Investigations were made of the 18-8 and 13Cr steels that had been exposed to the thermal fatigue under conditions of transient temperature gradient as to what was the effect of their holding time on them at maximum temperature and what was their crack-growth behavior in comparison with the results of Coffin's type thermal fatigue. In the case of Coffin's type the thermal fatigue in which the cross-section of specimen was thermal-cycled uniformly and the thermal strain was restrained by outer supports, it was seen that the compressive stress was introduced in the specimen during the holding process at maximum temperature and the thermal fatigue life was prolonged as the holding time was prolonged by the recovery of strain hardening at elevated temperature. But in the thermal fatigue under conditions of transient temperature gradient, though it had the same relationship between the plastic strain range and thermal fatigue life as that in the Coffin's type thermal fatigue and in addition the crack-growth ratio reduced with increasing the holding time, the thermal fatigue lives decreased as the holding time at maximum temperature was prolonged. It was likely that the working time of tensile stress on heating surface was prolonged by raising the internal temperature of the specimen during the holding process at maximum temperature.
One of the authors previously reported the results of the repeated tensile impact test on carbon steel and copper having notches with various fillet radii ρ to find the effect of notches on impact fatigue curves and cleared up the crossing of plastic fatigue curves. In this paper, the results of experiment are reported on the specimens having notches with constant radius ρ and various ratio of notch d/D where d is the diameter of root of notch and D is the diameter of the parallel part of the specimens. From the results of experiments, the following conclusions are obtained; (1) The impact value at N=1 decreases when the diameter ratio of notch d/D becomes smaller. (2) In the diagram of the relation between the repeated impact energy E and the number of repetitions of impact to failure N, the plastic fatigue curves start from the impact value at N=1 for each type of the specimen. Unlike the case with various fillet radii in the previous paper, they go down abreast to each discontinuous point, and do not cross each other. This seems to depend upon the fact the deformation preventing effect is almost identical in the low energy range of plastic fatigue, because the sharpness of the root of the notch is kept constant. (3) There was observed the changes of elongation φ and contraction of area ψ with impact energy.
The phase separation that occurred in SiO2-P2O5-Na2O glasses has been investigated by the measurements of density, weight loss caused by the acid treatment and by the observation of electron micrographs for their glass specimens. The region of composition in this system, SiO2-P2O5-Na2O, where the formation of glass was easily made is shown in Fig. 1. The relative change in density of the specimens No. 6, 7, 9, and 11 kept at fixed temperatures ranging from 450°to 580°C was determined by the sink float method. The results obtained are shown in Fig. 2. From the curves in the temperatures ranging 490°to 560°C, it is found that at first the density increases, but as the heat-treatment is continued it begins to decrease and reaches an equilibrium value after about 100 hours. This behaviour shows that there are two processes at least. Then we consider the following behaviours, namely, (i) the increase in density is based on the formation of compact structure in quenched glass and (ii) the decrease in one is based on the phase separation in the glass. The weight losses of the specimen-No. 11 from the acid treatments at 50°C with 3N HNO3, 3N H2SO4, and 3N HCl, are respectively shown in Fig. 4. The curves in Fig. 4 show that the weight loss of the specimen from the acid treatment increases as the duration of its heat-treatment at 500°C is prolonged. The electron-microscopic pictures of specimen-No. 9 heat-treated at 500°C for 20, 40 hours and untreated, are respectively shown in Fig. 5. The phase separation in the glass can be observed as the unevenness on the surface of glass etched with 6N HCl, as shown in Fig. 5.