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29 巻, 325 号
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疲労特性を中心として金尾 正雄1980 年 29 巻 325 号 p. 957-968
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーPDF形式でダウンロード (1886K) -
田中 道七, 服部 修次1980 年 29 巻 325 号 p. 969-975
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーBehaviors of the hysteresis loop of low carbon steels in the fatigue process have been studied systematically by the authors using interaction models between dislocations and solute carbon atoms.
In the present study the effect of oversaturated interstitial atoms such as carbon and nitrogen on the hysteresis behavior during fatigue process was investigated especially in the cyclic hardening stage. The samples of 0.1% carbon Al-killed steel with different interstitial solute contents were tested under a constant axial stress amplitude with zero mean stress at a frequency of 30Hz. The experimental results showed that the decrease of the plastic strain amplitude after reaching the peak value was accelarated with the increase of interstitial solute contents. By the analysis based on the Cottrell's pinning theory, it was demonstrated that the cyclic hardening behavior as described above was mainly caused by the migration of interstitial atoms into the highly strained field of dislocation from surrounding matrix under cyclic load.抄録全体を表示PDF形式でダウンロード (1060K) -
電顕連続観察による検討高尾 健一, 西谷 弘信, 坂口 英信1980 年 29 巻 325 号 p. 976-981
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーRotating bending fatigue tests have been carried out on smooth specimens of an annealed aluminum-killed steel, an annealed rimmed steel and a low temperature quenched rimmed steel. Successive observations on the surfaces of the specimens and fractographic observations have been made by SEM with special attention being given to the starting points of fatigue cracking, in order to investigate the effect of strain aging on fatigue crack initiation process.
The main results obtained are as follows;
(1) A low temperature quenched rimmed steel, which has the highest strain aging ability, had a higher resistance to initiation and propagation of fatigue cracks and had an about 50% higher fatigue limit comparing with other two steels. However, no qualitative difference was recognized among the steels in the process of initiation of a crack when the crack size was about the size of a grain. This process is such that the region, which is to become a crack in the future, is damaged as a whole with little increase in size at the specimen surface and gradually turns into a crack.
Moreover, this process is essentially different from the later crack propagation process. Fractography of the initial stage of fatigue cracking also seems to support the above statement.
(2) Non-propagating microcracks were observed on the unbroken specimen surface subjected to more than 107 cycles at the respective fatigue limit. Although some of them remained within the grain, the largest one propagated into neighboring grains and then stopped propagating.抄録全体を表示PDF形式でダウンロード (3925K) -
Al合金, S15CおよびS50Cの回転曲げ高尾 健一, 西谷 弘信, 坂口 英信1980 年 29 巻 325 号 p. 982-987
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーRotating bending fatigue tests were carried out on notched specimens of an age-hardened Al-alloy, an annealed 0.17% steel and a heat-treated 0.54%C steel. Microscopic observations on the surfaces of notch roots were made successively by using the plastic replica method with special attention being given to the starting points of fatigue cracking. The relationship between the crack initiation process and the notch sensitivity in fatigue was investigated.
The main results obtained are as follows;
(1) Initiation process of one grain size crack was different from one metal to another. In an Al-alloy, the crack initiated at a much smaller region than the grain size and then propagated toward the grain boundary. This process corresponds to the so-called stage I crack propagation process. In the two steels the region to become a crack in the future was damaged as a whole, with almost no increase in the size on the specimen surface, and gradually turned into a crack. This process in each steel is essentially different from the later crack propagation process.
(2) An Al-alloy and a heat-treated steel were more notch sensitive in fatigue than an annealed steel. This is ascribed to the difference in thickness of the surface layer affecting the crack initiation among the metals used.抄録全体を表示PDF形式でダウンロード (3111K) -
村上 敬宜, 河野 博之, 遠藤 達雄1980 年 29 巻 325 号 p. 988-992
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーThe effect of a small artificial defect (i. e., a drilled hole, the diameter ranging from 40 to 200μm) on the fatigue strength of high strength alloy (WT80C) was investigated. The experimental results were discussed in comparison with those on other marterials (i. e. carbon steels).
