Journal of the Society of Materials Science, Japan
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
Volume 21 , Issue 231
Showing 1-21 articles out of 21 articles from the selected issue
  • Hiroshi NAKAMURA, Takeshi HORIKAWA, Shozo OKAZAKI
    1972 Volume 21 Issue 231 Pages 1046-1051
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The surface treatment by tufftride effectively improves fatigue strength, resistance to corrosion and abrasion. This treatment is being used for many machine parts, but few studies on fatigue strength of tufftrided specimen have been made.
    We have been conducting the experimental studies on fatigue behavior of tufftrided specimen since few years ago, and found many, experimental facts which have many problems to be studied. This paper describes some of the problems about the fatigue behavior of tufftrided specimen.
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  • Shigetsune AOYAMA, Hirohiko NAMIKAWA, Hiromu KOHNO
    1972 Volume 21 Issue 231 Pages 1052-1057
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The variation of the diffraction line profile and the peak position with the operating conditions of X-ray diffraction apparatus was experimentally investigated with a view to attaining reasonable X-ray stress measurement.
    Cr-Mo steel (0.44%C) specimens of 25mmφ×10mm were selected for the experiment. The specimens were heat-treated at various conditions in order to obtain eight kinds of diffraction lines with half-value breadth from 1.6° to 7.2°. The surface of each specimen was electrolytically polished. The effects of time constant, scanning speed and direction of the counter were first examined. Then, the influences of the tube current, the irradiation area and the divergence angle of the Soller slit were observed.
    The results obtained are as follows:
    (1) The variation of line profile parameters had good correlation with the product of time constant T (sec) and scanning speed w(deg/min).
    (2) The peak position shifted to the scanning direction of the counter in proportion to T×w at any incident angle of X-ray. Consequently, the stress determined by sin2ψ method was not influenced by the time constant and the scanning speed. The tube current, the irradiation area and the divergence angle of the Soller slit had no effect on the shift of peak position.
    (3) The breadth of diffraction lines increased with T×w. However, the incident angle of X-ray, the irradiation area and the divergence angle of the Soller slit gave no effect on the half-value breadth in the range studied in this experiment.
    (4) The net peak intensity decreased with increasing T×w. The degree of this decrease was large as the diffraction lines were sharp, but small in case of the broad lines. The net peak intensity increased in proportion to the increase of the tube current, the irradiation area and the divergence angle of the Soller slit.
    (5) It is favourable for the determination of peak positions to have the smooth intensity contour recorded.
    When the intensity contour is jagged or saw-toothed, it is recommended to adopt the product of T and w, the tube current, the irradiation area and the divergence angle of the Soller slit as large as possible in the permissible range.
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  • Katsuhiko OGISO, Ukyo KAMINAGA, Takeshi SAITO
    1972 Volume 21 Issue 231 Pages 1058-1062
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    In the X-ray stress measurements heretofore in use, the plane containing incident X-ray beams was the same with the one on which the counter scanned. Ulrich Wolfstieg has conducted a stress measurement of the cog valleys of a gear, adapting the Schulz method (Reflection Method) of the pole figure attachment. One of the features of this measuring method is that the plane containing incident X-ray beams and the plane on which the counter scans cross at right angles each other, and that the passage of diffracted X-rays as a result are not intercepted by the projecting parts of the sample.
    The next feature is that the absorption of the diffracted X-rays by the sample has no effect on stress values. One more feature is that, though in the stress measurement heretofore in use the incidence angle of X-ray ψ0 was ψ0<π/2-η, in this method it is possible to make ψ0=π/2. The authors, having been engaged in the development of X-ray stress measuring apparatus by the parallel method so far, have just completed the development of an apparatus which can be used for the measurement by the Side Inclining method, or a modified Schulz method, as well as the ordinary X-ray stress analyzer (Strainflex).
    Features of this apparatus are:
    (1) That it can conduct both ordinary X-ray stress measurements and Side Inclining measurements.
    (2) That it can conduct the determination of retained austenite simultaneously with stress measurements.
    (3) That the measurements by the Sin2ψ method, Schaal method, Side Inclining method, etc. can be conducted, being linked directly and all automatically until the completion of measurements. The X-ray intensity values measured by step scanning, are punched in the data tape and can be analyzed by electronic computers.
    (4) That all of the measuring apparatus and accessories are mounted on a wagon and it can be moved to any arbitrary measuring places.
