The predicted life of a rolling stock truck frame under service load history is greatly influenced by the cycle counting method selected and the S-N curve used. However, little words have been done to evaluate and select the most suitable counting method and S-N curve for the prediction. In this paper, six kinds of cycle counting methods and three kinds of S-N curves were investigated by using the measured service stress data, and the predicted lives (a modified Goodman's method for evaluation of mean stress effect and a modified Miner's rule for fatigue damage calculation were applied) were compared to the service life. The following results were obtained; (1) Two cycle counting methods (the zero cross range pair and the zero cross range pair mean methods) showed the lives close to the service life, and the S-N curve B (which was used for the fatigue life prediction of fillet welded joint of truck frame by S. Tanaka) was good for the life prediction of the truck frame. (2) When the effect of mean stress was taken into account, the lives under full load and vacant load conditions became a half of those without considering the effect. (3) By using the zero cross range pair and the zero cross range pair mean methods for cycle counting and the S-N diagram B, the life under the full load condition was about 15% less than that of the vacant load condition.
Polybutylene terephthalate (PBT) has such good characteristics as high strength, wear and chemical resistance, etc. Recently, flame retardant PBT has been developed for electric appliances, but it shows more change in color than not-flame retardant PBT after UV light exposure. In this report, the dependence of the color change of flame retardant PBT on the content of titanium oxide and oxygen index, which is the measure of flame retardant degree, was determined. Furthermore, the effect of UV absorber on the color change was examined. By the addition of 1% titanium oxide and 0.5% UV absorber, the color difference of flame retardant PBT was reduced to about one-third of its initial value. The color difference was approximately the same for those having the oxygen index more than 25.
The elastic-plastic constitutive equations for large deformation are derived thermodynamically. Two internal state variables, a scalar and a tensor, were introduced, which represent the combined work-hardening. The stress, the strain, the translation, the temperature gradient and the heat flux are defined in a reference configuration. The constitutive equations in elastic state and the flow rule in plastic state are naturally derived from the Clausius-Duhem inequality and the assumed yield conditions. It is shown that the constitutive equations and the yield conditions include all natural and artificial crystal systems. For small deformation the theory derived here can be reduced to the one proposed by the author previously.
In order to study the possibility of calculating the Young's modulus, E, for a cold rolled mild steel sheet on the basis of its texture represented by the three-dimensional orientation distribution function, w(ψ, θ, φ), the E value calculated was compared with the experimental value. ψ, θ, and φ denote a set of Eulerian angles between the coordinate system of crystallite and the reference system of specimen. From the E value calculated, E(ψ, θ, φ), which was specified by means of Eulerian angles in the same definition as used in describing the orientation of a crystallite in a polycrystalline sheet, the E value for a polycrystalline sheet, Ecal, was computed by Ecal=4/π2∫π/20∫π/20∫π/20E(ψ, θ, φ)w(ψ', θ, φ) sin θdθdψ'dφ where ψ'=ψ+ω and ω is an angle between the folling direction and stretching direction. Experiments were made on rimmed steel, aluminium killed steel and decarburized rimmed steel, and their Young's modulus were measured by using the resonant vibration method. The results obtained are summarized as follows: (1) As for planar anisotropy of the calculated Young's modulus, Ecal at the transverse direction, ET, was smaller than that making an angle of 45° with the rolling direction, ED, and larger than that along the rolling direction, EL. The planar anisotropy of the observed one, Eobs, showed the same tendency as that of Ecal for all samples. (2) The observed Young's modulus Eobs, coincided with Ecal within the relative error of 1% for the sample having a strong preferred orientation. For the rimmed steel sample, which has the weakest preferred orientation, the ratio of Eobs and Ecal was 1.07. (where E=(EL+ET+2ED)/4) It was concluded from these results that the Young's modulus of a polycrystalline material can be, quantitatively, estimated from its texture analysed three-dimensionally.
