Mechanical behavior of glass/epoxy composites at liquid nitrogen temperature

The present experimental investigation deals with the mechanical behavior of glass/epoxy composites at cryogenic temperature. Woven and chopped E-glass fibers of 50 weight percentage were reinforced with epoxy matrix to prepare the laminated composites. 3-point bend tests were carried out to assess interlaminar fracture behavior at cryogenic and at ambient conditions. The specimens were tested at a range of 2 mm/min to 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 property by using SEM photographs. DSC was carried out to study whether there is any change in glass transition temperature. Glass/epoxy composites were found to be loading rate sensitive. DSC analysis shows increase in glass transition temperature after cryogenic conditioning which may be due to irreversibility of the chain mobility. The phenomenological behavior of these composite materials may be attributed to polymer relaxation at low temperature, cryogenic hardening, matrix cracking, and misfit strain due to a differential thermal coefficient of the fiber and the matrix and also by an enhanced mechanical keying factor by compressive residual stresses generated at cryogenic temperatures.