Qualification of Shorter Cure Cycle for fabrication of Carbon/Epoxy towpreg Pressure Vessel

A workable shorter curing cycle is required for the manufacturing of carbon/epoxy towpreg and is crucial for attaining defect-free component consolidation. A rational "processing methodology" based approach is established in this paper, and a cure cycle design protocol is proposed. For thick component, autoclave processing with conventional and shorter curing cycles was used. This has been validated through experimental studies. For thick composites, an uncontrolled exotherm could lead to a cure of the component from the inside out, with high process-postulated residual stresses. To determine and regulate the exotherm cross-linking reaction's maximal heat generation, thermal tests were conducted. These tests revealed isothermal holds and ramp rates were most effective in lowering the exothermic peak. Based on these findings, a shortened cure cycle was developed and applied to the material system. During the curing process, embedded thermocouples were utilized to track heat production and control temperature ramps and dwells. Both visual inspection and ultrasonic testing showed reduced porosity and satisfactory compaction. The proven-in method was validated by differential scanning calorimetry (DSC) on post-cured samples, which showed a high degree of cure across the thickness of the component. Using the shortened cure cycle, the mechanical qualities of the product were assessed using travel coupons and found to be comparable. Keywords: Towpreg; autoclave processing; residual stresses; Differential Scanning Calorimetry; Shorter cure cycle.