Water diffusion and swelling stresses in ionizing radiation curedepoxies as matrices for carbon fiber composites

Risultato della ricerca: Other

Abstract

Cross-linking polymerization initiated by high energy radiation is a very attractive technique for theproduction of high performance composite materials. This method in fact offers many advantages comparedto conventional thermal curing processes, due to the possibility to operate at mild temperature and in shorttime, limiting both energy and time consuming [1-2]. High performance composite materials mainly consistof epoxy resins as matrix and carbon fibers as reinforce, due to their excellent properties in terms of thermaland mechanical resistance. An important requirement of such systems for structural applications is their abilityto maintain the properties within a fixed range during their operative life, i.e. to show significant resistance tothe external aging factors. Among them, one of the recurrent ageing conditions is hydrothermal ageing, due toboth temperature cycles and water absorption-desorption [3]. These conditions induce some importantmodification in the thermo-mechanical behaviour of epoxies, including plasticisation and degradation of thenetwork, with a general lowering of the glass transition temperature, modification of the strength and fracturetoughness, and swelling which may induce important localized internal stresses [4]. All these phenomena arevery difficult to investigate, due to the several mutual effects occurring, and to a lack of reliable and simplemeasuring techniques. Some of the authors have recently proposed a new approach to evaluate the transitoryswelling/un-swelling stresses, by means of Photoelastic Stress Analysis (PSA) [5]. This technique provided arobust method to evaluate the material in terms of its ability to swell and to develop internal stresses, correlatingthis property to the kinetics of water uptake and to the thermal and mechanical properties of epoxies.In this work electron beam curing was used in order to obtain two epoxy resin systems with very differentcross-linking features in terms of both crosslinking homogeneity and water chemical affinity. The differentstress behaviour of the irradiated systems upon water absorption/desorption was investigated by means of PSAand the results were interpreted on the basis of the comparison to those of the same monomer thermally cured.The results evidenced the strict correlation between network structure of the resins and swelling inducedinternal stresses, allowing to evaluate the evolving stress field and providing a different point of view on theinvestigation of differently crosslinked structures associated to water diffusion.
Lingua originaleEnglish
Numero di pagine1
Stato di pubblicazionePublished - 2017

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