Cure Schedule Evaluation of SC15 and SC79 Low-Viscosity Epoxy VARTM Resins

摘要

Vacuum-assisted resin transfer molding (VARTM) is a manufacturing process to create fiber-reinforced composite parts in a fast and cost-effective fashion. This process uses vacuum pressure to infuse a low-viscosity liquid thermosetting resin (epoxy) through a woven fiber preform. This methodology is advantageous because composites are fabricated at higher fiber volume ratios than wet lay-ups and do not require the high-autoclave pressures of prepreg processing. There are several criteria required of an epoxy resin used in the VARTM process. Resins that have a viscosity below 1000 cPs and have long work times are required to insure wetting and flow through the woven fabric, which enables a low void content in the final cured composite part. Low-temperature curing epoxies. (250 degrees F) are of particular interest to the manufacturers of multicomponent composites. A lower curing temperature resin reducreduces residual stress in the final part, minimizes energy costs for curing, and reduces the effects of coefficient of thermal expaexpansion mismatches between dissimilar materials that can concentrate stresses at bonding interfaces. Therefore, VARTM resins can involve complicated mixtures of components. The resins often exhibit multiple cure paths and the dominant cure path is dependent on the cure protocol followed. In this paper, the effect of different cure paths on the ultimate glass transition temperature (Tg) and fracture toughness of Applied Poleramic SC15 and SC79 are studied. These low-viscosity, epoxy-based resins are both rubber toughened, with SC15 having a lower ultimate Tg than SC79. Resins were cured according to the cure schedules often encountered in a manufacturing environment. Neat resin bars were made for differential scanning calorimetry (DSC) analysis and fracture toughness measurements. The fracture toughness was measured using an Instron 4505. The samples were prepared using the Single Edge Notched Beam geometry with a crosshead rate of 10 mm/m in.