Journal of the Society of Materials Science, Japan
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
Volume 44 , Issue 500
Showing 1-28 articles out of 28 articles from the selected issue
  • Masaru ZAKO, Tetsusei KURASHIKI
    1995 Volume 44 Issue 500 Pages 512-516
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    When explosion occurs in a chemical plant, the destructive explosion pressure leads to pipe collapse and missile discharge by pieces of structures. Therefore, a disaster simulation program, which takes analysis of pipe behavior by explosion pressure into consideration, has been developed by using a personal computer. The consideration points for the computer program are as follows;
    (1) Three-dimensional explosion pressure applied on a pipe can be calculated based on the kind and weight of contents in the damaged tank, and can be also calculated as a function of distance from tank to pipe.
    (2) The mechanical behavior can be analyzed by FEM using beam elements.
    (3) The effects of dike height and hidden pipe region behind tanks can be calculated.
    (4) The computational results can be graphically shown on CRT.
    As an example, the effect of the height of oil dike was simulated for a model plant. The result shows that the damaged region and dangerous location of pipes can be analyzed. It is revealed that the proposed computer program is very useful for the reliability evaluation and installation of chemical plant pipes.
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  • Shoya OKUDA, Masaaki YONEZAWA
    1995 Volume 44 Issue 500 Pages 517-522
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    This paper is concerned with a reliability assessment of structural systems based on an improved importance sampling simulation, in which the importance sampling density is determined within the limit of the failure region. Basic random variables are assumed to be stochastically independent normal variates and the minimum reliability index β of the system to be known beforehand. The first step of the proposed method is to execute simulations, refered to the preliminary simulations, to get a rough estimate of the failure probability and data about the sample distribution. These data are utilized to determine the importance sampling density as a frequency distribution with respect to radius in polar coordinates. In the second step, the structural failure probabilities are estimated through the importance sampling simulations, samples of which are generated from the estimator of the importance sampling density determined in the first step.
    The proposed method is compared in a numerical example with the Monte Carlo simulation combined with partition of the region technique and ISPUD for multi mode failure etc. It can be said that the proposed method is effective for the estimation of structural failure probabilities.
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  • Takuzo IWATSUBO, Shozo KAWAMURA, Hiroyuki MORI
    1995 Volume 44 Issue 500 Pages 523-528
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    In this paper, the method to obtain the random response of a structure with uncertain parameters is proposed. The proposed method is a combination of the substructure synthesis method and the hierarchy method. The concept of the proposed method is that the hierarchy equation of each substructure is obtained using the hierachy method, and the hierarchy equation of the overall structure is obtained using the substructure synthesis method. Using the proposed method, the reduced order hierarchy equation can be obtained without analyzing the original whole structure. After the calculation of the mean square value of response, the reliability analysis can be carried out based on the first passage problem and Poisson's excursion rate. As a numerical example of structure, a simple piping system is considered. The damping constant of the support is considered as the uncertainty parameter. Then the random response is calculated using the proposed method. As a result, the proposed method is useful to analyze the random response in terms of the accuracy, computer storage and calculation time.
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  • Shinsuke SAKAI, Hiroyuki OKAMURA
    1995 Volume 44 Issue 500 Pages 529-533
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    To evaluate the cumulative fatigue damage under Gaussian random loading, the distribution of rainflow range must be evaluated from the random waves. It is considered difficult to evaluate the distribution of range from the geometry of the PSD of the waves except the narrow band random waves, the range distribution of which becomes Rayleigh distribution. As to the random waves with bimodal PSD, however, the authors have already shown that the range can be derived from the PSD analytically. The distribution of range can be represented by the ratio of two dominant frequencies and the ratio of two corresponding power.
    In this paper, the property of fatigue damage evaluated by the proposed method is examined. And the fundamental equations necessary for reliability analysis are formulated. The derived equations are compared with the results of Monte-Carlo simulations and good agreements are obtained. Finally, several diagrams, which enable us fatigue design easily, are presented.
