Micro-mechanical Model Of Hydrothermal Behavior For Resin Matrix Fiber-reinforced Composites

Resin matrix fiber-reinforced composites will suffer mismatch deformations and residual stresseswhen experience expansion and contraction under the environment of changing temperature andmoisture, thus affecting the deformation of structures and the damages in materials. Conversely, thedamages will also affect the deformation of materials under the hydrothermal load. In this thesis，hydrothermal behavior for resin matrix fiber-reinforced composites were studied in the view ofmicro-mechanics. The research is divided into three parts:1) Micro mechanical theoretical and FE models have been developed to predict the coefficient ofthermal expansion (CTE) of unidirectional composites. The effects of matrix micro-cracks andfiber/matrix interface debonding on CTE of composites were considered in the models. The modelwas adopted to predict the CTEs of glass fiber/resin matrix unidirectional composites with variousfiber volume fractions and damage degrees. The results reveal that: when composites expanded orshrunk during heating and cooling, the status of various orientated micro-cracks in them weredifferent, their opening or closing will cause the inconsistencies in CTE of composites during heatingand cooling.2) moisture absorption tests and free vibration tests were designed for three types of compositespecimens, i.e. glass fiber/epoxy unidirectional composite, tabby composite and asymmetric laminate.Based on this, moisture absorption curve was measured. Plus, elastic modulus were calculated duringthe course of moisture absorption by the changes of natural frequencies of composites.3) FE and theoretical models were built to simulate the transient moisture diffusion in the glassfiber/resin matrix unidirectional composites, on which the effect of fiber volume fractions wassignificant. And the coefficient of moisture expansion and moist mismatch stress with various fibervolume fractions were calculated. Based on the thermal expansion theory, a new theoretical modelwas developed to calculate coefficient of moisture expansion, which could predict more accurately, onboth longitudinal and transverse ones.