• Title/Summary/Keyword: Crack Reduction

Search Result 427, Processing Time 0.031 seconds

Contour Integral Method for Crack Detection

  • Kim, Woo-Jae;Kim, No-Nyu;Yang, Seung-Yong
    • Journal of the Korean Society for Nondestructive Testing
    • /
    • v.31 no.6
    • /
    • pp.665-670
    • /
    • 2011
  • In this paper, a new approach to detect surface cracks from a noisy thermal image in the infrared thermography is presented using an holomorphic characteristic of temperature field in a thin plate under steady-state thermal condition. The holomorphic function for 2-D heat flow field in the plate was derived from Cauchy Riemann conditions to define a contour integral that varies according to the existence and strength of a singularity in the domain of integration. The contour integral at each point of thermal image eliminated the temperature variation due to heat conduction and suppressed the noise, so that its image emphasized and highlighted the singularity such as crack. This feature of holomorphic function was also investigated numerically using a simple thermal field in the thin plate satisfying the Laplace equation. The simulation results showed that the integral image selected and detected the crack embedded artificially in the plate very well in a noisy environment.

A study of stress intensity factors at the crack tips in a finite plate (평판내의 직선 crack tip에서의 응력확대계수에 관한 연구)

  • 조선휘;조희복
    • Journal of the korean Society of Automotive Engineers
    • /
    • v.4 no.1
    • /
    • pp.31-39
    • /
    • 1982
  • In this paper, the stress intensity factors at the crack tips in a finite plate having a straight crack with arbitrary lengths and directions are analyzed by means of Boundary Collocation Method in Cartesian coordinates under the following two cases. A) Case of only considering stress components at the boundary collocation points B) Case of considering stress resultant at the boundary, in addition to case of )A) and analyzed by means of F.E.M. To certify the Boundary Collocation Method the solutions of B.C.M. are compared with the solutions of F.E.M. demonstrates the simplicity of input data preparation and the reduction of cpu time against F.E.M.

  • PDF

Mock-up Test on the Reduction of Hydration Heat of Mass Concrete for Transfer Girder (전이보 매스콘크리트의 수화열 저감에 관한 Mock-up 실험)

  • Yoon Seob;Hwang Yin Seong;Baik Byung Hoon;Han Cheon Goo
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • 2004.11a
    • /
    • pp.707-710
    • /
    • 2004
  • This paper reported the results of mock-up test on mass concrete for transfer girder using setting time difference of super retarding agent(SRA). According to test results, two mock-up structures were made. Plain concrete without placing layer reached maximum temperature after 24hours since placement and caused surface hydration cracks at top section. However, concrete with placing layer reached maximum temperature after 72hours and surface temperature was higher than center temperature, which did not cause surface crack. After form removing, no crack was observed at side surface of plain concrete, while concrete using SRA at mid section had surface scaling and settling crack. According to coring results, concrete with placing layer had a penetration crack from top section to bottom section. Therefore, the setting time difference method to reduce hydration heat will have difficulty in applying the mass concrete for transfer girder.

  • PDF

A Study on the Safety Evaluation of Design for Piping Materials (II) (배관용재료의 설계시 안전성 평가에 관한 연구(II))

  • 김복기
    • Journal of the Korean Society of Safety
    • /
    • v.10 no.3
    • /
    • pp.3-10
    • /
    • 1995
  • For most engineering materials are influenced by the dominant mechanism resisting crack extention under large scale yielding conditions. Continuum mechanics analysis shows that fracture toughness, in addition to depending on young's modulus, flow stress strain hardening exponent, and yield strain, should be nearly proportoinal to the effective fracture ductility obtained for the stress state characteristic for region ahead of the crack; plane stress or plane strain. It's known that, in most ductile materials, crack propagation of the material strongly governed by the $J_{IC}$ value, which is still difficult to determine for it's complicate and treble-some determinative process. This paper, on the assumption that, initiation of crack tip strain field reaches on the relationships between the critical value of J-integral ($J_{IC}$) and the local fracture strain(${\varepsilon}_c$) in uniaxial tensile test in the region of maximun reduction areas was described.

  • PDF

Effect of Crack Propagation Directions on the Interlaminar Fracture Toughness of Carbon/Epoxy Composite Materials (탄소섬유/에폭시 복합재료의 층간파괴인성에 미치는 균열진전각도의 영향)

  • Hwang, Jin-Ho;Hwang, Woon-Bong
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.23 no.6 s.165
    • /
    • pp.1026-1038
    • /
    • 1999
  • Interlaminar fracture toughness of carbon/epoxy composite materials has been studied under tensile and flexural loading by the use of width tapered double cantilever beam(WTDCB) and end notched flexure(ENF) specimens. This study has significantly examined the effect of various interfacial ply orientation, ${\alpha}(0^{\circ},\;45^{\circ}\;and\;90^{\circ})$ and crack propagation direction, ${\theta}(0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;45^{\circ})$ in terms of critical strain energy release rate through experiments. Twelve differently layered laminates were investigated. The data reduction for evaluating the fracture energy is based on compliance method and beam theory. Beam theory is used to analyze the effect of crack propagation direction. The geometry and lay-up sequence of specimens are considered various conditions such as skewness parameter, beam volume, and so on. The results show that the fiber bridging occurred due to the non-midplane crack propagation and causes the difference of fracture energy evaluated by both methods. For safer and more reliable composite structures, we obtain the optimal stacking sequence from initial fracture energy in each mode.