    The official examination of the reliability of this apparatus as a stress measuring apparatus was conducted by corresponding the mechanical stress measured by a strain gauge to the X-ray stress analysis by this apparatus, and the correspondence of the results was very good. The measured value of retained austenite can be obtained by the integrated intensity ratio of diffracted beams on both plane α {211} and plane γ {220}, using the Cr target.
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  • P. D. EVENSCHOR, V. HAUK
    1972 Volume 21 Issue 231 Pages 1063
    Published: December 15, 1972
    Released: June 03, 2009
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  • Hiroshi NAKAMURA, Shozo OKAZAKI, Takeshi HORIKAWA
    1972 Volume 21 Issue 231 Pages 1064-1070
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Although corrosion fatigue has been studied by many investigators, no report so far describes the corrosion fatigue under different corrosion atmospheres and stress conditions. In this study, a few corrosion fatigue tests have been made to clarify the effects of environmental conditions and of the superimposed wave or varing stress.
    The results obtained are as follows;
    (1) The atmospheric corrosion fatigue strength of S35C specimen (ρ=10R) under rotating bending (n=3600rpm) decreased by about 20∼30% as compared with the value obtained by the non corrosion fatigue test. And the fatigue strength decreased markedly after one month's exposure to atmosphere.
    (2) The fatigue life of SS 41 specimen, subjected to repeated wetting with 3% NaCl and drying under superimposed wave, became very short when the stress of the second wave was very small. This arises from the double effects of corrosion and superimposed wave.
    (3) The corrosion fatigue test on 13% Cr-Mo steel under varing stress in 3% NaCl showed that the fatigue life decreased extremely as compared with the corrosion life under constant stress.
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  • P. MENESES, G. CHAMPIER
    1972 Volume 21 Issue 231 Pages 1071-1074
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The yield stress of high purity Fe (less than 10 wt. ppm (C+N) content) containing 0, 1.14, 2, 4 and 6 at % Mo in solution was investigated at temperatures from 77 to 300°K. At 300°K, the yield stress varies linearly with Mo content. At low temperatures, alloy softening occurs with a minimum in the yield stress at about 2 at. % Mo; for higher concentrations, the variation of yield stress with Mo concentration is linear with the same slope as that obtained at 300°K. Our results suggest that the Mo atoms in solution have mainly an athermal influence on the yield stress and that the alloy softening is due to a scavenging process. The influence of Mo clusters in the Fe-6% Mo alloy was studied and it was found that they do not contribute to the yield stress.
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  • C. ESCARAVAGE, G. CHAMPIER
    1972 Volume 21 Issue 231 Pages 1075-1078
    Published: December 15, 1972
    Released: June 03, 2009
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    Indium-magnesium alloys single crystals were deformed in tension and compression for basal, prismatic and pyramidal slip and the variations of the critical resolved shear stress against the temperature are described. For basal slip, indium alloying shows a solution hardening with the power two thirds of the indium concentration and a repeated yielding phenomenon within a certain temperature range; the repeated yielding is related to the movement of indium atoms. For non basal slip, the concentration dependence of the yield stress is very small in alloys containing up to 2 at. % of indium strained with a low strain rate.
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  • Shuji TAIRA, Kozaburo HAYASHI, Shigeki KOE, Kazuro SHIRABE
    1972 Volume 21 Issue 231 Pages 1079-1085
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The directional dependence of mechanical behavior of pre-deformed polycrystalline metals is very important for the plasticity and the plastic working. X-ray diffraction techniques are believed very useful to study these anisotropic deformation properties, since some microscopic parameters concerned with such phenomena can be detected by these methods. In the present paper, the microscopic parameters obtained from the integral breadth of X-ray diffraction profile and from the shape of X-ray micro-beam pattern are examined on an Al-stabilized steel sheet pre-stretched to the strain of 12 percent in the direction of temper rolling.
    The results obtained are summarized as follows:
    (1) The directional dependence of integral breadth of diffraction profile, and also of the particle size and the effective strain calculated from the integral breadth, are observed on the material used.
    (2) The diffraction spots obtained by the X-ray micro-beam method give different values of subgrain size and total misorientation when the directions of their diffraction are different from each other with respect to the direction of the tensile axis.
    (3) The directional dependence of these microscopic parameters has some relation to the orientation of tensile axis of each crystal contributing to the diffraction.
