Polycarbonate is mechanically strong and dimensionally stable. In order to increase its mechanical strength, its reinforcement with glass-fiber was developed, and has been put to practical use. Compression creep tests and tension creep tests of polycarbonates reinforced with glass-fiber were carried out in order to examine mainly the effects of glass-fiber content on the long-term dimensional stability of polycarbonates under load. The following conclusions have been derived. (1) As the glass-fiber content is increased to 30wt% in the tests, the polycarbonate is released much of its initial deformation and of creep deformation rate. Consequently its long-term dimensional stability is much enhanced by reinforcement with glass-fiber. (2) Polycarbonate gains excellent long-term dimensional stability when stress is applied to it in parallel with the orientation of the glass-fiber. (3) There are more deformations in the tension creep tests of samples with glass-fiber content of 0wt% or less at 100°C and 3kg/mm2 than in their compression creep tests under the same condition. There are nearly equal amount of deformations in the compression creep tests and the tension creep tests of samples filled with much glass-fiber. (4) Nutting's equation is applied to the creep data of the samples filled with much glass-fiber. On the other hand, all the creep data after 25 hours are given by log(ε-ε0)=alogt+b (t≥25hr) where ε is total strain, ε0 is initial (Almost instantaneous) strain, t is time, a and b are constants.
In a previous paper, it was reported that various changes in structure and in hardness of Cu-6.0wt% Al alloy at different stages of repeated bending fatigue test were studied by hardness test and by both micro-and electron microscopic observation. In the present report, the author observed the changes of behaviour that appeared during the process to the final rupture in the above-mentioned fatigue tests, employing various kinds of measuring apparatuses, micro-and electron microscopes, hardness tester, internal friction tester and X-ray analyser. The experimental results are summarized as follows: (1) The initial formation of slip lines are observed during the first stress cycling, and they are all a type of homogeneous slip lines. (2) After the homogeneous slip lines, rippling phenomena of slip lines are observed. After the rippling phenomena, the intrusion and extrusion are observed. (3) After the intrusion and extrusion, the very large intrusion and extrusion change gradually to micro-cracks. (4) The hardness of the specimens increases with increase in stress cycling numbers and the maximum hardness is obtained around the fractured area. (5) The internal friction increases until 1×103 cycling numbers and after it decreases with increase in stress cycling numbers and 1×104 cycling numbers there is a large decrease in the internal friction. Then, the internal friction increases with increasing stress cycling numbers. (6) The X-ray diffraction pattern changes with increase in stress cycling numbers and the Laue spots above the Debye rings exhibit the phenomena of extensibility.
Rotating bending fatigue tests under constant stress and two stress levels were carried out on notched 18-8 austenitic steel at room and elevated temperatures, and fatigue crack propagation behaviors during the tests were investigated. The cumulative cycle ratios were discussed from the experimental results. The temperature dependence of fatigue fracture mechanism was studied by means of electron fractographic observations. The main results obtained are as follows: (1) On High-Low tests at room temperature the delay time in continued cracking was observed after stress change, while at 600°C this phenomenon was not observed. (2) Cumulative cycle ratios were almost unaffected by stress sequence. The fatigue life under double repeated stresses should be discussed not only from the delay time, but also from the differences in crack growth behaviors at low and high stress levels. (3) The regular striations peculiar to fatigue fracture were detected on the fracture surface tested at elevated temperature, while at room temperature these were not observed. This fact might be explained by the presence of the strain induced martensite detected at room temperature test.
It is the aim of the present study to elucidate the plastic deformation of polycrystalline metals, consequent on the cycle of stress to which the material was subjected, with respect to its strain history, as part of the series of studies to be made on the influence of strain history on the plastic deformation of polycrystalline metals. It will be considered that the aggregate plastic deformation of the material subjected to low cycle of stress is to be mainly interpreted from redistribution of stress field in the material. The experimental examination of this proposition was made by using the strain measurement apparatus specially designed. From the present analytical and experimental studies on low carbon steel at room temperature, the following conclusion has been made. (1) The yield function of Eqs. (1) and (2) is adaptable to the representation of shape of yield surface of the material under cyclic stressing. (2) The plastic deformation mechanism of polycrystalline metals under a cycle of stress is interpreted from an assemblage of single models as shown in Fig. 3. (3) The cycle-dependent plastic deformation occurs in a different manner of each part of the test specimen, because of the difference in each part of the material structure and its structural change during the stress cycle. It is to be ascribed to the anisotropy of the material, to Bauschinger effect and also to redistribution of yield stress of each part of the structural element.
In this paper, an experimental stress analysis is reported on flat plates with mixed U-V notches by the photoelasto-plastic method. The model material used is nitro-cellulose. As the preliminary experiment the yield condition of the material and its mechanical and optical properties in the plastic as well as in the elastic region were investigated. From the experimental result of the tension-torsion test using thin-walled pipes cut from the same material, it was found that the yield condition agreed with the Mises' criterion. And the bi-axial tension-tension and tension-compression tests revealed the fact that the stress sensitivity in the plastic region was governed by the equivalent stress. The tensile loads were applied to the specimens with mixed U-V notches in six steps. The first step was the load which produced a primary yielding at the notch root, and the last step the load causing the penetration of plastic regions through the minimum cross section. For the stress analysis in the plastic range, the Mises' yield criterion and the Prandtl-Reuß incremental strain law were adopted. The fringe order increments dN obtained photoelasto-plastically and the principal strain increments dε3 determined from the electrical analogy method allow the separation of principal stress increments (dσ1 and dσ2). From these values the principal strain increments dε1 and dε2 may be calculated. The principal stress σ2 and the principal strain ε2 in the minimum cross section were much smaller than the other values σ1 and ε1. It has been found as the result of this experiment that the plastic regions generated on both sides of the notches are united to a fairly large extent, including several maximum fringe order points on the longitudinal central axis.
