• 제목/요약/키워드: Plane Cracks

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Initiation and Growth Behavior of Small Surface Fatigue Cracks on SiC Whisker Reinforced Aluminum Composite (SiC 휘스커 강화 알미늄기 복합재료의 미소 표면 피로균열의 발생 및 진전거동)

  • Choe, Yeong-Geun;Lee, Taek-Sun;Kim, Sang-Tae;Seo, Chang-Min;Lee, Mun-Hwan
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.6 s.177
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    • pp.1584-1592
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    • 2000
  • Reversed plane bending fatigue tests were conducted on SiC whisker reinforced aluminum composite which were consolidated by squeeze casting process. Initiation and growth of small surface fatigue c racks were investigated by means of a plastic replica technique. The fatigue crack initiated in the vicinity of SiC whisker/matrix interface. It was found that a fatigue crack deflected along SiC whisker and grew in a zig-zag manner microscopically, although the crack propagated along the direction normal to the loading axis macroscopically. The coalescence of micro-cracks was observed in the tests conducted at high stress levels, but were not evident in tests in which lower levels of stress were applied. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn -ΔK realtionship.

Stress Intensity Factors and Possible Crack Propagation Mechanisms for a Crack Surface in a Polyethylene Tibia Component Subject to Rolling and Sliding Contact (구름마찰 접촉하중시 Polyethylene Tibia 표면균열의 응력확대계 수와 복합전파거동에 관한 연구)

  • Kim, Byung-Soo;Moon, Byung-Young
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.12
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    • pp.2019-2027
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    • 2003
  • Pitting wear is a dominant from of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In this study, stress intensity factors, K$\_$I/and $_{4}$, were calculated for a surface crack in a polyethylene-CoCr-bone system under the rolling and/or sliding contact pressures. Crack length and load location were considered in determination of probable crack propagation mechanisms and fracture modes. Positive K$\_$I/ values were obtained for shorter cracks in rolling contact and for all crack lengths when the sliding load was apart from the crack. $_{4}$ was the greatest when the load was directly adjacent to the crack (g/a=${\pm}$1). Sliding friction caused a substantial increase of both K$\_$I/$\^$max/ and $_{4}$$\^$max/. The effective Mode I stress intensity factors, K$\_$eff/, were the greatest at g/a=${\pm}$1, showing the significance of high shear stresses generated by loads adjacent to surface cracks. Such behavior of K$\_$eff/ suggests mechanisms for surface pitting by which surface cracks may propagate along their original plane under repeated rolling or sliding contact.

Study for Possible Crack Propagation Mechanisms for a Surface Cracked in a Polyethylene Tibia Component Subject to Rolling and Sliding Contact (구름마찰접촉하중 시 Polyethylene tibia 요소의 표면균열 복합전파 거동에 관한 연구)

  • Kim, B.S.;Moon, B.Y.
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.1222-1227
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    • 2003
  • Pitting wear is a dominant form of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In this study, stress intensity factors, $K_{I}$ and $K_{II}$, were calculated for a surface crack in a polyethylene - CoCr - bone system under the rolling and/or sliding contact pressures. Crack length and load location were considered in determination of probable crack propagation mechanisms and fracture modes. Positive $K_{I}$ values were obtained for shorter cracks in rolling contact and for all crack lengths when the sliding load was apart from the crack. $K_{II}$, was the greatest when the load was directly adjacent to the crack $(g/a={\pm}1)$. Sliding friction caused a substantial increase of both $K_{I}^{max}$ and $K_{II}^{max}$. The effective Mode I stress intensity factors, $K_{eff}$, were the greatest at $g/a={\pm}1$, showing the significance of high shear stresses generated by loads adjacent to surface cracks. Such behavior of $K_{eff}$ suggests mechanisms for surface pitting by which surface cracks may propagate along their original plane under repeated rolling or sliding contact.

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Initiation and Growth Behavior of Small Surface Fatigue Crack on SiC Particle Reinforced Aluminum Composite (SiC 입자 강화 알루미늄기 복합재료의 표면미소 피로균열 발생 및 초기진전거동)

  • Lee, Sang-Hyoup;Choi, Young-Geun;Kim, Sang-Tae;Lee, Moon-Hwan
    • Composites Research
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    • v.21 no.6
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    • pp.15-22
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    • 2008
  • Reversed plane bending fatigue tests were conducted on SiC particle aluminum composite. The initiation and growth behaviors of small surface fatigue cracks were continuously monitored by the replica technique and investigated in detail. The fatigue life of MMC is shorter than that of matrix because there exists interface debonding of SiC particles and matrix on the whole face of the notch part in the casting metal matrix composite(MMC). The coalescence of micro-cracks was observed in the tests conducted at high stress levels. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn-$K_{max}$ relationship.

Calculation of Stress Intensity Factor KI Using the Exact Solution in an Infinitely Deep Crack in a Half-Plane (반 무한 평판에 존재하는 반 무한 균열에서 엄밀 해를 이용한 응력확대계수 계산)

  • An, Deuk Man
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.1
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    • pp.7-11
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    • 2017
  • In this study, we develop the exact field of mode I in an infinitely deep crack in a half-plane. Using this field, we obtain the exact stress intensity factor $K_{I}$. From the tractions on the crack faces induced by exact field, we calculate the stress intensity factor of this field. We compare the results with the stress intensity factor calculated using Bueckner's weight function formula and that calculated by using Tada's formula listed in "The Stress Analysis of Cracks Handbook" It was found that Bueckner's formula yields accurate results. However, the results obtained using Tada's formula exhibit inaccurate behavior.

