Effects of the Hygrothermal Environments on the Tensile Properties of Epoxy Resin Composites
The moisture absorption characteristic curves of the glass fiber/L285 epoxy resin composites were obtained by the accelerated hygroscopic method.The effects of the hygrothermal environments on the glass transition temperature,damage mechanism,tensile strength and elastic modulus were investigated by comparing and analyzing the chemical structures,fracture microscopic morphologies,and mechanical properties before and after hygrothermal treatments.The hot-humid aging mechanisms were explored,providing theoretical and experimental basis for the safe operation of general aviation aircraft.The results show that the composite materials conform to the Fick's second law at the early stage of moisture absorption,and the moisture absorption curves gradually tend to flatten at the later stage.When the humidity is certain,the higher the temperature,the higher the moisture absorption rate,and the longer the time to reach the moisture absorption saturation.When the bath temperature is increased from 25℃to 85℃,the moisture saturation rate is increased by 209%,and moisture saturation time is increased by 46.50%.After the hygrothermal treatments,the tensile fracture failure form of the composite material changes,the tensile strength is reduced by 30.97%,and the elastic modulus fluctuates in the range of 6%.In the early stage of loading,the stress-strain curves are linear and show non-linear trends in the later period.Compared with the 25℃dry sample,the glass transition temperature of the 85℃wet sample is decreased by 24℃,the corresponding chemical structures do not change,but the fiber-matrix interfaces undergo irreversible physical changes.
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