Journal of the Society of Materials Science, Japan
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
Volume 42 , Issue 481
Showing 1-16 articles out of 16 articles from the selected issue
  • Mikio SUGANO, Tadaaki SATAKE
    1993 Volume 42 Issue 481 Pages 1146-1152
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Large grain specimens (0.3mm thick) with average grain size of 10mm in diameter were fatigued under alternate plane bending to clarify the micromechanism of fatigue crack growth in high purity titanium (KS40S). For a crystallographic study of fatigue fracture surface, the stereomicrophotogrammetry technique was incorporated with the X-ray microbeam Laue technique, which was used to determine the orientation of specimen surface. The fatigue fracture surfaces comprised of (0001), {1010}, {1011}, {1012}, {1121} and {1120} planes. The (0001) cleavage facet appeared in grains with specimen axes in the angular domain of φ<65°, φ being the angle between a specimen axis and a basal plane normal. Twinning played an important role on fatigue crack growth behavior. The formation of a microcrack on {1010} and {1120} planes was discussed in association with a sessile dislocation a/3 ‹1100› resulting from the following reaction of a/3 ‹1120› dislocations on the {1010} primary slip planes:
    a/3[2110]+a/3[1120]→a/3[1100]+2/9a[1120]+a/9[2110]
    Crystallographic aspects of fatigue deformation were heterogeneous in the process zone wake of a crack in one grain.
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  • Kenji HATANAKA, Junji OHGI, Fumio UENO
    1993 Volume 42 Issue 481 Pages 1153-1159
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Three kinds of Ti-6Al-4V alloy, annealed at 750°C, and solution-treated and then aged at 520°C and 660°C, which are denoted as the materials 7N, 5T and 6T, respectively, were low-cycle fatigued under an axial strain-controlled condition.
    Cyclic stress-strain response was most excellent in the material 5T, and the materials 6T and 7N followed in its superiority in this order. The logΔεp vs. logNf plot crooked downwards in the low plastic strain range for all the three materials. The material 5T exhibited slightly longer life than the other two materials of which life curves almost coincided with each other.
    The crack growth rate da/dN plotted against cyclic J integral range ΔJ was approximately expressed by a linear line on the double logarithmic scales. The da/dN vs. ΔJ plot for the surface crack on the smooth specimen, was situated on the lower crack growth rate side than that for the long through-thickness crack. This might be due to the difference in the growth processes of the two cracks; the surface crack grows accompanying coalescence and branching, while the through-thickness crack extends relatively monotonously without any coalescence.
    The resistance against the extension of surface crack was more superior in the materials 5T and 6T than in the material 7N. The materials 5T and 6T possess almost the same crack growth property.
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  • Toshiyuki TORIYAMA, Yukitaka MURAKAMI
    1993 Volume 42 Issue 481 Pages 1160-1166
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The fatigue limit of metals containing various small defects can be evaluated by the √area parameter model. The model is constructed with two parameters: a geometrical parameter (√area) and Vickers hardness Hv of matrix.
    In order to demonstrate the validity of the √area parameter model, it is experimentally shown that the fatigue limits of hard steel specimens (Hv=510) having an initial crack, a two-hole defect connected with fatigue crack and one hole defect with the same value of √area are approximately identical in spite of their big difference in stress concentration factor.
    In the next step, the method of evaluating the mutual interaction effect of small defects is proposed on the basis of the fatigue test results and three-dimensional numerical stress analysis of crack interaction.
    Finally, the method is applied to evaluate the mutual interaction effect of spheroidal graphite in a nodular cast iron. The lower bound of scatter in fatigue limit (σwl) is obtained by using the fatigue limit prediction equation with the expected maximum size of graphite (√areamax). The expected value of √areamax in a large number of specimens can be estimated by statistics of extreme values. In order to predict an accurate σwl, the value of √areamax must be estimated by considering the mutual interaction effect of spheroidal graphite. Otherwise, the prediction becomes unconservative.
