Generation of heat and stress during the cure of polymers used in fiber composites

The modeling of coupled heat generation, cure, evolution of mechanical properties, and stress generation during the solidification of a polymer epoxy is investigated. Heat conduction and cure kinetics are governed by a system of coupled nonlinear partial differential equations. In the special cases of perfect insulators or perfect conductors, the equations are solved in closed form. Otherwise they are solved numerically. The sensitivity of curing time, maximum temperature during cure and curing stresses are discussed with respect to the chemical and thermal parameters and the volume of material that is cured. It is seen that smaller volumes of the same material cure at a fairly uniform rate whereas a sharp increase in the curing rate is obtained as the volume of material to be cured is increased. Subsequently a model is introduced to describe the stress generation during cure. The cure dependent material properties of Epon 862/Epikure 9553 are presented. Finally it is shown that the volume dependency of temperature during cure leads to stresses in an otherwise homogeneous body. Proper knowledge of the post cure stress state is important as this may alter the effective, or in situ, properties of the cured epoxy (Song et al., 2008, Song et al., 2009, Song et al., 2007 and Yerramalli and Waas, 2002). In turn, the in situ properties are a crucial ingredient in any subsequent predictive methodology.