Micro-scale Hydrothermal Expansion/Contraction Analysis For Fiber Reinforced Composite

The hydrothermal deformation of composite could cause change of the structure dimension, itgenerates micro-scale stress mismatch also, which might lead to multiple modes of damage. In thisthesis, hydrothermal behaviors of fiber-reinforced composite (FRC) were studied in micro-scale,details are as follows:(1)Micro-mechanical theoretical model, which considering damages of matrix micro-cracks orfiber/matrix debonding, has been developed to predict the coefficient of thermalexpansion/contraction (CTE/CTC) of FRC. In the model, the transverse mismatch stresses areformulated un-uniformly. Meanwhile the quantities of CTE/CTC varying with damage models havebeen investigated. Micro FE models with periodic and random arrangement of fibers have also beenbuilt to validate the theoretical predictions. The results reveal that CTE and CTC of damaged FRC arenot identical and their discrepancy depends on damage modes.(2)Micro FE model was built to simulate the transient moisture diffusion in FRC, in which theeffects of moisture concentration dependent resin matrix softening and fiber packing pattern wereconsidered. The simulation results have also been verified by macro-theoretical model. The researchesindicate that the maximum moisture-induced micro-stress occurs near the fiber/matrix interface, andits value fluctuates with moisture diffusion. The resin matrix softening will reduce local mismatchstresses notably. Fiber packing pattern brings a little influence on the transient moisture diffusivitiesof FRC.(3)Micro-mechanical theoretical model has been developed to predict the coefficient of moistureexpansion (CME) of FRC. The effects of local humidity gradient and matrix moisture softening onCME were studied here. Micro FE model has also been built to validate the theoretical predictions.The studies reveal that, the CMC of a typical glass fiber/epoxy composite (GF/EC) will decrease inlongitude while increase in transverse with fiber volume fraction gaining. Matrix softening couldbring notable reduction of longitudinal CME, otherwise be ignorable to transverse one. The CMEspredicted by this model, applied uniform and gradient humidity distributions respectively, have littlediscrepancy.(4)FE and theoretical models have been developed to predict the CTC of laminated composite.The CTCs of laminates with regular symmetrical cross-ply, regular symmetric angle-ply and generalsymmetry ply have been calculated by the two models. Theoretical predictions are in agreement withFE results.