Thermal Shock Analysis of Spherical Shapes

Abstract

A method is described for studying the thermal shock characteristics of a brittle material. An analysis of the thermal stresses developed in a homogeneous isotropic solid sphere has led to the formulation of an equation relating the physical properties of the body to the temperature difference causing failure and time to maximum stress in a single‐cycle unsteady‐state test. The thermal shock test consisted of plunging a sphere at one uniform temperature into a medium at another temperature. If fracture occurred, the time to fracture was recorded. A large number of tests were run to determine the temperature difference which caused 50% of the spheres to fracture. The thermal shock relationships were tested using a high‐alumina body. The physical properties relating to the thermal shock equations were measured, and calculated temperature differences causing failure and times to maximum stress were compared with measured values. Sufficient agreement was found to lend support to the theory. Summary A method has been developed for studying the thermal shock characteristics of a brittle substance. The method consists of a single‐cycle test of unsteady‐state nature. Two testing conditions have been selected, one having a rather high surface heat transfer coefficient in a liquid bath and the other having a small finite surface heat transfer coefficient in an air bath. These two conditions are at either extremes regarding the thermal shock usually given a substance in practice. The only fair agreement found in the calculated and experimental data indicates that further investigation is necessary. The importance of certain factors, such as time to maximum stress, which was found to be in rather good agreement for the salt bath heat transfer, cannot be overlooked. There are many applications in the high temperature‐high stress field in which the concept of time to maximum stress might well be examined. For example, when repeated high‐temperature heatings are made on a refractory piece, the cycling might be arranged so that the time to maximum stress was never reached for the particular heating cycle, although the (ΔT) was higher than that necessary to cause failure. Much is to be learned from this type of study which may be applied to actual situations. It must be emphasized, however, that this work has been conducted on one single set of conditions and the factors found here do not necessarily apply to other situations.

Reverse Engineering the Ceramic Cooking Pot: Cost and Performance Properties of Plain and Textured Vessels

“…Several studies have documented how a variety of material and formal design characteristics can improve the potential durability of ceramic cooking pots (e.g., Bronitsky and Hamer, 1986;Crandall and Ging, 1955;Feathers, 1989Feathers, , 1990Feathers and Scott, 1989;Hasselman, 1970;Kingery, 1955;Manson, 1966;Rye, 1981;Schiffer et al, 1994;Skibo et al, 1989;Steponaitis, 1984;Tite et al, 2001;Wallace, 1989;West, 1992). This is done through either increasing resistance to stresses brought about by raising the critical level of stress needed to induce catastrophic failure and creating obstacles to crack propagation, or decreasing the magnitude of the stresses to which vessels are exposed.…”

The Middle and Neo-Assyrian Pottery in Iraqi Kurdistan

“…286 Furthermore, the thermal stress depends also on the size of the vessels, for by the big vessel the estimated effects are bigger and more intensive than in the case of the small vessels. 287 The firing temperature also has a big influence on the size of pores in the material. The higher firing temperature reduces the size and number of pores and the low firing temperature increases the pores and gives the vessel more permeability.…”

Crack propagation in catalytic pellets due to thermal stresses

“…The only criterion for mechanical failure was a comparison between the maximum tensile stress value and a breaking strength. Breaking strengths were reported by Crandall and Ging (1955) for a temperature range 20-1,200"C. Coble and Kingery (1956) reported the tensile strength of alumina at 750°C for different porosities and presented their results in the form of an empirical relation. Coble and Parikh (1972) also published an empirical expression relating the dependence of tensile strength of alumina with grain size and porosity.…”