Study On Coupled Thermomechanical Problems Of Fibre-Reinforced Composites Subjected To Thermal Shock

Coupled thermomechanical problem under high temperature gradient and high heatrate is one of key problems that many fields of engineering must be faced with. Itinvolves the thermal protection system (thermal barrier coatings), coupledthermomechanical problems of micro-nano instrument in micro electro-mechanicalfields (the process and preparation of MEMS instrument) and the thermodynamicsproblems in biological material (cold and heat treatment of tumour). Because of thecharacter of noteworthy microstructure and non-homogeneous inner structure, theremarkable non-Fourier effect is represented in heat transfer for short time and spaceunder high temperature gradient and high heat rate. The relaxation time is not limited tothe level of molecule or lattice. There are different heat transfer construction units innon-homogeneous medium, and it has larger relaxation time. On the other hand, thesublayers in the laminated structures meet many different purposes, such as stiffnessenhanced, weight control, thermal protection and electromagnetic filed shield, and theporous media or fibre multilayer material is the most common sublayer. Based on theworking condition, the coupled thermomechanical problem under high temperaturegradient and high heat rate is realistically meaningful and valuable for research.Aimed to traditional theory of thermomechanical propagating problems, threechallenges are put forword when it is subjected to the high temperature gradient andhigh heat rate for multilayer film materials which have remarkable microstructure.1)the traditional Fourier heat transfer law is doubted, and it is needed to introduce thenon-Fourier heat transfer law;2) the influence of stain and stress to temperaturedistribution is ignored in the traditional engineering analytical method, and it is neededto consider the influence of stain and stress to temperature distribution on theframework of the generalized thermoelastic theory;3) the one-order relationship amongstain,stress and temperature can’t meet the requirement in coupled thermomechanicaleffect in non-homogeneous material and cellular material in small scale. It is needed toimprove and complete the equations under constitutive theory. Especially, it is needed tointroduce stain gradient thoery and complete it under high temperature gradient.The thermomechanical response of fibre-reinforced composites and multilayerstructure under heat deposition according to generalized thermoelastic theory isintroduced in this dissertation. The classical thermoelastic theory and some common generalized thermoelastic theories are introduced in Chapter2, and the similarities anddifferences of them are represented through an example. The result shows that thedistributions of temperature and stress under classical uncoupled and coupledthermoelastic theories are almost same. The temperature distributions under twogeneralized thermoelastic theories are also almost same. However, the stress distributionunder G-L generalized thermoelastic theory is larger than that under L-S theory. Thestatic state and dynamics response of coupled thermomechanical problem ofphotothermal micro expansion arm under generalized thermoelastic theory is researched,and the applicability of generalized thermoelastic theory is proved.In Chapter3, the typical volume of fibre-reinforced composites is built, and theequivalent physical quantities are obtained. The distributions of temperature and stressin one-dimension problem under different conditions are obtained, and the differencesare discussed. The result shows that the influence of strain and stress to temperatureunder the given condition is small.In Chapter4, the two-dimension coupled thermomechanical problems offibre-reinforced composites under heat deposition on boundary are introduced. And thedistributions of temperature and stress are also researched at the same condition forfibre-reinforced composites with metal coating. The result shows that the place near theboundary has high temperature and larger compress stress. The temperature and stressof fibre-reinforced composites can be effectively reduced by the metal coating.In Chapter5, the distributions of temperature and stress in two-dimension coupledthermomechanical problems of multilayer materials under heat deposition on boundaryare introduced. The law of heat propagation at the interface is discussed. The resultshows that the reflected and transmitted temperature waves are formed at the interface.For multilayer structure, the place in ceramics layer near the interface has larger tensestress in three-layer structure. However, in two-layer structure, the tense stress inceramics layer is not formed, and the place near the boundary has larger maximumcompress stress.