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  • Michiko TOYODA, Hiroaki TANAKA
    1995 Volume 44 Issue 500 Pages 534-539
    Published: May 15, 1995
    Released: June 03, 2009
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    Thermal fatigue crack propagation under random temperature fluctuation is theoretically investigated from a probabilistic view point by the use of a Markov approximation method, under the condition that the temporary variation of the inner surface temperature of plate is modeled as a wide-band stationary Gaussian process. First, a crack growth equation is formulated on the basis of the Paris law under the assumption that the stress intensity factor range ΔK can be approximated by the local expectation of a relative maximum of the stress intensity factor K. Next it is extended to a random differential equation, where the randomness in crack propagation resistance is taken into account. The Markov approximation method is then applied to derive a residual life distribution function as well as a probability distribution function of the crack length. Finally, numerical examples are shown to examine the quantitative behavior of the residual life distribution, whose results indicate that the present model is applicable even if the spectrum of temperature is of narrowband type.
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  • Takashi MATSUMURA, Masahiro ICHIKAWA
    1995 Volume 44 Issue 500 Pages 540-545
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    In the estimation of maximum crack length in a structural component by the statistics of extremes, one encounters the problem of how to choose the sample area S (the ratio of the sample area to the whole area) and the number of division m. In a previous paper, the present authors showed that the root mean squared error of the estimated value, √V(Xmax) can be approximated by a linear function of log S for the case when individual crack lengths follow an exponential distribution. In the present paper, by conducting theoretical analysis and Monte Carlo simulation, it is shown that √V(Xmax)/σ can be approximated by a linear function of log T regardless of the distribution forms of individual crack lengths, where σ is the variance of the double exponential distribution which the largest crack length in each elemental area follows, and T(=m/S) is the return period. It is also shown that √V(Xmax)/σ by Monte Carlo simulation is 1.1∼1.9 times larger than that by the theoretical analysis. The causes for this difference are discussed.
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  • Masaru ZAKO, Masahiro ICHIKAWA, Hiroshi FUKUYOSHI
    1995 Volume 44 Issue 500 Pages 546-550
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    A fatigue curve for design in which the reliability is taken into consideration is generally obtained by ASME code. A constant safety factor is used for design in this code though the fatigue life shows some dispersion. Therefore, a design margin decision system based on reliability, which is capable of evaluating fatigue statistically, has been developed in this paper. In the developed system, the following assumptions are used: (i) the distribution of fatigue strength follows one of the normal, log-normal and Weibull, (ii) the distribution of fatigue life follows either log-normal or Weibull, and (iii) ηD, the coefficient of variance for cumulative cycle ratio, coincides with ηN, the coefficient of variance for fatigue life. By using the developed system, a design fatigue curve for a given failure probability and confidence level was obtained and compared with that of ASME code. As a result, it has been clarified that design margin can be calculated statistically for various materials with different dispersion of fatigue life by the developed system.
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  • Yoshihito KUROSHIMA, Shoji HARADA, Kazuhiko OGAWA, Masahisa ISAJI
    1995 Volume 44 Issue 500 Pages 551-556
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Pulsating loading fatigue tests were carried out on a very thin wire of 0.32mm in diameter being used for the load supporting component of high pressure hoses or tires. The fatigue tests were carried out in a special testing device developed in this study, utilizing electric resonance. To understand the fatigue strength controlling factor, the relationships between the fatigue strength and other mechanical properties such as tensile strength and hardness of the materials tested were examined. Although the large size inclusion contained in the matrix was presumably supposed to dominate the total fatigue life mainly, the results in reality showed that a local region with, lowest hardness determined the entire fatigue life. The lowest value of hardness was coincided with a threshold value estimated from the Weibull type distribution of hardness.
