材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
27 巻 , 292 号
選択された号の論文の20件中1~20を表示しています
  • 喜多 清, 坪田 一一, 山本 晋
    1978 年 27 巻 292 号 p. 2-8
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    Failures of case-hardened components appear to be responsible for a greater part of service failures of machines. Electron fractography is being used widely for failure analysis and, actually, it is successful for determining the causes of some failures. However, on high hardness materials, especially on case-hardened materials, the relationship between fracture modes and fracture mechanisms has been rarely investigated.
    In this paper, the characteristics of fracture surface of case-hardened materials broken in service were examined by means of fractography. From the results of examination, it was clarified that, in the hardened layer of carburized materials, dimple fracture occured at high cycles (3.4×109 cycles) and intergranular fracture occured under impact stress. Also the microcharacteristics of hardening cracks in induction hardened materials were clarified.
  • 西島 敏, 増田 千利, 下平 益夫
    1978 年 27 巻 292 号 p. 9-13
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    Microfractographic approach becomes very valuable in fracture analysis when it can be made in a quantitative way. This paper presents some examples of the actual fracture of aircraft parts related to fatigue, and describes a possibility of analysing them by using striation spacings, beach mark spacings, and undulating pitches of tear dimple facets due to fast overload fractures.
  • 小賀 正樹, 浅見 克敏, 寺沢 正男
    1978 年 27 巻 292 号 p. 14-20
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    Recently, surface hardening treatment is being given on many machine parts in order to improve their fatigue strength. Although these parts are often used under such environments that a corrosive action may cause a considerable change in fatigue strength, the fracture mechanism of corrosion fatigue on such a hardened steel has been hardly made clear. So, in this study, a fractographical investigation was carried out to clarify the relation between fatigue strength and corrosion fatigued fracture patterns for the smoothed specimens of tufftrided steel.
    The experimental results are summarized as follows.
    (1) In air, the 1st and 2nd stages of crack propagation were confirmed on the fracture surface of tufftrided steel when the fracture originated from surface. Its complicated fracture zone was wider than that of non-tufftrided steel and its succeeding zone where striations could be observed distinctly was limited to the region where HV hardness before fatigue was less than 180.
    (2) In pure water, tufftrided steel was ruptured by only one crack which nucleated at a corrosion pit, while non-tufftrided steel was ruptured by joining of several cracks. A zone of cleavage or quasi-cleavage fracture followed a mixed zone of intergranular and cleavage fractures as the crack propagation proceeded. The decrease in the applied stress level, i. e., the increase in fatigue life, brought the transition from the cleavage or quasi-cleavage fracture to the ductile fracture showing striations under the nitrogen diffusion layer.
    (3) On the final fracture, cleavage fracture dominated in pure water, while dimple fracture dominated in air. The size of the final fracture zone in pure water was larger than that in air.
  • 藤原 昌晴, 佐近 淑郎, 砂本 大造
    1978 年 27 巻 292 号 p. 21-25
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    The low-cycle fatigue tests with varying stress hold time at the tensile maximum stress were conducted on the circumferentially grooved specimens of 18 Cr-8 Ni-Mo stainless steel (SUS 316) at 550°C. The results of micro-fractographical study are as follows:
    (1) In general, the shorter hold time condition gave the transgranular fracture mode, and the longer hold condition gave the intergranular mode. Intergranular facets appeared when the average propagation rate (ΔS/tH) became less than 10-3mm/min.
    (2) The striation spacing was not affected by the duration of stress hold. Therefore, the stress hold time seems to affect the crack propagation rate only during the initial fatigue stage where the striation pattern is unobservable.
  • 林 英雄, 植村 幸生
    1978 年 27 巻 292 号 p. 26-30
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    The Charpy impact value of plastics is greatly influenced by the notch shape of test specimens. And there exists a close correlation between the Charpy impact value and the appearance of the fracture surface. In this paper, the relation between the notch shape and the appearance of the fracture surface of rigid PVC plates was studied.
    The results obtained are summarized as follows:
    (1) The fracture of the Charpy impact test specimens did not originate from the surface of notch root, but starts from the inside below the notch root.
