材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
40 巻 , 453 号
選択された号の論文の17件中1~17を表示しています
  • 橘内 良雄, 前田 豊, 吉久 悦二
    1991 年 40 巻 453 号 p. 656-662
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Failure causes for welded joints and brazing material in three cases were analyzed by means of fractography.
    During the work of attaching a 180 tonf sternpost to the stern frame in a dockyard, two small plates welded on the rudder horn to support the sternpost came off near the weld metal, and the sternpost dropped to ground. No weld defects were observed in the fillet weld. However, both the throat thickness and the leg length in the fillet weld were smaller than those required in joint design. Therefore, it was concluded that the weld metal could not withstand the weight of sternpost.
    When butt-welded steel sheet piles were driven into ground using a hydraulic pile-driver under construction of sewage work, a sheet pile failed at the welded joint. Many weld defects, such as lack of fusion, lack of penetration and some discontinuities were recognized on the fracture surface, and a half of the cross-sectional area of the sheet pile was occupied by these weld defects. The stress applied on the true cross section excluding the weld defects was found to exceed the yield strength of the sheet pile. Hence, the cause of failure for the sheet pile was concluded to be the welding defects resulting from poor workmanship.
    When a new circular saw consisting of 16 blades was used to cut a board, some of the blades suddenly failed and a fragment of blade chip stuck in an eye of the operator. The material of blade chip broken was WC-Co alloy and was brazed on a shank made of high carbon steel. The failure pass was limited in the WC-Co alloy. As a result of fractographic examination, a crack of about 150μm length was observed in a chip of the blade failed. The stress intensity factor of the blade chip approached the lower limit of the scatter of KIC for WC-Co alloy. Hence, the cause of failure was related to the pre-existing crack in the blade chip.
  • 冨田 恵之
    1991 年 40 巻 453 号 p. 663-668
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    A study has been made to determine a major metallurgical factor controlling low plane-strain fracture toughness (KIC) observed for desulfurized AISI 4340 ultrahigh strength steel and then to suggest a potential approach for improving the KIC of the steel. For the desulfurized steel containing a low sulfur content of 0.002wt%, intergranular failure occurred at the crack tip in the fracture toughness test though the mechanical isotropy was improved. So there was little difference between the KIC value in the longitudinal orientation for the desulfurized steel and that for the steel with a sulfur content of commercial level (0.016wt%). Metallographic observations and fractography revealed that the intergranular failure occurs by the mechanism that during slow cooling from hot-rolling temperature, manganese and sulfur resolved in the high-temperature range segregate to the grain boundaries and appear there as fine MnS after reaustenitizing followed by quenching. Calcium addition of 0.0059wt% (Ca/S≅3) in desulfurized melts just after vacuum-degassing modified the morphology of non-metallic inclusions from fine MnS to spherical CaS, which leads to improved KIC of the desulfurized steel independent of testing orientation. The beneficial effect of calcium treatment on KIC is briefly discussed in terms of crack extension model in fibrous mode.
  • 砂田 久吉
    1991 年 40 巻 453 号 p. 669-674
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    The impact fracture patterns of two kinds, ferritic and pearlitic matrix, of unalloyed spheroidal graphite cast irons austempered at either 573K or 673K for 5min or 2h have been correlated to Charpy impact values at room temperature. The results of this study are summarized as follows:
    (1) Austempering at 573K for both matrixes induced a sharp drop in Charpy impact strength as compared with that without austempering. The coarse upper bainite structure obtained by austempering at 673K was found to improve the impact strength. This improvement of the impact strength was attributed to the retained austenite in the structure.
    (2) The impact fracture surfaces with high impact strength, ferritic matrix and upper bainite structure austempered at 673K, showed a ductile dimple pattern accompanying localized plasticity in the vicinity of graphite.
    (3) Brittle quasi-cleavage modes with less plasticity were observed on lower bainitic structure austempered at 573K similar to pearlitic matrix. The number of graphites observed per unit area on the brittle fracture surface was less than that on the ductile fracture one.
    (4) A series of local cleavage facets were observed at the root of the notch coaxial to the fracture direction. It suggests that the impact values are associated with the plastic deformation ahead of these facets.
  • 杉山 好弘, 浅見 克敏, 松岡 忍
    1991 年 40 巻 453 号 p. 675-681
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    In the previous study on the fatigue crack propagation characteristics of ductile cast iron, it was found that the propagation resistance could be improved by austempering from (α+γ) phase region (partial-austempering) without decreasing static strength, especially in the low ΔK region. In this paper, to improve the static strength in addition to the propagation resistance without decreasing ductility, the influence of treating temperture in (α+γ) phase region was examined. Microstructure inspection, tensile tests, fatigue tests (stress ratio, R=0.1) and fractography were carried out on the ductile cast iron specimens which were partial-austempered at four different treating temperatures (800°C, 815°C, 830°C and 840°C). The results obtained were compared with those of the as-cast material whose matrix-structure consisted of ferrite (about 60%) and pearlite (about 40%) and the materials whose matrix-structures were changed into ferrite (about 100%) or bainite (about 100%) by heat-treating.
