Loading rate effects on mechanical properties of polymer composites at ultralow temperatures

E-glass fibers of 55, 60, and 65 weight percentages were reinforced with epoxy matrix to prepare the laminated composites. They were exposed to -40, -60, and -80 degrees C temperatures for different times. The 3-piont bend test was conducted on the conditioned samples at those temperatures. Mechanical test was carried out at 2 mm/min and 500 mm/min crosshead speeds. The main emphasis of the investigation was to evaluate the roles of percentage matrix phase and interfacial areas on the interlaminar shear failure mechanism of glass/epoxy composites at ultralow temperatures for different loading speeds. The mechanical performances of the laminated specimens at low temperatures were compared with room temperature property. The loading rate sensitivity of the polymer composites appeared to be inconsistent and contradictory at some points of conditioning time and as well as at a temperature of conditioning. This Phenomenon may be attributed to low-temperature hardening, matrix cracking, misfit strain due to differential thermal coefficient of the constituent phases, and also to enhanced mechanical keying factor by compressive residual stresses at low temperatures. (c) 2006 Wiley Periodicals, Inc.