Studies on the main cause of fracture of various bricks for bottom casting pit and the physical-mechanical load taking place at the time of teeming of molten steel have been carried out.
The distribution of internal stress in hollow circular cylinder bodies of various bricks due to the pressure of molten steel was calculated. Comparing the internal stress with the mechanical strength it was confirmed that the pressure of molten steel is not the immediate cause of the fracture of bricks. And, on the basis of above results, the economic lower limit of wall thickness of the bricks for standing the pressure of molten steel has been worked out.
Then, an analysis of temperature gradient and thermal stress developing in a brick due to the rapid heating by molten steel at the time of teeming was carried out, and it was made clear that the immediate cause of fracture is the thermal stress.
It was found by dimensional analysis that the factor f in the thermal stress equation is the number of dimensionless products, and that it's factor is expressed by
f=c(r/K^1/2⋅ρ^-1/2⋅C_p^-1/2) or f=c′(rh/K)^a′.
The effect of pyroplastic property, which fire clay bricks show at higher temperatures, on the distribution of thermal stress was estimated. And the author was able to elucidate the importance of the pyroplastic property for taking the preventive measure of the fracture of fire clay bricks.

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An apparatus for measuring the shrinkage of cermet in hydrogen atmosphere was designed, and was used successfully for following up the process of sintering. Also the close examinations under the optical and electron microscopes have added some useful informations. The results may be summarized in the following outline.
1) The velocities of shrinkage under different conditions, and the mode of approaching to an equilibrium value at a certain temperature as well as the subsequent shrinkage by the repeated heating at higher temperatures have revealed that the sintering was governed mainly by temperature but not by holding time. It may, therefore, be concluded that the heating schedule of very short holding time at higher temperature is by far better than the usual one.
2) Sintering started by the thermal diffusion of the materials along the contact surface between the particles which were pressed strongly by the forming process. The increase of the path of diffusion brought about of the decrease of the distance between the particles, and the shrinkage of the mass was observed. When the temperature was too high the perspiration of metal bonding was observed.
3) Sintering by an instantaneous heating, i.e. so called flash sintering method showed no sign of grain growth.
4) Observations under electron microscope have revealed that the rupture of TiC cermets occured in two ways, viz. trans-crystal and inter-crystal, according to tha heating temperature.

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The experimental results of the strength of glasses presented in this paper were discussed from the standpoint of the internal structure. The conclusion obtained are as follows:
i) The case of no fatigue (strength in liquid nitrogen)
a) The strength of un-abraded glass is determined by Griffith flaw which is interpreted as the weak points in the internal structure of glass locating at the boundaries between the “matrix” and the “glassy microphase”
b) The strength of abraded glasses of all chemical compositions is determined by the size of flaw locating at the tip of glassy microphase.
ii) The case of fatigued glass (strength in water)
a) The fatigue curves of the glasses covering all kinds of chemical compositions may be represented as reduced curves, and furthermore, by an universal fatigue curve.
The author advanced a theory of the mechanism of fatigue which states that the fatigue comes from the physico-chemical reaction between the microphase and water at the tip of abraded flaws, whose rate is governed by the constant t_0.5 of the respective glass (Fig. 11 and 12).
b) The number of flaws brought about by such chemical reaction is the function of load duration. The author worked out a theoretical formula of the universal fatigur curves by taking the ratios of the strength in water and in liquid nitrogen.

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