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  • Masateru OHNAMI, Tetsurou YAMAKAGE, Kazuaki SHIOZAWA, Masao SAKANE
    1972 Volume 21 Issue 231 Pages 1086-1092
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    As one of the series of study on the effect of hydrostatic pressure on plastic deformation of polycrystalline metals, in the present paper, the effect of hydrostatic pressure on tensile creep of polycrystalline metals at elevated temperatures was discussed based on the X-ray measurements. In the previous paper by the present authors, the remarkable decrease in creep strain rate of the materials subjected to combined hydrostatic pressure at room temperature was discussed from the viewpoint of continuum mechanics. It was also pointed out that the effect of hydrostatic pressure on tensile creep of metals at elevated temperatures was not fully explained from the extension of creep mechanics of the materials under confining pressure. Therefore, it became necessary to take account of the effect of hydrostatic pressure on the structural change of the metal in the creep process at elevated temperatures.
    In order to elucidate the structural change in metals creep under hydrostatic pressure at elevated temperatures, in the present study, the experimental measurements of misorientation was performed on the coarse-grained, commercially pure aluminum sheet specimen by using the X-ray back reflection Laue method. It is specially noted that misorientation is a useful measure to study the effect of hydrostatic pressure on creep of metals at elevated temperatures, because it represents not only the density of both edge and screw dislocations but also the grobal imperfection density such as the density of vacancy in plastically deformed metals. It is suggested from the present experimental results that the decrease in the minimum creep rate of the metal under combined hydrostatic pressure at elevated temperatures results mainly from the decrease in jog density which is closely connected to the density of vacancy in the material.
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  • Mitugi IWAMOTO, Tadao KONO
    1972 Volume 21 Issue 231 Pages 1093-1098
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    As the first step to elucidate the phenomena taking place during rolling contact between a rail and a wheel, some experiments on rolling contact have been performed using high carbon steel.
    A specimen rod cut out from a real rail was shaped into a circle of 500mm diameter and two small wheel-like pieces cut out from a real wheel were attached to both ends of an arm which rotates on the center of the circle. The test rolling contact conditions were of low loads and low speeds.
    After every 30 to 120 minutes of rolling contact, the test pieces were taken out and the changes in their sectional profile, wear and surface residual stress were measured. After 11 hours of rolling contact, the plastic deformation in their surface and the profile of worn powder were examined under the optical and electron microscopes.
    The results showed that plastic deformation causes a scaly pattern to develop on the surface of the rail specimen; cracks initiate in this area and propagate inward, making the specimen to flake from the surface. Meanwhile the worn powder, which has been torn off, adheres to the wheel surface and forms a film of about 5μ in thickness. The greater part of the worn powder after the rolling contact has become steady is the result of the adherent film on the wheel being torn off again.
    The amount of wear after one cycle of contact is nearly the same for both the rail and the wheel pieces. This indicates that the adherent film on the wheel contains the worn powder originating from both rail and wheel. Thus the mechanisms of plastic deformation and generation of worn powder during the rolling contact have been made clear.
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  • Yusaku NAKAGAWA, Takeo TAMAMURA, Tadashi NEMOTO
    1972 Volume 21 Issue 231 Pages 1099-1105
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The residual stresses in quenched, tempered and isothermally treated steels were investigated by the X-ray method.
    The materials used were plain carbon steels containing 0.08%∼1.03% carbon and Ni-Cr and Cr-Mo low alloy steels. Test specimens were 50×50×20(mm) plates and 25φ×100(mm) round bars. They were quenched in water or oil from 800°C∼1000°C and tempered at several temperatures between 100°C∼800°C. Ni-Cr low alloy steel specimens were martempered at 200°C or austempered at 400°C.
    Residual stresses were determined by Sin2ψ method, using Cr-Kα radiation.
    The experimental results are as follows;
    (1) The surface residual stresses and residual stress distribution of these specimens were affected mainly by the hardenability of steels. The surface residual stresses of the plain carbon steel specimens quenched in water were compressive, while those of the low alloy steel specimens were tensile.
    (2) The surface residual stresses of the specimens quenched in water or oil decrease with the increase in tempering temperature. Particularly, in case of tempering above 400°C, the surface residual stresses were very small.
    (3) In the 0.85% carbon steel specimen quenched in water, large compressive stress was found just beneath the surface.
    (4) At the surface of the Ni-Cr steel specimens quenched in water or oil, the residual stresses were 55∼58kg/mm2 on tensile side, while those martempered at 200°C for 4 hours and those austempered at 400°C for 4 hours showed the residual stresses of 6.4kg/mm2 on tensile side and 20.8kg/mm2 on compressive side, respectively.
    In the Ni-Cr steel with high hardenability, isothermal treatment was effective in lowering the residual stress.