A study on reduction of pre-crack deviation in CTOD specimen using reverse bending method (Reverse Bending을 통한 CTOD 시험 예비균열 형상균일화에 관한 연구)

  • Jeong, Sehwan;Park, Dong-Hwan;Kim, Hyeon-Su;Shin, Sang-Beom;Park, Tae-Jong
    • Journal of Welding and Joining
    • /
    • v.33 no.2
    • /
    • pp.62-68
    • /
    • 2015
  • This study investigates the appropriate range of reverse bending load for the CTOD test of thick weld by observing improvement of pre-crack shape and determination of the limit applicable load. In order to do it, the effect of the amount of the reverse bending load on the maximum deviation of the pre-crack length was investigated by the extensive tests, and the variation of plastic zone size in way of the crack tip under reverse bending load were evaluated by FEA. With the results obtained by the experiments and FEA, the proper range of reverse bending load was suggested. The effectiveness of the reverse bending method was verified by examining the pre-crack straightness after CTOD tests of thick weld specimens with various thickness and strength.

Damage Mechanism of Particle Impact in a $Cr_2O_3$ Plasma Coated Soda-lime Glass ($Cr_2O_3$ 플라스마 용사 코팅된 유리의 입자충격에 의한 손상기구)

  • Suh, Chang-Min;Lee, Moon-Whan;Kim, Sung-Ho;Jang, Jong-Yun
    • Journal of Ocean Engineering and Technology
    • /
    • v.12 no.3 s.29
    • /
    • pp.49-59
    • /
    • 1998
  • The damage mechanism of $Cr_2O_3$ plasma coated soda-lime glass and uncoated glass by steel ball particle impact was analyzed in this study. And the shape variation of the cracks was investigated by stereo-microscope according to the impact velocity and steel ball diameter. In order to improve the damage reduction effect by $Cr_2O_3$ coating layer, crack size was measured and surface erosion state was observed for both of two kinds of specimen after impact experiment. And the results were compared with each other. The 4-point bending test was performed according to ASTM D790 testing method to evaluate the effect of coating layer for bending strength variation. As a result, it was found that the crack size of $Cr_2O_3$ coated specimen was smaller than that of uncoated one, because of the impact absorption by interior pores in the coating layer and the load dispersion by the structural characteristic of the coating layer. For the specimens subjected to the steel ball impact, the bending strength of coated specimen was higher than that of uncoated specimen.

  • PDF

A Study of Crack Shape Analysis based on Properties of Member in Apartment Exterior Wall (부재속성에 따른 균열 형상 분석에 관한 연구 - 공동주택 외벽 균열을 중심으로 -)

  • Kim, Man-Jang
    • Korean Journal of Construction Engineering and Management
    • /
    • v.16 no.3
    • /
    • pp.143-151
    • /
    • 2015
  • The Crack, occurred in the concrete structure, is a major cause of function deterioration such as strength, durability and waterproof. Therefore the need for crack reduction will continue as long as there is concrete structure. But, it is not easy to reduce or prevent crack cause of impact factor of it. There are so many factors of crack such as material, construction and maintenance environment, and structure, and these are acting in combination. So, this study derives a correlation between the cracks and members through reviewing member crack occurred. And member's attribute, related crack, is analyzed by it. It consider that the basic attribute of member is similar when its requirements are similar. Through this study, therefore, foundation of countermeasure of crack will be provided by prediction of crack shape through member's attribute.

Fracture Mechanics Analysis of Cracked Plate Repaired by Patch (I) (보강재로 보수된 균열평판의 파괴역학적 해석(I))

  • Jeong, Gi-Hyeon;Yang, Won-Ho;Jo, Myeong-Rae
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.24 no.8 s.179
    • /
    • pp.2000-2006
    • /
    • 2000
  • The enhancement of service life of damaged or cracked structures is currently major issue to the researchers and engineers. In order to improve the life of cracked aging aircraft structures, the repair technique which uses adhesively bonded boron/epoxy composite patches is being widely considered as a cost-effective and reliable method. This paper is to study the performance of the bonded composite patch repair of a plate containing an inclined central through-crack. A 3-dimensional finite element method having three layers to the cracked plate, composite patch and adhesive layer, is used to compute the stress intensity factor. In this paper, the reduction of stress intensity factors near the crack-tip are determined to evaluate the effects of various non-dimensional design parameter including composite patch thickness, and material properties of the composite patch and thickness of the adhesive layer, materials of patch etc., and the crack length, Finally, The problem of how to optimize the patch geometric configurations has been discussed.

Thermo-Acoustic Emission Behavior of Composites (복합재료의 열-음향방출거동)

  • 김영복;우성충;최낙삼
    • Proceedings of the Korean Society For Composite Materials Conference
    • /
    • 2001.10a
    • /
    • pp.111-115
    • /
    • 2001
  • Thermo-acoustic emission (AE) from composite laminates under the repetitive thermal cyclic loads have been quantitatively analyzed in consideration of AE source mechanisms. The repetitive thermal load brought about a large reduction, i.e. an exponential decrease in AE total ringdown counts and AE amplitudes. It was thought that generation of thermo-AE during the first thermal cycle was not caused by crack propagation but by secondary microfracturing due to abrasive contact between crack surfaces.

  • PDF