The reversed torsion and rotating bending tests were carried out on the tufftrided steel specimens to investigate the influence of type of loading on fatigue properties. The changes in the fatigue limit, the hardness distribution, and the microstructure were examined. The results obtained are as follows: - (1) The fatigue limit under the reversed torsion increased after tufftriding by a factor of about 1.8, which was nearly the same as that obtained under the rotating bending. (2) The rise of hardness distribution with stress amplitudes and the precipitation of nitrides along slip lines in the specimen fractured by the reversed torsion, were similar to those observed under the rotating bending. (3) It appeared that the increase in hardness with stress cycles almost reached its upper limit within 10% of the total life, and then the precipitation of nitrides started to follow, though it was practically over in its early stage.
The reversed plane-bending fatigue tests were carried out on the hardened spring steel (Cr-V steel) specimens, the surfaces of which were prepared by operation actually used in production of plate spring. It was found that the fatigue limit of the specimens as heat treated was considerably lower than that of the ground ones, but it could be raised about 50% by the shot peening.
To clarify the understressing effect in the two-steps program load condition involving the transitional impact load at the rise time to higher stress level σ1, a series of the rotating bending fatigue tests have been planned and conducted. On this experiment, the maximum stress σmax introduced by the impact loading and the program period m, which is the sum of the period for the primary stress m1 and that for the secondary stress m2, were taken as the experimental variables. On the other hand, the period for the primary stress, m1, was held constant as m1=2sec., and the magnitudes of the primary and secondary stress, σ1 and σ2, were fixed to the values of 13.4kg/mm2 and 11.0kg/mm2 respectively to lie below the fatigue limit of the fundamental S-N curve obtained under the constant load condition. The main results obtained are as follows: It was recongnized that the understressing following the maximum stress acted as the weakening factor as a whole in the range of this experiment, and that the cumulative damage in the meaning of the Miner's rule became larger. In other words, the weakening effect of the understressing gradually decreased when the magnitude of the maximum stress took a higher value especially in the case of the relatively short program period m=4. And then, according to the estimation from the view point of the hysteresis energy calculated with the assumption that the cumulative hysteresis energy needed for failure takes the same value in spite of the difference in load pattern, it was revealed that the weakening effect of the understressing increased in its amount but decreased in its contribution fraction when the program period m became longer.
Three types of isoaxial symmetrical bicrystals and their component single crystals were tested in tension to clarify the effect of grain boundary on plastic properties. The <111> oriented bicrystal was deformed by the mode similar to that of the <111> oriented single crystal. Fine multiple slips which appeared from the early stage of the deformation was suppressed at the boundary. It was found that the flow stress of this bicrystal was almost equal to that of the component single crystal and the effect of grain boundary on the flow stress did not appear. In two bicrystals having. Σ7 and Σ21 coincidence tilt boundary respectively, each flow stress was increased by the presence of boundary. The boundary strength was rapidly increased from yield point to about 0.5% strain by the interaction between primary slips and additional slips in the vicinity of the boundary, and it was scarcely increased from about 1.0% to 5.0% strain. It was pointed out that the effect of grain boundary on the flow stress of a bicrystal is prominent by introducing multiple slips near the grain boundary in the stage-I region of the component single crystal but not prominent in the stage-II region. The effect of grain boundary on the flow stress is negligible after multiple slips take place.
The mechanism of divalent impurity aggregation in KCl-KBr mixed crystals has been studied by means of dielectric-loss measurements. When the concentration of KBr is low, the initial aggregation and the aggregation after the first plateau obey the third order kinetics. When the concentration of KBr is high, the kinetics order of the initial aggregation is not clear. However, the aggregation following the plateau obeys the third order kinetics. When the crystal containing KBr in low concentration is annealed at low temperature, another plateau is observed. But if annealed at high temperature, it is not observed. The activation energy for the dipole aggregation decreases with increasing concentration of KBr in the mixed crystals of KCl-KBr.
In order to clarify the effects of wind velocity on the drying shrinkage and development of shrinkage stress of concrete members, the shrinkage tests were performed by using an experimental blower and the analysis was made based on the diffusion theory proposed by Pickett. Mortar prisms having six kinds of mix proportions were used as the test specimens and three different wind velocities, 0, 5.6 and 9m/sec, were examined. The results obtained are summarized as follows: (1) At the early stage of drying, shrinkage was enhanced in a windy condition more rapidly than in a windless condition. Its rate of increase was nearly proportional to wind velocity. The final shrinkage value estimated from the hyperbolic experimental equation also increased with wind velocity. (2) The loss of moisture was accelerated in the initial stage of drying as the wind velocity was increased. The younger the age of specimen tested, the more remarkable its tendency. It was confirmed that the mechanism of the increase in shrinkage due to wind action was closely related to that of moisture loss. (3) Both the diffusivity of shrinkage and the surface factor in the diffusion equation increased due to wind action, but the rate of increase for the surface factor was much larger than that of the diffusivity. (4) The shrinkage stress at the exposed surface of mortar evaluated by using the above factors showed the following trends. The maximum value of the shrinkage tensile stress became larger, the time to reach the maximum stress became shorter, and the stress fell more rapidly from the maximum in a windy condition than in a windless condition. (5) Prolonged wet curing and lowering the paste content are recognized effective in order to prevent the increase in shrinkage and the development of shrinkage cracks by wind action.