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  • Masahiro SAKANO, Ichizo MIKAMI, Ken'ichi KANO, Eiichi YONEMOTO
    1995 Volume 44 Issue 500 Pages 557-561
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    A long-life variable amplitude fatigue test is performed using plate girder specimens with four types of transverse stiffener connections under highway traffic loading. Fatigue cracks are initiated from the fillet weld toe at the stiffener end on both the tension side and compression side, from blow holes contained in web-to-flange longitudinal fillet welds, and from the transverse fillet weld toe of the patch plate on the compression flange. The fatigue failure life of all four details of the transverse stiffener connections satisfies the condition of JSSC category D.
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  • Zhongxiao JIN, Yoichi OBATAYA
    1995 Volume 44 Issue 500 Pages 564-569
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The plastic constitutive equation in the random barrier theory can be expressed using two internal state functions which are the plastic potential function and the internal structure variable. The plastic potential function is an another expression of the distribution of barrier strength against the dislocation movement. In this paper, the barrier strength is assumed to be the quantity of the external stress by which an individual slip system can operate at a constant critical resolved shear stress. Simulated specimens consisting of many grains of FCC structure are used for evaluatingg the distribution of barrier strength in polycrystalline metals. It is shown that the Weibull distribution is most suitable for expressing the distribution of barrier intensity. The critical resolved shear stress is found to be the sole factor for regulating the property of the above distribution. The plastic constitutive equation can be described with the activated ratio of the slip system and the internal structure variable.
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  • Manabu GOTOH, Minoru YAMASHITA, Tae Hoon CHUNG, Masanobu MATSUNO
    1995 Volume 44 Issue 500 Pages 570-577
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    In the preceding work under plane strain compression of two blocks whose interface was sawtoothed, a peculiar behavior appeared such that the sawteeth grew markedly. But only the occurrence of the phenomenon itself was mentioned. In this paper, the degree of growth is experimentally investigated for various materials. Further, numerical simulations are carried out by the elastic-plastic FEM. Soft pure aluminum (A1050-O), soft or hard aluminum alloy (A5056-O, H) and copper (C1100-O, H) are used. The initial sawtooth angles of interface are 60° and 90°. In the experiments, the variations of the angle, area and side length of sawtooth are evaluated. In the FEM simulations the work hardening exponents are set at n=0.01, 0.15, 0.30, and the J2G constitutive equation is used. Corresponding to the experiment, shear-band formation is observed, and harder materials show a larger growth than the soft ones. The growth in the case of initial sawtooth angle 60° is larger than that in 90°. In the simulation of initial sawtooth angle 60° where n=0.01, the shear band appears and a lower n-value gives a larger growth. Based on the experiments and calculations performed here, this phenomenon is considered associated with the geometry and mechanical properties of the material. Especially, the shear-band formation from the tips of sawteeth governs the degree of growth. For comparison, the compression of axisymmetric blocks with sawtoothed interface is also performed. However, little growth appears in both the experiment and the corresponding calculation.
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  • Susumu SHIMA, Ming YANG
    1995 Volume 44 Issue 500 Pages 578-583
    Published: May 15, 1995
    Released: June 03, 2009
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    An intelligent V-bending process developed by the authors is briefly described and the importance of change in Young's modulus due to plastic deformation, which influences the amount of springback and therefore the accuracy, is emphasized. The change in Young's modulus in simple tension of a cold rolled steel sheet is experimentally investigated by affixing strain gauges on the specimen. It is shown that the Young's modulus changes drastically with plastic deformation and that this is much larger than that estimated from the change in apparent density. A model that explains this phenomenon is presented. By using the experimentally derived Young's modulus, V-bending process of the same metal is simulated by the finite element method in plane strain; the amount of springback is calculated and compared with the experimental results. It is shown that the springback calculated with the commonly used value of Young's modulus is far less than the experimentally derived one and that the calculation with varying modulus provides the better results. It is thus concluded that, for a better accuracy in sheet bending, the change in Young's modulus due to plastic deformation should be taken into consideration.
