Research On Heating Curve Optimization Aiming To Improve The Curing Uniformity Of Resin Matrix Composite And Its Influence On Cure-induced Deformation

Resin matrix composites have been widely used in aviation, aerospace and other manufacturing areas because of their notable performances, such as high specific strength and modulus, easy to integrally thermal cure. In actual production, the internal nonuniform distribution of temperature and curing degree fields in composite part lead to thermal stress and nonuniform curing shrinkage in curing process, generate cure-induced deformation and decrease dimensional accuracy. Current researches of improving curing uniformity are mainly aimed at the uniformity of temperature field, but the curing degree of field directly affects the curing shrinkage of material, improve the uniformity of degree-of-cure field also has important engineering significance.Based on this, a general method of heating temperature curve optimizing based on the finite element simulation results was proposed in this paper for improving the uniformity of degree-of-cure field of resin matrix composite part. The optimized heating temperature curve of AS4/3501-6 and phenol formaldehyde resin flat is established by utilizing optimization method in this paper. Experiments of phenol formaldehyde resin flat curing are implemented to verify the feasibility of the optimization method.Firstly, curing process of AS4/3501-6 composite flat is simulated and the processing parameters which influence the uniformity of degree-of-cure and temperature fields are analyzed.Secondly, a general heating curve optimization method is developed. The internal relation of maximum difference of curing rate of the flat and the first order differential equation of maximum difference of curing rate is studied. According to the relationship of function value with its first order differential and second order differential, coupled with the regularity of heat up and heat preservation influence the uniformity of curing, a optimized heating curve is established to improve the uniformity of cure degree and temperature fields. This method can be used for any kind of resin matrix composites heating temperature curve optimization.Thirdly, according to the actual demand of production, the cure kinetic equation of a kind of phenol formaldehyde resin prepreg which is currently applied in production was studied by DSC(Differential Scanning Calorimetry) experiments and model-fitting method. This cure kinetic equation can be used to subsequent heating curve optimization of phenol formaldehyde resin prepreg.Finally, the optimized heating curve of a flat part with thickness of 2.5mm was established by combining the heating curve optimizing method and cure kinetic equation of phenol formaldehyde resin prepreg. Calculate and compare the nonuniformity of plat parts with thickness of 1.5mm, 2mm and 2.5mm under direct heating curve respectively. The nonuniformity of plat part with thickness of 2.5mm under heating curve which is used in actual production and optimized heating curve are also analyzed, respectively. Corresponding flat part curing experiments are implemented. Results of simulations show that the curing uniformity of flat part improves under optimized heating curve. Accordingly, experiment results show that under the optimized heating curve, deformation of cured flat part reduces compares with under a direct heating curve, and the same shape of flat compares with the flat cured under heating curve which is used in actual production. The optimized heating curve saves 26.5% of the time compared with the existing process, means this heating curve optimizing method can improve the efficiency significantly, proves the feasibility of the optimization method.