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| 1.
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Makabe, C ; Naka, K ; Katsushima, Y
概要:
The unstable growth of fatigue cracks brings a material or structure to catastrophic failure. It is better than any fati
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gue crack does not initiate in engineering applications. However, fatigue crack initiation cannot be prevented in some applications because maintaining their efficiency or performance is important factor for usage. When a crack is initiated in machine equipment, it should be repaired or the equipment replaced. Sometimes, the cracked material was repaired and many repair methods were proposed. In this report, a simple method of stopping crack growth is proposed to apply to a cracked plate with varying thickness. The stop-hole and crack arrester were applied in the present method.
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| 2.
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真壁, 朝敏 ; 才本, 明秀 ; 福里, 真吾 ; 小倉, 正也 ; Makabe, Chobin ; Saimoto, Akihide ; Fukuzato, Singo ; Ogura, Masaya
概要:
Many literatures have been given for the stress intensity factors of a crack emanating from a hole or notch in infinite
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or semi infinite body. However, there has been few detailed discussion about applicability of such stress intensity factors for the finite body. In this study, the stress intensity factors of a crack emanating from a U shaped center notch in finite plate are analyzed for various crack lengths and parameters characterizing plate dimensions and notch shape on the bases of the body force method. These results are then compared with those for the center cracked plates. Also, the relationship between the variations of such stress intensity factors and the fatigue crack's behavior are discussed. The stress intensity factor of center cracked specimens can approximate that of center notched specimens with crack when an equivalent crack length is used for calculations in the cases of θ/W<0.1 and c/θ<1, where c, θ and W are crack length measured from notch bottom, notch root radius and semi width of specimen, respectively.
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| 3.
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真壁, 朝敏 ; Purnowidodo, Anindito ; 才本, 明秀 ; 福里, 真吾 ; 宮﨑, 達二郎 ; Makabe, Chobin ; Saimoto, Akihide ; Fukuzato, Singo ; Miyazaki, Tatsujirou
概要:
A simple method of evaluating the crack propagation rate of a specimen with sharp notch by using an effective stress int
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ensity factor range was proposed. This study also had a special purpose of evaluating the crack propagation after overload. A 6mm long U-shaped notch was cut in the center section of the specimen. The notch root raidus ρ was chosen as 0.1mm and 1mm. These were regarded as center notched specimens. The crack propagation behavior of these specimens was compared with a center cracked specimen. Push-pull fatigue tests were carried out under stress ratios R=0, -1, and -1.5. After overload, retardation of crack growth was observed under R=0 and -1, in the cases of the notched specimen and center cracked specimen. However, where R=-1.5, the acceleration of crack growth was observed after overload in both types of specimens. Even though crack growth was accelerated or decelerated, the rate was able to be evaluated by effective stress intensity factor range. The effective stress intensity factor range of the center cracked specimen could also be applied to that of the notched specimen with, ρ=0.1mm and 1mm.
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| 4.
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真壁, 朝敏 ; Socie, Darrell F. ; 末吉, 敏恭 ; 上原, 崇 ; Makabe, Chobin ; Sueyoshi, Toshiyasu ; Uehara, Takashi
概要:
The mechanism of shear mode fatigue crack growth in pure aluminum was investigated using pre-cracked specimen. The crack
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propagation tests were carried out by the cyclic torsion with a static axial load and the push-pull, respectively. In the case of the cyclic torsion, the fatigue crack grew by shear mode. The micro-cracks initiated perpendicular and parallel to the direction of main crack growth during the cyclic torsion. However, the interactions were not observed between the main crack and the micro-cracks, which directed perpendicular to the direction of main crack growth. The behavior of micro-cracks on pure aluminum was different from that of 4340 steel in which the pure shear mode crack growth hard to occurred. The crack growth behavior is related to the slip systems of the materials. The number of slip plane and the friction resistance between molecules of aluminum are smaller than those of steel. These and the loading conditions are related to the mechanism of the shear mode crack growth in aluminum. Under condition in the prenent study, the relation between the crack propagation rate and the stress intensity factor range was almost the same in the cases of the push-pull and the cyclic torsion with tension. However, the effects offriction between the crack surfaces on the crack propagation in a shear mode were not exactly evaluated.
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| 5.
