This article presents results from investigation of the effects of variation in autoclave pressure, temperature, and vacuumapplication time on porosity, hot/wet (H/W) and room temperature/dry (RT/D) short beam shear (SBS) strength, and failure mechanism of a commercial carbon fiber/epoxy prepreg, Cycom IM7/977-2 unidirectional tape. Fourteen cure cycles were designed to study a wide range of curing pressures, curing temperatures, and two different vacuumapplication durations, including vacuum vented at recommended pressure and vacuum held throughout the cure cycle. The results showed that the SBS strength did not vary significantly over a relatively wide range of curing temperatures and pressures if vacuum was vented at recommended curing pressure; however, after a certain point, a decreasing trend in the SBS strength was observed by reducing the curing temperature and pressure. The C-scan images of panels cured with the vacuum held throughout the cure cycles revealed presence of a high-porosity crossshaped defect at the center of the panels. The observed defect became larger as the curing pressure decreased. The correlation between the SBS strength and the void content was studied using theoretical models and experimental data. The investigation of the failure modes for each panel showed a change in both the H/W and the RT/D failure mechanism as a result of variation in curing temperature and pressure.

Thermal, rheological, and mechanical properties of a commercial carbon fiber epoxy prepreg, Cycom 977-2 UD, were obtained for isothermal cure temperatures ranging from 149 C to 182 C. For each cure profile, an encapsulated-sample rheometer (ESR) was used to measure the storage modulus. Each ESR cure profile was followed by the glass transition temperature (T g ) test. The degree of cure () during cure and the heat of reaction of the prepreg were obtained using a differential scanning calorimeter (DSC). Combined loading compression (CLC) and short-beam shear (SBS) tests were performed to obtain compressive properties and SBS strength, respectively. It was observed that the compressive properties did not vary significantly for the studied isothermal cure temperatures; likewise, the compressive failure mode was the same for all the CLC specimens. However, the SBS strength for the specimens cured at 149 C was approximately 10% less than that of those cured at isothermal cure temperatures ranging from 160 C to 182 C. Further, the failure mode of the SBS specimens cured at 149 C was also different from other specimens. The storage modulus of the ESR sample cured at 149 C also showed a 10% decrease compared to other ESR samples. The SBS strength exhibited a good correlation with the storage modulus and a weak correlation with T g and .

To predict the final geometry of carbon fiber-epoxy composite parts, a methodology is introduced that takes into account cure kinetics, cure shrinkage, thermal strains, tool-part interface, and development of mechanical properties during cure. These parameters affect process-induced residual stresses and distortion in the parts. A module was developed for each mechanism and a fully 3D coupled thermomechanical finite element analysis was utilized. To validate the simulation results, a square composite panel was fabricated and its pattern of distortion was obtained. The simulated distortion pattern agreed well with the actual pattern obtained from the experiments. Parallel processing and optimization of the developed codes were used resulting in 94% reduction in the computational time. The proposed methodology proved to be accurate and time-efficient in predicting the final geometry of the parts. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 941-950, 2013

In this study, flat composite panels were fabricated to find the effect of different manufacturing parameters, including stacking sequence, part thickness, and tooling material, on distortion of carbon fiber‐epoxy composite parts. L‐shaped and U‐shaped panels were also made to investigate the effect of stacking sequence on spring‐in angle and warpage of the curved panels. Results showed that distortion of the flat panels caused by asymmetry in the stacking sequence was an order of magnitude greater than distortion of the panels with an unbalanced stacking sequence; whereas in the curved panels, the panel with an asymmetric stacking sequence showed the least spring‐in angle, and the largest angle was observed in the symmetric panel. MSC Marc was used to predict distortion of the panels, and the simulation results were compared with the experimental results for several stacking sequences of the flat and the L‐shaped panels. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40439.