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  • Shogo IWANAGA, Hirohiko NAMIKAWA, Shigetsune AOYAMA
    1972 Volume 21 Issue 231 Pages 1106-1111
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    X-ray stress measurement is widely applied to the estimation of residual stress. In real machine parts, residual stress is often observed to have a steep gradient in their near surface layers. In the present study, the effect of the stress gradient on the stress data obtained by the X-ray stress measurement based on the sin2ψ method, was investigated experimentally and analytically.
    Three kinds of steel specimens were prepared, namely, (A) a shot-peened spring steel plate with decarburized surfaces, (B) a finish ground 0.55%C steel round bar and (C) a shot-peened spring steel plate with non-decarburized surfaces. The residual stress distributions of (A) and (B) specimens showed, respectively, steep negative and positive stress gradients in the near surface layers. But the residual stress near the surface of (C) specimen remained almost constant. The characteristic X-ray used was CrKα radiation.
    Experimental data for (C) specimen, when plotted on the sin2ψ-cosecθ diagram, can almost be represented by a straight line. But for (A) and (B) specimens, the data on the same diagram nearly fit to the concave and convex curves, respectively.
    The sin2ψ-cosecθ diagrams of the specimens with a steep stress gradient near the surface were also obtained by calculating the Bragg's angle as the weighted average value of the diffracted X-ray intensity. The analytical results mostly agree with the experimental ones.
    According to the theoretical analysis of residual stress on the assumption that it varies linearly with depth and σxy, the stress obtained by using the sin2ψ method with CrKα radiation was found to correspond to that of the layer 4.4μ deep from the surface.
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  • Kazuyoshi KAMACHI, Noboru TANI
    1972 Volume 21 Issue 231 Pages 1112-1117
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    To measure residual stress in a large construction by X-ray method, it is convenient to use a simple and small apparatus with the photographical system. Generally, these structural steels have a coarse grained structure which provides spotty diffraction ring, thus preventing the accurate measurement of ring radius. To avoid this difficulty, several attempts such as oscillating the film or moving the specimens have been made. But these methods have their own limitation.
    In the present paper, a method of determining ring radius from spotty X-ray diffraction rings obtained from a fixed specimen is presented. The method is basically to average the radial distance of each spot from the diffraction ring of the standard substance coated on the specimen surface. An automatic measuring device of these spotty rings is also discussed in the paper.
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  • Kenkichi HAYASHI, Yoshitaka NATSUME
    1972 Volume 21 Issue 231 Pages 1118-1123
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    In the previous report, the various factors that affect the endurance limit of induction hardened steel were examined. It was found that the microstrain and particle size are more influential than the residual stress on the endurance limit of both induction hardened smooth and notched specimens.
    The present paper describes an experimental study conducted on the surface hardness, residual stress, microstrain and particle size of smooth specimens tempered at various temperature in order to clarify the influence of tempering temperatures upon the fatigue strength.
    It has been found that a linear relation exists between the integral width of a diffraction pattern and the endurance limit. The physical meaning of this relation has been examined according to the diffraction profile analysis of Williamson and Hall. A linear relation also exists among the endurance limit, microstrain and particle size of induction hardened steel specimens tempered at various temperatures, which is a better relation than the one involving surface hardness and microstructure. Based on these results the significance of microstrain and particle size as strength-determining factors has been clarified.
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  • Mitugi IWAMOTO, Shohei MURAYAMA, Masayoshi KOHARA
    1972 Volume 21 Issue 231 Pages 1124-1129
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The fatigue phenomena due to pulsating repeated bending in a large plate specimen of spring steel which had been surface-strengthened by shot-peening were investigated experimentally. The change in the surface residual stress during fatigue process and the roughness in the fractured surface after rupture were measured by X-ray and surface roughness tester and the fractured surface conditions were observed under the optical and electron microscopes. The results obtained are as follows.
    (1) Up to the time just before a rupture in the fatigue process, the surface residual stress on the tension side changes only slightly, but just before the rupture it drops sharply. On the compression side, regardless of the measured position, the stress diminishes remarkably in the initial stage of the fatigue process, followed by a slight decrease continuing up to the occurrence of a rupture and then by a sharp drop just before the rupture.
    (2) A large number of fatigue cracks initiate near the boundary between the surface-strengthened layer on the tension side and the non-strengthened inside. These cracks propagate at a velocity of about 0.5∼4.0×10-4mm/cycle and, coupled with an acceleration of failure, lead to a rupture. Thus, the fractured surface presents a complicated look with coexistence of a fatigue fracture and a fracture by accelerated failure.
