Effects of variation in autoclave pressure, cure temperature, and vacuum-application time on the porosity and mechanical properties of a carbon/epoxy composite
The effect of variation in autoclave pressure, cure temperature, and vacuum-application time on porosity, hot/wet (H/W) and room temperature/dry (RT/D) short beam shear (SBS) strengths, and failure mechanisms of IM7/977-2 unidirectional prepreg was investigated. The stacking sequence for all panels was [00/902/0]4s. Fourteen cure cycles were designed to study a wide range of cure pressures, cure temperatures, and two different vacuum-application durations, including vacuum vent at recommended pressure and vacuum hold throughout the cure cycle. It was found that for panels cured at different temperatures and for panels cured at different pressures with a vacuum vent at recommended pressure, SBS strength did not vary significantly over a relatively wide range of cure temperatures and pressures. However, after a certain point, a decreasing trend in the average SBS strength for both H/W and RT/D was observed by reducing the cure temperature as well as the cure pressure. Panels with the same cure pressure and dissimilar vacuum-application durations showed different SBS strength, with higher properties associated with panels in which the vacuum was vented at the recommended pressure. For panels cured at various cure pressures and the vacuum hold throughout the cure cycles, C-scan results showed a cross-shaped high-porosity in the middle of the panels, which became larger as the cure pressure decreased. This defect is believed to cause higher variability of the SBS strength as the cure pressure is reduced. SBS strength was found to decrease with increasing void content in the test specimens. Theoretical models were compared to the experimental data of SBS strength vs. void content. Investigation of the failure mode for each panel revealed a change in both H/W and RT/D failure mechanism by lowering the cure temperature and cure pressure. However, the change was more dominant when the cure temperature was varied.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.