    (2) The distance between the notch root and the fracture origin increased with the radius of notch root, but it was not affected by the notch depth.
    (3) In the case of U notch (r=1.0mm, d=2.0mm), the surrounding neighborhood of the fracture origin formed a sphere-like or disk-like void of about 50μm in diameter.
  • 大路 清嗣, 小倉 敬二, 武藤 睦治, 伊戸川 博, 内田 秀紀, 堀木 正之
    1978 年 27 巻 292 号 p. 31-36
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    The processes of initiation and stable growth of craks in fracture toughness tests were observed in detail on various steels of moderate ductility by using fractographic and sectioning techniques. The effects of test temperature and specimen thickness on these processes were also investigated. The results are summarized as follows.
    (1) The stretched zone width increases with temperature for HT80, HT60 and CH1 steels, while it remains approximately constant for S35C steel, in the temperature range where the stable crack growth takes place preceding the unstable crack growth.
    (2) The distribution of the stretched zone width along the crack front is fairly flat and is little affected by the test temperature and specimen thickness, while that of the tear dimple region is considerably affected by these factors.
    (3) A good correlation is found to exist between the transition zone width and KcY.
  • 橘内 良雄
    1978 年 27 巻 292 号 p. 37-41
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    Precisely matched electron fractographs of the matching fracture surfaces of two kinds of carbon steels (S 35 C and SK 5) were examined to clarify the micromechanism of fatigue crack propagation.
    The occurrence of pearlite boundary cracking may be explained by the fact that the active slip lines are arrested by the lamellae cementite in the neighbourhood of crack tip.
    Most of the tear and equiaxed dimples containing inclusions or precipitated particles are formed at the fatigue fracture surface in the steel (S 35 C) tempered at 200°C. The width-to-length ratio of dimples for a given stress intensity factor (ΔK) is about 1.3∼1.5 and the average size of dimples is correlated with ΔK. The distribution of dimple size is approximated by a logarithmic normal distribution.
    The discrepancy between two matching fracture surfaces is created as: (a) Two sets of active slips at the crack tip are different in their magnitude. (b) Cracks are not propagating perpendicular to the apparent maximum stress direction. (c) One of the mating fracture surfaces is plastically deformed by some physical constraints after the crack front has passed.
  • 石原 守, 平石 茂樹, 杉本 威生
    1978 年 27 巻 292 号 p. 42-48
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    The fatigue crack growth rate in HT80 base plate and welded joints has been measured using compact tension specimens, and examined by means of fracture mechanics and electron fractography.
    The lowest fatigue crack growth rate was obtained in the heat-affected zone and the highest rate in the stress-relieved weld metal. In the weld metal, the compressive residual stress affected the crack growth rate and reduced the effective stress intensity factor range ΔKeff.
    The fatigue crack growth rate coincided almost completely with the microscopic growth rate calculated from the striation spacing for base metal and heat-affected zone. The fatigue crack growth rate for both weld metal and stress-relieved weld metal was, however, higher than the microscopic growth rate in the present stress intensity factor range. It is supposed that this discrepancy is caused by the fracture accompanied with dimples and striations. The relation between the dimple size, ds(mm), and the stress intensity factor range, ΔK(kg/mm3/2), has been obtained as follows, ds=1.4×10-5·(ΔK)
  • 大塚 昭夫, 森 要, 川村 貴保
    1978 年 27 巻 292 号 p. 49-53
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    A fractographic study of stage I (or shear mode) crack growth was made on mild steel specimens. The effect of the mode of load application on the shear mode crack growth was investigated by using plain and notched round bar specimens under direct stress and rotating bending stress conditions. The investigation was also made on the initiation of the growth from the end of a fatigue precrack. The main conclusions are as follows:
    (1) The shear mode pattern made up of parallel straight lines or bands is always observed in the region of fatigue crack initiation in mild steel. This pattern seems hardly affected by the modes of load application and notches.
    (2) Although relatively flat areas are sometimes observed in the region of the fatigue crack initiation from the specimen surface, they show a similar parallel line pattern, under higher magnification, to the one mentioned above.
