Experimental and constitutive modelling studies of semicrystalline thermoplastics under solid-state stamp forming conditions

Abstract

Experimental characterisation and constitutive modelling studies on the thermomechanical behaviour of thermoplastics, under solid-state stamp forming conditions, are required for understanding and optimising the stamp forming process. In this paper, two semicrystalline thermoplastics, Polyamide 6 (PA6, or Nylon 6) and Poly-Ether-Ether-Ketone (PEEK) are studied via uniaxial tensile tests at temperatures between their glass transition temperatures (Tg) and melting temperatures (Tm), and at different strain rates (0.001–50 /s). The temperature and strain rate effects are analysed quantitatively to further understand the thermomechanical response of these semicrystalline thermoplastics. The results show that temperature has significant effects on the thermomechanical behaviour of thermoplastic polymers, while the strain rate effects are relatively marginal in the investigated strain rate range. In addition, a new physically-based viscoelastic-viscoplastic constitutive model is proposed to simulate the thermomechanical behaviour of both materials. The model shows good prediction accuracy on tensile stress responses and provides an insight into the microstructural evolution of the semicrystalline thermoplastics; thus, it can be used to analyse solid-state stamp forming of pure semicrystalline thermoplastics and thermoplastic polymer matrix composites (TPMCs).