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  • Progress in dimension limit for thermal shock failure
    Author:   | Date:2015-05-05   | Click Rate:    | 【Close
    Progress in dimension limit for thermal shock failure

    Thermal shock resistance of the material refers to the ability of the material to resist damage when subjected to a sudden change in temperature. Thermal shock damage phenomena widely occur in our life, for instance, the glass cup may be broken when pouring boiling water into it in winter as it cannot afford the sudden temperature change.

    Recently, with the development of aerospace technology, the service environment of materials has become very harsh. Because ceramic has the advantages of high melting point, abrasion resistance and high temperature chemical stability, it becomes the most promising candidate material for aerospace. But its intrinsic brittleness makes the ceramic material easy to thermal shock failure and causes catastrophic damage, such as the US thermal protection tiles on Columbia spacecraft. According to statistics, more than one-third of the rejections of ceramic components are caused by thermal shock. Therefore, thermal shock resistance of the material has become one of the important criteria in the selection and design of materials.

    Previous studies point out that besides the properties of materials, two external factors of ceramics, the characteristic dimension and the temperature difference, play a key role in the thermal shock failures of ceramics. For example, the thermal shock resistance of ceramics increases with the decrease of characteristic dimensions, and ceramics are prone to thermal shock failures at higher temperature differences. However, the quantitative effects of the two factors on the thermal shock failures of ceramics have not been understood very well. In this study, firstly, we obtained a relationship between the two critical external factors of ceramics and thermal shock failures based on the theories of heat transfer and thermal stresses. The relation indicates that ceramics become insensitive to thermal shock as soon as the material size becomes smaller than the dimensional limit, or the temperature difference is lower than the critical one, because the maximum thermal stress during thermal shock will not exceed the inherent strength of material. Then, from the water quench tests of alumina (Figure 1), the relationship presented here proved to be in good agreement with the experimental results (Figure 2). The results provide a guide to prevent thermal shock failure in ceramic.

    This study was financially supported by the National Natural Science Foundation of China (NSFC) (Grant 11102208 and 11023001). More details can be found at Shao, et al, Philos. Mag., 94, 2647-2655(2014) .

    Figure 1. Thermal shock cracks on the surfaces of the spheres with the different radius, R = 2.10, 1.00, 0.56, 0.35 and 0.11 mm (from top to bottom), at the temperature differences T = (a) - 280 K; (b) - 380 K; (c) - 580 K; (d) - 780 K; and (e) - 1280 K.

    Figure 2. The critical curves using parameters of different temperature ranges separate the regions of the crack and the uncracked, and the marks around the curves stand for the experimental data corresponding to Figure 1. The solid marks represent the crack and the hollow marks represent the uncrack.

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