| Summary: | 博士 === 國立交通大學 === 材料科學與工程系 === 88 === Resin transfer process (RTM) is being considered as an alternate to the traditional prepreg lay-up/autoclave curing process for the manufacture of high performance composites because of its economics and flexibility. In RTM, a pre-catalyzed resin is injected under pressure into a fibrous preform in a hot closed die mold, then in-situ curing the resin to form the final parts. This study involves a resin transfer molding (RTM) process for making advanced composites based on high performance epoxies and high temperature resistant bismaleimide (BMI) resins. The curing kinetics and viscosity change of resins during the mold filling stage were studied and simulated with appropriate kinetic and rheological models. The effects of processing variables including injection temperature, injection pressure, gating arrangement, fiber volume fraction and fabric structure on the processing and performance of the resulting composites were investigated. The produced composites possess fiber volume fraction higher than 55﹪and void content lower than 1﹪. The glass transition temperature (Tg) is 208℃ and flexural strength reaches 585Mpa for 1581/PR500 fiberglass epoxy composites. For 1581/CPA-2350 fiberglass bismaleimide (BMI) composites, the Tg is 316℃ and flexural strength reaches 613Mpa. Moreover, the flexural strength of carbon fiber BMI composites approaches 808Mpa.
A modified Kamal''s kinetic model was adapted to describe the autocatalytic and diffusion-controlled curing behavior of PR500 epoxy resin over the temperature range of 160-197℃and of LY564/HY2954 epoxy resin over the temperature range 50-80℃for resin transfer molding (RTM) process. The cure reaction of CPA-2350 BMI resin follows first order kinetics over the temperature range of 115-145℃ in the initial stage of the cure reaction. An empirical model correlated the resin viscosity with temperature and the degree of cure for LY564/HY2954 epoxy and CPA-2350 BMI was obtained. Predictions of rate of reaction and resulting viscosity change by the modified Kamal''s model, first order kinetics and the empirical rheological model agreed well with the experimental data for the mold filling stage of the RTM process.
The optimized physical and mechanical performance of PR 500 epoxy based glass composites was obtained by processing the resin at 160℃under 392 kPa pressure. At 150℃resin temperature, restriction of resin flow and reduction in mechanical performance of the resulting composites were found due to particulate filtration of the hardener from resin matrix. Molding of highly permeable EF420 fabric required shorter mold filling time, but resulted in reduced flexural strength and storage modulus as compared to those of 1581 fabric. In RTM process of LY564/HY2954 two-part epoxy, molding aged resin with 55﹪fiber exhibited twice mold filling time and caused a 7-15﹪deterioration in the interlaminar shear strength(ILSS) and in the flexural strength of the composites as compared to that of the composites molded with fresh resin. At 55﹪fiber volume fraction, composites molded with aged resin resulted in 35﹪longer filling time, and 4-12﹪decreased ILSS and flexural strength as compared to that of the composites at 44﹪fiber volume fraction. Moldings with the perimeter inlet exhibited 65﹪shorter mold filling time, 28﹪reduced void content and 6﹪improved flexural strength as compared to that of the composites molded with the center inlet. As compared with those of PR500 epoxy, composites based on LY564/HY2954 epoxy resin behaved lower flexural strength (585Mpa vs. 394MPa), higher void content (0.37﹪vs. 0.83﹪) and lower Tg (208℃ vs. 153℃).
For CPA-2350 BMI based carbon composites, better mechanical properties and less void content were obtained for moldings at 125℃ and 135℃ as compared to moldings at 115℃ and 145℃. Decreased mold filling time, lowered void content and improved mechanical properties were observed with increasing injection pressure for moldings processed at 125℃. Moldings with a center inlet resulted in 3.8 times increase in mold filling time, 3.7﹪increase in void content and 3.3﹪decrease in flexural strength as compared with a perimeter inlet. Composites with 52﹪carbon fiber exhibited lower void content and higher mechanical properties as compared to those of 58﹪carbon fiber. In contrast to glass fiber counterpart, carbon fiber contributes to the superior mechanical performance of their composites due to the exceptional strength and modulus. Among moldings of varied fiber fraction and fabric structure, the higher fiber volume fraction is the key factor that resulted in the higher voids trapped in the resulting composites.
|
|---|