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  • Nobutada OHNO, Takashi YARI, Mineo KOBAYASHI
    1995 Volume 44 Issue 500 Pages 584-590
    Published: May 15, 1995
    Released: June 03, 2009
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    When a cylinder is subjected to a temperature front moving cyclically in the axial direction, the circumferential plastic strain may accumulate with the increase of the number of cycles. This is a thermal ratchetting problem induced by a liquid surface moving in a cylinder, and it is important especially in designing fast breeder reactors. In the present paper, the effect of kinematic hardening rule on the thermal ratchetting analysis is discussed by implementing the following four kinds of kinematic hardening rules in a finite element analysis; the perfectly plastic model (PP), the linear kinematic hardening rule (LKH), the classical nonlinear kinematic hardening rule of Armstrong and Frederick (AF), and the rule proposed recently by Ohno and Wang (OW). It is shown that disregard of transient hardening after yieding leads to overstimating the thermal ratchetting, that a rule predicting larger mechanical rathcetting under uniaxial cyclic loading makes the thermal ratchetting more serious, and that the Ohno and Wang rule can render the analysis most realistic among them.
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  • Tetsuo NAKA, Fusahito YOSHIDA, Masanobu OHMORI
    1995 Volume 44 Issue 500 Pages 591-596
    Published: May 15, 1995
    Released: June 03, 2009
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    Tension tests were performed on five α-brasses with 1 to 30-wt.% Zn, 60-40 brass and OFHC copper at a wide range of strain rates of 2.2×10-4 to 2.1×102s-1. The strain-rate sensitivity to flow stress in α-brasses reduces with increasing Zn-content, and almost no strain-rate effect is found in 70-30 brass. The fracture elongation, which strongly depends on the uniform elongation, increases with increasing Zn-content, whereas the reduction of area slightly decreases with Zn-content. The n-value in the Hollomon-type constitutive equation, which governs the uniform elongation, becomes smaller at the strain region just before the onset of local necking. To describe the above-mentioned mechanical properties, the Ludwik-type costitutive equation with the power law of strain-rate sensitivity: σ=(σ0+Cεnm, is proposed, in which two sets of material constants σ0, C and n should be determined for two different strain regions.
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  • Petr SITTNER, Masataka TOKUDA
    1995 Volume 44 Issue 500 Pages 597-601
    Published: May 15, 1995
    Released: June 03, 2009
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    Combined tension-torsion experiments with hollow bar specimens of Cu-Al-Zn-Mn polycrystalline shape memory alloy (SMA) were performed at temperature T=Af+25K. Pseudoelastic strain in non-proportional loading-unloading along various simple stress (strain) paths in stress (strain)-controlled tests were found fully reversible. The experimental data of non-proportional tests, particularly the recorded transformation pathways, provide the first experimental informations about the progress of the general stress induced thermoelastic martensitic transformation in SMA polycrystal under general stress conditions whose forward and reverse transformation pathways are not identical.
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  • Makoto YOKOI, Tsuyoshi KIRIMURA, Tadashi HASEBE, Yutaka IMAIDA
    1995 Volume 44 Issue 500 Pages 602-607
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    This study investigates the deep drawing of aluminum foil by using the closed type hydro spark forming method. The effects of several forming conditions on thickness distribution and limiting drawing height (LDH) of product are extensively investigated. Forming conditions are chosen to be the distance between electrodes, condenser capacity, exploding wire position, closed volume and inclination of blank holder surface. The charging energy significantly affects formability, i.e., the conditions with not only larger but also smaller charging energies result in breakage of blanks. The appropriate charging energy condition yields the largest amount of blank drawn into die. The explosion rate, represented by the full width at half maximum (FWHM) of electric power wave, is found to have an optimum value for obtaining the largest LDH. The optimum FWHM is applied to a forming condition with small LDH, and the LDH can be successfully improved by controlling FWHM.
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  • Tomio SATOH, Kunio OKIMOTO, Shin-ichi NISHIDA, Kenji MATSUKI
    1995 Volume 44 Issue 500 Pages 608-613
    Published: May 15, 1995
    Released: June 03, 2009
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    Rapidly solidified hyper-eutectic Al-25Si and Al-15Si pre-alloy powders have been produced at the cooling rate of 105-104°C/s using a centrifugal atomization process. The powders have been consolidated via hot extrusion with a reduction ratio of 110 at 490°C after vacuum hot pressing. Superplasticity of the P/M extruded bars has been investigated in the temperature range between 350 and 523°C.
