An experimental and numerical study of curing deformation considering tool-part interaction for two-step curing tooling composite materials

Abstract

The curing deformation of tooling composite material with specially designed two-step curing process (a low-temperature cure step with tool and a second high-temperature free-standing cure step without tool) has been systematically investigated experimentally and numerically for the first time. A set of thermo-chemical-mechanical coupled model has been utilized and incorporated to predict both the cure kinetics and mechanical properties of the tooling composite material during the two-step curing process, with which the prediction errors achieved for degree of cure (DoC) and modulus are within 5 % and 10 % respectively. Based on which, an FE model has been further developed to simulate the curing process of typical composite structures by considering too-part interaction with varying friction conditions. The effectiveness of the developed model has been validated by a set of basic thermal and mechanical tests of the material and a manufacturing trial of a typical thick-walled part with complex surfaces features. The difference of deformation between simulation and experiment is 0.18 mm in pre-cure, and the behavior and corresponding mechanisms of curing deformation due to the evolution of residual stresses have been analyzed and discussed according to both experimental and numerical results. It is found that significant deformation still occurs in the second free-standing cure step, which is believed to be caused by the stress-relaxation in the cured components. Another 3rd cure step could eliminate the further deformation significantly, by a percent of 87 %. In addition, the differences of magnitude and sensibility for curing deformation induced by master tool materials between the conventional one-step and designed two-step curing process have also been quantified based on the developed model and the results show that even with the aluminium alloys whose coefficient of thermal expansion (CTE) is 10 times higher than that of composites as the master tool materials, the difference in curing deformation can be controlled within 2 %.