Thermal residual stresses in freely quenched slabs of semicrystalline polymers: Simulation and experiment

Thermal residual stresses in freely quenched semicrystalline polymer slabs were calculated based upon the modifications of the Indenbom theory for ino rganic glasses and linear viscoelasticity. These modifications were introdu ced to include the influences of crystallization on mechanical and physical properties of the polymer during free quenching. The nonisothermal crystal lization kinetic model due to Nakamura et al, was employed to calculate the variations of crystallinity. In the case of the Indenbom theory, a polymer during crystallization was assumed to undergo an abrupt transition from an ideal plastic state to an elastic state upon the completion of crystalliza tion. In the case of linear viscoelasticity, the Morland-Lee constitutive e quation was utilized with the effect of crystallization on the time-tempera ture dependent shear relaxation modulus taken into account. The Spencer-Gil more P - V - T equation of state was employed to model the specific volume changes during crystallization and used to determine the local thermal load ing that results from inhomogeneous densifications and gives rise to the th ermal residual stresses in the slabs. Based on the above theoretical work, the thermoelastic and thermoviscoelastic models were developed, and the cor responding numerical simulation schemes were formulated to calculate the re sidual thermal stresses in freely quenched slabs of semicrystalline polymer s, Free quenching experiments were carried out under various cooling condit ions using isotactic polypropylene. The layer removal method due to Treutin g and Read was utilized to measure the residual thermal stresses. The simul ated and measured results were then compared. The effects of quenching cond itions and crystallization on the development of residual thermal stresses were evaluated. It has been found that both coolant types and coolant tempe rature have significant effects on residual thermal stresses, In contrast, initial temperature of the polymer melt shows a slight influence only. (C) 2000 John Wiley & Sons, Inc.