Theories of thermal stability for high-temperature materials based on the application of static thermoelasticity equations to nonstationary thermal processes are reviewed. A new criterion for thermal stability, R = ÄT d , is proposed. A new model, based on the maximum stress theory and the quantum theory of thermal field, is proposed; in terms of this model, the stress-strain state of a solid subjected to thermal shock can be determined by solving equations of thermal strength and heat conduction with allowance made for inertial terms in thermal stability equations. Thermostability is considered as a physical parameter characterizing the resistance of materials to failure in a nonstationary temperature field.Thermal stability of high-temperature materials has been a problem of major concern for researchers; a survey of the literature on the subject can be found in [1 -4]. Theoretical and practical interest in this problem stems out from the fact that thermal stability is a central property that determines the operational reliability of high-temperature materials exposed to intense thermal shock. Numerous materials, owing to their high thermal stability Ñ structural oxycarbide composites [5], refractory castables [6], high-temperature materials based on quartz glass and glass ceramics [7], fibrous heat insulators, to name but a few, have gained wide acceptance in industry.One will note the similarity and difference in objects of the physical world, viz. the material and the product.The material is an object of artificial or natural origin composed of discrete entities characterized by a mass at rest (atoms, molecules, or combinations thereof), a definite chemical and phase composition, a micro-and macrostructure, and physicochemical and physicomechanical properties.The product (optionally, the engineering component) is an object of artificial origin which is made up from a material, it is bounded in space by a surface forming a shape (a cube, a sphere, a prism, etc.) and is characterized by linear dimensions, a volume, a geometrical shape, a mass, and which is intended for a particular application.It has been argued [1, 2] that thermal stability is not a physical property, and for this reason, materials should not be classified in terms of their resistance to thermal shock. Thermal stability has been defined as the ability of materials, solid bodies, or structures to sustain temperature stresses without detriment to their structural integrity [1,2]. Temperature stresses may arise in a stationary temperature field (stresses of the zero and second kind) as well as in a nonstationary (transient) temperature field (stresses of the first kind) [2].In theoretical and practical studies of the thermal stability, emphasis is placed on macroscopic thermoelastic stresses of the first kind whose magnitude is controlled by a range of factors such as the temperature and rate of thermal loading, initial temperature of the solid, its modulus of elasticity, and thermal expansion coefficient.At low thermal loading rates (defined in...
Fused and castbaddeleyite--coruudumrefractories are characterized by chemical and phase inhomogeneity [1][2][3], which has a significant influence on the stable operation of glass melting furnaces and the quality of the glass.The zonality of the structure of the electrically melted refractories is the main factor preventing the production of parts with stable physicOtechnical properties.Earlier [4] the possibility was established of inspection of the macrostructure of baddeleyite--corundum refractories by a radiowave method. X-ray and ultrasonic methods are promising for evaluation of the local inhomogeneity of the macrostructure of large block refractories.This article presents certain data on the development of nondestructive testing of BKCh-33 fused and cast industrial refractories produced by Podol'sk Refractory Part Plant by the ultrasonic method.According to existing technical documentation [5] the quality indices of electrofused refractories are the chemical composition and the apparent density by measurement pm mwhere pm is the apparent density by measurement, m is the weight of the part, and V is the ap volume calculated from the external geometric dimensions without taking into consideration voids in the part and the curvature of its faces. Distribution parameters * of the apparent 'art Part dimen-Total ~o.. sions, mm number density by. measurement of parrs I a,.m_3 ..10_,[ R~_Rm,x mode~ien asym. excess I 600X 300X250 3,60 2,54 I 5~4 3,47--3,76 I 3,59 | 3,60 0,026 ] --0,022 2 600>~400X250 3,57 3,52 [ 5,93 3,40--3,68 I 3,56 [ 3,58 --0,630 1 0,132 3 3,59 3,08 [ 5,55 3,44--3,73 [ 3,61 l 3,60 [ --0,378 [ --0,132 6 3,76 15,6 3,40--3,99
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