22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-4.1.2

MODELLING OF DAMAGE IN FIBRE REINFORCED COMPOSITE LAMINATES UNDER MULTIAXIAL IN-PLANE LOADING

C. Soutis, M. Kashtalyan, G. A. O. Davies
Imperial College of Science, Technology and Medicine, Prince Consort Road, London, UK

Keywords: fibre reinforced composite laminates, matrix cracking, delaminations, multiaxial loading, 2-d shear lag method, equivalent constraint model

Resin-dominated damage modes, such as matrix cracking and delamination, are common failure mechanisms in composite laminates and are of primary concern in the current design with composites. Matrix cracking in the 90o ply has long been recognised as the first damage mode observed in composite laminates under static and fatigue tensile as well as thermal loading. It results in reduction of the laminate stiffness properties and is detrimental to the laminate strength. It also triggers the development of other harmful damage modes, such as delaminations at the free edges of the laminate and/or local delaminations, growing from the tips of matrix cracks. Under biaxial or general in-plane loading, damage may affect more than one layer of the laminate, and different damage modes can interact with each other. Until now, multilayer damage of fibre-reinforced composite laminates has been very little modelled theoretically or simulated numerically (by means of the finite elements), mainly because the analysis of a representative element defined by the intersecting pairs of cracks is cumbersome. In the present paper, a new approach based on the Equivalent Constraint Model (ECM) of the damage lamina is applied to investigate multilayer matrix cracking and delaminations. It provides closed-form expressions for the reduced stiffness properties due to these damage modes. It will be shown that in carbon/epoxy laminates transverse and longitudinal cracking and delaminations cause significant reduction of the laminate shear modulus and Poisson’s ratio, while the axial modulus is very little affected by the damage. Contribution of each damage mode into stiffness reduction will be established.

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