The conclusions are summarized as follows:
(1) Like carbon steels, the effect of hole size on the fatigue strength of WT80C changed according to the maximum length l0 of non-propagating cracks which are observed at the fatigue limit of the unnotched specimen. Thus, the length l0 is the measure to evaluate quantitatively the notch effect of the defects. The values of l0 is∼100μm for annealed low carbon steel(S10C), ∼50μm for annealed medium carbon steel (S45C), ∼60μm for WT80C, ∼20μm for quenched and tempered S45C and ∼20μm for quenched S45C. The notch sensitivity of these materials increases in the written order. If the hole diameter of the holed specimen of quenched or quenched and tempered S45C is greater than l0, the fatigue strength decreases remarkably. Accordingly, the fatigue strength may be improved by controlling the defect size smaller than l0. However, even if the control of defect size is accomplished in WT80C, such a control alone is insufficient for the improvement of the fatigue strength, because the decrease of fatigue strength of the holed specimen is due not only to the notch effect but also to the cyclic softening.
(2) In the fatigue tests of geometrically similar but different size specimens (D=6, 12mm) with a small artificial hole (d=40∼200mm), the fatigue strength of the large specimens was a little lower. The size effect is considered due to (1) the difference in specimen diameter and (2) the difference in hole diameter, but the latter is more effective.抄録全体を表示PDF形式でダウンロード (1322K) -
眞武 友一, 今井 康文1980 年 29 巻 325 号 p. 993-997
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーIn the previous works, the criterion for the fatigue strength of unnotched specimens under combined stress was proposed and treated separately from that of notched specimens, but it has been found that the former criterion is a special case of the latter. It has been also found that as long as the torsional fatigue strength is determined carefully, the same criterion can be applied to the results of both fracture and nonfracture tests, although the criterion was originally proposed for the case where the fatigue strength is defined to be the stress below which no 0.1mm slip-band cracks initiate. Slip-band cracks were found fractographically to correspond to the so-called stage I cracks. From several experimental results appeared in the literature, the criterion has been confirmed to be also applicable generally to the rolled steel products in spite of the fact that rolled metals possess inevitably the anisotropy due to rolling. Finally, it was concluded that the proposed criterion alone can be used successfully to estimate the fatigue strength under the combined stress state of bending and torsion, within experimental errors, for both ductile and brittle materials instead of using different empirical formulae which had been adopted previously.抄録全体を表示PDF形式でダウンロード (2277K) -
菊川 真, 城野 政弘, 村田 洋一1980 年 29 巻 325 号 p. 998-1004
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーIt is well known that the mean stress as well as the stress amplitude are often varied under the service loading conditions and the fatigue damage can be accumulated by the stress even below the fatigue limit.
In this study, therefore, the effects of the mean stress on the behavior of cyclic plastic strain and on the fatigue life were investigated in both regions above and below the fatigue limit with the smooth specimens of a 0.38% carbon steel. Cumulative damage below the fatigue limit was examined by the repeated two-step tests composed of a single cycle of high level stress range-pair and a large number of low level stress range-pair, the mean stress of which was changed variously.
Two effects of the mean stress were found; The one was the effect to cause one directional deformation which resulted in the increase of the plastic strain range-pair corresponding to the high level stress. The other was the damaging or strengthening effect, i. e. the tensile mean stress made the fatigue life shorter and the compressive one longer. This effect was found to be relatively marked at the low level of the mean stress. Moreover, it was noticed that, if the mean stress cyclically reversed, even the compressive mean stress might have the same damaging effect as the tensile one.抄録全体を表示PDF形式でダウンロード (1068K) -
北川 茂1980 年 29 巻 325 号 p. 1005-1010
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーFatigue tests with two levels of cyclic stresses were conducted on mild steels (aluminum killed steels). The higher stress levels were 1.20 and 1.42 times of the endurance limit and the lower ones were 0.80, 0.57 and 0.38 times. Two cycles of higher stresses and various cycles of lower ones in a loading period were repeatingly applied. Fatigue lives in terms of number of loading cycles, Zf, lineally decreased by log nL, where nL is the total number of lower stress cycles in a loading period. When the frequency of higher stress cycles was low, 1Hz in the present study, the lives to failure also decreased compared with the ordinary frequency. It was concluded that the modified Miner's method was unable to be applied to these experimental results, because the values estimated by that method varied widely with nL. Emphasis was placed on the need for a modified estimation method in which the rate of fatigue damage by lower stess cycles is not constant but decreases as increase of the lower cycles in a loading period.抄録全体を表示PDF形式でダウンロード (1410K) -
村上 理一, 秋園 幸一1980 年 29 巻 325 号 p. 1011-1017
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーThe influence of prior austenite grain size and stress ratio on near threshold fatigue crack growth behavior has been studied by means of fracture mechanics and fractography on quenched and tempered Ni-Cr alloy steel where the prior austenite grain size was varied from 21 to 210μm. The results obtained were as follows.
