A combined impregnation and heat transfer model for stamp forming of unconsolidated commingled yarn preforms

Non-consolidated woven fabrics of carbon fibre and poly(laurolactam) fibre commingled yarns were subjected to stamp forming. The temperature profile through the thickness of four ply fabric stacks was experimentally assessed by continuous temperature recording during both heating and moulding. Cooling of the laminate during the combined moulding/consolidation/cooling process step was described by a combined heat transfer and consolidation model. The thermal equation of energy conservation including the heat generation term was solved by means of the method of finite differences, also accounting for variable material parameters such as laminate density and thermal conductivity due to progressing consolidation. The suggested model delivers temperature profiles that excellently agree with experimental data. Moreover, this combined heat transfer and consolidation model is capable of predicting the void content of a laminate made from commingled yarn at any time during stamp forming. Simulation of void content evolution at various processing parameters and yarn architectures demonstrates the practical use of the suggested model and allows for determining processing boundary conditions and requirements of yarn characteristics for the successful use of stamp forming for unconsolidated commingled yarns.