    The values of maximum elongation of Al-25Si and Al-15Si P/M extruded bars are 154% and 307%, respectively. The above P/M extruded bars show the maximum elongation at a temperature just below the solidus line of the Al-Si alloys. A filament-like elongated microstructure is formed on the surface of the P/M extruded bar under the optimum condition of superplastic deformation. The formation of such a microstructure is considered to be based on the grain boundary sliding resulting from superplastic deformation. The elongation of the P/M extruded bar, which was directly extruded without pre-compaction of the powder by vacuum hot pressing, is larger than that of the extruded bar through vacuum hot pressing.
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  • Toru FUJIMURA, Michio KATAYAMA, Jun-ichi SHIMOMURA, Kenji SHIRAGAMI, K ...
    1995 Volume 44 Issue 500 Pages 615-619
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The crystallization and formability of polyvinylidene fluoride resin (PVDF) coated steel sheet were examined by the thin film X-ray diffraction method. The integrated intensity of (020) diffraction peak increased and the integrated intensity of (110) decreased with increasing cooling water temperature after glazing of fluoride resin and acrylic polymer. At the temperature of cooling water from 20 to 45°C, the lattice spacing of (020) decreased continuously, and that of (110) increased continuously. Above 45°C, the lattice spacings of (020) and (110) did not change. At the temperature of cooling water from 20 to 40°C, the integral breadths and the full widths of half maximum of (110) and (020) did not change, while they decreased continuously above 40°C. It was clarified that when the cracks in PVDF are generated, the integral breadth decreases, and therefore when the decrease of the integral breadth is suppressed, the formability of the PVDF-coated steel sheet becomes excellent.
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  • Atsutoshi TSUCHIYA, Nobushige KOISO
    1995 Volume 44 Issue 500 Pages 620-624
    Published: May 15, 1995
    Released: June 03, 2009
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    In order to investigate the fracture strength properties of as-sintered surface, fast fracture tests at room temperature and 1000°C and static fatigue tests at 1000°C were conducted using silicon nitride specimens with as-sintered surface. From the fast fracture tests, it was clarified that the fast fracture strength of as-sintered specimens was dominated by the size of flaw which existed on the specimen surface. But it was clarified by the static fatigue tests that the fatigue life time at 1000°C was not dominated by the size of flaw only. The above property is due to the difference in crack propagation property of each specimen, and this fact was confirmed by the measurement of static fatigue life of controlled surface flaw specimens.
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  • Hyung-Seop SHIN, Ichiro MAEKAWA, Akira KOBAYASHI
    1995 Volume 44 Issue 500 Pages 625-630
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    A simple experimental method of repeated low-energy impact was devised to provide some insights into the impact damage behavior of CFRP laminates. The macroscopic failure mode and the internal damage as a consequence of repeated impacts were investigated, at some different levels of incident impact energy, with the laminated specimens prepared from different stacking sequences. The results indicated that there existed a critical incident impact energy which led to the delamination and the critical size of delamination which produced the degradation of residual strength. The delamination behavior in the laminated specimens depended largely upon the level of incident impact energy. The stiffer the specimen, the larger the delamination.
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  • Katsushi SARUKI, Shoji HOTTA, Tohru ARAI
    1995 Volume 44 Issue 500 Pages 631-636
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The effect of mean stress on the endurance limit of thin hard coatings has been studied by utilizing bending fatigue tests on SCM440 and ASP30, and axial loading fatigue tests on SKD11 and SKD61. The fatigue tests have been made on the specimens VC-coated by the thermo-reactive deposition and diffusion method, namely the molten salt bath immersion method, and the quenched-and-tempered specimens for reference.