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  • Akihiko OHTA, Yoshio MAEDA, Naoyuki SUZUKI
    1993 Volume 42 Issue 481 Pages 1167-1171
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The basic fatigue strength of welded joints, which corresponds to that of the real large scale welded structures containing high tensile residual stresses of yield strength magnitude, was investigated by the maximum stress constant test. The plate thickness effect was revealed to be an imaginary phenomenon occuring from the small residual stresses induced by a variation in maximum stress with the applied stress. The Miner's law was applicable for the basic fatigue strength. The basic fatigue strength increased with a decrease in yield strength.
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  • Yasuo OCHI, Akira ISHII, Shigemi SASAKI, Ichiro OHDACHI
    1993 Volume 42 Issue 481 Pages 1172-1178
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    In this study, the low cycle fatigue deformation properties and the surface crack propagation behaviour of α/β-rolled plates of Ti-6Al-4V alloy with conventionally annealed equiaxial microstructure were investigated under the constant strain amplitude and the single over-straining conditions. Two types of the single over-straining were performed; that is, tension only (T waveform) and tension-compression (T-C waveform) over-straining, and the effects of the overstraining ratio λ on the cyclic deformation and the crack acceleration or the crack retardation behavior were also studied from the stand-point of the changes in crack opening displacement Φ and tensile peak stress σpt. As the results, in the T waveform test in the range of λ≥1.62, the crack ratardation occurred when compared with the crack propagation of the constant amplitude test, and the retardation effect increased with the ratio λ. On the other hand, in the T-C waveform test, the crack propagation curve after over-straining was almost coincident with the curve of the constant amplitude test. It became clear that the retardation behaviour of surface crack propagation after the over-straing of the T waveform resulted from both of the changes in Φ and σpt after the over-straining. The relation between the crack propagation rate da/dN and the J integral range ΔJ under the over-straining conditions was in good agreement with the da/dN and ΔJ relation of the constant strain amplitude test.
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  • Shin-ichi NISHIDA, Chikayuki URASHIMA, Noriyuki TAKANO
    1993 Volume 42 Issue 481 Pages 1179-1185
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The fatigue strength in a high cycle region has been evaluated in this test using the representative titanium alloy, Ti-6Al-4V, under the rotating bending fatigue and the fractographic consideration is adopted to analyze the testing results. In addition, the fatigue crack initiation process has been investigated with the successive observation in the scanning electron microscope (SEM) equipment under out-of-plain bending fatigue.
    The main results obtained in this test are as follows:
    (1) Rotating bending fatigue tests in air; The fracture was often observed even after 107 cycles. When the specimen was broken by less repetitions than 1×106 cycles, the fracture mostly initiated from the outer surface with facet-like pattern at the origin. On the other hand, in the case of higher repetitions than 2×106 cycles, the fracture initiated from the sub-surface, where there were neither observed inclusions nor the facet-like fracture pattern.
    (2) Out-of-plain bending fatigue test in SEM; The ratio of crack initiation life of one grain length to total fatigue life is between 3 to 9% and the fatigue cracks are initiated by 90% from α grains and by the residual ratio from α/β boundaries. In addition, the slip bands are at first generated in α grains under the cyclic stress, then there appear cross-slip bands and finally those portions become micro cracks like cleavage-cracks.
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  • Takeshi OGAWA, Yasumasa HAYASHI, Keiro TOKAJI, Motohisa HIROSE
    1993 Volume 42 Issue 481 Pages 1186-1192
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Fatigue crack growth has been investigated in Ti-6Al-4V alloy at ambient and elevated temperatures, i.e. 200, 400 and 500°C. Special attentions were paid to the nucleation and the morphology of secondary cracks. The roughness of fracture surface was evaluated quantitatively using three dimensional reconstruction of fracture surface based on stereo matching technique. The results indicated that the crack growth rates at the elevated temperatures became lower than that at room temperature with increasing stress intensity factor range, ΔK. This behavior was attributed to the nucleation of secondary cracks, which led to the increased roughness of fracture surface and the reduction of crack driving force. The nucleation of the secondary cracks was observed more markedly with increasing test temperature. On the other hand, the crack growth rate at 500°C increased compared to that at room temperature in the region of ΔK≤20MPa√m. This enhanced crack growth may be due to the reduced elastic modulus with increasing temperature. Therefore, the crack growth characteristics at elevated temperatures were controlled by the competing effects between the nucleation of secondary cracks and the reduction of elastic modulus.
