材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
29 巻 , 321 号
選択された号の論文の19件中1~19を表示しています
  • 林 英雄, 小林 政治郎, 植村 幸生
    1980 年 29 巻 321 号 p. 528-532
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    The effect of notching method on the Charpy impact values of rigid PVC plates was studied and fractographic consideration of the reason why such effect had taken place was given.
    The results obtained are summarized as follows:
    (1) Although no geometric difference in the notch shape and the radius of notch root between the test specimens made by a shaper and those by a milling machine was found, the Charpy impact value of the former was about twice of that of the latter.
    (2) The fracture of the test specimen made by the shaper originated at the inside a little below the notch root as reported previously, while the fracture of the test specimen made by the milling machine originated at the notch root or just inside below the notch root.
    (3) In the test specimen made by the milling machine, very fine cracks were produced by notching at the deformed layer or at the boundary between the matrix and the deformed layer. It is considered that these very fine cracks act as fracture origins and make the Charpy impact values lower.
  • 中村 春夫, 小林 英男, 中沢 一
    1980 年 29 巻 321 号 p. 533-537
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    On the fracture surface of a KIc specimen, there exists a critical stretched zone between the fatigue pre-crack and overload fracture regions. This width, SZWc, has been correlated with the critical values of various fracture mechanics parameters. On the other hand, a sub-critical stretched zone appears as the loading progresses. In this paper, the data of sub-critical stretched zone width, SZW, obtained by many researchers were summarized and the relation between SZW, as a measure of crack tip plastic blunting, and the J-integral was investigated.
    The followings are the summary of the results obtained.
    (1) The relation between SZW and Jflow showed an apparent dependence on flow stress, σflow: there was a tendency for SZW to become smaller for the same value of Jflow as σflow became smaller. S0, the following equation did not stand,
    SZW=C1J/σflow (C1: const.).
    (2) The change of Young's modulus, E, had little influence on the relation between SZW and J/E, and no influence of test temperature was observed. SZW was given by the following expression,
    SZW=89J/E
    (3) The above mentioned relation between SZW and J was similar to the one between the striation spacing, S, and J. Under a small scale yielding condition, S was given by the following expression, in the case that the stress ratio is 0,
    S=9.4J/E
    That is to say, the width of the stretched zone as well as that of a striation formed by the same micromechanism of glide plane decohesion, was characterized by the very same fracture mechanics parameters.
    (4) If the above-mentioned relation between SZW and J is established on other materials, there is a possibility of evaluating JIc simply by measuring SZWc with a single specimen by failured overload.
  • 大井 利継, 長尾 幸男
    1980 年 29 巻 321 号 p. 538-543
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    This paper presents some failure examples of actual machine components caused by corrosion fatigue, stress corrosion and hydrogen embrittlement, and describes their fractographic features.
    Rotary machine components and chemical plant components were taken as examples of corrosion fatigue cracking, and stress corrosion or hydrogen embrittlement cracking, respectively.
    Microfractographic observations of fractured surfaces were carried out by a scanning electron microscope.
  • 砂田 久吉
    1980 年 29 巻 321 号 p. 544-549
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    A study has been made on the tensile properties of 1.56% plain carbon steel without special elements at room temperature. The specimens were subjected to various working processes and heat treatments. Tension tests were carried out by changing cross-head speeds and the fracture surfaces were examind by means of scanning electron microscopy.
    The main results obtained are as follows.
    (1) The first type of structure was obtained either by hot forging or by hot rolling at a temperature between 1373K and 973K. This structure was composed of needle-like primary cementite and pearlite. The size of grain and carbide became small with increasing working ratio. The strength and hardness for forged steel increased with decreasing grain size. The strength of rolled steel was almost the same as that of forged steel when the grain size was the same, but the hardness of rolled steel was low.
    (2) The main crack initiated at primary cementite for both steels and propagated farther into grain or pearlite-colony with decreasing strain rate.
