In general, the results of the fatigue tests on the metallic material are found to be widely scattered, accordingly, even if a test were performed under the same condition, the values of the fatigue lives obtained would be widely dispersed because of its "structure-sensitive" properties. Since we can not equalize these experimental factors, a statistical interpretation of the fatigue data would be necessary.
In the present study, the authors have carried out the fatigue tests of the low carbon steel (0.23%C) with large sample (many test specimens per single stress level), and from the experimental data, the following three items have been discussed; (i) the effect of the cutting position of specimens taken from the original bar stocks on the fatigue life, (ii) the statistical distribution of the fatigue life under the higher and lower stress levels, and (iii) the effectiveness of the heat-treatments (normalizing and annealing) on the dispersion of the fatigue life, by means of F-test for the fatigue data.
As a result, the following conclusion has been obtained:
(1) The correlation coefficient (absolute value) between the cutting position of the specimen and the fatigue life amounts to 0.1-0.3 in cases of the as-rolled material and the normalized material, and 0.04-0.06 for the annealed material. It is concluded that the cutting position of the specimen from the original rolled bar has no influence on the fatigue life.
(2) Under the higher applied stress level, the statistical distribution of the fatigue life is normal, but when the applied stress is lower, the log-normal distribution, or the extreme value distribution is applicable to the fatigue life.
(3) No significant difference of variances of the fatigue life is recognized between the asrolled material and the normalized material, while the variance of the fatigue life of the annealed material is smaller than that of the as-rolled material, under the same applied stress level.

View full abstract

It is generally admitted that, at the elevated temperatures, the fatigue strength of materials is affected more or less by the frequency of stress reversals, and numerous investigations have been made in this respect. The experimental results indicate that, at the temperature where the creep phenomenon of materials is predominant, the number of stress cycles before failure increases, as the frequency becomes higher. However, the investigations have been conducted usually in the range of frequency up to 3000cpm, and none of them exceeding a frequency of 10000cpm.
The purpose of this study is to obtain the fatigue strength of steels at elevated temperatures in a high frequency range of 7500-15000rpm. The materials used here are 0.21% carbon steel and Cr-Mo-V steel. Cantilever type rotating bending fatigue test was conducted at room temperature, 300°C and 500°C.
Experimental results obtained are as follows:
At room temperature, the fatigue strengths indicate no difference for both frequencies of 7500 and 15000rpm, but at the temperature of 300°C and 500°C, the discrepancy of the fatigue strength based on the different frequencies of 7500 and 15000rpm is observed distinctly for both steels, and the frequency of 15000rpm causes a smaller number of stress cycles before failure than that of the frequency of 7500rpm.
This results have a different tendency against those obtained by past investigations carried out at comparatively low frequencies of stress reversals.
In conclusions, the fatigue strength of materials at elevated temperatures does not increases in proportion to the frequency of stress reversals, but decreases rather for high frequencies as adopted in the present investigation.
Together with the experiments mentioned above, the deflection of specimens in the course of the fatigue test was observed with the micro-scope. The observation shows no large alteration of the deflection for most of the fatigue life except for the case of high stress level. But as the temperature increases, the estimated plastic strain occurring to the specimen reduces gradually, and in particular, for 0.21% carbon steel the plastic strain is almost eliminated at the temperature of 500°C, and the fatigue failure is seemed to be fairly brittle

View full abstract

Corrosion fatigue tests were carried out in the solution of NaCl at -5, 20, and 70°C. The corrosion effect k, which is the ratio of the fatigue strength in air to the one under corrosion at the same cycles, is indicated by k=1+Ae^-B/T, by using the absolute temperature T of the corrosive solution. Further, the corrosion fatigue strength σ_C is given by σ_C=σ_B×A'e^B'E, where σ_B is the ultimate tensile strength and E is the potential vs. saturated calomel cell. It may be concluded that the corrosion fatigue strength is decided by the intensity of corrosion and the strength of materials and also by the notch sensitivity of corrosion cracks.

View full abstract

When we discuss the fatigue strength, we tend to think not of time strength (finite life) but of endurance limit. If A is stronger than B in endurance limit, we generally conclude that A is also stronger in time strength.
But as we will report in this paper, S-N curves sometimes intercept with each other and the intercepting point is as high as 10⁶ stress cycles.
The explanations concerning the influence of many factors on the fatigue strength which have been reported so far, can not by any means be extended to this phenomenon, and in fact this may be a very complicated one affected by various factors.
In this paper, the authors emphasize that this phenomenon should be given more attention, and try to analyse a case of the phenomenon caused by cold working. The authors use the following formula to represent the S-N curve:
where p is a variable which represents a degree of cold working, and φ(p) is a function of p, representing the change of endurance limit. ψ(p) is another function of p, standing for the change of slope of the S-N curve, and a and m are constants.
In this paper, the authors report some experimental resuits and emphasize again our conceptions as have been previously reported concerning the relation of the notch factor to the form factor and the double notch effect.