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真壁, 朝敏 ; 末吉, 敏恭 ; Purnowidodo, Anindito ; 宇都宮, 登雄 ; Makabe, Chobin ; Sueyoshi, Toshiyasu ; Utsunomiya, Takao
概要:
In the present study a detection method of an overload application during stress cycles under constant amplitude was inv
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estigated. Also, the effect of a tensile overload was shown at three stress ratios: R = 0, -1.5, in order to understand the effects of R on crack propagation after an overload. At a baseline of R = 0, after an overload retardation in the crack propagation was observed. However, in the case of R = -1.5, the fatigue crack growth rate actually accelerated after a tensile overload. That behavior of crack propagation was tried to be detected by the information of strain waveform h; h = ε_y + 1.2λε_x, where, ε_y and ε_x are the local strains at the specimen axis, and λ is the strain range ratio Δε_y/Δε_x. The waveform shape of h was changed after the overloading. Also, the application of an overload can be detected by the variation of the strain range ratio λ. Specially, the present method is useful for cases of the crack propagation stage under negative R conditions.
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| 6.
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兼城, 英夫 ; 我那覇, 簾 ; 真喜志, 隆 ; 真壁, 朝敏 ; Kaneshiro, Hideo ; Ganaha, Ren ; Makishi, Takashi ; Makabe, Chobin
概要:
Fatigue properties of the nitrided rolled steel are investigated on the basis of the observations of the substructures p
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roduced by nitriding and fatigue. It is found that the fatigue limit of the nitrided rolled specimens is much higher than that of the nitrided annealed ones and the substructures before the nitriding are effective for the improvement of the fatigue strength. The substructure of the rolled steel consists of cells with dislocation clusters within them. By means of nitriding treatment, cell structures and twins appear in the inner part of the compound layer, while uniformly distributed dislocation clusters in the region just below the compound layer and the inner part of the diffusion layer. After fatigue test, most of these substructures are preserved except for the region just below the compound layer where the cell structures due to active dislocation motions were formed.
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| 7.
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宇都宮, 登雄 ; 石井, 宏紀 ; 真壁, 朝敏 ; 飯田, 國廣 ; Utsunomiya, Takao ; Ishii, Hironori ; Makabe, Chobin ; Iida, Kunihiro
概要:
If fatigue crack initiation and growth behavior in structures and materials can be detected based on strain information
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on the surface, the detecting method becomes a practical one for evaluating the fatigue damage and the residual life. From this standpoint, the strain interference method of detecting crack initiation and crack growth becavior was proposed by one of authors and the effectiveness of the method has been shown mainly through the fatigue tests using center-cracked specimens. In this paper, the applicability of the strain interference method to double V-notched specimens is investigated. First, the finite element analyses are carried out for double V-notched specimens, which are subjected to the tension-compression axial loading. The locations of strain measurement for detecting crack initiation and crack tip opening and closing points are discussed. After that, the exial loading fatigue tests of the specimen are carried out referring to the result obtained in finite element analyses. As a result of the experiment, it is shown that the crack initiation and crack growth behavior can also be detected by the strain interference method.
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| 8.
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兼城, 英夫 ; 下地, 義光 ; 真壁, 朝敏 ; 真喜志, 隆 ; 片桐, 一宗 ; Kaneshiro, Hideo ; Shimoji, Yoshimitu ; Makabe, Chobin ; Makishi, Takashi ; Katagiri, Kazumune
概要:
Fatigue properties of the nitrided SS 400 are investigated on the basis of the observation of dislocation structures, su
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rface topography and fracture surface by means of optical and electron microscopy. Both slip bands and dislocation structures during stress cycling are not formed in the compound layer. The dislocation morphology of the diffusion layer is composed of the untangled and uniformly distributed dislocations and the clusters of the dislocation dipoles at lower stress amplitude, but well defined cell structures at higher stress amplitude. It is also found that the fatigue cracks of the nitrided specimen are initiated without the formation of slip bands and the separation between the compound layer and the diffusion layer occurs during cyclic loading. On the basis of these observations, a mechanism of fatigue fracture for the nitrided SS 400 is proposed.
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| 9.