Stress Fields Along Semi-Elliptical Interfacial Crack Front with Yield-Strength-Mismatch (항복강도 불일치 반타원 계면균열 선단에서의 응력장)

  • Choi, Ho-Seung;Lee, Hyung-Yil
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.1
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    • pp.126-137
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    • 2003
  • Many research works have been performed on the J-T approach for elastic-plastic crack-tip stress fields in a variety of plane strain specimens. To generalize the validity of J-T method, further investigations are however needed fur more practical 3D structures than the idealized plane strain specimens. The present study deals mainly with 3D finite element (FE) modeling of welded plate and straight pipe, and accompanying elastic, elastic-plastic FE analyses. Manual 3D modeling is almost prohibitive, since the models contain semi-elliptical interfacial cracks which require singular elements. To overcome this kind of barrier, we develop a program generating the meshes fur semi-elliptical interfacial cracks. We then compare the detailed 3D FE stress fields to those predicted with J-T two parameters. The validity of J-T approach is thereby extended to 3D yield-strength-mismatched weld joints, and useful information is inferred fur the design or assessment of pipe welds.

Prediction of Fatigue Life using Extreme Statistics Analysis (표면미소균열의 극치통계해석을 이용한 피로수명예측)

  • Lee, Dong-U;Hong, Sun-Hyeok;Jo, Seok-Su;Ju, Won-Sik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.9
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    • pp.1746-1752
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    • 2002
  • Fatigue fracture in machine components is produced by surface micro-crack from stress concentration area such as notch and material defect. It is difficult to predict the remaining fatigue lift of mechanical components because the surface micro-crack on critical area initiates and grows with statistical distribution. Plane bending fatigue tests were carried out on the plain specimen of Al 2024-T3 and the initiation and growth behavior of surface micro cracks were observed. The statistical distribution of surface length of multiple micro cracks and their maximum length were investigated. The maximum surface crack length distributions were analyzed on the basis of the statistics of extremes in order to examine the prediction of remaining life.

J-T Characterization of Stress Fields Along 3D Semi-Elliptical Interfacial Crack Front (J-T에 의한 3차원 반타원 계면균열선단 응력장의 기술)

  • Choi, Ho-Seung;Lee, Hyung-Yil
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.7
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    • pp.1250-1261
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    • 2002
  • Many research works have validated the J-T approach to elastic-plastic crack-tip stress fields in a variety of plane strain specimens. To generalize the validity of J-T method, further investigations are however needed for more practical 3D structures than the idealized plane strain specimens. In this work, we perform 3D finite element (FE) modeling of welded plate and straight pipe, and accompanying elastic, elastic-plastic FE analyses. Manual 3D modeling is almost prohibitive, since the models contain semi-elliptical interfacial cracks which require singular elements. To overcome this kind of barrier, we develop a program generating the meshes for semi-elliptical interfacial cracks. We then compare the detailed 3D FE stress fields to those predicted with J-T two parameters. Thereby we extend the validity of J-T application to 3D structures and infer some useful informations for the design or assessment of pipe welds.

Multiaxial fatigue behaviors of open-rib to crossbeam joints in orthotropic bridge structures

  • Yang, Haibo;Qian, Hongliang;Wang, Ping;Dong, Pingsha;Berto, Fillipo
    • Steel and Composite Structures
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    • v.42 no.6
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    • pp.843-853
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    • 2022
  • The fatigue behavior of welded open rib-to crossbeam joints (ORCJ) in orthotropic bridge structures is investigated using a traction structural stress method. The fatigue behaviors of welded open rib-to crossbeam joints have been a subject of study for decades for ensuring operational safety and future design improvement. A mesh-insensitive combination of traction structural stresses in ORCJ was obtained considering the effect of in-plane shear stress and validated by fatigue test results. The proposed method is advantageous for predicting fatigue cracks that initiate from the crossbeam cutout and propagate along the crossbeam. The investigations carried out with the proposed approach reveal that the normal structural stress decreases with the propagation of fatigue cracks, while the ratio of shear stress to normal stress increases. The effect of shear structural stress is significant for the analysis of fatigue behavior of ORCJ in multiaxial stress states.

An Experimental and Analytical Study on Shear Transfer for Safety Evaluation of Concrete Structure (콘크리트 구조물의 전단 안정성 평가를 위한 전단전달 실험 및 해석)

  • Kim, Kwang-Soo
    • Journal of the Korean Society of Safety
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    • v.23 no.3
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    • pp.42-50
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    • 2008
  • This study, push-off tests for the initially uncracked specimens were conducted to investigate shear transfer mechanism in reinforce concrete elements. Experimental programs for shear transfer were undertaken to investigate the effect of the concrete compressive strength, the presence of steel stirrups as shear reinforcement and the amount of steel stirrups. As the shear plane is loaded, several cracks form in a direction inclined to the shear plane, creating compression struts in the concrete. For this stage, shear is being transferred through a truss-like action produced by the combination of the compressive force in the concrete struts and the tensile force that the steel reinforcement crossing the shear plane develops. In the normal strength concrete specimens with steel stirrups, ultimate failure occurred when the compression struts crushed in concrete. In the high strength concrete specimens, on the other hand, ultimate failure occurred when the steel stirrups developed their yield strength.