Probabilistic Assessment of Fatigue Delamination Growth in Fibre Reinforced Composite Laminates

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This First Grant research project aims to expand the current understanding of the uncertain behaviour of polymeric fibre reinforced composites subjected to fatigue loading. The primary goals are characterising and predicting the effect of scatter in delamination propagation data, which is intrinsic to compositesComposite materials are employed in primary load bearing elements of aerospace, automotive and naval structures. The excellent specific stiffness and strength of composites allow reducing the structural weight with respect to alloy based design solutions, thus maximising vehicle payloads and reducing fuel burn. Composite structural elements exhibit peculiar failure modes, having excellent in-plane strength but being extremely weak through-the-thickness, i.e. prone to delaminations, i.e. fracture between contiguous plies. The latter are held responsible for about 60% of structural failures affecting composite elements in aerospace structures. Fatigue is particularly important in rotating components subject to high vibration and cyclic loading, e.g. aero engines; moreover delamination growth from barely visible damages represents a significant hazard for composite fuselage and wing panels. Therefore the prediction of the onset and growth of delaminations due to fatigue is crucial for assessing the operating performance and reliability of composite structures. Modelling the delamination propagation under fatigue represents the corner-stone of a damage tolerance approach to the design of composite structures. Delamination growth exhibits a significant statistical dispersion, so damage tolerance design requires estimating the probability of having interlaminar cracks reaching critical detectable lengths between inspections, following which the defective structural elements can be eventually repaired or substituted. The majority of primary composite structural elements are still designed according to safe-life criteria, i.e. limiting the allowable strains so that initial defects do not grow. Thus designers employ large safety factors, and there is potential for substantial weight savings as a result of the work proposed here, which essentially aims to better understand the variability in fatigue behaviour.