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Effect of processing on the behaviour of laminated composite structures : a numerical and probabilistic approach Arafath, Abdul Rahim Ahamed

Abstract

The manufacturing of composite structures made of fibre-reinforced thermoset matrix materials generally results in residual stress build-up during the curing process. As a consequence, the precise geometry and material properties of the final structure after tool (mould) removal are often difficult to control. To account for such process-induced variations, engineers either have employed empirical knockdown factors, which are determined experimentally for a range of distinct structures, materials and manufacturing processes or have incorporated the measured variations as input into sophisticated finite element analyses. The first approach may lead to an unconservative design while the second approach is not suitable for normal design practice. In this study, a combined deterministic-stochastic simulation approach is presented to demonstrate the manner in which manufacturing-induced variabilities in composite structures can be controlled to achieve targeted reliability levels in structural performance. A finite element code, COMPRO, which deterministically simulates the various physical phenomena during manufacturing of composite structures, is integrated with non-linear structural analysis and reliability analysis to compute the statistics of the parameters that must be controlled at the manufacturing level in order to result in an optimum or reliable structural performance during service. The methodology is demonstrated through a case study that examines the buckling behaviour of a composite plate in the presence of manufacturing-induced imperfections. The intrinsic and extrinsic process parameters that affect the dimensional stability of more complex composite structures such as L- and C-shaped angular laminate sections, are numerically investigated using COMPRO. The predictive capability of COMPRO is examined by comparing the simulation results with available experimental measurements. Finally, to account for all sources of residual stress build-up required for accurate assessment of failure, the micro-level stresses arising from the mismatch between the coefficient of thermal expansions of the fibre and the matrix and the matrix cure shrinkage are computed through micromechanical finite element analysis of a representative volume of the fibre and the matrix. The ply- and laminate-level residual stresses computed by COMPRO during the curing process are then transferred to the micro-level using suitably derived stress magnification factors.

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