Shock failure

Thermal shock failures using water result from the water vapor entering the enamel layer through small, submicroscopic cracks formed at the instant of shock. The water condenses in the cracks and in the bubbles of the enamel traversed by the cracks. On subsequent heating, the vapor from the entrapped water expands to cause spalling of the enamel layer. Other quenchant Hquids, such as toluene, oils, and other organic Hquids, also cause fine, almost invisible cracks, but thermal shock failures do not result with these quenchants on subsequent heating (39). 

Thermal shock resistance is a direct function of enamel thickness. The greater the residual compressive stress in the porcelain enamel, the greater is the resistance to thermal shock failure. Thin coatings, such as one-coat enamels or the two-coat enamels having alow expansion titania covet coat, provide excellent thermal, shock resistance. 

Figure 1. For several glass ceramics, the temperature interval causing thermal shock failure, AT, is approximately inversely proportional to the linear coefficient of thermal expansion of these materials. Glasses and alumina ceramics have less thermal shock resistance than glass ceramics of comparable thermal expansion. ...

Fig. 9. Mean thermal shock failure temperature (burner test, minimum 15 units) for 400 cell ceramic monoliths and catalysts of various types.

G Montes, M Robertson and A Puckett, A characterisation of thermal shock failures in cultured marble vanity tops . Proceedings ofANTEC 88, Brookfield, CT, USA, Society of Plastics Engineers, 1988. 

Fellner, M. and Supandc, P. (2002) Thermal shock failure ofbritfle materials. Key Eng. Mater., 223, 97-106. 

Kitagawa,], etal. (1989). Effect of DPF volume on thermal shock failures during regeneration, SAE Paper No. 890173. 

Kitagawa,], et al. (1990). Analyses of thermal shock failure on large volume DPF, SAE Trans. 900113. 

Thermal shock failure occurs when tlie thermal gradients generated in a part are so pronounced that differential thermal strains exceed the ability of the material to sustain them witliout yielding or feature. 

Parametric model for hazard rate We assume two classes of subassembly failure mechanism, shock and wearout, which occur in sequential phases. During the first phase shock failures occur at a constant rate, p. The second phase relates to wearout which, for the purposes of this paper, we assume to have a Weibull rate, with scale parameter a and shape parameter b. We assume that the transition between the first and second phases occurs at time w. Thus the parametric form of the hazard rate at time 5 is given by ... 

The model introduced by Atwood (1980) considers that the system components are subject to two types of failures independent failures and shock failures. Two kinds of shock failures are defined lethal shocks and partial (or non-lethal) shocks. In a large redundant systems with N components, a shock is assumed to be non-lethal when it affects k components among N with 1 < A < N. A shock is lethal when it affects all components. In the case of a non-lethal shock, only the failure of some components is considered. Each component has then a conditional probability p of failure. Individual failures, non-lethal and lethal shocks are assumed to follow independent processes. The occurrence frequencies of shocks (denoted ju for non-lethal shocks and o) for lethal shocks) are assumed to be constant. 

Heat shock failure is the mechanical failure of a material due to sudden exposure to high heat. 

Disadvantages. Because of their high thermal expansion, soda-lime-sihca glasses are prone to thermal shock failure, and because of their relative softness, they have limited... 

Stress cracking as discussed above need not only be due to an active environmental. Often a thermal stress can lead to cracking. Heat shock failure is also seen to relate rather linearly with MFI, as given in Fig. 9.73 taken from Ref. 48. 

---