Assessment of Microstructural Integrity of Glass/Epoxy Composites at Liquid Nitrogen Temperature

Abstract

Polymer composite materials have received increased attention for applications in a cryogenic environment because of their light weight and unique properties. The research presented in this article is an effort to understand the interlaminar fracture behavior of glass/epoxy composite laminates at cryogenic conditions and at different loading rates. This study uses a three-point flexural test to qualitatively assess such behavior for 50 wt% E-glass fibers reinforced epoxy composites during cryogenic and ambient conditions. The specimens were tested at a range of 2—500 mm/min crosshead speed to evaluate the sensitivity of mechanical response during loading at these conditions. The mechanical performances of the laminated specimens at cryogenic conditions were compared with room temperature properties by using SEM photographs. Phenomenological behavior of these materials may be attributed to polymer relaxation, low-temperature hardening, matrix cracking, and misfit strain due to differential thermal coefficient of the constituent phases, and also by an enhanced mechanical keying factor by compressive residual stresses at cryogenic temperatures.