Effect of cure cycle heat transfer rates on the physical and mechanical properties of an epoxy matrix composite

Although the autoclave technique produces composite parts of high-quality, the process is time consuming and has intrinsically high-capital and operating costs. Quickstep™ is a novel polymer composite manufacturing technique designed for the out-of-autoclave processing of high-quality, low-cost components with a reduction in cure cycle times. This paper assesses the use of the Quickstep method for the processing of an epoxy/carbon fibre aerospace material and compares this to equivalent composites produced using an autoclave process. Higher process ramp rates, achievable using Quickstep, have been shown to reduce resin viscosity thus facilitating void removal. Manipulation of the Quickstep cure cycle, while the resin is at low-viscosity, has significant effects on the mechanical properties of the product whilst simultaneously reducing the cure cycle time. Using Quickstep curing, samples were produced exhibiting comparable interlaminar properties but lower flexural strength as compared to those produced using the autoclave. However, normalisation of the data to a common fibre volume fraction showed that better interlaminar shear strengths could be obtained using Quickstep. This improvement in specific interlaminar shear strength was postulated to be due to the lowering of the resin viscosity over the duration of the cure, resulting in better wet through of fibres by resin and improved interfacial adhesion between fibre and matrix. This study identifies key parameters associated with the Quickstep process, providing a basis for further optimisation.