    (3) The electron microscope observation showed coexistence of complicated striation patterns and dimple patterns at the fatigue fracture surface.
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  • Kenkichi HAYASHI, Heisaburo NAKAGAWA
    1972 Volume 21 Issue 231 Pages 1130-1135
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Many studies reported so far on fatigue fracture mechanisms suggest that slip deformation in crystals plays the most fundamental role in fatigue damage formation. In this study, fatigue damages in each crystal grain, such as development of slip bands, formation of extrusion and intrusion or persistent slip bands and crack initiation, have been observed in conjunction with Schmid factors which are useful to explain quantitatively the easiness of slip deformation in each crystal grain. A mechanism of fatigue damage formation is discussed here on the basis of the relationship between these results and the misorientation measured by back-reflection Laue method.
    The results obtained are as follows;
    (1) A fatigue crack appears in the crystal which has two equally large Schmid factors on Critical-slip-plane and Primary-slip-plane. The formation of such critical damage as a crack is independent of the other two Schmid factors on Conjugate-slip-plane and Cross-slip-plane.
    (2) A fatigue crack is always observed in the persistent-slip band on Primary-slip-plane.
    (3) Before the crack initiation, only the slip bands on Primary-slip-plane can be observed, but after the initiation, slip traces of Critical-slip-plane also appear around the crack, forming the structure of the double slip bands.
    (4) The formation of fatigue damage is considered to be promoted by the activity of the second slip system on Critical-slip-plane.
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  • Masao TERASAWA, Yasuo YOSHIOKA, Katsutoshi ASAMI
    1972 Volume 21 Issue 231 Pages 1136-1141
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    It has been pointed out by many researchers that substructure affects crack propagation in case of fatigue of metallic materials. However, the materials used in the past investigations were mostly homogeneous, and the microscopic behaviour of surface hardened materials such as tufftrided steel is only little known.
    In the present study, some investigations were made to obtain the relation between the crack propagation and substructure of tufftrided steel specimens with notch root through the observations of the crack propagation and the change in substructure in the vicinity of notch root and crack during the fatigue process by using the back reflection X-ray microbeam diffraction technique.
    The results obtained are summarized as follows;
    (1) The life to fracture or the period preceeding crack initiation of a tufftrided steel specimen increases remarkably as compared with that of a non-tufftrided steel specimen under the same stress amplitude.
    (2) The crack initiates at a comparatively early stage in the life to fracture and grows rapidly. However, when the crack tip passes through the position 1∼2mm away from the notch root, the crack propagation rate gradually decreases.
    (3) The substructure had already formed at the places with high content of soluted nitrogen after tufftriding, and the same substructure can be observed in the vicinity of crack tips irrespective of crack length.
    (4) It is evident from the observations by microbeam X-rays and by a scanning electron microscope that the plastically deformed area in the vicinity of crack in the tufftrided steel is very small and the magnitude of deformation of each crystal is also small as compared with that in the non-tufftrided steel.
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  • Shuji TAIRA, Keisuke TANAKA, Tomoaki SHIMADA
    1972 Volume 21 Issue 231 Pages 1142-1149
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    A new method of the X-ray microbeam diffraction technique was used to measure the local residual stress near the fatigue crack tip. The residual stress was compressive at the crack tip and changed to tensile away from the crack tip. The shape of the residual stress distribution ahead of the crack tip was found to agree with the analytical result derived by using Rice's rigid plastic strip model, although the maximum compression at the crack tip was lower than that expected from the analysis. The calculated distance from the crack tip to the point where the residual stress changed from compression to tension was 1.5∼2 times as long as the distance measured by the X-ray method.
    Three kinds of plastic regions were observed ahead of the fatigue crack tip, i.e., (1) the region calculable from Dugdale's equation (ζ-region), (2) the slip band region (ξ-region), and (3) the substructure-formed region where the formation of substructure was evidently observed by the X-ray microbeam method (η-region).
    Fatigue crack propagation under doubly-repeated stress was discussed on the basis of the results of microscopic observations mentioned above. The influence of stress cycling at the first stress level on the propagation rate under the second stress level was quantified with a parameter κ as
    κ=Kp/K,
    where K is the applied stress intensity factor and Kp is the value of the stress intensity factor obtained by substituting the measured value of dl/dN into the K vs. dl/dN relation for the constant stress amplitude fatigue. Five components were first considered to affect the κ value as
    κ=1+Δκr+Δκd+Δκs+Δκb+Δκp
    where Δκr, Δκd, Δκs, Δκb and Δκp represent the contributions of residual stress, fatigue damage, strain hardening, the blunting of the crack tip and the profile of the crack front within the specimen thickness, respectively.