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  • Kazutaka FUJITA, Ryoichi KOTERAZAWA
    1993 Volume 42 Issue 481 Pages 1193-1199
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Microscopic and macroscopic surface fatigue crack propagation studies were carried out under periodic overstressing with Ti-6Al-4V alloy. Relatively small acceleration of crack propagation (less than 10 times) occurred when the crack length was of macroscopic scale more than 200μm. The fracture surface morphology showed that the crack propagated in zigzag manner similarly to the cases of macroscopic cracks with large acceleration in carbon steels and aluminum alloys reported previously. The acceleration was compared with that of through-thickness cracks as well as macroscopic and microscopic surface cracks in steels and aluminum alloys reported previously. A relatively good correlation was obtained in terms of the tensile strength-Young's modulus ratio σB/E and the acceleration became larger as σB/E became smaller. The surface crack growth rate in Ti-6Al-4V alloy, steels and aluminum alloy under constant amplitude loading agreed well with each other and with the through-thickness crack growth rate in different materials published in literature in the ΔKeff/E diagram.
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  • Chobin MAKABE, Hisashi SAKIHAMA, Hideo KANESHIRO, Shin-ichi NISHIDA
    1993 Volume 42 Issue 481 Pages 1200-1206
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Fatigue crack propagation law in the following two cases was investigated under the negative stress ratio R(=σminmax) condition. The one is the crack propagation in the field of welding-residual stress, and the other is that after the overloading. In the former case, the crack propagation rate da/dN depended on the stress ratio R. Due to the tensile residual stress, the crack propagation rate increased as the stress ratio decreased in the range of 0≤R≤-2. In the latter case, the crack propagation rate da/dN after the overloading was higher at first and then became lower than that of the constant stress amplitude. In the present experimental cases, the crack propagation rate was affected by the residual stress and the overloading. However, the crack propagation behavior had a good correlation with the crack closure behavior. Therefore, in the present cases, the crack propagation law was reasonably evaluated with the effective stress intensity factor range ΔKeff.
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  • Haeng-Nam KO
    1993 Volume 42 Issue 481 Pages 1207-1211
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    A rotary bending test was carried out on sintered Al2O3 at room temperature to study the effect of grain size on the fatigue behavior. The plain specimens with three kinds of grain size were prepared by controlling the sintering temperature. The fatigue test was performed within the range of 104 to 109 stress-cycles using an Ono's rotary bending fatigue testing machine (3420rpm). The test results were compared with the static bending strength measured by the non-rotating fatigue machine. The fractured surfaces after the two tests were also examined by SEM. It became clear that the fatigue strength of the finer grain material was higher than that of the larger grain one. The life of each material increased remarkably as the stress amplitude decreased, and the knee seemed to exist at a cyclic number more than 108. The ratio of the assumed fatigue limit to the static bending strength decreased as the grain size increased. Each S-N curve, including the static strength, could be represented by a straight line up to about 108 stress-cycles and could be expressed by the formula, σnN=constant. The exponent n for the finer grain material was higher than that for the larger grain one. It was considered that the fatigue crack growth behavior was different due to the grain size. Mirrors were not revealed clearly on the fractured surfaces and microscopic observations on the fractured surface of the finer grain material were similar to those of the larger grain one. The fracture features after both fatigue and static tests could not be distinguished, and the fatigue fractured morphology could not be found.
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  • Kazunari FUJIYAMA, Itaru MURAKAMI, Yomei YOSHIOKA, Nagatoshi OKABE
    1993 Volume 42 Issue 481 Pages 1212-1217
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Actual components used under severe conditions often suffer from the complicated material damage affected by multiple influencing factors. “Multifactor damage simulation analysis” was proposed to solve such complex damage problems. In this paper, a discrete cluster model of material and the associated damage state matrix [DN] are introduced to solve a high temperature low cycle fatigue damage problem of Co-base superalloy FSX414.
    The damage state at Nth cycle is determined by the damage state at (N-1)th cycle expressed as follows.
