Residual stress in the cured epoxy resin is generated by non-uniform temperature profile during curing and cooling process and influences the mechanical strength, dimensional stability and other properties of the epoxy molded article. Two kinds of epoxy resin were used in this study. One is the diglycidyl epoxy system, consisting of EPON 9405 epoxy resin(diglycidyl ether of bisphenol A type) and EPON 9470 curing agent and the other is the tetraglycidyl epoxy system, consisting of MY-720 epoxy resin(tetraglycidyl 4,4' diaminodiphenyl methane, TGDDM type) and diaminodiphenyl sulfone(DDS) curing agent. Residual stress distribution of the epoxy plate was measured by the layer removal method and calculated by the computer simulation using physical properties measured and basic equations describing the reaction kinetics, thermal conductivity, density and relaxation modulus change during the process. Residual stress generated during the cure of the difunctional epoxy system is negligible since the curing temperature is always higher than the glass transition temperature. But during the cooling process, thermal stress is developed owing to the differences in volume contraction across the thickness direction. During the rapid cooling process, residual stress distribution in the epoxy plate calculated by the linear thermoviscoelastic theory considering specific volume relaxation agreed well with the results measured by the layer removal method. When the starting temperature of the cooling process was near the glass transition temperature of the cured epoxy, residual stress in the epoxy plate was smaller than when the starting temperature was higher than the glass transition temperature. However, the transient stress in the cured epoxy plate was higher when the starting temperature was near the glass transition temperature than when the starting temperature was higher than the glass transition temperature. The quenched epoxy plate was compressed in the parallel direction at the surface and extended at the center. During the cure of the tetrafunctional epoxy system, the residual stress was generated due to the vitrification effect. Residual stress distribution obtained from computer simulation for the cure process was similar to the result measured by the layer removal method.
