材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
47 巻 , 8 号
選択された号の論文の13件中1~13を表示しています
  • 許 金泉, 武藤 睦治
    1998 年 47 巻 8 号 p. 804-807
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    It is well known that the stress becomes oscillatory singular near an interface crack tip. Due to the oscillation, the definition of the stress intensity factor for an interface crack would be different from that for a crack in a homogenous media. Several definitions for an interface crack have been reported. However, in application of interfacial fracture mechanics, there is still lack of the definition with physical meanings so that researchers may use different definitions. In the present paper, natures of the existing definitions have been discussed in detail. Then, based on the similarity principle for an interface crack in which a relative distance is accepted instead of an absolute distance, a new definition with physical meanings has been proposed. In the new definition, K1 and K2 approximately correspond the remote tensile and shear stresses, respectively. The tensile and shear stresses in the domain of stress intensity factors are also dominantly expressed by K1 and K2, respectively. These two properties make the new definition more convenient for the strength evaluation of dissimilar joints than the existing definitions. It is also noted that the stress intensity factors for interface cracks based on the existing definitions can be easily reduced to those based on the new definition.
  • 祖山 均, 朴 貞道, 坂 真澄, 阿部 博之
    1998 年 47 巻 8 号 p. 808-812
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    In order to strengthen materials, the improvement of residual stress in stainless steel by using a cavitating jet was investigated. In case of cavitating jet, the cavitation intensity can be controlled by hydraulic parameters such as upstream pressure and downstream pressure. In general, cavitation produces damage on hydraulic machinery. However, at the initial stage of cavitation erosion process, plastic deformation takes place on the material surface, then it is possible to do peening without damage considering the cavitation intensity and the exposure time. In order to evidence the suitable condition on the improvement of residual stress by the cavitating jet, the residual stress in SUS304 and SUS316 was examined. The three normal stresses in different directions were measured by X-ray diffraction method, then the principal stresses were calculated. Both principal stresses were changed from tension to compression within 10 seconds by the cavitating jet. The compressive stress resulted by the cavitating jet was saturated after a certain time. It was concluded that the cavitating jet improved the residual stress in stainless steel SUS316 as well as SUS304.
  • 才本 明秀, 沢田 博司, 今井 康文
    1998 年 47 巻 8 号 p. 813-818
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    A non-uniform temperature rise in the vicinity of crack tip often causes crack propagation. Taking advantage of this phenomenon, some brittle materials can be cleaved without any cutting tools but with an adequate controlling of a temperature distribution in the body.
    In the present paper, based on the linear fracture mechanics, a possibility of the thermal stress cleaving is discussed for a brittle rectangular plate which is heated along its symmetrical axis. A time dependent thermal stress intensity factor of an edge crack was analyzed systematically by changing the plate dimensions and crack length. Experimental findings were compared with the analytical results and good agreements were found.
    Especially, the crack extension characteristics in a cleaving test of a lime-soda glass can be well understood through the dependence of stress intensity factor on heating time and crack tip location.
  • 高松 徹, 市川 昌弘, 松村 隆, 河崎 達也
    1998 年 47 巻 8 号 p. 819-824
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    Indenter tests on a Al2O3 film-WC-Co substrate system using a Al2O3 sphere indenter were carried out to evaluate the fracture strength of the thin film coated on a substrate. Film thickness of the specimen was varied as 2.0, 4.0, 6.0μm, and two kinds of substrate with different hardness and sphere indenter with a daiameter of 16, 19, 25mm were used. The micro fracture strength was evaluated from the load at which a ring crack initiated. Initiation of a ring crack was detected using AE. The fracture strength of the film was evaluated using the micro fracture strength, the residual stress of the film, and the concept of effective area based on the Weibull distribution. Residual stress was measured by the X-ray diffraction method. It was shown that estimated fracture strength of the film a little increased with decreasing the indenter size, and the effect of the film thickness and the substrare hardness on the fracture strength of the film was hardly shown.
  • 小紫 公也, 神谷 哲介, 藤山 大士, 上田 恵嗣, 藤原 俊隆
    1998 年 47 巻 8 号 p. 825-829
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    A numerical code has been developed to simulate the sampling process of an 'asteroid-material sampler' in a sample return mission planed for astrophysics researches. A projectile is lunched at the velocity of several hundred m/s to crush the asteroid surface, which is assumed to consist of hard rocks. In order to analytically reproduce such high velocity impact phenomena of brittle materials, particle methods have been employed in this study. The SPH (Smoothed Particle Hydrodynamics) method and the particle joint method are used to calculate the static pressure and the deviation stress, respectively. Instant failure model and Birch-Murnaghan equation of state are used to describe material characteristics of a granite target. The calculated results could reproduce cracks generated in the granite target.
  • 宮本 昭彦, 村上 敬宜
    1998 年 47 巻 8 号 p. 830-835
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    On crime scenes, plate glass is frequently shot by bullets. The fracture of plate glass by a pachinko ball (steel ball) impact also occurs. Experiments were carried out to obtain basic data for estimating the impact velocities of projectiles from the morphology of the fracture. Projectiles {11mm dia. steel balls and 0.38 inch (9mm dia.) lead bullets} were shot onto ordinary glass plates firmly held around a circular periphery.
    It was assumed that projectile kinetic energy would all be converted into surface energy of fractured glass. The relationship between crack area Af and kinetic energy of projectiles was investigated. A strong experimental correlation was found between Af and the change in kinetic energy. A unique relationship was obtained between crack area and energy consumed during fracture regardless of the projectile material (steel and lead).
