar results for both stacking sequences. However, no plateau was seen on any of the measured R-curves, implying that even the largest specimens are not large enough to generate a full R-curve. a) Scaled OCT tests with two quasi-isotropic stacking sequences b) Initial R-curves showing the same linearly increasing trend but no plateau yet. [Display omitted] [ABSTRACT FROM AUTHOR]

Composite components are required to be resilient against Foreign Object Damage (FOD) induced by localised high velocity impact events. Here an experimental investigation into high velocity oblique impacts and residual tensile strength of thin quasi-isotropic carbon/epoxy laminates is reported. Oblique (45°) impacts between 100 m/s and 350 m/s were carried out using 3 mm steel cubes on the edge and the centre of the laminates, mounted as a cantilever beam. Impact induced damage was characterised using X-ray Computed Tomography (CT) and the residual strength of impacted laminates was determined through quasi-static tensile tests. The residual strength shows a strong dependence on the impact damage size, characterised in terms of fibre fracture width and delamination area. Machined notches were then investigated and compared to impacted laminates in terms of residual strength. [ABSTRACT FROM AUTHOR]