Thermal stress in ceramics

T. Suga, K. Mizuno and K. Miyazawa, "Thermal Stresses in Ceramic-to-Metal Joints" pp. 137-142 in Metal-Ceramic Joints, Proc. MRS International Meeting on Advanced Materials, Vol. 8. Edited by M. Doyama, S. Somiya and R. P. H. Chang. Materials Research Society, Pittsburgh, PA, 1989. 

D. Munz, M. A. Sckuhr and Y. Yang, "Thermal Stresses in Ceramic-Metal Joints with an Interlayer," J. Amer. Ceram. Soc., 78 [2] 285-290 (1995). 

A. R. Boccaccini, Incorporation of Porosity to Control the Residual Thermal Stresses in Ceramic Composites and Laminates, The European Physical Journal. Applied Physics % 197-202 (1998). 

Priest, D. H. and R. Talcott Thermal Stresses in Ceramic Cylinders Used in Vacuum Tubes, Amer. Ceram. Soc. Bull, vol. 38, no. 3, pp. 99-105, March, 1959. 

It is often necessary to remove thermal stresses in ceramic materials as a means of improving their mechanical strengths and optical characteristics. This may be accom-pUshed by an annealing heat treatment, as discussed for glasses in Section 13.10. 

High mechanical stability To moderate the thermal stresses in ceramic systems, it is essential to shorten the relaxation times for thermal fluctuations by using materials with low thermal expansion coefficients and high thermal... 

Brun, M.K. and Singh, R.N. (1988). Effeet of thermal expansion mismatch and fiber coating on the fiber/ matrix interfacial shear stress in ceramic matrix composites. Adv. Ceram. Mater. 3, 506-509. 

Hsueh, C.H., Becher, P.F. and Angelini, P. (1988). Effects of interfacial films on thermal stresses in whisker-reinforced ceramics. J. Am. Ceram. Soc. 71, 929-933. 

Powell, K.L., Smith, P.A., Yeomans, J.A. (1993), Aspects of residual thermal stresses in continuous-fibre-reinforced ceramic matrix composites , Comp. Sci. Tech., 47, 359-367. 

Jung, Z., Xing, A., Chuanzhen, H., (2003), An analysis of unsteady thermal stresses in a functionally gradient ceramic plate with symmetrical structure , Ceram. Int., 29, 279-285. 

The choice of permeation barrier materials selected here for coatings is reasonable based on permeation resistance, but external coatings of ceramics on metals are difficult to perfect since many metals have high thermal expansion coefficients and most ceramics have low ones. This causes large thermal stresses in the coatings to develop, which leads to defect formation in the coatings and lowers permeation resistance. A better technique, which will be discussed in the next section, relies on the formation of intrinsic oxide films on the surface of the metals, either by direct oxidation or by alloying followed by oxidation." ... 

One type of pore that is worthy of further consideration is the extreme case of a microcrack. In Section 2.9 it was shown that thermal expansion anisotropy can lead to residual stresses in ceramics and, in some cases, the formation of localized (spontaneous) microcracking. Microcracks may only represent a small fraction of porosity in a body but their ability to concentrate stress can lead to substantial reductions in the elastic constants. For a random array of circular microcracks, radius a, the SC approach shows the elastic constants ix and B of the microcracked material can be approximated by... 

With increasing demands for electric transportation systems and/or electric vehicles, semiconductor power modules such as electric power converters and DC-AC inverters will continue to expand in terms of their applications. In these systems, in order to transmit a high electric current, thick copper electrodes are often directly bonded to ceramic substrates, the structures of which may cause major residual stresses in ceramic parts. Thus, to avoid failure due to residual stress, ceramic materials are required to have a high strength and, in order to further improve the reUabUity of the systems, improvements in the mechanical properties of high-thermal conductivity materials are clearly required. Consequently, the electrical industries are continuing an active search for alternative materials with both high thermal conductivity and superior mechanical properties. 

Leaded vi. Leadless Surface-Mount Components. Leadless surface-mount components with peripheral solder joints (e.g., leadless ceramic chip carriers, LCCCs) are more susceptible to solder joint failures due to thermal and mechanical stresses than leaded components because there is no compliance in the system (see Fig. 57.21). A compliant lead can take up relative displacement between the component body and the substrate during mechanical or thermal stressing. In doing so, it minimizes the stress and strain imposed on the solder joint, thus reducing the likelihood of failures. Large leadless components should be avoided whenever possible. If they must be used, the substrate must have as close a CTE mismatch as possible and be protected from mechanical stresses. A conformal coating should be considered. 

Thermal Stresses in Particle-Matrix System and Related Phenomena. Application to S1C-S13N4 ceramics... 

SiHcon nitride (see Nitrides) is a key material for stmctural ceramic appHcations in environments of high mechanical and thermal stress such as in vehicular propulsion engines. Properties which make this material uniquely suitable are high mechanical strength at room and elevated temperatures, good oxidation and creep resistance at high temperatures, high thermal shock resistance, exceUent abrasion and corrosion resistance, low density, and, consequently, a low moment of inertia. Additionally, siHcon nitride is made from abundant raw materials. 

Thermal Stresses and Properties. In general, ceramic reinforcements (fibers, whiskers, or particles) have a coefficient of thermal expansion greater than that of most metallic matrices. This means that when the composite is subjected to a temperature change, thermal stresses are generated in both components. 

Most ceramics (as we have seen) contain flaws holes and cracks left by processing, cracks caused by thermal stress, corrosion or abrasion. Even if there are no cracks to start with, differences in elastic moduli between phases will nucleate cracks on loading. And most of these flaws have a size which is roughly that of the powder particles from which the ceramic was made. If the flaw size can be reduced, or if samples containing abnormally large flaws can be detected and rejected, the mean strength of the ceramic component is increased. 

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