A Rate-independent thermomechanical Constitutive Model for Fibrous Reinforcements

Abstract

In Liquid Composite Moulding (LCM) processes, the constitutive behaviour of fibrous reinforcements has a strong bearing on the choice of manufacturing parameters and final part properties. In many LCM processes, the fibrous preform is subjected to loading and unloading, the latter also occurring during filling and post-filling phases of the manufacturing process. Fibrous materials display inelastic behaviour with rate-dependent and rate-independent components and this must be modelled accurately over several load-unload cycles in order to accurately simulate such processes. An important feature of the material behaviour is its unchanging response to successive load cycles once a large number of load cycles have been applied. Inelastic effects such as fibre-fibre frictional sliding occur during loading as well as unloading and the inelastic deformation remaining after successive cycles appears unchanged. The model presented is developed within a thermomechanical framework and reproduces such behaviour using a single internal variable to account for inelasticity. It is compared to cyclic loading experiments and serves as a starting point for the incorporation of effects such as cyclic softening and rate-effects through additional internal variables.