| The recent paradigm shift in the aerospace industry from a performance to a cost driven business environment has imposed new challenges on the development and utilization of polymeric composites. Novel manufacturing technologies involving fewer processing steps together with the introduction of standards for materials and processing are believed to provide the basis for the desired cost reductions. Among the most promising techniques is the resin transfer molding (RTM) process where impregnation and cure of the fiber-reinforced thermosets are performed in the same manufacturing operation. The inherent difficulty with this technology is that only homogenous and low viscosity resin systems can be employed leading to relatively brittle network structures. Thus, after first establishing a methodology for the systematic characterization and development of RTM composites, various concepts for improving the toughness of this class of materials were investigated. The approaches ranged from chemical to process modifications providing comprehensive insight about the effectiveness of the different toughness mechanisms from a process-structure-property standpoint. A novel toughening concept was developed that utilized modified processing aids, termed tackifier materials, to create heterogeneous interlayered laminate structures. Substantial mode I and mode II toughness improvements were obtained using preformed elastomer particles without significantly reducing thermal mechanical and other bulk properties. The basic effects of tackifier composition, concentration, and distribution were studied in relation to processing and performance. In addition to these material and process initiatives, strategies for lowering costs of polymeric composites through material and testing standardization were explored. By combining operational, logistical, and technological considerations, a strategy was developed that could provide an effective process for industry-wide cost reduction. |
