Continuum modelling of composites consolidation

Doctoral thesis, 2006

This work describes the consolidation of commingled yarn-based thermoplastic composites. The consolidation operation involves deformation of the preform, wetting and compaction of fibre bundles, and resin flow through the preform. The model framework comprises a continuum formulation of a non-linear compressible porous solid saturated with an incompressible fluid. In this model, the solid phase represents the fibres plus any uninfiltrated void space within the fibre bundles, and the fluid phase represents the resin. Constitutive equations governing the forming process are developed. These are the effective stress response of the preform, compaction of the solid phase, and Darcian interaction between the phases. Particular attention is paid to the compaction of the solid phase (consisting of a fibre packing mechanism and a viscous wetting process), the volumetric response of the preform and the tension-compression asymmetric response of the fibres. The fibre packing is described by a hyperelastic packing model, and the wetting of bundles by microscopic Darcy flow is described as a viscous compaction of the solid phase. An experimental method for the measurement of the volumetric response of the preform in separation from other processes is introduced. A phenomenological constitutive model for tension-compression asymmetric of a fibre is proposed. The constitutive equations for solid and preform compaction are assessed against experimental data, while the tensioncompression asymmetric model is fitted to a simple tension-compression experiment. Finally, the work is concluded by a numerical example that demonstrates the versatility of the approach, where the material science is combined with two-phase continuum mechanics.