• Title/Summary/Keyword: Surface Crack

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Bounary Element Analysis of Thermal Stress Intensity Factors for Cusp Cracks (커스프 균열에 대한 열응력세기 계수의 경계요소해석)

  • 이강용;조윤호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.1
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    • pp.119-129
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    • 1990
  • In case that the body with a cusp crack is under uniform heat flow, thermal stress intensity factors are calculated by using boundary element method with linearized body force term. The crack surface is under insulated or fixed temperature condition and the types of crack are symmetric lip and airfoil cusps. Numerical values of thermal stress intensity factors for a Griffith crack and cusp cracks in infinite bodies are proved to be in good agreement within .+-.5% when compared with the previous numerical and exact solutions, respectively. The thermal stress intensity factors for symmetric lip and airfoil cusp cracks in finite bodies are calculated about various effective crack lengths, configuration parameters, and heat flow directions. With the same crack surface thermal boundary conditions, heat flow directions and crack lengths, there are no appreciable differences in variations of thermal stress intensity factors between symmetric lip and airfoil cusp cracks. The signs of thermal stress intensity factors for each cusp crack are changed with each crack surface thermal boundary condition.

The Characteristics of Fatigue Cracks Emanating from Small Hole Defects Located Opposite Position of the Shaft Cross Section (축단면 내 대칭위치에 존재하는 원공결함에서 발생하는 피로균열 거동)

  • Song, Sam-Hong;An, Il-Hyeok;Lee, Jeong-Mu
    • Journal of the Korean Society for Precision Engineering
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    • v.19 no.10
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    • pp.84-91
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    • 2002
  • The shaft with the circular cross section have symmetric structural combination parts to keep the rotating balance. Hence the crack usually emanate from symmetric combination parts due to the stress concentration of these parts. In this study to estimate the fatigue behavior of symmetric cracks, the fatigue test was performed by using rotary bending tester and the specimen with symmetric defects in circular cross section. From the facts the characteristics of crack initiation and propagation on the symmetric surface cracks in circular cross section was examined. Also we observed the internal crack using oxidation coloring and investigated the fatigue behavior using the relationship between surface crack and internal crack. As a result of fatigue lift of symmetric cracks was reduced to 35% compared to single crack’s. We examined the characteristics of fatigue behavior in element with symmetric cracks using internal crack propagation rate and maximum stress intensity factor range obtained from approximation method.

Fatigue Crack-Tip Stress Mapping Using Neutron Diffraction

  • Choi, Gyudong;Lee, Min-Ho;Huang, E-Wen;Woo, Wanchuck;Lee, Soo Yeol
    • Korean Journal of Materials Research
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    • v.25 no.12
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    • pp.690-693
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    • 2015
  • Fatigue crack growth experiments were carried out on a 304 L stainless steel compact-tension(CT) specimen under load control mode. Neutron diffraction was employed to quantitatively measure the residual strains/stresses and the evolution of stress fields in the vicinity of a propagating fatigue-crack tip. Three principal stress components (i.e. crack growth, crack opening, and through-thickness direction stresses) were examined in-situ under loading as a function of distance from the crack tip along the crack-propagation path. The stress/strain fields, measured both at the mid-thickness and near the surface of the CT specimen, were compared. The results show that much higher compressive residual stress fields developed in front of the crack tip near the surface than developed at the mid-thickness area. The change of the stresses ahead of the crack tip under loading is more significant at the mid-thickness area than it is near the surface.

Thermoelastic Finite Element Analysis of Double horizontal Subsurface Cracks Due to Sliding Surface Traction (마찰열을 고려한 미끄럼 접촉시 내부 복수 수평균열 전파해석)

  • 이진영;김석삼;채영훈
    • Tribology and Lubricants
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    • v.18 no.3
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    • pp.219-227
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    • 2002
  • A linear elastic fracture mechanics analysis of double subsurface cracks propagation in a half-space subjected to moving thermomechanical surface traction was performed using the finite element method. The effect of frictional heat at the sliding surface on the crack growth behavior is analyzed in terms of the thermal load and peclet number. The crack propagation direction is predicted in light of the magnitudes of the maximum shear and tensile stress intensity factor ranges. When moving thermomechanical surface traction exists, subsurface horizontal cracks are propagation in-plane crack growth rate at the beginning but they are propagation out-of-plane crack growth rate by the frictional heat which is occurrence by the repeated sliding contact.

Measurement of Surface Crack Length Using Image Processing Technology (영상처리기법을 이용한 표면균열길이 측정)

  • Nahm, Seung-Hoon;Kim, Yong-Il;Kim, Si-Cheon;Ryu, Dae-Hyun
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.96-101
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    • 2001
  • The development of a new experimental method is required to easily observe the growth behavior of fatigue cracks. To satisfy the requirement, an image processing technique was introduced to fatigue testing. The length of surface fatigue crack could be successfully measured by the image processing system. At first, the image data of cracks were stored into the computer while the cyclic loading was interrupted. After testing, crack length was determined using image processing software which was developed by ourselves. Block matching method was applied to the detection of surface fatigue cracks. By comparing the data measured by image processing system with the data measured by manual measurement with a microscope, the effectiveness of the image processing system was established. If the proposed method is used to monitor and observe the crack growth behavior automatically, the time and efforts for fatigue test could be dramatically reduced.