The influence of tensile direction on the mechanical properties of directionally solidified Al-4.5wt.% Cu alloys was examined and compared with the analyses. Angular variations of the elastic constants (Young's modulus and Poisson's ratios) qualitatively agreed with the analysis with the Voigt average and the finite element method. An angular variation of the yield strength agreed with the analysis with the Sachs average except when the angle between the tensile direction and the growth direction of columnar crystals was about π/4 rad. At this angle, the grain boundary slip had to be considered. An angular variation of the tensile strength was explained by the three fracture mechanisms of composites.
The residual stress distribution in injection molded PP, HD-PE and glass fibre reinforced PP has been studied. The test specimens were of the standard shape and size prescribed in ASTM D955, namely, DISK and BAR type, having the thickness of 1, 2 and 3mm. The residual strees distribution throughout the thickness from the surface to the middle showed an unexpectedly large change. In PP, the surface layer, the highly oriented layer and the core layer were under compression, tension and again compression stress, respectively. In HD-PE, on the other hand, the residual stress distribution pattern differed greatly depending on the specimen thickness and orientation. Such residual stress distribution may result from the differences in cooling rate across the thickness and in molded-in fine structure. In the case of glass fibre reinforced PP, the orientation of the glass fibre has an dominant effect on the residual stress distribution. Higher melt stock temperature has a tendency to increase residual stress.
The mechanisms of ductile and brittle fracture in the fracture toughness tests of structural low-carbon steel at low and ambient temperatures were discussed based on the plastic strain measured at the crack tip and beneath the fracture surface with the X-ray diffraction technique. The plastic strain in the close vicinity of pre-fatigue cracks increased proportionally with J integral and the crack-tip opening displacement during the process of ductile fracture at an ambient temperature. The critical strain at the crack tip corresponding to the point of crack nucleation was much smaller than the fracture strain obtained in simple tension testing. The plastic work for fracture was calculated from the distribution of plastic strain measured beneath the fracture surface. In the case of ductile fracture, the plastic work done in the fracture process zone was about 10 percent of JIc. On the other hand, in the case of cleavage fracture, the plastic fracture work was nearly equal to the toughness value, when the influence of X-ray penetration on the measured distribution was corrected.
Tensile Tests on circumferentially notched round bar tensile specimens with notches of various acuity have been made on SS41 and SM50C in order to clarify the effect of stress triaxiality on ductile fracture initiation. Tests on tensile and bend specimens with a slit or fatigue cracks have also been made in order to obtain the relation between the fracture toughness and the condition of ductile fracture initiation. The plastic strain at the ductile crack initiation decreased sharply with increase of stress triaxiality in the range where σm/σ (σm: mean stress, σ: effective stress) is smaller than about 1.2, but it became almost constant for larger σm/σ than 1.2. A similar dependence on stress triaxiality σm/σ was observed in the dimple size distribution on the fracture surface. The fact that the crack tip opening displacement at fibrous crack initiation is almost independent of various factors, such as specimen thickness, crack depth, loading mode and so on, may be explained by this stress triaxiality dependence of ductile fracture initiation, because the value of the stress triaxiality σm/σ around the crack tip is larger than about 1.2 regardless of the factors above mentioned.
In order to elucidate the influence of graphite on the rolling contact fatigue strength of flaky and spherulitic graphite cast iron, experiments were conducted on the quenched and tempered samples by using a Nishihara-type rolling contact fatigue testing machine under a lubricated state with sliding. The results obtained are summarized as follows: (1) The rolling contact fatigue endurance limit of flaky or spherulitic graphite cast iron with various hardness was lower than that of the carbon steel having the same hardness and similar microstructure to the matrix of cast iron. (2) The rolling contact fatigue endurance limit of flaky or spherulitic graphite cast iron decreased remarkably with increasing amount of graphite regardless of its shape, especially at high matrix hardness. (3) Since graphite is considered as a sort of internal defect, the reduction factor of the rolling contact endurance limit for cast iron against carbon steel with same hardness was examined. The reduction factor for flaky graphite cast iron was larger compared with that of spherulitic graphite cast iron, regardless the amount of graphite and matrix hardness.
