In this study, a simple two step finite element model is developed to predict the spring-in of C-sections parts made of AS4/8552 composite. The development of resin properties throughout the MRCC were derived using Group Interaction Modelling and the mechanical properties of the composite predicted by using micromechanical models. Important mechanisms during manufacturing that are effective in the formation of residual stresses and shape distortions are defined. The finite element method implemented is composed of two steps before and after the vitrification of the resin. Vitrification is treated as a point at which the material suddenly changes from the rubbery to glassy state with constant properties in each state. The spring-in angles predicted by the finite element analysis are compared to the angles measured on C-section specimens of various lay-ups and thicknesses. The correlation is good showing the validity of the assumptions adopted.

In this paper, the development of physical and mechanical properties of a thermosetting composite which are relevant to the modelling of residual stresses and process induced deformations are discussed. Findings of previous work on cure kinetics and cure shrinkage of the composite are summarized. The development of resin modulus throughout the Manufacturer’s Recommended Cure Cycle (MRCC) is modelled by Group Interaction Modelling (GIM). The moduli of AS4/8552 composite are calculated by two micromechanics methods: by an analytical approach based on the Self Consistent Field Micromechanics (SCFM) and by Finite Element Based Micromechanics (FEBM). The predictions show good agreement with the available experimental data and provide a fundamental understanding of how the properties of a thermoset resin and its composite develop through cure.

A novel approach has been developed to measure in-situ chemical shrinkage of epoxy resins at the temperature of cure, during which the epoxy resins pass through liquid, rubbery and glassy states. A small sample of MY750/HY917/DY073 epoxy resin system, sealed in a thin-walled silicone bag, was suspended in a pot of silicone fluid and weighed independently of the silicone bath. The buoyancy of the sample was monitored as its density increases with respect to the constant density fluid during isothermal cures at three different temperatures. The relationship between the chemical shrinkage and degree of cure was deduced from a cure kinetics model for the resin. The good match of the results for the three different cure cycles suggests that chemical shrinkage is only a function of degree of cure regardless of time and temperature. A bi-linear relationship was fitted to the experimental data. The break point is at a degree of cure of about 28%, with corresponding chemical shrinkage of 3%. This point is linked to the gel point of the resin, which was measured as approximately 25% degree of cure in previous work. Total cure shrinkage of 6.9% for the MY750 resin system was obtained by extrapolating the results to a degree of cure of 100%. The method is sensitive, reliable and keeps the resin stress-free; therefore it should be applicable to a wide range of materials.