• Title/Summary/Keyword: Fracture Surface Shape

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Numerical Simulation of Fatigue Growth of Multiple Surface Crack under Fatigue Load (피로 하중하에서의 복수표면크랙진전에 관한 수치시뮬레이션)

  • 한문식
    • Transactions of the Korean Society of Automotive Engineers
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    • v.10 no.6
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    • pp.133-141
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    • 2002
  • This paper describes a versatile finite element technique which has been used to investigate wide range of structural defects of practical importance. The procedure automatically remeshes the three-dimensional finite element model during the stages of crack growth. Problems include the surface cracks in leak-before-break situations, the shape development of multiple surface defects.

A Model Estimating the Propagation Behavior of through cracks in Aluminum alloy A5083-O for LNG Tank (LNG탱크용 알루미늄합금 A5083-O의 관통균열 전파거동 예측 모델)

  • 김영식;조상명;김종호
    • Journal of Ocean Engineering and Technology
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    • v.12 no.1
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    • pp.50-57
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    • 1998
  • The leak before break(LBB) concept is generalized on the design of LNG tanks, pressure vessels and nuclear reactor in that any leakage of containment, in whatever amount, will not result in catastropic failure. For this purpose it is necessary to determine the surface crack shape, the opening displacement and the risk of catastropic brittle fracture when it becomes a through crack. In this study the crack propagation behavior of surface flaws and the crack opening displacement of through cracks under combined membrane and bending stresses were investigated with fatigue tests and fracture toughness test of aluminium alloy A5083-O. And fracture mechanics analysis of the crack opening displacement of through cracks were made in order to develop a new model expressing the behaviors of COD under combined membrane and bending stresses.

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High Cyclic Fatigue Life and Fracture Behaviors of Shot-Peened Bearing Steel (쇼트피닝 처리를 한 베어링강의 고사이클 피로수명 및 파괴거동)

  • Yoon, Sang-Jae;Choi, Nak-Sam
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.9
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    • pp.1119-1129
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    • 2011
  • Shot-peening effects on the fatigue behavior of bearing steel were investigated under the high cyclic loading. Hourglass shape specimens were made of bearing steel(JIS-SUJ2) for rotary bending fatigue tests. Two kinds of treatments were performed : a heat treatment and a shot-peened surface treatment after the heat treatment. The fracture surfaces of specimens were classified into two types of fracture mode : the surface fracture mode induced by a surface defect and the internal fracture mode induced by a nonmetallic inclusion. Inclusion depth and shape affected considerably the fatigue life. Shot-peening treatment improved much the fatigue life of the bearing steel under low and high levels of cyclic loads. Probabilistic-stress-life (P-S-N) curves were suggested for the reliable fatigue life estimation of the improved bearing steel.

A Study on the Surface Characteristics n the Alumina Grinding (알루미나 연삭표면 특성에 관한 연구)

  • 하상백
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 1999.10a
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    • pp.519-524
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    • 1999
  • To manufacture alumina products, sintering and grinding process are needed. In Al2O3 grinding, macro/micro surface fracture and cracks are easily occurred on the ground surface because of its high brittleness. In view point of fatigue fracture, surface profile produced by grinding is considered as notches. Therefore, it was reasonable that magnitudes and shapes of surface profiles effects on fatigue strength and life. Particularly, surface finish of Al2O3 which have high hardness and brittleness have an effect on fatigue strength. In this paper, some experiments are carried out to examine influence of grinding conditions to magnitude and shape of surface profile as well as the relationships of Ra, Rmax, Rmax/Ra, and Ku. Through the experimental results, It is found that Ra and Rmax was affected by grinding conditions, but Rmax/Ra and Ku was not. There are linear relations between Ra and Rmax, and between Rmax/Ra and Ku.

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A fracture mechanics evaluation on the fatigue crack propagation at spot welded aluminum joint in passenger car body (스폿용접된 자동차 차체용 알루미늄 박판의 피로균열진전의 파괴역학적 평가)

  • 박인덕;남기우;강석봉
    • Journal of Ocean Engineering and Technology
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    • v.11 no.3
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    • pp.20-28
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    • 1997
  • The fatigue crack propagation properties and fatigue life of two kinds of Al body panel for automobile were examined experimentally by using the plate specimen and the single spot welding specimen. The fatigue limit of spot welding specimens was lower than that of a plate specimen. The fatigue limit was similar in two kinds of spot welding specimen. The shape and size of crack propagation were observed and measured on beach mark of fracture surface. The crack propagation of surface crack specimen showed almost same tendency to that of a thick plate as almost semi-elliptical. In spot welding specimen, the fatigue crack occurred in inside surface of nugget area was almost semi-elliptical. The crack growth rate can be explained using equation of stress intensity factors.

