Generic Tube Crush Program: Crush Tests of Structural Reaction Injection Molded Tubes

Abstract

Abstract This paper documents the structural reaction injection molding (SRIM) portion of a generic crush study of glass fiber reinforced composite tubes conducted by the Energy Management Working Group of the Automotive Composites Consortium (ACC). Static and dynamic crush tests were performed to evaluate the crush performance of square, circular, and rectangular shaped cross-section tubes. Manufacturing of the tubes for this study required feasible processes for production such as resin transfer molding (RTM) and SRIM, in conjunction with rapid preforming and foam core fabrication. Square (55 × 55 mm), circular (63.5 mm diameter), and rectangular (38.1 mm × 71.1 mm) crush tubes had a nominal wall thickness of either 2.54 or 5.08 mm and a length of 230 mm. Dow Spectrim MM364 resin was used for all the tubes in this portion of the study. Seven different fiber architectures were considered ranging from random chopped mat (RCM) to a tri-axial braid. The principal fiber was E-glass with a limited number of tubes being constructed with S-2 glass. A plug-type initiator was used in combination with a 45° bevel on the outside edge of the lead end of the crush tube to ensure progressive crush. Crush tests were performed at −40°C, room temperature, and 82°C. The tubes tested at high temperature were immersed in distilled water for 24 hours prior to heating. Various fiber architectures, wall thicknesses, and temperatures were evaluated for their effect on energy absorption characteristics during axial crush using plug-type initiators. Principle findings were that different fiber architectures can produce significant differences in tube specific energy absorption (SEA), that SEA increases dramatically with increasing tube wall thickness, and that post-curing can increase the SEA of the tubes. Static tests produced higher values of SEA than those measured in dynamic tests for most fiber architectures at cold and room temperatures, while at elevated temperature / humidity, the opposite effect is seen in that static values were lower than dynamic values of SEA.