HYGROTHERMAL DAMAGE MECHANISMS IN GRAPHITE-EPOXY COMPOSITES

摘要

An experimental and analytical study of T300/5209 and T300/5208 graphite-epoxy laminates was conducted:(1) to determine the coupling between applied stress, internal residual stress, and moisture sorption kinetics, (2) to examine the microscopic damage mechanisms due to hydrothermal cycling, (3) to evaluate the effect of absorbed moisture and hydrothermal cycling on inplane shear response, (4) to determine the permanent) loss of interfacial bond strength after moisture absorption and drying, and (5) to evaluate the three-dimensional stress state in laminates under a combination of hygroscopic, thermal and piechanical loads. Specimens were conditioned to equilibrium moisture content under steady exposure to 55 or 95% RH at 70 or 93°C. Some specimens were tested subsequent to moisture conditioning and 100 cycles between -54º c and either 70º C or 93 C.nThe transverse and through thickness expansion of unidirectional composites due to absorption of equilibrium moisture concentrations were determined. Desorption of moisture at 70 C was found to be insensitive to initial moisture content, applied stress and internal residual stress. Dimensional changes on (04, 904) laminates were measured during hydrothermal cycling to assess alteration of laminate residual stress. Elastic laminated plate theory was successfully used to predict the moisture altered residual stress state of T300/5208 laminates. In T300/5209 the strong dependence of residual stress on hydrothermal history was indicative of viscoelastic behavior.