Microwave Irradiation Processing Technique Adopted For Making Thermal Expansion And Glass Transition Gradient Temperature Materials

Functionally gradient materials (FGMs) are inhomogeneous composite materials, in which structure or composition changed continuous or step-wisely as a function of position. Corresponding with the variation of structure and composition, their mechanical properties also varied gradually. FGM has been attracted considerable attention due to their unique performance, sophisticated designation and great potentiality in engineering application. Recently, research efforts focus on the designing for function and structure and exploiting new FGM.In this paper, based on the concept of FGMs, mineral filler/polymer and polymer/polymer FGMs for thermal barrier application were designed and fabricated. Necessary parameters for the designing of FGM come from the samples cured by microwave. Preparation of the above two kinds of FGMs was also completed by means of microwave irradiation.For the mineral filler /polymer FGM, silicon dioxide (SiO2) and epoxy resin (EP) was selected for obtaining thermal expansion gradient material. For the polymer/polymer FGM, polyurethane (PU) and EP were chosen in order to getting glass transition or modulus gradient material. We set up the methods of designing, characterizing, preparing mineral filler /polymer and polymer/polymer FGMs by studying above systems and hoped our researches will be valuable for other people who want to study analogous FGMs.Research on every system has been completed br three steps: (1) investigating curing behavior of SiCVEP composite and EP/PU system under microwaveirradiation; studying effects of various factors such as curing time, microwave power on their properties, including modulus(E), thermal expansion coefficient, strength and glass transition(Tg) et al. Optimizing technology of microwave curing. (2) Based on the concept of FGM, SiO2/EP and PU/EP FGMs which can effectively relax thermal stress concentration were designed and the structure optimization were fulfilled by use of computational mathematical method and finite element method (FEA) respectively. (3) According to the calculated results, with layer-by-layer casting and microwave irradiation, SiCVEP and PU/EP FGMs having rational structures were fabricated. The thermal stress distribution in FGM under steady gradient temperature field was analyzed and the structure and mechanical properties were studied.SiO2/EP system (mineral/polymer)Firstly, thermal behavior of SiCVEP composite during microwave irradiation was investigated. Effects of microwave power and curing time on modulus(E) and thermal expansion coefficient of the sample were discussed. At the given curing time and microwave power, E, strength, and thermal conductivity with different composition were tested. The relationship between E, with SiO2 content was quantitatively described respectively.Results showed that at set microwave power, temperature within SiCVEP increased to maximum (Tmax) then dropped down slowly. Time reaching Tmax reduced with power increasing. The SiO2 content did not affected the absorption of the system. When the composition of system and microwave power were set, modulus and strength increased with irradiation time, while the thermal expansion coefficient decreased. The "composition-modulus" relationships of the SiCVEP composite deduced from Voigt and Reuss model combining with the experimental value of the modulus. Kenner and Maxwell empirical equation was employed satisfactorily to express the thermal expansion coefficient and thermal conductivity dependence with composition for SiCVEP composite.Secondly, the fundamental equations for SiCVEP FGM plates were obtained using the classical theory of laminated plates and the computational mathematicalmethod. At non-uniform steady state temperature field, by Utilizing the material properties of each hypothetical layer from the first stage, temperature solution was obtained, the effective properties and the thermal stress distribution were established, the relationship between the thermal stress and compositional distribution exponent K for SiO2/EP FGMs were calculated, and the...