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真壁, 朝敏 ; Makabe, Chobin
概要:
科研費番号: 07650109
平成7年度～平成8年度科学研究費補助金（基盤研究（C)(2))研究成果報告書 研究概要：疲労き裂の伝ぱによってこれまでに多くの破壊事故が生じている。従って、疲労破壊事故を未然に防ぐには,き … 裂の発生を検出することが重要である。また,それと同時に発生したき裂の進展を遅らせることや阻止することも重要であると思われる。本研究では,部材の加工形状,複合化等によって,き裂の進展を遅らせる(抑制する)ことができるかどうかについて検討した。まず,き裂が進展する方向に溝を設けた試験片を用いて板厚の急変によってき裂伝ぱ速度が抑制できるかどうかについて検討した。その結果,き裂伝ぱ速度は溝の前で加速し,溝を通過した後に減速することがわかった。しかし,平均的なき裂伝ぱ速度は溝の配列や深さによって異なった。1つの溝を加工した試験片では,溝のない試験片の場合を基準にした場合,溝の深さを板厚の6割以上にした場合に基準より寿命が長くなった。このことから,板厚を急に変化させた場合にはき裂伝ぱが抑制できる場合があることが期待できることがわかった。そして,この理由としては,き裂先端に過大な応力が単発的に加わり,圧縮の残留応力が生じたことが考えられた。また,密接して溝を加工した場合は溝の深さにかかわらず,き裂伝ぱ寿命は基準の場合より長くなることはなかった。この場合には溝による応力集中の干渉とき裂先端に複雑な変動応力が加わるため,き裂伝ぱが加速することが考えられた。き裂のある板とない板を貼合わせた場合には,最終的に試験片が分断するのを防ぐ効果はあったが,き裂伝ぱそのものは1枚の板の場合と大差がなかった。また,局所的に試験片の硬さや組織を変化させた場合には,き裂伝ぱ方向にその変化した部分がある場合にき裂伝ぱ速度が抑制されることがわかった。以上のことから部材の加工法等に工夫をすることによってき裂伝ぱ速度が抑制できる可能性があることがわかった。 研究概要：If we can detect the crack initiation and control the crack propagation, the fracture accident owing to the metal fatigue can be reduced. Therefore, an improvement in the resistance ability of fatigue crack propagation in a metal was studied. For this purpose, the materials were machined and heat-treated by some method. One of these specimen has a groove which is cut in the loading direction. In this specimen the fatigue crack propagation was investigated when the material has a cross-section of complicated shape. The nondimensional depth of groove to the specimen thickness b/t was chosen three values, that is, b/t=0.125,0.45,0.65. The delay of crack propagation was observed in the case of b/t=0.65. Therefore, the resistance ability of fatigue crack propagation of a material can be improved, if the material was machined in a special shape. The crack propagation behavior of a local-heated specimen was investigated. This specimen was used for the substitution of a composite material. When the local-heated zone was located in front of the crack tip, the crack propagation rate was decelerated. From those results, it is found that a material can be improved in the resistance of the fatigue crack propagation, if the material is machined or heat-treated by a special technique. Also, it is expected that composite material can be designed for the purpose that the fatigue crack propagation rate is decelerated. 未公開：P.26以降（別刷論文のため） 研究報告書 続きを見る |
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| 10.
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兼城, 英夫 ; 片桐, 一宗 ; 真壁, 朝敏 ; 糸村, 昌祐 ; Kaneshiro, Hideo ; Katagiri, Kazumune ; Makabe, Chobin ; Itomura, Shousuke
概要:
Although a number of models for the initiation of intergranular cracks under fatigue have been proposed, most of them ar
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e not considered to be sufficient qualitatively. In this study, the mechanism of intergranular crack initiation in fatigued copper is investigated on the basis of the observation of dislocation structures and surface topography by means of transmission and scanning electron microscopy. At the intersections of ladder-like structures with the grain boundary, extrusion-type intergranular deformations are frequently observed. It is also found that the ladder-like structures are sometimes formed along the grain and twin boundaries. On the basis of these observations, a mechanism of crack initiation at the grain boundary is proposed.
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| 11.
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真壁, 朝敏 ; 玉寄, 博道 ; 兼城, 英夫 ; Makabe, Chobin ; Tamayose, Hiromichi ; Kaneshiro, Hideo
概要:
Fatigue crack propagation behavior under the mixed-mode condition which combined modes I and III and modes I, II and III
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was investigated in a push-pull fatigue test of notched specimen. The notch inclined in the thickness direction was cut at the center of the specimen. Four values were selected for the notch length 2b, that is, 2b=9,15, 25, 35 mm. In the present study, the crack propagation behavior under the mixed modes is assumed to be dominated by the maximum principal stress criterion. The stress intensity factor K_p of mode I was calculated with the projected crack length along the load direction and the crack propagation rate da/dN under the mixed modes was evaluated using it. This stress intensity factor K_p can approximate relatively well the stress intensity factor determined on the basis of the maximum principal stress criterion in the case of the specimen used in the present experiment. The crack propagation rate da/dN can reasonably be evaluated with the effective stress intensity factor range of K_p independent of the applied mean stress.
