Analysis of Cure Dependent Residual Deformation in Thermosetting Composite

Abstract

Constrained thermoset deformation has been shown to exhibit cure history dependence. The practical significance of this problem is due to the necessity to ensure dimensional stability and tolerance in composite structures especially with curvilinear geometry. During manufacturing of curved composite laminates, cure shrinkages produce so-called spring-in or spring forward effect, as a result of material thermo-elastic anisotropy. The residual cure deformation in a thermosetting composite laminate was considered by subjecting bi-lamina strip samples, composed of [0/904] plies, to cure cycles with different heating profiles. This allowed to separate and study different sources of shrinkage in thermosetting composites, namely chemical resin shrinkage, which occurs due to cross-linking reaction, and thermal shrinkage or expansion, result of applied change in temperature. The significant dependence of the residual strip deflection was found to relate to (i) interaction between chemical and thermal shrinkages and (ii) resulting resin cure strain rate, which affected elastic modulus development in the composite. The constitutive material model of composite during cure was developed and applied to reduce residual deformation during the manufacturer recommended cure cycle (MRCC) by enabling different interactions between thermal and chemical shrinkage. Consequently, the modified cure cycle (MCC) was proposed allowing to further reduce the amount of residual deformation in bi-lamina laminate prior to cooling. The presented approach of establishing the constitutive cure model of composite provides an insight of how to control the laminate final shape by selecting the parameters of the cure cycle. Consequently, cure cycle can be used to mitigate the adverse effects of the residual deformation on the performance of laminated composites.