In order to clarify the order-disorder transformation mechanism of the hot-rolled 2V Permendur sheet, the characteristics of various heat-treated specimens were investigated with regard to their roll directions. The results obtained in this study can be summarized as follows: (1) The magnetostriction is dependent upon the roll directon, and shows its maximum value at the angle 45° except in the furnace-cooled state from 1050°C. (2) The magnetostriction vs. heat-treatment curves at H=1600 Oe are almost similar in any direction. The magnetostriction becomes largest after furnace cooling 1050°C, and decreases to the minimum after water quenching at 680°C, but increases at 750°C, then decreases again at 850°C and shows the tendency of slight increase at higher temperatures. These tendencies do not change at H=50 Oe, although the magnetostriction shows again the minimum at 950°C. (3) The intensity curves of magnetization vs. roll direction at H=50 Oe after various heat-treatments are found to be analogous to those for magnetostriction. (4) Young's modulus in γ phase is dependent upon the roll direction. (5) The effects of roll direction on Young's modulus in an ordered state are quite different from those in a disordered state, and Young's modulus in the former is generally larger than that in the latter. (6) In (α+γ) phase, Young's modulus is largest after a water quenching at 950°C. (7) Young's modules vs. heat-treatment curves are much the same in all directions. (8) The cooling effect due to quenching is pronounced rather in cold water than in liquid nitrogen.
Hereunder is presented a brief report of the experiments that have been made of the effects of working the understressing and coaxing procedures on the two kinds of fatigue-limit, the fatigue-limit for crack-initiation σw1 and the fatigue-limit for failure σw2, on sharply notched specimens of 0.32% carbon steel. The results show that the strengthening effects of understressing and coaxing are apparent for both σw1 and σw2, and these fatigue-limit increments have been compared with the experimental results that have appeared on the smoothed specimens. Measurements of the non-propagating cracks show that cracks have been propagated with stress increment under the understressing and coaxing procedures. This means that the strengthening effects that have been observed at the crack tip are not limited to such sorts.
On of the problems in metallurgic technicality in Japan is concerning the delay in fracture, which is common in a hexagon bolt, when its high friction strength at the grip joint is desired, and the fact has been a source of great worry of technicians for improvement of bolt strength. In our investigation, we dipped the V notched test specimen made of low carbon boron steel into 10% H2SO4 to introduce hydrogen, and observed the effect of hydrogen upon the steel by performing static bending test and fracture test with an electron microscope, noticing delay in fracture. It has been found as the result of experimentary investigation that the range within which the hydrogen embrittlement occurs, in the case of the 10% H2SO4 dip, is limited to the thin surface layer of the specimen. The delay in fracture has been ascertained to be due to the effect of hydrogen, for the fracture surfaces both in the natural delayed fracture and in the acid are alike intercrystalline. Under the delayed fracture limit no crack ever occurs at the notch root, and when a crack has once occurred, the specimen leads to final failure in short time. It is obvious in this way that no delay in fracture ever occurs until (a crack has been caused) by the gathering of hydrogen at the stress concentrated part.
In order to obtain quantitative information in regard to the characteristics of friction in the rolling contact of the rolling body in the main shaft bearing of aircraft engines, the test apparatus was designed on the following basis: (1) that it would afford accurate measurement of the rolling friction torque, (2) that it would afford automatic detection of the lifetime of the rolling by means of an oscillograph, and (3) that it would enable us to impose three kinds of load, static load, pulsating load and partially pulsating load, to the test piece. In the present paper, as the continuation of the previous reports, the life characteristics of the rolling piece under repeated compressive loading was discussed by the use of the test apparatus mentioned above. The following conclusions have been obtained from the present test. (1) The equipment is satisfactory for performing rolling fatigue tests under repeated compressive loading, especially so for automatic detection of the lifetime of the rolling body in the range of measurement by means of a strain-meter. (2) The value of the torque measured under repeated compressive load is nearly the same as that obtained under static compressive load which is equal to mean the load in the dynamic loading. (3) The lifetime curve of the rolling piece under repeated compressive load is closed to that under static compressive load in the common basis of the mean load.
Many mathematical formulas have so far been proposed to represent the stress-strain curve in the plastic range. However of these formulas, there are many that are not fit to express the actual curves accurately and are too complicated for convenient application, and it is often difficult to determine the constants in these formulas. In this paper, the following stress-strain formula which contains three constants is proposed for the plastic range. σ/E=εy+k2/εy+a-k2/ε+a, where σ: the true stress, E: the modulus of elastisity, ε: the natural strain and k, a, εy: the constants. As a result, the experimental values of several materials which have been obtained by tension and compression test agree well with this formula within 10% strain. It is shown, furthermore, that this formula can be applied to the prestrained materials as well as to the fully annealed materials, and the constants in it have well-defined physical meanings. The term k is the constant which suggests the characteristic of strain-hardening, a the constant which is varied by the magnitude of prestrain, and εy the yield strain.