    (3) The shear mode growth pattern similar to the one observed in the region of fatigue crack initiation in plain and notched specimens as mentioned in (1) is also observed in the case of the fatigue crack growth from the precrack under low ΔK.
    (4) It was confirmed by the etch pit method that the direction of the parallel lines in the shear mode fatigue crack mentioned in (1)∼(3) coincides to the direction of slip in iron crystal <111>. This fact seems to show that the pattern which consists of parallel lines is the surface of so-called “pencil glide”in iron crystals.
  • 小寺沢 良一, 志茂 大治郎, 近藤 潤一
    1978 年 27 巻 292 号 p. 54-58
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    The effect of periodic overstressing on fatigue crack propagation was studied with sharp notched specimens of low carbon steels (a rimmed steel and an Al-killed steel), a medium carbon steel, a high strength steel and an aluminum alloy. A very small number of cycles of overstress applied intermittently during a very large number of cycling of understress below the fatigue limit or threshold stress intensity Kth caused a remarkable acceleration of crack propagation (about or more than one hundred times) in all materials tested except the high strength steel. The fracture surface morphology in the cases with such remarkable acceleration was quite different from that of the cases without it, the characteristic feature being clam-shell markings with saw-tooth profile of hill-to-valley matching. This indicates the occurrence of crack propagation in zig-zag fashion in contrast to the straight propagation under steady cyclic stress conditions. The cracks propagated also under the understress below Kth. These results raise a question on the validity of Kth as a design criterion.
  • 増田 千利, 西島 敏
    1978 年 27 巻 292 号 p. 59-63
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    Microfractographic aspects of fatigue fracture were examined in relation to the strength level of material and the microcrack propagation rate, da/dn, with a particular emphasis on the low da/dn range. The materials investigated were heat-treated carbon and low alloy steels characterized by different levels of Vickers hardness (HV=140, 330, 480, and 780). Fatigue tests were conducted under repeated tensile loads.
    For low da/dn values (<10-4mm/cycle), the fatigue fracture surface exhibited a certain amount of intergranular facets, except for the material of HV 330. The coverage of intergranular facets was variable depending upon the da/dn level, but was found to take a maximum value when the size of cyclic plastic zone at the crack tip was nearly equal to the size of ferritic grains (steel of HV 140), or prior austenitic grains (steel of HV 480).
    While for ordinary propagation rates (da/dn)>10-4mm/cycle), the striation spacing was confirmed practically coincident with the da/dn value, except for steel of HV 780, the spacing was greater than the da/dn value by the order of 2, for very low propagation rates (da/dn<10-6mm/cycle). The striation patterns observed in such cases were very irregular for steel of HV 140, but regular, though in small amounts, for steel of HV 780.
  • 江原 隆一郎, 貝 敏雄, 井上 慶之助, 益本 功
    1978 年 27 巻 292 号 p. 64-68
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    Fractographic analysis and surface observations were carried out by SEM to clarify the corrosion fatigue behavior of 13Cr stainless steel. Rotating bending fatigue tests with a speed of 3400rpm were conducted up to 109 cycles in 0.03% NaCl aqueous solution.
    Samll corrosion pits were found at the initiation region of fracture surface. The depth of these corrosion pits was 10∼20μm and was almost constant notwithstanding stress amplitude, which confirms the previous results5) that the depth of corrosion pits is 10∼20μm and is almost constant notwithstanding NaCl contents (3∼3×10-3%) in aqueous solution. Intercrystalline fracture was predominant in the propagation region. The percentage of intercrystalline fractures increased with decreasing stress amplitude. In the neighbourhood of the initiation region, the number of intercrystalline fractures was fewer than that in the propagation region. Corrosion pits and subcracks accompanied with corrosion pits were observed on the surface near the fracture path. Cracks were also seen on the surface of unbroken specimens subjected to the bending of more than 109 cycles. It is considered that Cl- concentration at the bottom of corrosion pits is one of the predominant factors to affect the corrosion fatigue behavior of 13Cr stainless steel in aquous solution containing Cl-.