    The experimental results indicated that the endurance limit σw was predicted by treating the mean stress σm and the substrate residual stress σr in equivalence. The endurance limit was not influenced by the existence of a coating layer, even when the coating layer was cracked by high compressive stress under the first cyclic loading. This can be explained by the fact that the cracks, formed on the coating layer by compressive stress, do not play the role of trigger in the fracture of substrate because they have an obtuse angle (>120°).
    The equations, obtained over the Vickers hardness of substate Hv 300, are as follows:
    At σmr≥0,
    σw={(Hv/10)+20}×9.8-(1.04Hv/1000)×(σmr)
    Hv: Substrate Vickers hardness (kgf/mm2), σw, σm, σr: (MPa)
    However, in the case of steels containing a large inclusion,
    σw=1.56×(Hv+120)/√area1/6-(1.04Hv/1000)×(σmr)
    area: Projected inclusion area (μm2)
    At σmr<0, irrespective of the existence of inclusion,
    σw={(Hv/10)+20}×9.8×{1-(σmr)/σT}
    σT: True strength of fracture (MPa)
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  • Tashiyuki TORII, Akira IBATA, Kazuo HONDA
    1995 Volume 44 Issue 500 Pages 637-642
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    A new fatigue testing method was developed by which fatigue cracks can be initiated and propagated in the film adhered to cover a circular hole in a base plate subjected to push-pull cyclic loads. The Boundary Element Method Analysis for this testing showed that the stress was constant in the film until crack initiation and the stress intensity factor was almost constant during the greater part of crack propagation. When the commercial-grade iron films of 100, 50 and 40μm thickness were used, the data of fatigue crack propagation rate under various stress amplitudes gathered together in a narrow band showing a power law of stress intensity factor range, but strictly speaking a little higher side for the thinner film. Also, a residual plastic layer was left considerably in the wake of the crack propagation. It was found that the stress intensity factor estimated from the crack opening displacement was smaller and the slip/crack initiation life was shorter for the thinner film.
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  • Nobuaki OTSUKI, Makoto HISADA, Shigeyoshi NAGATAKI, Toshiro KAMADA
    1995 Volume 44 Issue 500 Pages 643-648
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Many kinds of approaches have been studied to produce high-performance concrete. Such concrete is required to have high-strength, durability, and flowability. In general, some kinds of chemical or mineral admixtures are used to attain these properties, but it is very difficult to obtain the mix proportions such as to get high-strength, durability and flowability at the same time. In the field work, however, it is unnecessary to satisfy all properties at the same time.
    In this paper, a method to decide a reasonable replacement ratio of mineral admixtures to produce high-performance concrete is proposed and investigated. This method is based on the principle of total diffrential. In this principle, the objective functions are compressive strength and/or flowability (slump or slump flow), and the independent variables are the replacement ratio of admixtures, water cement ratio, and/or water content. Furthermore, the applicability of this method is investigated for the case of silica fume concrete. It can be shown that this proposed method is very useful and has a great possibility of other application.
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  • Masashi KUROSE, Akira MORIKAWA, Masaaki TSUDA, Yukio HIROSE
    1995 Volume 44 Issue 500 Pages 649-655
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The mechanical properties of materials often decrease due to corrosion. For example, stress corrosion cracking (SCC) is one of the major issues in this problem, because it is difficult to estimate the remaining life of the materials by SCC. A tarnish film is usually created on the surface of copper during corrosion. SCC for pure copper is attributed to the film. In this study, an attention is paid to the growth of the tarnish film. The specimens used were made of pure copper annealed in a vacuum, and were corroded in 1.0kmol·m-3 NaNO2 solution up to 100ksec. The experiments were conducted by immersing the specimen in the solution under two different conditions: One at free corrosion and another at several electrode potentials. The brightness of specimen surface changed with corrosion. The film was observed by using a CCD camera; the distribution and the extension of the corrosion were examined by using an image processing technique (IPT). A fractal analysis was applied and the applicability of the fractal analysis was investigated. The fractal dimension was effective to evaluate the corrosion stage of pure copper. The results obtained in this study are summarized as follows:
    (1) Change in average brightness of images against the immersion time occurred at each point of the more anodic electrode potentials. The brightness values measured by IPT showed the corrosion stage of pure copper.
