Prediction of process induced shape distortions and residual stresses in large fibre reinforced composite laminates: With application to Wind Turbine Blades

The present thesis is devoted to numerical modelling of ther momechanical phenomena occurring during curing in the manufacture of large fibre reinf orced polymer matrix composites with thick laminate sections using vacuum assisted res in transfer moulding (VARTM1). The main application of interest in this work is modelling ma nufacturing induced shape distortions and residual stresses in commercial wind turbi ne composite blades. Key mechanisms known to contribute to shape distortions and residua l stress build-up are reviewed and the underlying theories used to model these mechanisms a re presented. The main mechanisms of thermal-, chemicaland mechanical origin ar e; (i) the thermal expansion mismatch of the constitutive composite materials, layer an d tooling, (ii) chemical cure shrinkage of the composite matrix material and (iii) the too ling (i.e. the mould, inserts etc.) influence on the composite part. In the modelling approach taken in the current study, 1D and 3 D thermomechanical models are utilized. A 1D thermomechanical model in a finite diff erence (FD) framework, capable of predicting heat transfer, internal heat generat ion, cure degree development, as well as process induced in-plane strains and residual stres ses i initially presented. This 1D model is the framework for the first attempt at a void growth model, capable of predicting the laminate through-thickness discretized void s ize distribution, as a function of processing parameters. Using a 3D thermomechanical finite element (FE) model in ABAQ US, different constitutive modelling approaches are investigated, including a cure hardening instantaneous linear elastic (CHILE) approach, a viscoelastic approach a nd a path-dependent approach. The latter is a limiting case of viscoelasticity. These appr oaches are investigated with regards to their accuracy in predicting process induced str ain and stress development in thick section laminates during curing, and more precisely r ga ding the evolution of the composite thermoset polymer matrix mechanical behaviour d uring the phase transitions experienced during curing. The different constitutive app roaches are utilized in various case studies and compared, where possible, to experimental r sults from measured in situ internal total strains in laminates using embedded fibre Bra gg grating (FBG) sensors. Due to reasonable model accuracy, ease of implementation an d use of relatively simply obtained material characterization data, the CHILE and pat h-dependent approaches are found to be most favorable. It is shown that use of the viscoel astic approach to accurately predict process induced strains and stresses in modelling m a ufacturing cases where mild tooling constraints on the composite part exist, is not viab le. In a final case study, process Also known as Vacuum Infusion or Vacuum Infusion Resin Trans fer Moulding