A rate-independent thermomechanical constitutive model for fiber reinforcements

Abstract

In liquid composite molding (LCM) processes, the constitutive behavior 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 occurring during both filling and postfilling phases of the manufacturing process. Fiber reinforcements display inelastic behavior with rate-dependent and rate-independent components and this must be modeled accurately over several load–unload cycles in order to accurately simulate such processes. An important feature of the material behavior is its unchanging response to successive load cycles once a large number of load cycles has been applied. Inelastic effects such as fiber–fiber 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 behavior using a single internal variable to account for inelasticity. It is compared to cyclic loading experiments on three fiber reinforcements of different architecture, showing that the model is effective in capturing the repeatable compaction behavior of debulked preforms and serves as a starting point for the incorporation of effects such as cyclic softening and rate effects through additional internal variables.