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An Experimental Study on the Crack Pattern of Concrete by Corrosion of Steel Reinforcing (콘크리트의 균열발생 거동에 관한 실험적 연구)

  • Paik, Min-Su;Kim, Youn-Kyoung;Lee, Young-Do;Lim, Nam-Gi;Choi, Eung-Kyoo;Kim, Young-Hoi;Chung, Lan;Jung, Sang-jin
    • Proceedings of the Korea Concrete Institute Conference
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    • 1997.04a
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    • pp.235-240
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    • 1997
  • The purpose of this experiment is to verify processing crack direction and state by the corrosion of electrifying re-bar in the salt water. The result of this experiment is the fact that the first crack appear on the surface of water-because of supplying of oxygen and water. The crack processing is on a surface to be contacted by air and to bottom as mainly the vertical direction from a surface of water. The crack by corrosion of steel reinforcing is emerged by the inside of concrete rather than surface concrete.

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Thermoelastic Finite Element Analysis of Multiple horizontal Subsurface Cracks Due to Sliding Surface Traction (마찰열을 고려한 미끄럼 접촉시 내부 복수 수평균열 전파해석)

  • 이진영;김석삼
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2000.11a
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    • pp.50-58
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    • 2000
  • A linear elastic fracture mechanics analysis of multiful subsurface cracks propagation in a half-space subjected to moving thermomechanical surface traction was peformed using the finite element method. The effect of frictional heat at the sliding surface on the crack growth behavior is analyzed in terms of the thermal load and peclet number. The crack propagation direction is predicted in light of the magnitudes of the maximum shear and tensile stress intensity factor ranges. When moving thermomechanical surface traction exists, subsurface horizontal cracks are propagation in-plane crack growth rate at the beginning but they are propagation out-of-plane crack growth rate by the frictional heat which is occurrence by the repeated sliding contact.

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Suppression of interfacial crack for foam core sandwich panel with crack arrester

  • Hirose, Y.;Hojo, M.;Fujiyoshi, A.;Matsubara, G.
    • Advanced Composite Materials
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    • v.16 no.1
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    • pp.11-30
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    • 2007
  • Since delamination often propagates at the interfacial layer between a surface skin and a foam core, a crack arrester is proposed for the suppression of the delamination. The arrester has a semi-cylindrical shape and is arranged in the foam core and is attached to the surface skin. Here, energy release rates and complex stress intensity factors are calculated using finite element analysis. Effects of the arrester size and its elastic moduli on the crack suppressing capability are investigated. Considerable reductions of the energy release rates at the crack tip are achieved as the crack tip approached the leading edge of the crack arrester. Thus, this new concept of a crack arrester may become a promising device to suppress crack initiation and propagation of the foam core sandwich panels.

Fatigue Crack Growth Simulation of Arbitrarily Shaped Three Dimensional Cracks Using Finite Element Alternating Method (유한요소 교호법을 이용한 임의 형상의 삼차원 균열의 피로균열 성장 해석)

  • Park, Jai-Hak;Kim, Tae-Soon
    • Journal of the Korean Society of Safety
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    • v.21 no.1 s.73
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    • pp.15-20
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    • 2006
  • The finite element alternating method is a convenient and efficient method to analyze three-dimensional cracks embedded in an infinite or a finite body because the method has the property that the uncracked body and cracks can be modeled independently. In this paper the method was applied for fatigue crack growth simulation. A surface crack in a cylinder was considered as an initial crack and the crack configurations and stress intensity factors during the crack growth were obtained. In this paper the finite element alternating method proposed by Nikishkov, Park and Atluri was used after modification. In the method, as the required solution for a crack in an infinite body, the symmetric Galerkin boundary element method formulated by Li and Mear was used. And a crack was modeled as distribution of displacement discontinuities, and the governing equation was formulated as singularity-reduced integral equations.

A Fatigue Life Prediction by Growth Characteristics of a Small Surface Crack (작은 표면균열의 성장특성에 의한 수명예측)

  • Suh, Chang-Min;Lim, Chang-Soon;Gang, Yong-Gu
    • Journal of Ocean Engineering and Technology
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    • v.3 no.2
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    • pp.617-617
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    • 1989
  • This paper deals with a fatigue life prediction of a surface crack based on the experimentally obtained relationship between surface crack length ratio $a/a_{f}$ and cycle ratio $N/N_{f}$ using micro computer. Firstly $a/a_{f}$-$N/N_{f}$ curves obtained from experimental tests, were assumed as three curves UC(the upper limit curve), LC(the lower limit curve) and MC(the middle curve), and these were utilized to predict the fatigue life. Comparing the calculated values which represent the characteristics of crack growth behaviors from the three assumed curves with the experimental ones, it has been found that in the stable crack growth region, they coincide reasonably well each other. And the differences between the fatigue lives obtained from the assumed curves and the experimental fatigue life did not exceed 20%. Using the characteristics of $a/a_{f}$-$N/N_{f}$ curves, it is possible to predict the da/dN-Kmax curves and the S-$N_{f}$ curves.