    The matrix-structure of the partial-austempered materials consisted of ferrite and bainite. When partial-austempered at 800°C, 815°C, 830°C and 840°C, the ratio of bainite became approximately 20%, 40%, 80% and 90%, respectively. The static strength (0.2% proof stress and tensile strength) was improved with an increase of the ratio of bainite, but the ductility and propagation resistance decreased except the propagation resistance in the material whose matrix-structure was ferrite. The reasons were discussed in terms of fractography. The most effective treating temperature to improve the static strength and propagation resistance without decreasing ductility was 830°C for the ductile cast iron used in this study.
  • 荒木 孝雄, 広瀬 明夫, 松広 克之, 湖東 雅広, 富田 晋也
    1991 年 40 巻 453 号 p. 682-688
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Present investigation discusses the relationship between formation of fiber-matrix reaction zone and fracture morphology in SiC/Ti-6Al-4V composite material. A SiC/Ti-6Al-4V composite material was fabricated by using a vacuum hot pressing method, and microscopic observations of its reaction zone and fractography of the composite on three point bending test with acoustic emission detector were carried out. The major phase present in the reaction zone was TiC. A small amount of Ti5Si3 and Ti5Si4 was detected in the zone in the as-fabricated specimens, but was not detected in the annealed specimens. The fracture stress of the composite decreased with increasing thickness of the reaction zone, and many AE events which correspond to cracking of the thick reaction zone were counted during fracturing in the bending test. Fracture morphology of the composite was different depending on the tension or compression side of specimen: in the tension side both brittle and radial types of fracture occurred while in the compression side chop marking fracture took place. The brittle type of fracture was mainly observed in the thick reaction zone. The cracking in the thick zone brings about reduction in fracture stress.
  • 小林 英男, 荒居 善雄, 長島 伸夫
    1991 年 40 巻 453 号 p. 689-694
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Four point bending tests for Si3N4/steel joints were conducted and their fracture surfaces were examined by advanced fractographic method. Based on these results, the fracture mechanism was discussed by the fracture mechanics approach.
    The crack initiates at the ceramics/adhesive interface. A part of crack front is arrested at the microcrack in the ceramics side of the interface. Another part of the crack front grows along the interface. Then, the stress intensity factor, K, at the arrested crack front increases as the profile of the whole crack front becomes like a Chevron notch. The unstable fracture occurs when K at the arrested crack front reaches KIC for ceramics.
  • 岸本 秀弘, 上野 明
    1991 年 40 巻 453 号 p. 695-699
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Fractographic analysis was carried out on the fracture surfaces of two kinds of sintered silicon nitride fractured under static or cyclic loads. The main results obtained are as follows.
    (1) As for the final fracture surface, 80% to 90% of the whole area was intergranular fracture, regardless of kinds of materials, loading stress mode or temperature. It was concluded that the strength of grain boundary of the materials used in this study was very low as compared with the strength of columnar beta silicon nitride crystal.
    (2) Although the percentage of transgranular fracture was low, it varied with the crack velocity. It was higher on the final fracture surface than on the slow crack growth surface.
    (3) Debris of the fractured grains and wear marks were observed only on the fracture surface of CT specimens under cyclic load.
  • 大塚 昭夫, 菅原 宏人
    1991 年 40 巻 453 号 p. 700-705
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    A fractographic analysis was made on two kinds of silicon nitride, glass ceramics and borosilicate glass fractured under monotonic tensile loading and tension-compression cyclic loading. Emphasis in the fractographic investigation was placed on the fracture initiation area. The relation between mirror size and fracture stress was investigated under various stress conditions. The mirror sizes observed on the fracture surfaces of tensile fractured specimens were approximately 60% of those for bending tests when the comparison was made at the same fracture stress. The fractographic observation on the area of fracture initiation revealed that the fracture in silicon nitride-B always occurred from the defects formed during sintering, while in silicon nitride-A, in which fracture always occurred from the surface, no defect was observed in the fracture initiation area. This result means that the fracture in silicon nitride-B occurs by the crack growth from these defects (formed during sintering), while in silicon nitride-A, fracture initiation occurs by the cracking formed along the grain boundaries by SCC in the surface layer, and then these cracks grow by SCG to final failure. The results of EDX analysis on the fracture initiation area of silicon nitride-A showed that the relative content of Y, which is the main element of sintering aid additions, was higher in the region inside of the critical crack size than in the region outside this region. This will probably show that the crack growth occurred by SCG in this area and by rapid growth in the area outside of the critical crack size. This observation seems to support the fracture intiation process discussed above on the fracture of silicon nitride-A.
