• Title/Summary/Keyword: Crack-tip field

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Effect of Transverse Electric Fields on Fracture Behavior of Ferroelectric Ceramics (횡전기장이 강유전체 세라믹의 파괴거동에 미치는 영향)

  • Lee Jong Sik;Beom Hyeon Gyu;Jeong Kyoung Moon
    • Journal of the Korean Society for Precision Engineering
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    • v.22 no.2
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    • pp.120-125
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    • 2005
  • Effect of transverse electric fields on fracture behavior in ferroelectric ceramics under purely electrical loading is investigated. It is shown that the shape and size of the domain switching zone depend strongly on the ratio of the transverse electric field to the coercive electric field as well as the direction of the applied electric field. Under small-scale conditions, the crack-tip mode I and II stress intensity factors induced by ferroelectric domain switching are numerically obtained. The crack kinking in ferroelectric ceramics is also discussed.

A Study on the Fracture Behavior of a Crack in 9% Ni Steel Considering Constraint Effect (구속효과를 고려한 9% Ni강 균열의 파괴거동 해석에 관한 연구)

  • Kim, Young Kyun;Yoon, Ihn soo;Kim, Jae Hoon
    • Journal of the Korean Institute of Gas
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    • v.25 no.6
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    • pp.14-21
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    • 2021
  • Inner shell material of LNG storage tanks that store ultra-low temperature LNG at -162℃ requires structural integrity assessment of a crack-like defect. From the viewpoint of conventional fracture mechanics, the assessment has mainly performed by single parameter using stress intensity factor K, J-integral and CTOD. However, the stresses in a material of crack tip are not unique caused by constraint loss due to size and geometry of the structure. Various attempts have been made to complement a single parameter fracture mechanics, typically with Q-stress. In this paper, we have performed a two-parameter approach by deriving the Q-stress coupling with J-integral suitable for the evaluation of the crack tip stress field in the non-linear elastic region. A quantitative evaluation of the constraint effect has performed by using the J-Q approach. It was evaluated that the SENB type specimen had a crack ratio of 0.1 to 0.7 and the wide type specimen had a crack ratio of 0.2 to 0.6.

Hybrid Photoelastic Stress Analysis Around a Central Crack Tip in a Tensile Loaded Plate Using Isochromatic Data (등색프린지 데이터를 이용한 인장하중 판재 중앙 균열선단 주위의 하이브리드 광탄성 응력장 해석)

  • Baek, Tae-Hyun;Chen, Lei
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.12
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    • pp.1200-1207
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    • 2007
  • An experimental test is presented for photoelastic stress analysis around a crack tip in tensile loaded plate. The hybrid method coupling photoelastsic fringe inputs calculated by finite element method and complex variable formulations involving conformal mappings and analytical continuity is used to calculate full-field stress around the crack tip in uniaxially loaded, finite width tensile plate. In order to accurately compare calculated fringes with experimental ones, both actual and regenerated photoelastic fringe patterns are two times multiplied and sharpened by digital image processing. Regenerated fringes by hybrid method are quite comparable to actual fringes. The experimental results indicate that Mode I stress intensity factor analyzed by the hybrid method are accurate within three percent compared with ones obtained by empirical equation and finite element analysis.

A Study on the Near-Field Stresses and Displacement of a Stationary Interfacial Crack in Two Dissimilar Isotropic Bimaterials (두 상이한 등방성 이종재료 정지계면균열의 선단 응력장과 변위장에 관한 연구)

  • Shin, Dong-Chul;Hawong, Jai-Sug;Nam, Jeong-Hwan
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.12
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    • pp.1897-1905
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    • 2004
  • In many part of machines or structures that made of bimaterial bonded with two dissimilar materials, most failures occur at their interface. Therefore, the accurate analysis of fracture characteristics and the evaluation of mechanical strength for interfacial crack are essential when we design those structures. In this research, stress and displacement components in the vicinity of stationary interfacial crack tip in the two dissimilar isotropic bimaterials are established. Hereafter, the stress components established in this research can be applied to the photoelastic hybrid method which can be used to analyze the fracture behavior of the two dissimilar isotropic bimaterials.

Measurement of Deformation field in CT specimen using Laser speckle (레이저 스페클을 이용한 CT 시험편의 변형장 측정)

  • Jean, Moon-Chang;Kang, Ki-Ju
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.192-197
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    • 2001
  • To obtain $A_2$ experimentally in the $J-A_2$ theory, deformation field on the lateral surface of a CT specimen was to be determined using Laser speckle method. The crack growth was measured using direct current potential drop method and most procedure of experimental and data reduction was performed according to ASTM Standard E1737-96. Laser speckle images during crack propagation were monitored by two CCD cameras to cancel the effect of rotation and translation of the specimen. An algorithm to pursue displacement of a point from each image was developed and successfully used to measure $A_2$ continuously as the crack tip was propagated. The effects of specimen thickness on J-R curve and $A_2$ were explored.