    (3) The second type of structure for hot rolled steel was obtained by tempering after quenching from 1023 and 1123K. The fracture surface of the specimen quenched tempered at 673K showed quasi-cleavage, while that of the tempered at 873K showed both quasi-cleavages and dimples. The surface of the annealed at 1023K showed dimples only. The dimple size and amount in the fracture surface increased with heat temperature. They seemed to be associated with carbide particles.
  • 大路 清嗣, 小倉 敬二, 大森 和郎, 野水 寿夫
    1980 年 29 巻 321 号 p. 550-555
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Observations of ductile fracture processes were made on the high strength materials of SNCM 8, HT 80, 2024-T4 aluminum alloy and a sintered steel. A special interest was put on the initiation of microvoids. Ductility of these materials was widely varied by the application of hydrostatic pressure up to 10000kg/cm2 and by the use of artificially necked (notched) specimens. It was found that the initiation of microvoids did not take place until very late in the fracture process and that the final fracture was triggered by the microvoid initiation over a wide range of ductility for these high strength materials. The critical condition for the microvoid initiation was discussed. The Mises equivalent stress was found to be constant for SNCM 8, HT 80 and 2024-T4. The local particle-matrix interface stress, which was estimated from the macroscopic stress and strain at fracture on the basis of the finite element analysis, was also found to be constant for SNCM 8 and HT 80.
  • 菊田 米男, 荒木 孝雄, 米田 理史
    1980 年 29 巻 321 号 p. 556-561
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    An investigation was carried out on the reheated zone toughness of a 80kg/mm2 class high strength, multi-pass weld metal.
    The reheated zone toughness deteriorated at the reheating temperature range of 750°C-950°C in both single thermal cycle and double thermal cycle conditions. This result was discussed in relation to both fractographic and metallurgical aspects.
    The cause of embrittlement seems as follows.
    When reheated to 750°C, the absorbed energy at the ductile fracture region (vEshelf) decreased. This is due to the strengthening of matrix caused by the precipitation of fine carbide and/or nitride by the tempering of ferrite matrix or martensite island.
    When reheated to the temperature range of 850°C-950°C, the absorbed energy at low temperatures (for example vE-20) decreased. This is due to (1) the reversed austenization mainly along pre-austenite grain boundaries, (2) the transformation to martensite island of reversed austenite and the precipitation of cementite from reversed austenite during the subsequent cooling treatment, and (3) as a result, the increase in micro-crack initiation site and the decrease in resistance for cleavage fracture.
  • 橘内 良雄
    1980 年 29 巻 321 号 p. 562-567
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Stereo measurements of the stretched region in the fracture toughness specimens used for J-integral tests were carried out by examining the shape and the angle to the crack plane with a scanning electron microscope.
    It was found that the shape of the stretched zone consisted of two portions, one of which forms a gradual slope and the other a steep slope to the plane of pre-crack. The scatter of the measured values of the angle of the stretched zone to the crack plane was very large, ranging from 10 to 48 degrees. However, in many cases the angle was about 33 degrees. As the result of stereo matching observations, unsymmetrical profiles of the stretched zone were often found even though the widths were equal in a pair of the fracture surfaces. As compared with the scanning and transmission electoron fractographs taken from the same stretched zone, the same features in size were obtained from both fractographs.
  • 大塚 昭夫, 森 要, 津山 青史
    1980 年 29 巻 321 号 p. 568-573
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    A fractographic investigation on shear mode fatigue crack growth in annealed mild steel has been made. Although it is well known that shear mode growth is seen in the initial stage of fatigue crack growth in smooth or mildly notched specimens and is called stage I growth, a fractographically similar mode of fatigue crack growth has been observed in several other cases, too. In this study, the crystallographic similarlity of these cases of shear mode fatigue crack growth was investigated by the use of etch pits.