    [DN]=[Λ][DN-1]
    As this equation is similar to the discrete dynamical system and operator matrix [Λ] is non-linear, the chaotic behavior, of damage evolution may occur. Instead of solving the matrix equation directly, simulation was conducted using 2-dimensional model of 2500 clusters at 5×5mm area for the dendrite and grain boundary structure of FSX414. Damage of crack initiation and growth was calculated deterministically and the randomness was only introduced at the initial condition of the material.
    High temperature low cycle fatigue test was conducted to follow up the damage process at the total strain range of 1% and at the temperature of 1123K. Surface crack morphologies were investigated by the replication technique at 20% and 40% of the failure life.
    The trends of crack numbers, maximum crack length and mean crack length against fatigue cycles were obtained by the simulation. These trends were complicated like chaos due to the interaction of cracks and material structure. The crack length distribution by the simulations agreed well with the experimental results and better agreement was obtained by using intermittent inspection informations. These results suggested that the method would be effective for damage prediction of actual components based on inspection informations.
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  • Hitoshi ISHII, Ryuichiro EBARA, Yoshikazu YAMADA, Kuninori MINAKAWA
    1993 Volume 42 Issue 481 Pages 1218-1223
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    In order to investigate the fatigue strength of Ti-6Al-4V alloy at a large number of cycles, ultrasonic fatigue tests were performed. Three heat treatment, i.e. mill anneal (MA), duplex anneal (DA), and solution treatment and aging (STA), were applied to the specimens. Although the fatigue strength obtained from this method was approximately 15 percent higher than that obtained from the conventional fatigue test, the general trend of these two S-N diagrams was the same. Usefulness of the ultrasonic fatigue test as an acceleration method to determine the S-N diagram was confirmed on this alloy and the fatigue strength of the above mentioned heat treated specimens at a large number of cycles up to 2×109 cycles was determined. The noteworthy result was that there seemed to exist a fatigue limit in this alloy from the data up to 108 cycles, but the fatigue strength became decreased at further number of cycles. This result was obtainable only by performing the fatigue test in a longer period like up to 109 cycles. Similarly to the tensile strength, the STA specimen showed the highest fatigue strength and the MA and the DA specimens followed. Judging from their FCP properties and fractographies, the difference in fatigue strength among these specimens with various microstructures was caused in the stages of crack nucleation and/or microcrack growth.
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  • Chobin MAKABE, Shin-ichi NISHIDA, Hideo KANESHIRO, Chikayuki URASHIMA, ...
    1993 Volume 42 Issue 481 Pages 1224-1230
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Usually, the fracture accident of a machine equipment originates in the notched section. However, it is very difficult to monitor the fatigue crack initiation for all parts of the machine equipment. In this study, a method of detecting and monitoring fatigue crack initiation in the notched section of running machine equipment is proposed. Fatigue crack initiation can easily be detected by the observation and analysis of the waveform of the strain function composed of the strains in the vicinity of the notch, because the waveform of the strain changes its shape after the crack initiation. In the present study, the crack initiation under the constant or fluctuating stress amplitude was monitored using the specimen with a small hole. It was found that the crack initiation can be detected when the crack length reaches about 1mm.
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  • Akira ISHII, Vakhtang LACHKHIA, Yasuo OCHI, Tsutomu AKITOMO
    1993 Volume 42 Issue 481 Pages 1231-1237
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    A radiated projection method (RPM) has been applied to the detection of small surface fatigue cracks which initiate during a low cycle push-pull fatigue test. RPM is one object recognition algorithm which detects only specified objects by representing their features such as size, shape, and color or shade into the radiated frames geometrically. Observed images involve so many regions similar to the local part of the crack that it is difficult to detect small cracks by the simple thresholding method based on a certain intensity level at the crack, or by the edge detection method based on the intensity level change at the crack edge. The result is successful in detecting a small crack initiated at the edge of a small hole. Also the crack tip position is detected by RPM in order to measure its precise length. The result is also successful in detecting the crack tip position at the same place by visual inspection. Their algorithms are presented and the effective usage of RPM is discussed.
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  • Yoshisada MUROTSU, Takehito FUKUDA, Hiroo OKADA
    1993 Volume 42 Issue 481 Pages 1238-1244
    Published: October 15, 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
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  • 1993 Volume 42 Issue 481 Pages 1244
    Published: 1993
    Released: June 03, 2009
    JOURNALS FREE ACCESS
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