    Several examples of the variation of κ with the increment λ of the crack length after the time of stress change were measured for fatigue with a high-low drop of the stress amplitude. These variations were explained with three values: a negative value of Δκr in the region with the compressive residual stress, a positive value of Δκd in ηv-and ξv-regions, and a negative value of Δκs in the region of ξv<λ<ζv. As λ approached to ζv, the κ value became unity.
    In the case of stress-raise fatigue, the variation of κ with λ was explained by a negative value of Δκd in ηv-region and a positive value of Δκs in the region of ξv<λ<ζv.
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  • Toshiro YAMADA, Kenji HATANAKA, Tomohide HIRAO
    1972 Volume 21 Issue 231 Pages 1150-1156
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The notched copper specimens of rectangular cross section were fatigued by the cyclic bending tests using superimposed sinusoidal and square stress patterns. One of the superimposed sinusoidal stress patterns was the sinusoidal stress superimposed only on the compression side of square stress wave, and the other the sinusoidal stress wave superimposed both on the tension and compression sides of square wave. All sinusoidal stress waves were superimposed in the pulsating tensile or compressive condition. Based on these test results and the fractographic observations, the crack propagation behavior under the superimposed sinusoidal loading was discussed.
    The crack propagation rate under sinusoidal stress wave superimposed only on the compression side of square stress wave is slightly larger than that in the simple square stress wave having the maximum tensile and compressive stresses equal to those of the superimposed stress. On the other hand, the crack propagation rate remarkably increases as the amplitude of the superimposed sinusoidal stress wave increases. Thus it is concluded that the increase in the crack propagation rate under superimposed loading only on compression side is mainly due to the increase in the amplitude between the maximum tensile stress and the maximum compressive stress.
    Fractographic observations show that the sinusoidal stress wave superimposed on the compression side of square stress wave does not form the striation. The slightly larger crack propagation rate in the sinusoidal stress wave only on the compression side of square wave than that in the simple square stress wave equivalent to this might be due to the effect that the superimposed sinusoidal stress in pulsating compression develops the substructure at the crack tip. The striations formed under the sinusoidal stress superimposed both on tension and compression sides of square wave are composed of those corresponding to the pulsating tensile stress and the clear grooves corresponding to the pulsating compressive stress.
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  • Kenkichi HAYASHI, Yousei MAKINO
    1972 Volume 21 Issue 231 Pages 1157-1162
    Published: December 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The stress-strain relation at the vicinity of fatigue crack tip is one of the most demanded points in the study of fatigue crack propagation. Recently, the oscillating crystal X-ray microbeam diffraction technique which enables to measure the stress in such a minute domain as the vicinity of fatigue crack tip has been devised by K. Honda and T. Konaga.
    In the present study, the stress condition at the crack tip was studied by this technique. An alternating tension-compression load was applied to the annealed and recovered plate specimens of 0.05%C low carbon steel with notches at the both sides. The stresses at the vicinity of fatigue crack tip in the area of 180μ in diameter were measured under several loading conditions. The results obtained are summarized as follows;
    (1) The stress concentration factor, which is the ratio of the stress at the maximum load or the minimum load to the applied nominal stress, is approximately the same for both annealed and recovered specimens: it's value is nearly unit for compression load, nearly 2.5 for tension load in the case of annealed specimens and nearly 2.2 in the case of recovered specimens.
    (2) The mean value of cyclic stress at the vicinity of fatigue crack tip is an almost zero as a consequence of compressive residual stress when the applied mean stress is zero.
    (3) No remarkable distribution of residual stress is measured in the vicinity of crack tip.
    (4) The result mentioned in (1) suggests that the cyclic stress-strain relation at the tip of crack having a relatively low propagation rate is similar to the relation obtainable after the saturation of cyclic hardening or softening.
    (5) The residual stress at the crack tip tends to change in reverse direction to the applied mean stress so that the cyclic stress at crack tip is almost in a fully reversed stress condition almost irrespective of the mean applied stress.
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  • K. Kamachi
    1972 Volume 21 Issue 231 Pages 1163-1171
    Published: November 15, 1972
    Released: June 03, 2009
    JOURNALS FREE ACCESS
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