Abstract
The objective of this research is to investigate the effect of long-term exposure of plain woven 240-D S2 glass epoxy composite laminate to dry, moist and various temperature cycles. Interlaminar shear stress was evaluated to assess the delamination tolerance on both virgin (preexposed) and harsh environment-exposed composites specimens. Delamination tests were performed with the pattern of four-point bending and tensile and compression shear tests under different combinations of humidity and temperature exposure, ranging from zero to 32 weeks. During the tests, the stress at the onset of delamination was taken as the first deviation of the load-displacement curve. Experimental study revealed that the delamination load-carrying capability reduced to 40% with the exposure time. Throughout the aging process dimensional stability was almost unchanged; however, 1.29% moisture absorption was noticeable in laminated composites. Microstructures of the delaminated surface revealed that failure occurs suddenly in a macroscopically fragile mode by crack initiation and proliferation. The delamination mechanism involved interlaminar processing flaws that favored the initiation and propagation of the interlaminar cracks, which are responsible for the delamination of the composite. As load carrying capacity dwindles substantially, therefore the effect of temperature and moisture must be taken into account in the experimental characterization of the laminates when establishing a design limit for composite structure.
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