Abstract
1) Hitherto no fundamental paper has been published in Japan on the warpage of clay ware taking place in firing while it is a basic problem for the improvement of the Japanese pottery and porcelain. Therefore explanations are given on the importance of the study and its scientific significance. Then the general plan and items of the study are described.
2) It is shown that the phenomenon of glost-warpage is closely connected with that of crazing and shivering. The internal stress originating to the discordance of body and glaze produces not only the defects of the latter but the warpage by the elastic deformation of the ware before crazing or shivering takes place. General explanations are given theoretically on the relations among these phenomena.
3) That the stress distribution can be found correctly by determining the thermal expansion, modulus of elasticity, and warpage of body and glaze individually and that the stress can be appropriately calculated from the theory and formulae on the bending of bi-metal are explained.
4) It is explained that the fundamental theoretical equations for the warpage can be derived from the mathematical analysis based on the theory same to the bending theory of bi-metal. Furthermore, as a theoretical analysis of the warpage or central deflection of the test pieces which has been determined in the study, the following equation has been derived for the approximate relation among the warpage δ, the thickness of glaze h1, that of body h2, the coefficient of the thermal expansion of the glaze α, that of the body β, the modulus of elasticity of the glaze E1, that of the body E2, the length of the test piece l, and the temperature difference which takes place while solidified glaze cools to room temperature θ:
δ=l2(α-β)θ/4[1/3{E1h13+E2h23/h1+h2}{1/E1h1+1/E2h2}+(h1+h2)]………(7)
An approximate theoretical equation has also been given for the internal stress P, compression or tension, as follows:
P=b{(α-β)θl2-4δ(h1-h2)}E1E2h1h2/l2(E1h1+E2h2)………(8)
Where b is the breadth of the test piece.