  • 村上 敬宜, 金縄 勝幸, 古川 勝明, 西田 新一, 白石 暢彦
    1991 年 40 巻 453 号 p. 706-711
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    For the prediction of service load from fatigue fracture surface, not only the measurement of striation spacing(s) but also the information on stress ratio are necessary.
    In the previous paper, the authors found that there was one to one correspondence between the ratio of striation height H to s (H/s) and the stress ratio R for 2017-T4 aluminum alloy. Since s ranges approximately from 0.1 to 2μm and H is smaller than s, the prediction of accurate R value requires the accurate measurement of H and s. For this purpose the procedure composed of cutting, polishing by emery paper and buff polishing was utilized previously. In this paper, an improved method using Microtome to reveal sharp striation sections is proposed and the improvement of measurement accuracy is shown.
    In addition to 2017-T4 aluminum alloy, type 304 stainless steel was investigated in order to study the effect of mechanical properties on the relationship between H/s and R. The experimenal results gave almost the same relationship for type 304 stainless steel and 2017-T4 aluminum alloy. This result implies that the H/s-R relationship is independent of material properties, suggesting that one master curve of H/s-R and striation spacing s give a crucial information about the service load at the occurrence of fatigue fracture accidents.
  • 藤原 昌晴, 近藤 良之, 服部 孝博
    1991 年 40 巻 453 号 p. 712-717
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Quantitative evaluation of applied stress by fractography is not always easy if fatigue striations are not seen on the fatigue fracture surface. The authors have often experienced such a problem in case of industrial machines which failed under low vibrational stress. In this report, the quantitative characterization of the fatigue crack surface created by low stress amplitude is attempted. A good correlation between the proposed surcace roughness parameter (S1) and the stress intensity factor range (ΔK) was obtained for low ΔK level. This technique is expected to be a supplemental method of quantitative stress evaluation of fractured component.
  • 内田 仁, 井上 尚三, 大井戸 敏宏, 小寺澤 啓司
    1991 年 40 巻 453 号 p. 718-722
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    The stress corrosion cracking (SCC) of SUS 310S steel single crystals was investigated by the slow strain rate technique. The smoothed specimens oriented for [001], [101] and [111] were prepared, and each susceptibility to SCC was evaluated from the nominal stress-strain curves in a boiling 42% MgCl2 solution at 416K. The results indicated that the transgranular cracks occurred at the strain rate below 2.38×10-5S-1, and the tensile strength and elongation decreased with decreasing strain rate. The fracture surface of which the appearance was changed by the tensile axis orientation, was formed by the crack growth along ‹110› direction on {100} plane. The susceptibility index to SCC defined by comparing with the nominal stress-strain curves in noncorrosive oil decreased with decreasing strain rate, whereas it was independent of tensile axis orientation. With a longer time to fracture (a lower strain rate), the normal stress to the (001) crack plane nearly became coincident with that on the threshold of SCC obtained by the constant load technique. This fact demonstrates that the susceptibility to crack growth is strongly controlled by the normal stress to the crack plane.
  • 村田 雅人, 王 静波, 向井 喜彦
    1991 年 40 巻 453 号 p. 723-729
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    The mechanism for hydrogen embrittlement type stress corrosion cracking (HESCC) in a duplex stainless steel and its welded joints was studied by facet pit method. From the fractographic observation on the fracture surfaces of base and weld metals, it was found that the ferritic phase fractured in quasi-cleavage mode and the austenitic phase in ductile mode. The weld metal was more susceptible to HESCC than base metal. From the morphologies of facet pits formed in the ferritic phase on the fracture surface, it was clarified that the fracture planes in the ferritic phase were mainly along {100} plane in the lower stress intensity region but became {110} or {112} plane in the higher one. Consequently, the mechanisms for HESCC in duplex stainless steel contain lattice decohesion at lower stress intensity and slip-off at high stress intensity.
  • 黒田 敏雄, 文能 一成, 圓城 敏男
    1991 年 40 巻 453 号 p. 730-735
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Effect of microstructure on hydrogen embrittlement in the weld heat-affected zone (HAZ) of SUS 329J1 duplex stainless steel has been investigated by means of fractography and transmission electron microscopy. The hydrogenation to the specimen was carried out using cathodic charging in 5% H2SO4 aqueous solution. The susceptibility to hydrogen embrittlement was evaluated by fracture strain.
