Durability-based design criteria for a chopped-glass-fiber automotive structural composite

This paper describes durability-driven design criteria developed for the use of a chopped-glass-fiber polymeric composite in automotive structural applications. The composite, which was made by a rapid molding process suitable for high-volume automotive applications, consisted of a chopped-fiber E-glass mat, made by the programmable powder preform process (P4), in a urea/urethane matrix. The durability issues addressed include the effects of cyclic and sustained loadings, temperature extremes, and automotive fluid environments. The paper briefly describes the laboratory tests, summarizes the results, and explains how the experimental information was used to formulate coherent and practicable design criteria. The criteria include design analysis guidance, a biaxial strength criterion, time-independent and time-dependent allowable stresses, and rules for assessing cyclic loadings. Environmental degradation factors and the degrading effects of prior loadings are included.