    The fractographically similar fatigue crack growth to the stage I was observed in the initial stage of fatigue crack growth from a sharp notch or precrack. It was also observed when ΔK was decreased to make very slow crack growth after the transition to the stage II growth, or in the Mode II fatigue crack growth under a specially made apparatus. The crack growth of this mode was named shear mode growth here. The fracture surface of shear mode growth usually showed cylindrical surface formed by parallel lamellae of the length of about one grain. It was shown by the use of etch pits that the direction of these parallel lamellae coincides with the direction of slip in iron <111>. Accordingly, it was concluded that the fracture surface of shear mode growth was the pencil glide surface known in the slip in iron under monotonic loading.
  • 西谷 弘信, 鹿毛 正治
    1980 年 29 巻 321 号 p. 574-579
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Rotating bending fatigue tests were made using the specimens cut out from a rolled steel for structures in rolling and thickness directions. The fatigue processes on specimen surface were observed successively by an optical microscope, and then the fracture surfaces of the same place were observed by a scanning electron microscope.
    The main results obtained are as follows:
    (1) It was clarified that the shape of an inclusion in this material was a circular-plate type. The boundary between the inclusion and the matrix was smooth when observed from the thickness direction.
    (2) Circular-plate type inclusions in the thickness directional specimen could be regarded as cracks; that is, the total life of the thickness directional specimen was almost equal to the life of crack propagation. This is the main cause of the anisotropy of fracture life, that is, the difference in life between the rolling and thickness directions.
    (3) The fatigue cracks in the rolling directional specimen originated along grain boundaries in most cases and the fracture surface at the boundaries was very smooth.
  • 小林 英男, 藤田 健太郎, 小峰 厚友, 中沢 一
    1980 年 29 巻 321 号 p. 580-584
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    The influence of fracture mechanism on the stage 2 fatigue crack growth resistance in center-notch plate and compact type specimens of high-strength steel 4340 has been studied in relation to the different microstructure and stress intensity, particularly in a wide range of growth rate, by means of fracture mechanics and fractography. The fractographic examination has shown three general mechanisms of growth, namely a structure sensitive mechnism (stage 2a), a striation mechanism (stage 2b) and a pseudo-monotonic fracture mechanism like microvoid coalescence or intergranular cracking (stage 2c). Departure from the exclusively striation mechanism to include the pseudo-monotonic fracture mechanisms has been found to result in accelerated crack growth rates. The roles of microstructure, strength level and fracture mechanics parameters in promoting the different crack growth behaviour was also discussed.
  • 秋園 幸一, 村上 理一, 竹ノ内 省一
    1980 年 29 巻 321 号 p. 585-591
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    The impact fatigue tests were carried out using a rotating disk type impact fatigue testing machine. The influence of ductile-brittle transition temperature and test temperature on the impact fatigue crack growth rate was investigated by means of fracture mechanics and fractography in quenched and tempered Cr-Mo alloy steel in which the prior austenite grain size was varried from 8.3 to 25.4μm, and the results of impact fatigue tests were compared with those of non-impact fatigue tests. The results obtained were as follows.
    (1) The impact fatigue and non-impact fatigue crack growth rates associated with striation formation at stage IIb were insensitive to the change in ductile-brittle transition temperature and test temperature.
    (2) In impact fatigue, it was found that the impact loading gave rise to transition of dominant fracture appearance from striation formation at stage IIb to intergranular cracking and cleavage at stage IIc as the Charpy impact value was decreased.
    (3) In impact fatigue, the transition of dominant fracture appearance from exclusively striation formation to intergranular cracking and cleavage was found to result in the acceleration of crack growth rate. The relation between the m value in Paris's equation and the ratio of test temperature, T, to ductile-brittle transition temperature, TM, was expressed as follows.
    m=1.12(T/TM)-1.99.
  • 小寺沢 良一, 森 時彦, 中井 友充
    1980 年 29 巻 321 号 p. 592-598
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    The crack propagation of a 304 stainless steel under repeated load at elevated temperatures was critically examined using specimens of different size to clarify the successful correlating parameter, and the results were discussed in the light of electron fractography. The crack propagation rate at 250 and 500°C where creep is not significant in this material was correlated with the stress intensity range ΔK. At 550 and 650°C where creep is significant, the crack propagation rate was correlated with ΔK at low propagation rate, whereas it correlated with J at high propagation rate and coincided with the rate of creep crack. Cyclic J integral ΔJ appeared to be a somewhat better correlating parameter than ΔK and J in the intermediate rate range.