    The base metal had duplex structure consisting of α phase and elongated γ phase. The microstructure in the HAZ depended on the peak heating temperature. The volume fraction of γ phase decreased and the precipitation amount of Cr2N in the α phase and at the α grain boundary increased with increasing heating temperature.
    When the specimens were sensitized at 923K, M23C6 precipitated at α/γ interface, and the growth of γ* phase to the α phase occurred. And then, σ phase precipitated in the α phase side at the α/γ* interface for any specimen.
    The hydrogen embrittlement occurred in the α phase at any heat-treated specimen. The susceptibility increased with increasing heating temperature in the HAZ. In the case of sensitization, the hydrogen embrittlement occurred not only in the α phase but also at the α/γ interface.
    The fracture morphology of hydrogen was characterized in the stripe pattern in the α phase. and the secondary cracks occurred at the α/γ interface.
  • 福山 誠司, 横川 清志, 荒木 道郎, 小鑓 幸雄, 山田 良雄
    1991 年 40 巻 453 号 p. 736-742
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    The tensile properties of Inconel 718 and Udimet 720 Ni-base alloys being used for liquid hydrogen fueled rocket engine materials were investigated in a high pressure hydrogen of 19.7MPa at room temperature. The results obtained are as follows;
    (1) Elongation, reduction of area and ultimate tensile strength in hydrogen were smaller than those in argon for both Inconel 718 and Udimet 720. The effect of hydrogen on the tensile properties increased with decreasing strain rate.
    (2) Dimple rupture was mainly observed in argon both of Inconel 718 and Udimet 720. In hydrogen, the fracture along the interface between δ phase and γ matrix for Inconel 718 and that along the interface between γ' phase and γ matrix for Udimet 720 were observed on the fracture surface, respectively.
    (3) For Inconel 718, the crack initiation occurred at carbide and then the crack propagated along the interface between δ phase and γ matrix in hydrogen. For Udimet 720, the crack initiation occurred at precipitate and then the crack propagated along the interface between γ' phase and γ matrix in hydrogen.
  • 江原 隆一郎, 山田 義和, 山田 保
    1991 年 40 巻 453 号 p. 743-747
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    In order to clarify the influences of HF gas on the low cycle corrosion fatigue strength and static corrosion velocity of 2014-T6 aluminum alloy, low cycle corrosion fatigue tests and static corrosion tests were conducted in a {HF gas (3ppm)+humid air (80°C, 70% relative humidity)} environment by using a laboratory made gas corrosion fatigue testing apparatus. The fatigue strength at 105 cycles in the {HF gas (3ppm)+humid air (80°C, 70% relative humidity)} environment was about 56% lower than that in air at room temperature. Corrosion pits were observed at the crack initiation region and brittle striation was predominant at the crack propagation region. The maximum corrosion velocity in the {HF gas (3ppm)+humid air (80°C, 70% relative humidity)} environment was 2×10-3mm/year. A tough fluoride film was formed on the surface of specimens due to the reaction of aluminum with humid HF. It can be considered that the static corrosion velocity was extremely low because the tough fluoride film prevented the further reaction of the fresh surface of aluminum with humid HF. However, the fluoride film was destroyed by repeated stress, and corrosion pits were initiated at the surface of low cycle corrosion fatigue test specimens influenced by the humid HF gas environment. These corrosion pits accelerated the initiation of corrosion fatigue cracks, which caused an extreme reduction in the corrosion fatigue strength of 2014-T6 aluminum alloy.
  • 田中 義久, 増田 千利, 山本 元弘, 深沢 稔
    1991 年 40 巻 453 号 p. 748-754
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
    Fatigue properties and fatigue fracture mechanism were examined for SiC whisker reinforced A2024 aluminium matrix (SiCw/A2024) composite at 150°C. The fatigue strength tested at 150°C increased with increasing the volume fraction of SiC whisker up to 20%, although they were generally lower than those tested at R.T.. Fractographic analysis revealed that Mode I fatigue crack was formed by Stage I mechanism in SiCw/A2024 composite at 150°C in the same manner as that in A2024 matrix alloy. In the fatigue crack propagation region, the area fraction of dimple patterns for SiCw/A2024 composite tested at 150°C was smaller than that for the same composite tested at R.T.. It is suggested that SiC whiskers would have a much effect to Mode I crack initiation and propagation, but this effect becomes less significant at 150°C than that at R.T..
  • 本間 寛臣
    1991 年 40 巻 453 号 p. 755-760
    発行日: 1991/06/15
    公開日: 2009/06/03
    ジャーナル フリー
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