(1) For the mid-range of crack growth rates above 5×10-6mm/cycle, the dominant fracture appearance was striation formation regardless of prior austenite grain size and stress ratio. On the other hand, for the near threshold crack growth rate below 5×10-6mm/cycle, the striation-like appearance was mixed with microstructure sensitive fracture appearance such as intergranular facet.
(2) The crack growth rate associated with striation formation was insensitive to the change in prior austenite grain size for all stress ratio, and increased slightly as the stress ratio increased from 0.05 to 0.3. On the other hand, no marked difference in crack growth rate appeared for stress ratio of 0.3 and 0.6. The effect of stress ratio was explained by the crack closure phenomenon.
(3) The near threshold crack growth rate at low stress ratio was sensitive to the change in prior austenite grain size, while that in high stress ratio was little sensitive. The greatest sensitivity to stress ratio appeared at near threshold crack growth rate regardless of prior austenite grain size.
(4) The consequence of coarsening of prior austenite grain size was to reduce ΔKth in all stress ratio. The ΔKth of both prior austenite grain size decreased with increasing the stress ratio. Also, the grain size dependence was observed to decrease with increasing stress ratio.抄録全体を表示PDF形式でダウンロード (2138K) -
橘内 良雄1980 年 29 巻 325 号 p. 1018-1023
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーThe fatigue crack growth behavior of four kinds of carbon steels (SB42, S35C, S55C and SK5) which have different microstructures formed by heat treatments was examined on the centernotched sheet specimens. Particular attention was given to the influence of microstructure on the fatigue crack growth near the threshold stress intensity ΔKth and at the high ΔK region.
The values of ΔKth in the specimens with pearlite structure were higher than those with beinite and martensite structures. In the pearlite structure, the growth rate near the threshold region may not be always influenced by the cementite, because the fatigue crack tends to propagate in the ferrite or to grow along the ferrite-cementite boundary. ΔKth and the crack growth resistance near the threshold region were found to be inversely proportional to the strength of the steels. The values of ΔKth were correlated with the yield strength better than the ultimate tensile strength.
The fatigue crack growth in the pearlite and beinite structures at the value of ΔK above 50kgmm-3/2 was governed by striation formation. Hence, the growth rates in both structures were the same regardless of their differences in microstructure and mechanical properties. In the martensite structure, the crack growth at the high ΔK region was greatly influenced by the microstructure, and the growth rate markedly increased in comparison with that in the pearlite or beinite structure. This result was attributed to the occurrence of static fracture modes (intergranular, microvoid coalescence) during striation growth.抄録全体を表示PDF形式でダウンロード (2564K) -
新井 淳一, 井野 幸雄, 岩城 秀夫1980 年 29 巻 325 号 p. 1024-1028
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーThe fatigue crack growth in very large CCT specimens of Al alloy (A 5083-O) was measured in different environments, that is, in nitrogen gas, in laboratory air and in 3% NaCl solution. The crack growth rate was highest in 3% NaCl solution and lowest in nitrogen gas, and the relation between the crack growth rate and the stress intensity factor range was typical of corrosion fatigue.
From the observation of the environmental effect on the fatigue crack growth rate of the same material, it is considered that the reversed slip which contributes the recovery at the crack tip during unloading procedure is strongly dependent on testing environments; the reversed slip is hardly blocked in innert nitrogen gas, but the almost all of reversed slip is blocked in aggressive 3% NaCl solution.
From the above consideration, the relation between the crack growth rate, da/dN, and the stress intensity factor range, ΔK, with two material coefficients, C1, and C2, and one environmental coefficient, CR, having respective constant dimensions, can be written as
da/dN=C2ΔK2-CR(C2ΔK2+C1ΔK4)
=AΔK2+BΔK4, where A=C2(1-CR), B=C1×CR
It is expected that this equation is not only applicable to the experimental results of Al alloy A 5083-O, but also to other materials.抄録全体を表示PDF形式でダウンロード (1354K) -
本田 和男, 鳥居 太始之, 三宅 雄二郎, 坂本 達治1980 年 29 巻 325 号 p. 1029-1034
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーThe laminated inhomogeneity and the residual stress are important factors controlling the fatigue strength of the surface hardened metals.