    The fracture surface of specimens tested at 250 and 500°C was fully covered with striations. At 550 and 650°C, striations were predominant at low propagation rate where ΔK was the correlating parameter, and dimples and occasionally intergranular fractures predominantly appeared at high propagation rate where J was the correlating parameter. In the ΔJ correlating region, striations were the predominant feature of fracture surface.
  • 江原 隆一郎, 井上 慶之助, 窪田 勝昭
    1980 年 29 巻 321 号 p. 599-604
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Impact failure of hot forging die occurrs frequently from surface cracks due to fatigue or thermal fatigue. However, useful information for failure analysis of hot forging dies is scarce because few data exist on the fracture behavior and fractography of hot forging die steels. Therefore, instrumented impact tests were conducted from room temperature to 500°C to get crack initiation and propagation energies as well as dynamic fracture toughness (K1d) of SKD 62 and SKT 4. Fractographic analyses were carried out by SEM. Measurements of the stretched zone width (SZW) on the fracture surface of hot forging die was found useful to determine the fracture toughness and temperature at the time of hot forging die failure by using the obtained relationship between K1d and temperature or SZW. Low cycle fatigue life tests on the notched round bar specimens with or without such surface hardening as ion nitriding and tuftriding were also conducted to clarify the influence of surface hardening on low cycle fatigue strength. of SKD 62. The effect of ion nitriding (500°C×30hr) was found at the stress lower than 80% ultimate tensile strength of this steel and after 3×103 cycles. Striation appeared on the fracture surface after 102 cycles.
  • 内田 仁, 小寺沢 啓司, 山田 巌
    1980 年 29 巻 321 号 p. 605-610
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    The effect of environmental factors such as concentration, temperature, pH and dissolved oxygen on the initiation and propagation during stress corrosion cracking of SUS 301 stainless steel in MgCl2 solutions has been investigated by measuring the elongation of specimen throughout the test.
    It was shown that each of the environmental factors mentioned above gave a remarkable effect on the process of crack initiation: the crack initiation period decreased with increasing concentration and temperature, and with decreasing pH. The dissolved oxygen became necessary to initiate cracks as the concentration and temperature of testing solutions were decreased. The crack was often observed originating at a pit, a corrosion groove along slip trace or a tripple point of grain boundary. Such a crack nucleation was dependent on the environmental factors. On the other hand, the process of crack propagation was mainly affected by the concentration and temperature of testing solutions, and was cosely related to the fracture surface morphology. The susceptibility of intergranular cracking increased with increasing above factors. Furthermore, the both processes of crack initiation and propagation were dominated by the applied stress also.
    On the basis of the results obtained above, the effect of environmental factors on the process of crack initiation and propagation was discussed.
  • 村田 雅人, 向井 喜彦
    1980 年 29 巻 321 号 p. 611-616
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    In metastable austenitic stainless steel such as Type 304 steel, strain induced martensite appears by cold working at lower temperatures than Md point. In this paper, the effect of preplastic strain and strain induced martensite by cold working on the sensitivity of stress corrosion cracking (SCC) in 42 percent Magnesium-Chloride solution (143°C) was studied. The summary of the results obtained are as follows.
    In the case of material without cold working, the crack growth rate, da/dt was approximately proportional to the square of stress intensity factor, K. The SCC fracture surface was almost transgranular fracture characterized“Fan-shaped pattern”constituted with {100} plane.
    In material free from strain induced martensite cold worked at a temperature near Md point, this tendency in da/dt vs. K curve was almost similar to the one without cold working, but remarkable intergranular fracture was recognized on the SCC fracture surface.