    (2) The extension of the corrosion state of pure copper showed fractal characteristics at every electrode potential in the present experimental conditions. The fractal dimension of Dark OR image measured by Box counting method showed remarkable change at the current density corresponding the range of the repassivation potential.
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  • Yukio YAMASHITA, Ken-ichi HIRASHIMA
    1995 Volume 44 Issue 500 Pages 656-662
    Published: May 15, 1995
    Released: June 03, 2009
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    In works of tunnel excavation, it is constantly required to estimate the stability of cavern based on in-situ measuring data. The present paper describes a simple method for deciding Young's modulus of rock mass and the directions of applied initial stresses in the ground and their values, graphically, using nomographs calculated by exact elastic solutions. As the analytical theory for nomographs, the complex variable method with conformal mapping transformation developed by the authors is used, and the nomographs take complete consideration of a characteristics of displacement in the ground such as pre-displacement occurring before setting NATM measuring pins. The poisson's ratio of rock mass is assumed to be 0.25 in these homographs. The influence of variation of in-situ rock elasticity and the setting error of measuring pins are additionally discussed in this paper.
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  • Kasaburo HARUMI, Jun-ichi OOSHIMA, Masanori UCHIDA, Kouji ASAKUMA, Yuk ...
    1995 Volume 44 Issue 500 Pages 663-668
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The most effective means of ultrasonic defect sizing is considered to be the tip wave method. However, the intensity of the tip wave is very weak, and sometimes it prevents the use of tip waves. Several digital flaw detectors have been recently developed which are appropriate for use in the tip wave method, since they have rather low noise and more convenient functions of recordability and flexibility than the conventional analogue flaw detectors. The effectiveness of the full digital flaw detector HITACHI-DT-2000 has been described for the defect sizing of an artificial slit with round tip shape on a free surface. The newly developed model DT-2200 is greatly improved and almost noiseless, with a wide range of intensity of 100dB and very high resolution of 0.1mm. The sizing of five types of fatigue cracks is attempted here by using the result of numerical experiment. The knowledge obtained from the numerical experiment is proved to be very effective in discriminating several (multi-) tip waves generated in the reflection of ultrasonics by a fatigue crack. The technique is very easy and simple to use, but the accuracy of defect sizing is greatly improved at below 0.2mm: for the conventional analogue detectors, the accuracy is possible only at larger than 2mm. This level of accuracy will make it possible to estimate the defect sizing of fatigue crack, which is considered to be impossible by using ultrasonics. It is anticipated that this method will fill the gap and eliminate the distrust which has existed between ultrasonic testing and fracture mechanics.
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  • Hoon KIM, Tetsuo SHOJI
    1995 Volume 44 Issue 500 Pages 669-674
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    ICFPD technique has been developed to detect nondestructively the defects and to estimate their sizes in components with not only simple shape such as plain surface but also more complex shape and geometry such as curved surface and dissimilar joint. In this technique a constant alternating current is induced in an exploratory region by a straight induction wire and potential drops are measured by the potential pick-up pins of which spacing is constant. In this study, new improvements have been made on the probe material and induction wire in order to solve the problems encountered in aluminum probe (Al. probe) used in the 1st report. The new probe (Ac. probe) is made of non-conductive acrylic resin. The specimens with 2-dimensional surface defects were evaluated by this probe. It was shown that the surface defects could be detected by the difference of potential drop, and the shape of potential drop distribution was similar for each specimen irrespective of defect depth and measuring frequency. It was also found that, for the depth less than 5mm, the ICFPD technique had higher sensitivity than the conventional ACPD.
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  • Koichi NISHIZAWA
    1995 Volume 44 Issue 500 Pages 675-680
    Published: May 15, 1995
    Released: June 03, 2009
    JOURNALS FREE ACCESS
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