  • 岸本 喜久雄, 井上 裕嗣, 納冨 充雄, 渋谷 壽一
    1998 年 47 巻 8 号 p. 836-840
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    Polycarbonate (PC) and acrylonitrile butadiene stylene copolymer (ABS) are known as materials having relatively high impact resistance. Recently, polymer alloy of these two materials has been developed to attain higher impact resistance and has become to be used in various engineering products. However, toughening mechanisms of PC/ABS alloy are not still understood very well. In this study, impact fracture toughness of PC/ABS alloy was evaluated for several weight fractions of PC and ABS. Three-point bend specimens were fractured by a drop weight. The time variation of the dynamic stress intensity factor was evaluated and the critical value of the stress intensity at crack initiation was determined. Fracture surfaces were also observed by SEM. The higher fracture toughness has been obtained for the case that the ABS particles are distributed in PC matrix. ABS particles would play a similar role as the butadiene particles in ABS resin during fracture process, i.e., reduction of the stress triaxiality due to the formation of the voids.
  • 佐藤 清
    1998 年 47 巻 8 号 p. 841-845
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    In this study, the influences of loading rate, crack length, notch acuity, moisture content of specimen, heat-treatment, and polyethylene glycol (PEG) treatment on the fracture toughness of wood were examined experimentally at room temperature. The materials used for the experiment were douglas fir, spruce, western hemlock, Alaska cedar, castor aralia, Japanese beech, ramin, ash, false arbor-vitae and red lauan.
    The results were summarized as follows:
    (1) The fracture toughness was independent of the loading rate in the range of the present experiment.
    (2) The fracture toughness decreased with increasing crack length (a/W) of specimen.
    (3) The fracture toughness increased with inceasing notch root radius (ρ).
    (4) Above moisture content of 15%, the fracture toughness decreased with increasing moisture content.
    (5) The fracture toughness of wood heat-treated at 120°C was larger than that of solid wood, but the fracture toughness decreased with increase of treatment temperature over 120°C.
    (6) The fracture toughness of the PEG impregnated wood was larger than that of the solid wood.
  • 村上 敬宜, 高橋 宏治
    1998 年 47 巻 8 号 p. 846-851
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    Reversed torsional fatigue tests were carried out on the 0.47%C steel specimens containing an initial small crack. The initial small semi-elliptical cracks ranging from 200μm to 1000μm were introduced by the preliminary tension-compression fatigue tests using specimens which contains a hole of 40μm diameter. The crack growth behaviour from a semi-elliptical surface crack was investigated. The effects of artificial small defects on torsional fatigue strength are also reviewed in relation with those of small cracks. The conclusions are summarized as follows:
    (1) In rotating-bending and tension-compression fatigue, the effects of artificial small defects and small cracks are identical from the viewpoint of fatigue limit. However, in torsional fatigue these effects are not identical.
    (2) Cracks leading to fracture were Mode I branched cracks initiated at crack tips. Initiation of Mode II cracks at the pre-crack tip was also observed in most cases in addition to Mode I branched cracks. However, these cracks stopped propagating as the Mode I branched cracks propagated.
    (3) Torsional fatigue limit for a semi-elliptical small cracks is determined by the threshold condition for non-propagation of Mode I branched cracks.
    (4) Torsional fatigue limit of specimens containing a small crack can be successfully predicted by the √area parameter model with a combination of σθmax criterion.
  • 崔 成鐘, 石井 仁, 東郷 敬一郎
    1998 年 47 巻 8 号 p. 852-857
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    Atomic Force Microscopy (AFM) was shown to be the powerful tool for nano-scale characterization of a fracture surface. The fatigue striations of 2017-T351 aluminum alloy were observed using AFM, and from their cross sectional profile of the three-dimensional images, widths and heights of the striations were analyzed. The following results that will be helpful to understand the fatigue crack growth mechanism were obtained. (1) Crack growth rate was the same as a striation width down to the range of 10-5mm/cycle. (2) The striation height increased with the striation width. (3) A ratio of the striation height to its width increased as the stress intensity factor range increased. (4) Effect of a precipitate on the morphology of striation was changed by the relative dimensional difference between the striation width and the precipitate. (5) Both striation height and its width showed a power law relation with a crack tip opening displacement (CTOD).
  • 井上 隆夫, 横幕 俊典, 酒井 忠迪, 能勢 士郎
    1998 年 47 巻 8 号 p. 858-863
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
    The hydrogen-assisted crack propagation behavior of 2·1/4Cr-1Mo steel for a petroleum reactor was examined using a rising CMOD test which used a direct current potential difference (dcPD) method to measure crack extension. The initial hydrogen content in the specimens was about 5ppm when treated with thermal hydrogen charging. The equation to calibrate dcPD, defined in ASTM E647 for fatigue crack growth, gave a shorter crack extension than the actual hydrogen-assisted crack measured on fracture surfaces. A calibration curve for hydrogen cracking was derived from the relation between the actual crack extension and dcPD. The stress intensity factor at the hydrogenassisted crack initiation, KIH, was 23 to 28MPa√m and depended on the loading rate, dK/dt. Crack extension near the side surfaces was less than inside and the crack front was curved. The apparent stress intensity factor at the hydrogen-assisted crack arrest, KTH, calculated using ASTM E813 was 52 to 67MPa√m. The KTH on deepest crack front was estimated using FEM, and found to be smaller than the apparent KTH.
  • 村上 敬宜
    1998 年 47 巻 8 号 p. 865-873
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
  • 江原 隆一郎
    1998 年 47 巻 8 号 p. 874-880
    発行日: 1998/08/15
    公開日: 2009/06/03
    ジャーナル フリー
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