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| 12.
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真壁, 朝敏 ; 西田, 新一 ; 浦島, 親行 ; 兼城, 英夫 ; Makabe, Chobin ; Nishida, Shin-ichi ; Urashima, Chikayuki ; Kaneshiro, Hideo
概要:
A method of detecting fatigue crack initiation in some weak section of a machine element is examined using a holed speci
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men under random load conditions. Waveforms of two strain functions, that is h1 = ε_
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| 13.
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兼城, 英夫 ; 日賀, 正貴 ; 真壁, 朝敏 ; 片桐, 一宗 ; 糸数, 真哉 ; Kaneshiro, Hideo ; Higa, Masaki ; Makabe, Chobin ; Katagiri, Kazumune ; Itokazu, Masaya
概要:
Fatigue properties of polycrystalline copper films subjected to pulsating stresses are investigated on the basis of obse
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rvations of surface topography, fracture surface and dislocation structure. Fatigue limit corresponding to 10^7 cycles of a rolled copper film is 2. 3 times higher than that of an annealed one, but the fatigue limit ratio of the rolled specimen is lower than that of annealed one. From the observations of the surface crack and fracture surface, it is found that fatigue crack initiation and early-stage crack growth mechanisms of annealed bulk copper are not necessarily applicable to those of film. No striations are formed in both films. In annealed films, cell structures are formed under high-cycle fatigue whereas no band/ladder structures are formed. Dislocation structures near the fatigue crack in annealed films are similar to those of bulk specimens except for the absence of intensely elongated cells observed in the shear flow regions in the bulk specimen. No appreciable change during fatigue was found in the dislocation structures of rolled films.
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| 14.
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真壁, 朝敏 ; 崎浜, 寿 ; Makabe, Chobin ; Sakihama, Hisashi
概要:
The effect of tensile overload on fatigue crack propagation behavior of Fe-3% Si alloy was investigated by the measureme
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nt of surface crack length and crack closure level. Crack propagation after the overloading was observed to be delayed under constant stress amplitude. The delayed propagation was predominated by the crack closure behavior, and when the crack propagation rate da/dN became lower, the crack closure level became higher. Also, the crack propagation law could be reasonably evaluated with the effective stress intensity factor range ΔK_
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| 15.
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真壁, 朝敏 ; 兼城, 英夫 ; 玉寄, 博道 ; 屋富祖, 建樹 ; 屋良, 秀夫 ; Makabe, Chobin ; Kaneshiro, Hideo ; Tamayose, Hiromichi ; Yafuso, Tateki ; Yara, Hideo
概要:
Fatigue crack propagation behavior under the mixed-mode condition which combined modes I , II and III was investigated i
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n a push-pull fatigue test of the notched specimen. The notch inclined in the thickness direction was cut at the center of the plate specimen. Some fatigue cracks were initiated from the notch root, and the interaction of these cracks was observed in the crack propagation stage. However, in the present study, the crack length including notch length was treated as a single-center crack. The fatigue crack propagation rate da/dN was evaluated with effective stress intensity factor range ΔK_
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| 16.
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真壁, 朝敏 ; 大場, 克巳 ; 兼城, 英夫 ; 糸数, 真哉 ; Makabe, Chobin ; Ohba, Katsumi ; Kaneshiro, Hideo ; Itokazu, Masaya
概要:
Fatigue crack propagation behavior was observed by means of the beach mark method on the fracture surface. In the specim
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en with perpendicularly intersecting two holes, the fatigue crack was initiated at the internal corners of two holes and propagated from the internal section to the outside. In the first stage of crack propagation, the crack front formed a straight line and the cracked area in the form of a triangle was observed. This shape gradually changed with the crack propagation. In the final stage of crack propagation, a parabola-like crack front was observed. The crack propagation was examined with the change in the cracked area S. The crack propagation rate of the area, dS/dN, was found to be proportional to the area S, and the crack propagation law could be expressed as dS/dN=CΔσ^nS (Δσ is the cyclic stress range, n and C are constant).
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| 17.
