• Title, Summary, Keyword: Biaxiality

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Influence of elastic T-stress on the growth direction of two parallel cracks

  • Li, X.F.;Tang, B.Q.;Peng, X.L.;Huang, Y.
    • Structural Engineering and Mechanics
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    • v.34 no.3
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    • pp.377-390
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    • 2010
  • This paper studies fracture initiation direction of two parallel non-coplanar cracks of equal length. Using the dislocation pile-up modelling, singular integral equations for two parallel cracks subjected to mixed-mode loading are derived and the crack-tip field including singular and non-singular terms is obtained. The kinking angle is determined by using the maximum hoop stress criterion, or the ${\sigma}_{\theta}$-criterion. Results are presented for simple uniaxial tension and biaxial loading. The biaxiality ratio has a noticeable influence on crack growth direction. For the case of biaxial tension, when neglecting the T-stress the crack branching angle is overestimated for small crack inclination angles relative to the largest applied principal stress direction, and underestimated for large crack inclination angles.

Prediction of Fatigue Crack Initiation Direction around a Hole under Biaxial Loads Considering Phase Difference and Biaxiality (이축성과 위상차의 영향을 고려한 이축 하중하에서 구멍 주위에서의 피로 균열 발생 방향 예측)

  • Huh, Yong-Hak;Park, Pil-Ip;Kim, Dong-Jin
    • Proceedings of the KSME Conference
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    • pp.156-161
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    • 2004
  • To predict the direction of the fatigue crack initiated from a hole under various types of biaxial fatigue loads with different phase difference and biaxiality, fatigue parameters were investigated. Axial and torsional biaxial fatigue loads were selected with the respective combination of five different phase differences of 0, 45, 90, 145 and 180 degrees and five biaxialities of 0, $1/{\sqrt{3}}$, 1, ${\sqrt{3}}$, ${\infty}$. Directions of the fatigue crack initiation around the hole were found to approach to the circumferential direction of the specimen with increment of the phase difference for fatigue tests with phase differences less than $90^{\circ}$. Whereas directions for tests with phase differences greater than $90^{\circ}$ went away from the circumferential direction and those were symmetric to the directions for tests with phase difference less than $90^{\circ}$. With increase of biaxilities, the fatigue crack initiated more apart from the circumferential direction of the specimen. These crack initiation direction were predicted using maximum tangential stress range and maximum shear stress range obtained at far-field and around the hole. Comparing these two stress parameters, The crack initiation direction can be successfully explained by using the direction of the maximum tangential stress range obtained around the hole and at far-field.

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Coatable Retarder Technology for LCD Home TV

  • Lazarev, Alexander;Geivandov, Artur;Kasianova, Irina;Kharatiyan, Ellina;Lazarev, Pavel;Palto, Sergey
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.1083-1086
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    • 2008
  • Crysoptix KK has developed low-cost coatable retarder technology. A full range of coatable retardation films with tunable value of biaxiality (NZ factor) has been developed for the first time. Tunable NZ factor allows efficient compensation of modern VA and IPS mode LCD with just single retardation film.

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Fatigue Crack Initiation around a Hole under Out-of-phase Biaxial Loading (이상 이축 하중 하에서 구멍 주위에서의 피로 균열 발생)

  • Huh, Yong-Hak;Park, Pi-Lip;Kim, Dong-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.10
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    • pp.1695-1702
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    • 2003
  • Fatigue crack initiation around a hole subjected to biaxial fatigue loads with a phase difference was investigated. Axial and torsional biaxial fatigue loads with different phase differences and biaxiality of 1/√3 were applied to thin-walled tubular specimens. Five phase differences of 0, 45, 90, 145 and 180 degrees were selected. Directions of the fatigue crack initiation around the hole were found to approach to the circumferential direction of the specimen with increment of the phase difference for fatigue tests with phase differences less than 90$^{\circ}$. Whereas directions for tests with phase differences greater than 90$^{\circ}$ got away from the circumferential direction and those were symmetric to the directions for tests with phase difference less than 90. . Furthermore, it was shown that the fatigue initiation life decreased with increment of phase difference for fatigue tests with phase differences less than 90$^{\circ}$, but it increased for tests with phase difference greater than 90$^{\circ}$. The crack initiation direction can be successfully explained by using the direction of the maximum tangential stress range obtained around the hole and at far-field.