There have been reports of formulas for calculating residual stresses in curved beam or ring respectively made by the mechanical method.1)2) In this study, the calculation formulas for obtaining residual stress distributions in curved beam and ring by the X-ray method are shown. These formulas were applied to curved beams with two different radii of curvature (24mm and 48mm) and a ring with the inner radius of 42mm and the outer radius of 54mm. The cross sections of both specimens were of the same dimension of 6×8mm2. All the specimens were made of S45C carbon steel, and thermal residual stresses were introduced in them. Residual stresses were measured by the X-ray as well as the mechanical methods, and the experimental results showed fairly good agreements between the two methods in all cases. Unlike the case of flat plates, residual stresses show unsymmetrical distribution with respect to the central axes, with the result that compressive stresses are a little larger on the concave surfaces and tension peaks are shifted to the concave sides. This tendency is more remarkable in the curved beam with larger curvature, and most conspicuous in the ring. The plate formula is also applied to the curved beams, and it is found that this formula may be used for the curved beam with smaller curvature.
It was shown in the previous paper1) that the absolute value and characteristics of the Charpy impact strength of rigid PVC plates varied with different shapes of impact test specimens which were specified by various standards. Besides the standard-size specimen, the ISO R 179 specifies the standard-small-size specimen mainly for the testing of moulded materials. In order to obtain the relation of the Charpy impact strength based on the standard small ISO specimen to the other impact strength based on the JIS, the ASTM, and especially the standard ISO specimens, the same ten kinds of rigid PVC plates as were used in the previous paper have been tested this time using the standard small ISO specimen. The standard small ISO specimen had flatwise notch, whereas the JIS, the ASTM and also the standard ISO specimens had edgewise notch. So for comparison, the test of those plates has been conducted by using the same dimension as the standard small ISO specimen with the edgewise notch instead of flatwise notch. The results obtained are summarized as follows: (1) The standard small ISO Charpy impact strength (ss·ISO·akC) of the test plates takes the value from 2.1 to 4.0kg-cm/cm2, and the standard small ISO (Edgewise) Charpy impact strength (ss(e)·ISO·akC) of the test plates the value from 1.5 to 3.0kg-cm/cm2, in spite of the fact that the standard ISO Charpy impact strength (S·ISO·akC) of the test plates takes roughly constant value i.e. 2.5kg-cm/cm2 as was shown in the previous paper. (2) The value of ss·ISO·akC and that of ss(e)·ISO·akC are both divided into two groups, thougth their characteristics differ from each other. (3) Generally speaking, it can be Said that the strength of ss·ISO·akC shows the characteristic similar to that of the ASTM Charpy impact strength (ASTM·akC).
In order to investigate what different types of anisotropy (Foliation, stratification or shistosity) in rocky materials will have influence on their ultimate strength and failure pattern, a series of uni-, bi- and tri-axial compression tests were performed using the mortar specimens with construction joints. The results obtained are as follows: (1) The in fluence of the inclination of jointed plane on strength is maximum for α≈30°(α: angle between max. principal stress σ1 and jointed plane). The decrease in strength is descending as confining pressure is high; for 30°-specimens there occurs respectively 80% and 15% decrease in strength under confining pressure 0kg/cm2 and 200kg/cm2. (2) Fracture criterion can be approximated by Jaeger's theory. (3) Fracture surface in the principal stress space is a slightly bulged pyramidical convex surface, being crooked in σ1>σ3>σ2 (σ3: principal stress parallel to the jointed plane).
The present paper is concerned with the theoretical determination of stresses and deformations around a tunnel with an arbitrary cross section excavated in anisotropic elastic ground. In the first part are proposed the methods in general for determining these phenomena based on the use of their conformal transformations, and in the second are given the numerical results of computation of various typical cross sections.
The viscosity of glass in the system As-Se, As-Se-S, As-Se-Te and As-Se-Tl was measured by a new penetration viscometer2) at temperature ranging approximately from room temperature to 285°C. The results are shown in Fig. 1, 2, 4, 5 and 6. The density of the glass was also determfined within the same temperature range. The results of variation of viscosity with composition and temperature in the system As-Se, are summarized in Fig. 2, which show that the viscosity increases steadily at all temperatures with the As content up to 45 atomic per cent. The maximum at 45 atomic per cent As in the curves is interpreted as evidence of structural grouping in the glass corresponding to the compound As2Se3. From tine values of viscosity of the glass at different temperatures, the apparent activation energy Ep, that is, the activation energy at constant pressure was calculated. Its values are given in Fig. 10. Using the Macedo's equation3) for the viscosity of glass containing both the activation energy and the free volume, the relation between the activation energy at constant volume Ev and the composition of the glass was made clear. The effect of lowering viscosity (η) of glass in the ternary system was found as ranging in the order η(s)>η(Te)>η(Tl).