Study On Thermo-Chemistry Behavior And Its Influence Mechanism Of Thick Section Composite

The temperature overheating,nonuniform solidification and serious residual stress during curing process were the main problems of thick section composite,seriously affecting the composite product quality and performance.In this dissertation,thick section G_f/860E composite prepared by vacuum infusion molding process,which were used on wind turbine blade,was the object of study.The thermo-chemistry behavior and its influence on the residual stress and mechanical properties of thick section composites were investigated.The main research work and conclusions are as follows:?1?The temperature field distribution of thick section composite during curing was investigated by thermocouple monitoring.The results showed that the in-plane temperature field in thick section composite of 25mm,50mm and 100mm thickness was serious imbalance.The maximum temperature reached 32?.The temperature in the thickness direction was gradient distribution at beginning of curing.Then temperature mutation occurred with curing and the center of specimen was overheating.The severity of overheating increased with the thickness of composite and the maximum difference to the setting temperature in mold were up to 35?.?2?The curing reaction kinetics of 860E/866H resin system and the distribution of the curing degree of thick composite were analyzed by the method of DSC.The results showed that the curing degree at different position in composite were heterogeneous,caused by difference of curing temperature field.The curing degree of 50mm thickness specimen at the conner in top and the center in bottom were 71.6%and 73.6%respectively,which were lower nearly 25%to the curing degree of the theoretical solidification system?97.6%?.The curing degree of 100mm thickness specimen at the vertex position and the center in bottom were 56.8%and 77.6%respectively,with the maximal difference of 36.1%for the curing degree of the theoretical solidification system?93.1%?.?3?The distribution of residual stress in thick section composite was investigated by deep-hole method.The results show that the residual stress increases with the increase of the thickness.The residual stress along the fiber direction??_x?is generally higher than the residual stress perpendicular to the fiber direction??_y?and shear stress(?_xy).The residual stress distribution along the thickness direction of the thick-section composite is not uniform.The residual stresses at different depths from the surface to the interior of the composite are significantly different.?4?The effects of thermochemical behavior during curing on the mechanical properties of thick-section composites were investigated.The results show that the nonuniform solidification is not the main factor that leads to the decrease of the thickness of the composite.The interlayer performance,the defect distribution and the residual stress are the main factors for the thickness effect of the composites.