Plastic yield behaviour of perforated sheets (천공판재의 항복거동)

  • 백승철;이동녕;오규환
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.101-108
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    • 1994
  • The sheet perforated with a uniform triangular pattern of round holes and subjected to in-plane stress f arbitrary biaxiality was investigated. The equivalent continuum approach was employed to develop a theoretical model for global analysis, which includes defining a yield criterion and the strain hardening in terms of apparent stresses and apparent strains. Finit element analysis and experiment tension test were performed to examine the validity of proposed yield criterion and strain hardening models of perforated sheets.

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Prediction of the Critical Stress for the Inclined Crack in Orthotropic Materials under Biaxial load (2축하중을 받는 직교이방성 경사균열에서 임계응력의 예측)

  • Lim, Won-Kyun;Cho, Hyung-Suk;Jeong, Woo-Kil;Lee, Ill-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.11
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    • pp.1384-1391
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    • 2006
  • The problem of an infinite anisotropic material with a crack inclined with respect to the principal material axes is analyzed. The material is subjected to uniform biaxial load along its boundary. It is assumed that the material is homogeneous, but anisotropic. By considering the effect of the horizontal load, the distribution of stresses at the crack tip is analyzed. The problem of predicting critical stress in anisotropic solids which is a subject of considerable practical importance is examined and the effect of load biaxiality is made explicitly. The present results based on the normal stress ratio theory show significant effects of biaxial load, crack inclination angle and fiber orientation on the critical stress. The analysis is performed for a wide range of the crack angles and biaxial loads.

Synthesis and Properties of Biaxial LC from Dumbbell-shaped Molecules

  • Xu, Fei;Choi, E-Joon
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.651-654
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    • 2009
  • Novel compounds with rod and disc mesogens were synthesized and characterized. The molecular structures were confirmed by FT-IR, $^1H$-NMR spectroscopy and elemental analysis. The optical properties of these molecules were investigated by UV-vis absorption spectroscopy and photo-luminescence spectroscopy. We found that they are a novel series of blue light-emitting molecules. The absorption spectra peaks of these compounds varied from 336 nm-341 nm, while the maximum emissions centered form 410 nm-450 nm in chloroform solution. However, unexpectedly we could not found their biaxiality and mesomorphic properties by POM, conoscopy and DSC method.

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High Cycle Fatigue Damage under Multiaxial Random Loading through Dynamic Simulation for an Automotive Sub-Frame (동력학 시뮬레이션에 의한 다축 랜덤하중 하에서 자동차 서브프레임의 고 되풀이수 피로손상 평가)

  • Lee, Hak-Joo;Kang, Jae-Youn;Choi, Byung-Ick;Kim, Joo-Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.6
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    • pp.946-953
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    • 2003
  • A FEM-based analytical approach was used to evaluate the multiaxial high cycle fatigue damage of an automotive sub-frame. Elastic Multi Body Simulation (MBS) has been applied in order to determine the multiaxial load histories. The stresses due to these loads have been given by FE computation. These results have been used as the input for the multiaxial fatigue analysis. For the assessment of multiaxial high cycle fatigue damage, the signed von Mises, the signed Tresca, the absolute maximum principal stress and critical plane methods have been employed. In addition, the biaxiality ratio, a$\sub$e/, the absolute maximum principal stress, $\sigma$$\sub$p/ and the angle, $\phi$$\sub$P/, between $\sigma$$\sub$1/ and the local x-axis, have been calculated to evaluate the stress state at each node.

Interfacial Crack-tip Constraints and J-integrals in Plastically Hardening Bimaterials under Full Yielding (완전소성하 변형경화 이종접합재의 계면균열선단 구속상태 및 J-적분)

  • Lee, Hyung-Yil;Kim, Yong-Bom
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.7
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    • pp.1159-1169
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    • 2003
  • This paper investigates the effects of T-stress and plastic hardening mismatch on the interfacial crack-tip stress field via finite element analyses. Plane strain elastic-plastic crack-tip fields are modeled with both MBL formulation and a full SEC specimen under pure bending. Modified Prandtl slip line fields illustrate the effects of T-stress on crack-tip constraint in homogeneous material. Compressive T-stress substantially reduces the interfacial crack-tip constraint, but increases the J-contribution by lower hardening material, J$\_$L/. For bimaterials with two elastic-plastic materials, increasing plastic hardening mismatch increases both crack-tip stress constraint in the lower hardening material and J$\_$L/. The fracture toughness for bimaterial joints would consequently be much lower than that of lower hardening homogeneous material. The implication of unbalanced J-integral in bimaterials is also discussed.