  • 菊田 米男, 荒木 孝雄, 黒田 敏雄
    1978 年 27 巻 292 号 p. 69-74
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    The implant weld cold cracking test was carried out on the longitudinal rolling (X-), 45° direction of short transverse and short transverse (Z-) direction specimens prepared from 80kg/mm2 class high strength steels, and the fracture morphologies of weld cold cracking and lamellar tearing were investigated by means of electron fractography.
    The fracture morphology of weld cold cracking changed from dimple rupture (DR) to quasi-cleavage fracture of hydrogen embrittlement (QCHE) and intergranular fracture (IG) with decreasing applied stress.
    The fracture morphology of lamellar tearing was a terrace and wall like fracture at high applied stress levels and fast fracture parts, which include DR.+inclusion (MnS) and/or QCHE+inclusion at the terrace part. But its morphology at low applied stress levels changes to QCHE and IG without inclusion at the fracture surface, which is similar with the weld cold cracking observed at low applied stress levels.
    On the basis of the results of internal friction, these fracture morphologies can be explained by the microscopic gathering of hydrogen at lath and grain boundaries which brings in the decrease of ductility.
    One of the characteristic morphologies for hydrogen embrittlement is the quasi-cleavage fracture of hydrogen embrittlement (QCHE) which involves sub-cracks along martensite lath boundary.
  • 土田 栄一郎, 松尾 政弘, 小林 英男, 井上 信彦, 小玉 正雄
    1978 年 27 巻 292 号 p. 75-80
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    Delayed fracture experiments were performed in tap water by using the compact tension specimens of SNCM8 (AISI 4340 steel) tempered at 200°C, 400°C and 600°C. The effects of tensile strength and thickness on the characteristics of delayed fracture under the plane-strain condition were discussed.
    The results obtained are summarized as follows:
    (1) In thick specimens, hydrogen is not fully dissolved, so that the crack front has a curvature. Thus, the specimen thickness affects the shape of apparent da/dt-K1 curves. The thicker the plate, the slower da/dt becomes.
    (2) The feature of delayed fracture surface is predominantly intergranular. The fractographic feature along the crack front varys qualitatively with the change of crack front curvature.
    (3) The delayed fracture toughness, defined as (Kdc)eq on the basis of equivalent crack length, shows no dependence on the thickness, i. e. there exists no effect of hydrogen on (Kdc)eq. The value of (Kdc)eq is larger than the plane strain fracture toughness KIC. This difference may be explained by the existence of the effect of stress history on stress intensity.
    (4) The material tempered at 400°C shows a larger value of da/dt than the one tempered at 200°C, and is more sensitive to the delayed fracture. In the material tempered at 600°C, no delayed fracture occurred.
  • 日野谷 重晴, 池田 昭夫, 寺崎 富久長
    1978 年 27 巻 292 号 p. 81-86
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    The fracture surfaces of ferritic-perlitic steel caused by hydrogen induced cracking (HIC) and sulfide stress cracking (SSC) under the wet H2S environment were investigated by a scanning electron microscope. It was clarified that HIC and SSC were caused by hydrogen embrittlement. The cracks of HIC initiated around the nonmetallic inclusions (MnS) and they grew in a step-wise manner by connecting each other. On the other hand, the process of SSC took place as follows; the separated small cracks of HIC were connected by the cracks perpendicular to the stress axis. The fracture due to hydrogen embrittlement exhibited some characteristic fracture patterns, such as a river like pattern, flat pattern and so on. It was supposed that these fracture patterns were formed depending on the crystallographic orientation of grains. The striation type pattern was observed on the river like pattern as well as on the flat pattern. This striation type pattern seemed to correspond to the discontinuous propagation of hydrogen embrittlement cracking. In order to determine the sharp of the river like pattern, the stereo-matching technique was applied and it was found that this pattern could be classified into three types.