    In the case of material cold worked at lower temperatures than Md point, the resistance to SCC propagation increased remarkably, but the dispersion of data broadened and the regularity of correlation between da/dt vs. K decreased as compared with the one free from martensite or cold working. This may be caused by the keying effect of martensite to SCC propagation. And in the SCC fracture surface, a peculiar“Plate-let pattern”constituted with martensite lath was recognized.
  • 圓城 敏男, 黒田 敏雄
    1980 年 29 巻 321 号 p. 617-622
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    An investigation was made on the effect of microstructure on the stress corrosion cracking (SCC) in 3.5% NaCl+0.5% H2O2 solution for Al-Zn-Mg series 7N01-T4 alloy welds. Its susceptibility to SCC is known to be affected by microstructure. The microstructure consisting of G. P. zone has high susceptibility to SCC, and that consisting of η' precipitates and η phase has low susceptibility to SCC. The microstructure in which G. P. zone and a few η' precipitates or η phase are mixed, has lower susceptibility to SCC than that consisting of G. P. zone only. SCC of the welds occurred at the area of G. P. zone microstructure such as the weld bond area and base metal of non-heat affected zone, but the SCC hardly occurred at the area where only a few η' precipitates or η phase existed in the weld heat affected zone. The fracture morphology of SCC in the microstructure consisting of G. P. zone showed intergranular fracture with plain surface, while that of SCC in the microstructure consisting of η' precipitates or η phase seemed to show intergranular fracture associated with grain boundary precipitates.
  • 土田 栄一郎, 松尾 政弘, 小林 英男, 井上 信彦, 小玉 正雄
    1980 年 29 巻 321 号 p. 623-627
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    In the previous paper, the results of constant load delayed fracture tests by using the compact tension specimen of SNCM 8 (AISI 4340) steel were presented and the characteristics of crack growth rate and delayed fracture toughness were discussed.
    In this study, constant deflection delayed fracture tests were performed in tap water by using modified wedge-opening (WOL) specimens of SNCM 8 to examine the effects of specimen thickness and strength level on delayed crack growth rate and threshold stress intensity KISCC. Hydrogen was cathodically charged into the specimen before and during the testing. The results obtained are as follows:
    (1) The shape of crack front was almost a straight line regardless of the specimen thickness, in contrast with the constant load test results. Thus, there is no effect of the specimen thickness on da/dt-KI curves and the threshold stress intensity factor KISCC.
    (2) The material tempered at lower tempering temperatures had a larger value of da/dt than that tempered at higher tempering temperatures. In this case, the only exception was the material tempered at 300°C. This could be due to tempering embrittlement of the material.
    (3) da/dt-KI curves obtained by two types of loading were in excellent agreement over their applicable KI limits.
  • 吉岡 純夫, 出水 通之輔, 熊沢 道夫, 土方 明躬
    1980 年 29 巻 321 号 p. 628-633
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Fatigue crack growth tests were conducted on 25mm thick compact tension specimens of Ni-Mo-V steels exposed to both laboratory air and hydrogen gas environments. The fatigue crack growth rates were determined under various frequencies and wave forms and the relation between the fatigue crack growth rate and fatigue fracture morphology was discussed by using fractographical observations.
    The main conclusions which characterize the fatigue behavior in the hydrogen gas environment are summarized as follows.
    (1) The relation between the fatigue crack growth rate and the stress intensity factor range in hydrogen gas was classified into three regions. In the regions II and III, a considerable raise in fatigue crack growth rate was observed.
    (2) The fatigue crack growth rate in hydrogen gas was not affected by frequency, nor by wave form.
    (3) The fracture morphology of fatigue failure in air showed normal transgranular fracture which includes ductile striations. However, the fracture morphology in hydrogen gas showed intergranular fracture in the region I and cleavage fracture in the region II and III. Brittle striations appeared on the cleavaged fracture surface.
    (4) A fair correspondence between the striation spacing and the fatigue crack growth rate was observed for ductile and brittle striations in both air and hydrogen gas.
  • 寺崎 富久長
    1980 年 29 巻 321 号 p. 634-638
    発行日: 1980/06/15
    公開日: 2009/06/03
    ジャーナル フリー
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