| The three-dimensional(3-D)angle-interlock woven composites have been widely applied to impact-resistance engineering structure design because of the fabric structure integrity.3-D woven composites after high temperature atmospheric aging are popular and important question in engineering structure design.In this thesis,we investigate the quasi-static indentation and low velocity-impact behaviors of the 3-D carbon/epoxy woven composites after the 90?,180? aging for different days.The scanned electron microscope(SEM)was empolyed to observe the cross-section characteristics and the fiber pull-out status after atmospheric aging.The thermal gravimetric analysis(TGA),differential scanning calorimetry(DSC),infrared spectroscopy(IR)techniques were used to characterize the thermal aging behaviors of the epoxy resin and the 3-D woven composites.1)DSC and IR analysis of epoxy resin,the thermal-release peak in DSC spectrum curve and epoxy peak(916cm-1)in IR curve disappearred.The epoxy resin post-curing phenomenon was inferred form this observation.From TGA,DSC and IR analysis,we found the thermal degradation speed at 180? is 2.5 times of that in 90?.And the degradation ratio increased as the temperature and time increased.The thermal-oxidation degradation occurred at 90? and 180?,while more serious at 180?.It was found there are post-curing and thermal-oxidation mechanisms during high temperatures aging.At the early stage of 90? thermal aging,the quasi-static compressive strength and modulus increase owing to crosslinking development.For example,the strength and modulus increase by 9.4% and 8.5% respectively after 16-day ageing,while they decrease slightly after 32-day ageing for the oxidation degradation.At the ageing of 180? atmospheric environment,the strength and modulus decrease by 9.0% and 35.5% respectively after 32 days.2)At 90? atmospheric ageing,there is almost not surface color change and cross-section crack.At 180? ageing condition,the surface color has been changed form grey-back to light yellow,and finally dark-yellow.From SEM observation,we found the debounding between carbon fibers and epoxy resin has been developed to huge cracks rapidly as the ageing time lasted.While this phenomenon could not be observed at 90? aging condition.And also,the fiber pull-out could be found during ageing.The amount and length of pull-out fibers increased as the aging time increased.3)The compressive strength and modulus increase at 90? ageing owing to post-curing mechanism.The maximum strength and modulus will be happened after 16-day ageing,which increased by 5.0% and 1.8% respectively.At 180? ageing,the strength and modulus increased intially and then decreased by 20.5% and 6.9% after 32-day ageing.4)There are the same tendency of low-velocity strength and modulus afer ageing with those in quasi-static loading conditions.For the 90? ageing,the strength and modulus increased by 6.5% and 4.9% respectively after 16 days.For 180? ageing,they decrease by 24.2% and 6.5% after 32-day ageing.5)The elastic energy absorption increased by 29.1% at 90? ageing after 32 days,while decreased by 19.1% at 180? ageing after 16 days.However,the energy absorption increased slightly for the ageing at 180? after 32 days because the elastic stage continus to the stage with the large amount of fiber breakage.The atmospheric high temperature ageing of the 3-D angle-interlock woven composites is an important topic for the engineering applications.This project could be extended to other 3-D textile composite design for the different environment temperatures and service lifes.Such an investigation is also an extension for the current composite design on the basis of simple environmental parameters... |
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