The rotating bending fatigue tests were performed on the carburized SCM21 steel specimes, and the relation between the fatigue strength and the case hardness distribution was examined on two series of specimens having different hardness distributions. The plain and notched specimens were carburized at 930°C, under 0.9% carbon potential atmosphere for 4hrs, and oil-quenched from 830°C. Tempering was carried out at 180°C for 2hrs. The results obtained are as follows. (1) In the case of the plain specimen with a gradual stress gradient, fatigue damage seems to progress in a wide field of the carburized layer. So the initiation of fatigue cracks may occur either on the surface or inside of the carburized layer. The present test results show that the fatigue cracks initiate on the surface of the carburized layer, and the specimen having higher case hardness possesses lower fatigue strength than the one of lower case hardness. (2) In the case of the notched specimen with a steep stress gradient, the progress of fatigue damage is limited to the notch root portion or the crack tip. So the crack initiating stress σw1 and the crack propagating stress σw2 of the specimen seem to be decided by the hardness and the residual stress of the critical portion where the fatigue fracture occurs. The present test results show that the fatigue crack initiating stress of the notched specimens is related to the effective case depth. The fatigue crack propagating stress of the notched specimen is proportional to the hardness of the crack tip, and the stress range between σw1 and σw2 is almost constant for both series of the specimens having different effective case depth.
The crack resistance of heat-shrinkable tubing during heating was related to the material properties at temperatures higher than its melting point. The crack initiation temperature was derived from the temperature dependence of breaking stress and strain of heat-shrinkable tubing. The oxidative induction time of heat-shrinkable tubing was measured by a differential scanning calorimetry method, and the relationship between its induction time and the thermal oxidative deterioration was discussed. The notch resistance was investigated in the range of various % shrinks of notched heat-shrinkable tubing. When heat-shrinkable tubing is used in the range of 30∼60% shrink and has normal shrink stress (radius direction stress caused by shrink) of about 100g/cm2 in the % shrink, the material properties required for good crack resistance must be as follows: (1) When the tubing temperature rises up to 350°C, the breaking strain is more than 9 at 130°C. (2) To prevent the thermal oxidative deterioration, the oxidative induction time at 200°C is more than 90min. (3) Tangential shrink stress (circumference direction stress caused by shrink, σT) at 30% or 60% shrink is more than 100r/t0g/cm2, where t0 is the thickness of completely shrank tubing and r is the radius at 30% or 60% shrink. In this case, the ratio of breaking stress (σb) to σT is more than the stress concentration factor at notch.
The purpose of this study was to obtain the relationship between specific volume v and compressive stress P of tobacco shreds during compression and to disclose the influences of experimental factors, physical properties and compressive hysteresis of shreds upon the v-P relation. Experiments were carried out with five experimental factors, that is, the variety of tobacco V (Fluecured V1 and Domestic V2), the leaf position on a stalk p (5 levels), the moisture content w (7∼18% WB), the number of compression N (1∼3) and the loosening of shreds after compression. The experimental data thus obtained were analyzed by means of a statistical method. The important results obtained were as follows: (1) The relationship between v and P of tobacco shreds during compression was able to be shown by the following formula, ln P=K0+K1v. (2) The sign of the direction coefficient K1 was minus, and the absolute value of K1 increased as p decreased or w increased. The absolute value of K1 in V1 was larger than that in V2. (3) The sign of the intercept K0 was plus, and the absolute value of K0 was nearly constant, independent of the condition of V, p and w. (4) The physical properties, which affected the direction coefficient, were the elastic modulus, the specific volume of tobacco itself and the correlative specific volume between shreds after loose fill. Among these properties, the elastic modulus was the most influential one. (5) The increase of N caused stress relaxation and made the absolute values of K0 and K1, higher. The loosening of shreds after compression decreased the degree of stress relaxation.
The corrosion rate of the inner surface of iron tubes was measured under turbulent flow conditions of air-saturated solution. The corrosion process was assumed to be controlled by mass transfer of oxygen dissolved, and the diffusion rate of oxygen was evaluated by the non-dimensional groups: Sh, Re, and Sc. The experimental results agreed well with the theory of mass transfer at the smooth surface when corrosion was relatively mild. On the other hand, the diffusion rate of oxygen was affected by the roughness of tube wall if corrosion was severe.