  • 渡辺 正紀, 向井 喜彦, 村田 雅人, 辻井 元
    1978 年 27 巻 292 号 p. 87-91
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    Fracture surface of SUS 304 stainlests steel subjected to stress corrosion cracking (SCC) in boiling 42% MgCl2 solution was investigated fractographically by scanning electron microscopy. To determine the orientation of fracture surface, etch pits were formed on the fracture surface by the electro-etching method in 1N H2SO4+100mg/L NH4SCN solution. It was found that the fracture surface of SCC was mostly in {100} plane, which was determined by the morphology of etch pits. This shows that the crack path depends on the orientation of crystal grain and the direction of stress.
  • 小寺沢 良一, 西川 義富美, 森 時彦
    1978 年 27 巻 292 号 p. 92-98
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    The applicability of fracture mechanics parameters to creep and fatigue crack propagation at elevated temperatures was critically examined using specimens of different geometry, and the results were discussed in the light of the electron fractography. The propagation rate of creep cracks was best correlated with the modified J integral J. The stress intensity factor K failed to describe the crack propagation rate adequetly. The net section stress σnet was a better correlating factor than the stress intensity factor. As for fatigue cracks, the propagation rate correlated well with the stress intensity range ΔK at low stress levels. At high stress levels, however, it correlated better with the maximum net section stress σnet max or J rather than ΔK, and it was close to the value of the static test. There appeared the transition of macroscopic crack propagation.
    The fracture surface of creep cracks was intergranular with much reduction in area. With regard to fatigue cracks, the low stressed specimens exhibited flat fracture surfaces with little reduction in area and, microscopically, plateaus and striation-like patterns were their characteristic features. The high stressed specimens, on the other hand, exhibited rough surfaces with much reduction in area like creep fracture. Microscopically, however, plateaus and well-defined striations were predominant in the early stage. Dimples and intergranular creep fractures appeared later in the propagation process and the transition in microscopic fracture features did not agree with that of macroscopic propagation.
  • 喜多 清, 清重 正典, 富永 昌武, 藤岡 順三
    1978 年 27 巻 292 号 p. 99-103
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    The modes of crack initiation and propagation of low cycle fatigue at high temperature were studied on HA-188 cobalt base alloy by means of scanning electron microscopy. Low cycle fatigue tests were carried out at 700°C in the strain rate range of 3×10-5 to 2×10-2sec-1. In the high strain rate region, crack initiation occured at twin boundaries, and crack propagation was transgranular. In the middle strain rate region, crack initiation occured at grain boundaries, and the mode of crack propagation was a mixture of intergranular and transgranular. Striations were observed on all transgranular fracture surfaces at high and middle strain rates. In the low strain rate region, both crack initiation and propagation were entirely intergranular. The strain rate being lower than 6.5×10-5sec-1, where crack initiation and propagation were entirely intergranular, the fatigue life was constant at any strain rate, that is, the fatigue behavior was time dependent. The cause of intergranular crack propagation was discussed.
  • 平野 一美, 小林 英男, 中沢 一
    1978 年 27 巻 292 号 p. 104-108
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
    Thermal shock tests were carried out on AISI 304 steel and tool steel (JIS SKD62) by using a new thermal shock testing apparatus. Analysis of their quasi-static thermal stress intensity factors was performed. Fractographic features of thermal shock cracking were examined. Then, the critical J-integral values corresponding to the critical stretched zone widths were evaluated by applying the JIc test concept. These values were compared with the fracture toughness values obtained in the same high temperature range.
    The results obtained are summarized as follows;
    (1) Fracture toughness under thermal shock can be evaluated by means of either the analysis of quasi-static thermal stress intensity factor or the application of JIc test concept.
    (2) The fracture toughness values under thermal shock are smaller than the fracture toughness values with in the same high temperature range.
    (3) An intergranular facet pattern is observed for thermal shock cracking, whereas a dimple pattern is mainly observed on a fracture toughness specimen. The difference of fracture mode corresponds to the degree of disagreement between the fracture toughness under thermal shock and the fracture toughness at a high temperature.
  • 駒井 謙治郎
    1978 年 27 巻 292 号 p. 109-114
    発行日: 1978/01/15
    公開日: 2009/06/03
    ジャーナル フリー
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