Stress-Rupture Life and Strength Retention of an Aramid Fiber/Epoxy Composite under Accelerating Conditions

摘要

The long-term tensile strength retention of Kevlar 49 (aramid fiber)/epoxy composite under sustained loading at 56.4 percent of the ultimate fiber tensile strength (3400 MPa) was studied to evaluate the lifetime to failure of the composite under the same load level. To obtain data in a conveniently short time, elevated temperature was used according to an acceleration relation (Arrhenius type) developed for the Kevlar 49 composite. Although the acceleration relation gave a calculated stress-rupture lifetime of 526 h, the actual median lifetime was 272 h. This indicates that the acceleration relation probably should be broadened to describe stress-rupture behavior at stress levels other than those from which the relation was originally developed. The strength retention tests indicate that at 110 exp 0 C stress (sustained loading) does cause a small but statistically significant loss of strength (8 percent) by 200 h. Heat alone (no stress) degrades the strength only after 500 h have elapsed, and then only a small amount. Exposure to ultraviolet light similar to room light for 500 h at 110 exp 0 C does not have any additional degrading effect. (ERA citation 03:019153)