In this report, the fatigue crack propagation of the sheet specimens which have tensile or compressive uniaxial residual stress but no laminated inhomogeneity was discussed. The main results obtained are as follows;
The fatigue crack propagation rate increased in the region of tensile residual stress but decreased in the region of compressive residual stress at the condition of the stage II b of the fatigue crack propagation mechanism, where the striations are predominant on the fractured surface. It seems that the effect of the initial compressive residual stress on the fatigue crack propagation does not always follow the above result, and it is closely related to the fatigue crack propagation mechanism.抄録全体を表示PDF形式でダウンロード (2145K) -
大路 清嗣, 小倉 敬二, 原田 昭治, 佐野 正美1980 年 29 巻 325 号 p. 1035-1041
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーThe fatigue crack growth and crack closure behaviors of an explosively-bonded and a roll-bonded brass-steel clad plate were examined. An emphasis was put on the comparison of the behaviors between the two kinds of clad plates manufactured through the different bonding processes.
It was found that poor correlations were observed between the crack growth rate and the stress intensity range both for the explosively-bonded and the roll-bonded clad plates. The crack growth and closure behaviors were affected by the residual stresses which had been introduced in the production processes both for the two clad plates, although the reduced influence was observed in the roll-bonded clad plate. A good correlation was found between the crack growth rate and the effective stress intensity range, ΔKeff, which was calculated on the basis of the crack closure behavior. However, the adjustment was not fully successful for the crack growth behavior very near the material interface. Further studies are needed for more detail of the fatigue crack growth behavior of clad materials.抄録全体を表示PDF形式でダウンロード (910K) -
大塚 昭夫, 森 要, 大島 崇文, 津山 青史1980 年 29 巻 325 号 p. 1042-1048
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーThe behavior of fatigue crack growth under mode II loading has been investigated on steels (JIS SPCC and SM 50B) and aluminum alloys (7075-T6 and 2017-T4). Tests were made by a specially designed apparatus under various combinations of ΔKII and KIS, where ΔKII is the range of the repeated mode II loading and KIS is the statically applied KI. Under mode II loading, two modes of fatigue crack growth, mode II growth and tensile mode growth, were usually observed, though in some cases only one was observed. Here, mode II growth and tensile mode growth mean the fatigue crack growth in the plane of precrack and that in the plane which makes about 60°to the precrack, respectively. In the latter, the plane of crack growth may be taken as the plane of the maximum tensile stress.
Aluminum alloys showed continuous mode II growth in the region of ΔKII larger than ΔKII-threshold for mode II growth. In the case of mild steel (SPCC), however, tensile mode growth occurred in the region of ΔKII larger than ΔKII-threshold for tensile mode growth, and mode II growth was observed only in the narrow region of ΔKII smaller than the above ΔKII-threshold for tensile mode growth. In weldable structural steel (SM 50B) only tensile mode growth was observed under mode II loading. The mode II growth rate in aluminum alloys was much larger than that of mode I growth, while the mode II growth rate was very small in mild steel specimens.抄録全体を表示PDF形式でダウンロード (2345K) -
小林 英男, 渋谷 栄一, 中沢 一1980 年 29 巻 325 号 p. 1049-1055
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーFatigue crack growth rates and striation spacings have been examined for a high-strength material, Ti-6Al-4V, and a low-strength material, 304 steel, ranging from the linear elastic fracture mechanics (LEFM) regime to the elastic-plastic fracture mechanics (EPFM) regime. The limitation of LEFM fatigue crack growth law was discussed. Departure from the LEFM regime to the EPFM regime was found to result in acceleration of crack growth rate as well as retardation of resharpening of crack tip. The results suggest that the EPFM approach to fatigue crack growth may not be extended by the use of the J-integral concept, so that unloading effects are not included.抄録全体を表示PDF形式でダウンロード (1336K) -
10. 鋳造品の破壊喜多 清1980 年 29 巻 325 号 p. 1056-1061
発行日: 1980/10/15
公開日: 2009/06/03
ジャーナル フリーPDF形式でダウンロード (4565K)
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