The sand erosion behavior of polymethyl methacrylate (PMMA) has been studied by the falling particle test. The impact velocity of glass beads (Vp) was varied from 12 to 35m/sec, and the impact angle was from 20 to 85 deg. As the result of testing, a unique phenomenon showing two erosion peaks at about 30 and 70 deg. was found. At low impact velocity, the peak of erosion rate at 30 deg. was higher than the other peak at 70 deg. At high impact velocity, on the other hand, the peak at 30 deg. became lower and then disappeared at 25m/sec. The erosion rate was proportional to Vp2 at low impact angles but to Vp5 at high impact angles. In order to investigate the erosion mechanism at these two angle range, optical microscopic observations were further made. The results showed that the material was removed to form pits at a low impact angle, but was eroded just like spalling from transverse cracks propagated near under the specimen surface at a high impact angle. In conclusion, PMMA revealed two different erosion behaviors and mechanisms depending upon the impact angle and velocity.
The main purpose of this study was to obtain a numerical simulation method for dynamic fracture in blasting. As a model of simulation analysis, cement mortar plates were selected and subject to in-plane impacting load by an explosive. In the numerical anaylsis, finite element method with lumped mass was used for spacial discritization and Newmark's method with γ-dispersion was employed for time integration. The numerical results showed good simulation of the fracture of mortar plates and the fracture mechanism was clarified.
The knowledge about the electrochemical behavior of various metals in molten glasses during voltage application is essential to electric melting of glass. In this paper, the anodic dissolution, passivation and cathodic deposition of metals were investigated in molten sodium diborate glass by linear potential sweep method. As the electrodes, metals such as Pt, Ni and Fe were selected. The relationship between current and applied potential was determined at various linear potential sweep rates (0.001∼5V/sec) between 0∼±5V by using platinum wire as a reference electrode and an auxiliary electrode under N2 atmosphere. By anodic potential sweep of Pt electrode, S shape current-potential curves were obtained at various potential sweep rates. This limiting current might be attributed to the diffusion current of oxygen ions. When the applied potential was more than ca. 3V, the oxygen gas evolution was observed because of electrolysis of the solvent glass. Pt electrode acted as an insoluble electrode. Due to anodic polarization, Ni electrode dissolved as soon as a potential was applied, but the dissolution current decreased suddenly at a certain voltage. The respective plots of the peak currents and peak potentials against (potential sweep rates)1/2 were shown to be straight lines. These phenomena can be explained by coverage of the electrode surface by poor conductive oxide films formed by the reaction, Ni+O2-=NiO+2e. There was no peak on the current-potential curve for Fe electrode and Fe dissolved rapidly.
In the previous paper, the results of the studies on anodic dissolution, passivation and catholic deposition of some metals such as Pt, Ni and Fe in molten sodium diborate glass had been reported. In this paper, the electrochemical behaviors of other electric conductive materials such as Co, graphite, W and Cr were investigated in the same melt by the linear potential sweep method and potential step chronoamperometry. Current-potential curves were obtained at various potential sweep rates (5∼0.5V/sec) and various potential spans between 0 and 5V for anodic polarization and between 0 and -4V for cathodic polarization. All the measurements were carried out under N2 atmosphere at 900°C. By anodic potential sweep of a Co electrode, the current-potential curve having a large current peak at ca. 1V was obtained. Such a passivation phenomenon may be explained with the oxide film formation on the electrode surface by the reaction, Co+O2-=CoO+2e. By applying higher potential than 3V, a plateau accompanied by small vibrating waves resulting from the oxygen gas evolution was observed on the current-potential curve. A graphite electrode showed a S-shape current-potential curve by anodic polarization in the same way as Pt. Graphite acted as an insoluble electrode, but a marked gas evolution was observed at the anodic potential more than 3V. A W electrode readily dissolved, and no peak was observed. A Cr electrode showed a broad and weak current peak during anodic polarization. As the current density for the Cr electrode on applying further potential was as small as the value for Pt, it seemed that Cr acted as an insoluble electrode.