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A Study on the Effect of Clearance and V-Ring Shape in a Fine Blanking Process (파인블랭킹 공정 시 클리어런스 및 V링 형상의 영향에 관한 연구)

  • Kim, Hyung-Rak;Park, Jong-Yeon;Kim, Hyung-Jong
    • Journal of Industrial Technology
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    • v.24 no.A
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    • pp.29-35
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    • 2004
  • Fine blanking can be considered as a manufacturing process capable of producing sheet metal parts with completely smooth edges that may be hardly obtained by conventional shear-cutting procedures. This fact, together with the considerable economic advantages offered by this process, has been responsible for the rapid acceptance of fine blanking throughout the manufacturing industry all over the world, and the discovery of many new applications. This study was performed to investigate the effect of clearance and V-ring shape on the quality of sheared surface in a fine blanking process. The critical value needed to apply the normalized Cockcroft-Latham fracture criterion to the simulation of fine blanking is obtained by correlating the result of finite element analysis and that of experiment for the uniaxial tensile test. From finite element analysis of an axisymmetric fine blanking process, it has been found that punch load, die-roll depth, burnish zone size and shape of sheared surface are considerably influenced by clearance and V-ring shape.

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A Numeric Modelling Technique for the Shape Development of Fatigue Crack (피로 균열 형상 진전의 수치 모델링 기법에 관한 연구)

  • Han, Moon-Sik
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.2 s.95
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    • pp.225-233
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    • 1999
  • This paper describes a versatile finite element technique which has been used to investigate of wide range of structural defects of practical importance. The procedure automatically remeshes the three-dimensional finite element model during the stages of crack growth. Problems analyzed to date include the surface cracks in leak-before-break situations, the development of quarter-elliptical corner defects, planar semi-elliptical surface defects and the fatigue growth of defects.

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Comparison with R Curve Behavior fer the K and J Parameter of structural Steel Hot-Rolled Thin Plates (일반구조용강 열간압연 박판의 K와 J 파라미터에 대한 R곡선 거동의 비교)

  • 이계승;이억섭
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2002.10a
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    • pp.812-815
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    • 2002
  • The shape of K-R curve for an ideally brittle material is flat because the surface energy is an unvaried material property. However, the K-R curve can take on a variety of shapes when nonlinear material behavior accompanies fracture. By the way, a general metallic material is nonlinear, structural steel is such. Therefore, the J-R curve form J-integral value instead of K parameters can be used to evaluate elastic-plastic materials with flaws in terms of ductile fracture that can be significant to design. In this paper, R-curve behaviors form K and J parameter is considered for the precise assessment of fracture analysis, in case of JS-SS400 steels.

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Analysis of the fracture surface morphology of concrete by the method of vertical sections

  • Konkol, Janusz;Prokopski, Grzegorz
    • Computers and Concrete
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    • v.1 no.4
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    • pp.389-400
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    • 2004
  • The examinations carried out have confirmed a relationship existing between the character of fracture surfaces and the composition and structure of (basalt and gravel) concretes. For both concretes investigated, a very good correlation was obtained between the profile line development factor, $R_L$, and the fracture surface development factor, $R_S$. With the increase in the $R_L$ parameter, the fracture surface development factor $R_S$ also increased. Agreement between the proposed relationship of $R_S=f(R_L)$ and the proposal given by Coster and Chermant (1983) was obtained. Stereological examinations carried out along with fractographic examinations made it possible to obtain a statistical model for the determination of $R_L$ (or $R_S$) based on the volume of air voids in concrete, $V_{air}$, the specific surface of air pores, $S_V_{air}$ the specific surface of coarse aggregate, $S_{Vagg.}$, and the volume of mortar, $V_m$. An effect of coarse aggregate type on the obtained values of the profile line development factor, $R_L$, as well as on the relationship $R_S=f(R_L)$ was observed. The increment in the fracture surface development factor $R_S$ with increasing $R_L$ parameter was larger in basalt concretes than in gravel concretes, which was a consequence of the level of complexity of fractures formed, resulting chiefly from the shape of coarse aggregate grains.

A Study on a Relationship Between the Surface Roughness of Fracture CT Specimen Broken by Fatigue Crack Growth and the Moments (피로균열성장에 의해 파단된 CT시험편의 표면조도와 모멘트의 관계에 관한 연구)

  • Kim, Kyun-Suk;Jung, Hyun-Chul;Kim, Kyung-Su;Park, Chan-Joo;Jang, Hos-Seob
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.19 no.4
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    • pp.462-468
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    • 2010
  • Fatigue crack growth caused by surface defects is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LPG/LNG fuel tank and other various structures. So, this paper aims to investigate the relationship between the surface roughness of fracture CT specimens and the moments on the specimen when doing fatigue test for the evaluation and the assurance of safety of structures from fatigue crack deconstruction. In this experiment, the CT specimens were loaded by a fatigue testing machine with changing loads until they are broken. The surface roughness of the fracture CT specimens was measured using 3D precise shape measuring equipment and digital holography. As a result of this study, It was identified that the average roughnesses are similar at the positions that has a same moments by comparing the results with the moments on the specimen according to the position.