Hybrid Helmet Cure Cycle Optimization

Abstract : Some of the recent work involving the use of thermoplastic materials for combat helmets has shown significant weight savings and improved protection. Unfortunately, the change to thermoplastic materials brings with it some important concerns. First, the stiffness is compromised with these materials so a hybrid type of helmet (a thermoplastic shell with thermoset inner or outer skins) is needed to reduce the deflection properties. This brings us to the second concern, processability. A typical combat helmet is made with a thermoset phenolic/polyvinylbutyral material, usually cured at 250 deg. F with a 1-hour soaking time. Thermoplastics require higher temperatures for the fusion process to commence but require a much shorter soaking time. This work investigates potential cure cycles for a carbon fiber-epoxy prepreg, BT250-E, cured at higher temperatures, faster ramp rates, and shorter soaking times. A differential scanning calorimeter was used for measuring the degree of cure for the various cure cycles from which the most optimized cycle was selected, based on degree of cure and process time.