This work has been developed for a comparative purpose concerning the processing and respective mechanical performance of CFRP composites processed by resin transfer molding (RTM) and compression molding (CM) techniques. Thermal and viscosimetric tests before processing certified the optimal parameter procedure. Both composites were submitted to short-beam shear tests and through microscopy to determine failure mechanisms. CM specimens presented a decrease of 27% in shear strength caused by the presence of macro porosity that induced crack initiation and connection of different delamination plies, causing the speeding up of crack propagation and jump of the interlaminar layer. The low capillary effect and higher viscous force were responsible for macro porosity, inducing heterogeneous impregnation in CM and to the direction reduce in mechanical behavior. On the other hand, more homogeneous impregnation in RTM specimens was responsible for the absence of macro porosity, ensuring higher values of shear strength and lower void volume fraction.
In the present study, the creep behavior of polyetherimide semipreg and epoxy prepreg composites was studied using dynamic mechanical analyzer and focused on structure vs. property relationships in glassy, glass transition, and elastomeric regions. The main contribution to the field is to study pre-impregnated materials concerning creep behavior, mainly based on different analytical models, and microstructure. Two different reinforcements were used (carbon fiber and glass fiber) for each matrix. Findley, Burger, and Weibull analytical models were applied with an excellent fit for the most of them. The impregnation quality, verified by C-scan and the void content by acid digestion, shows different impregnation behaviors, mainly for epoxy/CF, which also influenced molecular motion behavior. The creep behavior was mainly influenced by matrix type than reinforcement architecture and void content. In addition, the creep was higher for epoxy in the glassy region; however, in the glass transition region, higher deformation was found for polyetherimide composites. Previous behavior is mainly attributed to higher energy storage in the glassy region which plays a significant role in the dissipation (glass transition energy), resulting in the energy loss or the drop of storage modulus in a narrow temperature range – more abrupt. This behavior was corroborated by time-temperature superposition curves in which the low deformation obtained for polyetherimide composites at low temperatures is maintained only until the glass transition temperature. Epoxy composites showed a higher initial creep deformation, but the values were almost constant with temperature, even when the temperature passes by the glass transition temperature.
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