A series of studies have hitherto been made on the influence of strain history on the plastic deformation of polycrystalline metals, and as an instance thereof is given in the present paper, a report of investigation that was made from the viewpoint of crystal plasticity, on the behavior of plastic deformation of metals subjected to low-cycle pulsating stresses. In order to discuss the structural change of the material under low-cycle stressing, the experimental measurement of misorientation was performed in the course of low-cycle tensile stressing on the coarse-grained sheet specimen by application of X-ray back-reflection Laue method. From the present analytical and experimental studies, the following conclusions have been obtained: (1) The measured value of misorientation in the coarsed grain of the specimen has increased with advanced number of cycle of low-cycle stressing. Moreover, the change of misorientation in the polycrystalline structural grain under cyclic stressing is larger than that in the monocrystalline structural grain. (2) The misorientation in the polycrystalline structural grain is dependent not only on the orientation factor of each diffraction plane but also on the Schmid factor of the grain at an early stage of cyclic stressing. But these dependency has decreased at the stage of an advanced cycles. (3) The variation in distribution of misorientation in the polycrystalline structural grain is remarkable at the stage of an advanced cycles in its favor in comparison with that in the monocrystalline structural grain.
Epoxy resin has hitherto been extensively used as insulating material by virtue of its favorable properties both in its electric conducting and mechanical engineering functions and in its capacity for being cured at room temperature. In view of the fact, however, that the mechanism of its dielectric breakdown has not yet been made clear enough, experimentary researches have been conducted from various standpoints. Three types of epoxy resin were selected for specimens, bisphenoidal, novolac and cycloaliphatic, and measurement was made of their electric condition before their breakdown, and of the electric field in the breakdown, in order to ascertain the mechanism of dielectric breakdown of the material. Measurement was also made, on the other hand, of the γ-ray irradiated samples with respect to their electric current conducted in them, and to their dielectric breakdown, and study was made concerning how to determine the effective irradiation. In other words measurement was made of the electric current at the various degrees of voltage applied, and of the temperature. The temperature dependence in dielectric breakdown strength was also measured. The results obtained are summarized as follows. (1) The electric current conducted in the epoxy resin before its dielectric breakdown is the ionic current which is show by the formula exp (KE) in the high electric field. (2) There is slight variation in the property of the electric current e. g. its temperature dependence among the rest, dependent on the kind of the material, epoxy resin, and the curing agent, through which the current is conducted. Abrupt increase of current is generally observable at a point higher than transition temperature for glass. Decrease of current which is sometimes observable at temperature a little over 100°∼120°C is considered to be an hygroscopically affected incident. It is the commonest phenomenon with epoxy resin reinforced with curing agent of acid anhydrous type that it, being of smaller hygroscopicity than the same material with curing agent of amine type, rarely presents decrease in the electric current conducted in the material. (3) Irradiation promotes conductivity. This is considered to be due to the increase in density of charged particles caused by irradiation. (4) The voltage required for dielectric breakdown depends upon the thickness of the specimen, and upon the lapse of time required for the rise of voltage. The voltage decreases according to the rise of temperature. The mechanism of dielectric breakdown, though it is electronic when but a short time is required for the rise of voltage, is considered to be therefore impulsively thermal when a longer time than circ. 5×10-5sec is required for the rise of voltage.
In the evaluation of plastic materials at their deterioration, it is regretable that there have been but poor discussions made so far concerning the correlation between their physical properties and internal structure during their deterioration. Hereunder is presented the report of kinetic studies made of the accelerated aging of plastic films (polystyrene, polyvinyl chloride and polypropylene) in ultraviolet rays. The deterioration is evaluated as follows; (1) By changes of their physical properties (ultimate strength and relative elongation at break) which are measured by the auto-graph, and their activation energy and the entropy of activation are calculated by using the accelerated aging time as the criterion for their kinetic evaluation. The degree of deterioration is evaluated by these two values. (2) By changes of their internal structure which are measured by the infrared spectrophotometer (NaCl system), and their activation energy and the entropy of activation are calculated by using the changes in percent transmission of each characteristic absorption group during their deterioration. (3) By the suitable mechanism of their deterioration which is proposed by the infrared absorption method and by using these two values as the measure. The correlation of their physical properties with changes of internal structure is thus evaluated from the kinetic point of view.