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真壁, 朝敏 ; 西田, 新一 ; 兼城, 英夫 ; 玉城, 史郎 ; Makabe, Chobin ; Nishida, Shin-ichi ; Kaneshiro, Hideo ; Tamaki, Shiro
概要:
A method of detecting fatigue crack initiation in some weak section in an actual working machine is examined using a par
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tially notched specimen. The waveform of the strain function composed of strains in the vicinity of the partial notch is successionally observed. It is found that such a strain waveform changes its shape at crack length 1mm due to the crack closure behavior. Therefore, in this experiment, the crack initiation can be detected at about crack length 1mm. Since the engineering crack initiation size is frequently taken to be 1mm, the present method for detection of crack initiation can be applied to actual machine equipment. Also, this waveform is analyzed with FFT. The power spectrum density of the waveform changes immediately after the crack length reaches 1mm. Furthermore, the shape of the coherence of two waveforms composed of same strains clearly varies at the same length, 1mm. Thus, the engineering size crack initiation is expected to be easily detected through the analysis of the strain waveform.
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| 18.
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真壁, 朝敏 ; 糸数, 真哉 ; 大場, 克巳 ; 兼城, 英夫 ; Makabe, Chobin ; Itokazu, Masaya ; Ohba, Katumi ; Kaneshiro, Hideo
概要:
A detection of fatigue crack initiation and growth behavior of a blind-holed specimen was carried out by means of the st
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rain interference method. The strains on the center axis of the hole are used for the determination of the strain function 'h'. The crack initiation can be detected using the waveform of the strain function 'h'. The waveform of 'h' of the precracking can be distinguished from that of the postcracking. The penetration of crack depth into the specimen thickness can also be inspected using the waveform of the strain function 'h'. Such variations of the waveform are based on the crack tip opening and closing behavior. Furthermore, the approximate estimation of crack length was carried out using the value of the strain function 'hh' measured at the maximum stress point.
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| 19.
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真壁, 朝敏 ; 西田, 新一 ; 兼城, 英夫 ; 大場, 克巳 ; 屋良, 秀夫 ; Makabe, Chobin ; Nishida, Shin-ichi ; Kaneshiro, Hideo ; Ohba, Katsumi ; Yara, Hideo
概要:
The measurement of fatigue crack tip opening stress σ_
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| 20.
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真壁, 朝敏 ; 西田, 新一 ; 兼城, 英夫 ; Makabe, Chobin ; Nishida, Shin-ichi ; Kaneshiro, Hideo
概要:
Fatigue crack tip opening stress σ_
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| 21.
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真壁, 朝敏 ; 兼城, 英夫 ; Makabe, Chobin ; Kaneshiro, Hideo
概要:
A simple and new method of detecting for crack initiation at a notched section of a moving machine element is proposed a
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nd applied to a specimen with a blind hole. In this experimental case, the fatigue crack tip opening and closing point can be measured using the relation between the following function h and cyclic stress σ:h=ε_y+λε_x, λ=Δε_y/Δε_x, where ε_y and ε_x are the strains measured in the vicinity of the edge of the hole in the center axis, and Δε_y and Δε_x are the ranges of ε_y and ε_x, respectively. Crack initiation at the hole edge can also be detected with the waveform of such a function h. Furthermore, until the crack reaches the hole bottom, the crack length can be evaluated with the range of the subtractive function related to h. The detective method proposed can be expected to be applicable to the monitoring of crack growth in many real cases.
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| 22.
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真壁, 朝敏 ; 兼城, 英夫 ; 糸数, 真哉 ; 屋富祖, 建樹 ; Makabe, Chobin ; Kaneshiro, Hideo ; Itokazu, Masaya ; Yafuso, Tateki
概要:
Effective stress intensity factor range ΔK_
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| 23.
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兼城, 英夫 ; 真喜志, 康二 ; 屋富祖, 建樹 ; Kaneshiro, Hideo ; Makishi, Yasuji ; Yafuso, Takeki
概要:
同一のα相で積層欠陥エネルギの異なる純銅, 85/15黄銅, 70/30黄銅について大気中と真空中で疲労試験を行い, 寿命の延び率と応力振幅および積層欠陥エネルギとの関係について検討した. その結果, 積層欠陥エネルギが低い材料ほど真空中で
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の寿命は延び, また大気腐食効果は切欠き材より平滑材に, き裂進展の第2段階より第1段階に顕著に現れること, 真空中ではき裂は粒界を進展しにくいことが明らかになった.
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