View full abstract

In the study of fatigue, the effect of cyclic speed on the fatigue strength has been investigated at room temperature as well as at elevated temperatures. In the fatigue at elevated temperatures and in corrosion fatigue, cyclic speed seems to have a considerable effect on the fatigue strength. In this study, the effect of cyclic speed on the change in residual stresses was, at first, investigated with plate specimens. Three cyclic speeds of 2000, 1000 and 780cpm were given to specimens. Specimens used were of quenched S45C steel and low-temperature quenched S35C steel. Alternating stressing was given at two stress levels, below and above the fatigue limit, for both steels. The results obtained revealed that cyclic speed had a considerable effect on the change in residual stresses, and that the fading of residual stresses was larger under a lower cyclic speed. It was found that the fading of residual stresses under a low cyclic speed was nearly in agreement with that under a high cyclic speed, when the equivalent number of stress cycles under the high cyclic speed obtained from the condition of an equal duration time was used. Since the inverse is also true, it may be concluded that the fading of residual stresses under any cyclic speed can be predicted from the known fading under a definite cyclic speed by using the equivalent number of stress cycles.
The fading of residual stresses is assumed to occur in a larger degree for soft material than for hard one. To confirm this experimentally, second investigation was made on the fading of residual stresses for two materials with different hardness. In the previous experiments on the residual stresses produced by shot peening treatment and also on those produced by plastic torsion, experimental formulas on the fading of surface residual stresses in the second stage were established. Materials used were S25C steel (shot peening) and S35C steel (plastic torsion), each having a smaller hardness than that of the material used in the previous experiment. In choosing the stress levels of alternating stessing, alternating stress ratio (ratio of stress amplitude to the fatigue limit) was made the same for the two materials. The results obtained verified the above mentioned assumption, that is, the fading of residual stresses occurred in a degree inversely proportional to the hardness number of the material. Basing on these fading lines, experimental formulas for the fading of surface residual stresses involving the three variables of alternating stress ratio, cycle ratio and hardness number were established. Moreover, to obtain experimental formulas which are applicable to a wider range of hardness, the results of the previous experiment on the residual stresses produced by carburizing and quenching, and a new experiment on the residual stresses produced by plastic tension were employed. The calculated values from these formulas were compared with several experimental results obtained by other investigators, and the approximate applicability of these formulas to all cases was proved.

View full abstract

This paper describes some fundamental features obtained through application of the technique of measuring the sonic modulus of materials used in the field of ceramics to the nondestructive testing of mechanical properties of Shell Mold; namely, the authors try to find the relation of Young's modulus determined from the fundamental frequencies of prismatic samples to the modulus of rupture and the internal structure of the same samples that depends upon the packing properties of molding sand and physical properties of bonding materials, and considerable correlations are found between these quantities at least under limited conditions.

View full abstract

It is important for anyone engaging himself in the construction of some earth structures, such as earth dam, subgrade and base course of the road, to have a comprehensive knowledge respecting the relationship between the moisture content of remolded soils and their compacted density. From the viewpoint of engineering purposes, however, it is also necessary to know the influence of compacted densities which correspond to various moisture contents on the shear strength of the soil.
So far, some investigations have been made with respect to physical properties of sandy soil or clay. As for silt whose particle size is situated between sand and clay, on the other hand, there exist many unknown parts in its engineering behavior.
In this paper, some experimental considerations are treated for interesting characters encountered in compacting silty soil. Socalled Rhein-silt, a wind-laid deposit existing widely near the Rhein in Germany, is used as the specimen.
The experimental research performed in this study consists of two procedures; one is the compaction test accompanied with measuring the penetration resistance of Proctor's needle, and another is the triaxial compression test of the compacted soil with pore pressure measurement.
It is clarified from this study that there is a remarkable difference between the compaction curves (i.e. density vs. water content curves) obtained by either the wetting process or the drying one, and that the maximum shear strength of the compacted Rhein-silt exists at the water content somewhat smaller than the optimum, which corresponds to that of maximum negative pore pressure in the specimen.

View full abstract