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Influence of Anisotropic Property Ratio of Orthotropic Material on Stress Components and Displacement Components at Crack tip Propagating with Constant Velocity Under Dynamic Mode I (동적모드 I 상태에서 직교 이방성체의 이방성비가 등속전파 균열선단의 응력성분과 변위성분에 미치는 영향)

  • 이광호;황재석;최선호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.1
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    • pp.87-98
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    • 1995
  • When the crack in orthotropic material is propagating under dynamic model I load, influences of anisotropic property ratio $E_{L}$/ $E_{T}$ on stress and displacement around propagating crack tip are studied in this paper. When M<0.55 and .alpha.=90.deg.(.alpha.; the angle of fiber direction with crack propagating direction, M; crack propagation velocity/shear stress wave velocity), the influence of $E_{L}$/ $E_{T}$ on stress .sigma.$_{x}$, .sigma.$_{y}$, .tau.$_{xy}$ and .sigma.$_{\theta}$ is the greast on .sigma.$_{y}$. Except M<0.55 and .alpha.=90.deg., it is the greast on .sigma.$_{x}$ in any situation. Increasing $E_{L}$/ $E_{T}$, stress components are increased or decreased. When maximum stress is based, the stress .sigma.$_{x}$(.alpha.=90.deg.), .sigma.$_{y}$(.alpha.=0.deg.) and .tau.$_{xy}$ (.alpha.=90.deg.) are decreased with increment of $E_{L}$/ $E_{T}$ in M=0. any stresses except .sigma.$_{*}$x/(.alpha.=0.deg.) are decreased with increment of $E_{L}$/ $E_{T}$ in M=0.9. When .alpha.=90.deg., the influence of $E_{L}$/ $E_{T}$ on displacement U and V is V>U in any velocities of crack propagation, when .alpha.=0.deg., it is VU in M>0.75 and when $E_{L}$/ $E_{T}$ is increased, U and V are decreased in any conditions.sed in any conditions.tions.tions.tions.

Dynamic Interface Crack Propagating Along a Line Between Two Holes

  • Lee, Ouk-Sub;Park, Jae-Chul;Yin, Hai-Long;Byun, Kwi-Hwan
    • Journal of Mechanical Science and Technology
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    • v.15 no.2
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    • pp.172-179
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    • 2001
  • The effects of the interface and two holes located near the crack path in the hybrid specimen on the dynamic crack propagation behavior have been investigated using dynamic photoelasticity with the aid of Cranz-Shardin type high speed camera system. The dynamic stress field around the dynamically propagating interface crack tip in the three point bending specimens under a dynamic load applied by a hammer dropped from 0.6m high without initial velocity are recorded. The complex stress intensity factors for the dynamically propagating interface crack are extracted by using a overdeterministic least square method. Theoretical dynamic interface isochromatic fringe loops generated by using the numerically determined complex stress intensity factors are compared with the experimental results. Furthermore, the influence of the hole to the dynamic interface crack velocities has been investigated experimentally.

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Critical Stress for a Crack Inclined to Princinal Material Direction in Orthotropic Material (직방성체에서 재료주축과 경사진 균열의 임계응력)

  • Lim, Won-Kyun;Cho, Hyoung-Seok
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.1021-1026
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    • 2003
  • The problem of predicting the fracture strength behavior in orthotropic plate with a crack inclined with respect to the principal material axes is analyzed. Both the load to cause fracture and the crack direction of crack growth arc of interest. The theoretical results based on the normal stress ration theory show significant effects of biaxial loading and the fiber orientation on the crack growth angle and the critical stress. The additional term in the asymptotic expansion of the crack tip stress field appears to provide more accurate critical stress prediction.

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Analyses of Stress Intensity Factors for Slant Crack Emanation from Circular Inclusion by Boundary Element Method (경계요소법에 의한 원형함유물에서 파생되는 경사균열의 응력확대계수 해석)

  • Park, Sung-Oan;Hwang, Soon-Won
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.7 no.5
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    • pp.72-84
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    • 1998
  • In order ot study the influence of a circular inclusion on a stress field near a crack tip, mutual interference of a slant crack and the circular inclusion is analyzed of a bimaterial inclusion. As the crack emanates at the equivalent slant crack angle the correction factors FⅠ and FⅡ for the inclusion wit small Young's modulus were found to decrease as the inclusion radius increased. The correction factors for inclusion with large Young's modulus increase as the inclusion radius increases at the equivalent radius of the inclusion, the correction factors decrease as the slant crack angle increases for the aspect ratio $\frac{c}{W}$ = 0.1 irrespective of the Young's modulus. For $\frac{c}{W}$ greater than 0.2, they increase as the slant crack angle increases. There is no influence of stress mutual interfce after crack emanates beyond the inclusion radius.

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Effect of initial coating crack on the mechanical performance of surface-coated zircaloy cladding

  • Xu, Ze;Liu, Yulan;Wang, Biao
    • Nuclear Engineering and Technology
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    • v.53 no.4
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    • pp.1250-1258
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    • 2021
  • In this paper, the mechanical performance of cracked surface-coated Zircaloy cladding, which has different coating materials, coating thicknesses and initial crack lengths, has been investigated. By analyzing the stress field near the crack tip, the safety zone range of initial crack length has been decided. In order to determine whether the crack can propagate along the radial (r) or axial (z) directions, the energy release rate has been calculated. By comparing the energy release rate with fracture toughness of materials, we can divide the initial crack lengths into three zones: safety zone, discussion zone and danger zone. The results show that Cr is suitable coating material for the cladding with a thin coating while Fe-Cr-Al have a better fracture mechanical performance in the cladding with thick coating. The Si-coated and SiC-coated claddings are suitable for reactors with low power fuel elements. Conclusions in this paper can provide reference and guidance for the cladding design of nuclear fuel elements.