Many studies on the problem of fracture strength due to the Griffith crack in glassy amorphous polymers have hitherto been presented. The specific value of energy on the fracture surface can be calculated upon the relation between the fracture stress and the size of the Griffith crack. The measurement of the specific value of energy on the fracture surface is shown as extremely high over the theoretical value. This discrepancy is attributed to the energy consumed in a viscous flow in a thin layer of material at the fracture, resulting in molecular orientation such as craze. In this paper is reported the effect of the craze at the tip of the Griffith crack on the tensile strength of polycarbonate and polystyrene at various strain rates that has been studied. Craze was artificially induced by bringing the material into contact with kerosene, n-pentane, n-hexane and n-heptane as craze accelerators. The results show that the craze at the crack tip has reduced the tensile strength both of polycarbonate and polystyrene at high strain rates where the Griffith theory could be applied. However, the mode of fracture in polycarbonate at low strain rate has changed from brittle to ductile fracture and no effect of craze on the tensile strength has been noticed. The tensile strength of polycarbonate has not been affected by mere absorption of environmental reageants without craze. Conversely, an increase has been observed in polystyrene. It is indicated, in consequence, that almost 50% of the apparent specific value of energy on the fracture surface have been consumed for craze formation at the crack tip prior to fracture both in polycarbonate and in polystyrene.
It is generally recognized that craze cracks are not mere voids, but are filled with molecules oriented to certain microvoids. However, there has been scarcely any precise quantitative studies hitherto made on the mechanism of the formation of crazes. This is partly due to the statistical nature of crazing phenomena. In this paper, what is the statistical nature of the crazing phenomena in polymethyl methacrylate and polycarbonate has been made clear. Fluctuation of time required for the initiation of crazes after loading were analyzed on the basis of a stochastic theory. The results show that the frequency distribution curves of the time for craze initiation are markedly a skew. This fact indicate that the fluctuation that is observed has not been produced by an experimental error nor by the inhomogeneity of the specimens. The cumulative frequency can be expressed by P=exp(mt), where m is probability of the craze initiation. A slight delay in time for m to approach the constant value is recognized. The relation between m and applied stress is expressed by m=A exp(Bσ), where σ is applied stress, A and B are constants independent of the stress. This expression is in accordance with the Eyring equation dependent on stress. Therefore, the crazing phenomena are explained as a kind of rate process. The value of 16kcal/mol has been obtained as an activation energy for both cases with and without kerosene. This value is much lower than that of macroscopic yielding behaviors. This difference means, therefore, that crazing is not regarded as a local yielding or flow of polymers.
Following up the previous paper on the fracture strength of helically wound composite cylinders under axial tension, the torsional strength is discussed in the present paper. By making use of the in-plane stress components in each layer of the helically wound laminate under torsional loading, the three-dimensional stress components on the planes containing fibers have been calculated, taking into account the plastic deformation due to the yielding of the matrix or separation between the fibers and the matrix before fracture. And then, by relating these analytical stress components with the fundamental strength which corresponds with the four kinds of fracture mechanism that has been obtained in the authors' experiments on unidirectional fiber-reinforced composites, the torsional fracture strength has been predicted analytically. The fracture is found to be mainly governed by the compressive fracture in the fiber direction in one layer over almost all the ranges of winding angle, exhibiting good agreement with the torsional fracture stresses and fracture behaviors obtained in the experiments on glass-epoxy composites. The torsional buckling experiments are also carried out on the helically wound thin cylinders in order to ascertain that the above-mentioned fractures are not due to the buckling. The experimental buckling value is about two thirds as large as the theoretical value.
In the present paper are described the results of analytical and experimental studies made on the strength of helically wound composite cylinders under internal pressure, following up the previous papers on the axial tensile strength and the torsional strength. The burst strength can be predicted by the same analytical procedure as that for axial tension or torsion; in other words, the three-dimensional plastic stress components on any plane containing fibers in each layer of the laminated composite cylinder will be analysed and related with the four kinds of fundamental strength of unidirectional reinforced composites. The results of the experimental studies on glass-epoxy composite cylinders show good agreement with the analytical fracture values including the fracture behaviors. The netting analysis customarily applied to the pressure vessel design is found to be of no use except the range of winding angle around 55°. On the other hand, the authors' views for the analysis of fracture strength of filament-wound structure can be consistently applied throughout the range of all winding angles under any kind of external loading, and the good agreement with the various kinds of experimental results proves the availability of these views of the authors'.