Freezing and thermal spikes effects on interlaminar shear strength values of hygrothermally conditioned glass fibre/epoxy composites

Abstract

tive humidity (RH). The different batches of specimens were removed from the humidity chamber after different exposure times. Some of the specimens at each stage were exposed to -4 °C for 24 h. Then three-point bend tests at each stage for both types of conditioned (plain moist and frozen moist) specimens were carried out with an Instron machine. The effect of the loading speed on the ILSS values of frozen moist specimens were observed at 1 and 10mmmin -x crosshead speeds. The high-temperature excursion was carried out at 250 °C for 10 rain (thermal spike), for two series of moist glass/epoxy composites specimens: one hygrothermally conditioned at 90 °C and 95% RH and the other immersed in a hot water bath controlled at 90 °C. Then the variation of ILSS values due to the effects of the thermal spike were investigated. The ILSS values of both plain moist and frozen moist specimens were recorded for the same level of moisture content and plotted against the square root of the exposure time (Fig. 1). The figure shows that except for the initial period of exposure, the shear strength of specimens with frozen moisture was lower than that of plain moist specimens with the same exposure time. When the moisture inside the materials becomes frozen, this may lead to a further increase of swelling stresses, due to the volume expansion of moisture during freezing, so this treatment turns out to be more deleterious to ILSS values for the same amount of moisture. The initial exception may be due to the strain-free state of the