• Title/Summary/Keyword: stress invariant

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Yield Functions Based on the Stress Invariants J2 and J3 and its Application to Anisotropic Sheet Materials (J2 와 J3 불변량에 기초한 항복함수의 제안과 이방성 판재에의 적용)

  • Kim, Y.S;Nguyen, P.V.;Kim, J.J.
    • Transactions of Materials Processing
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    • v.31 no.4
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    • pp.214-228
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    • 2022
  • The yield criterion, or called yield function, plays an important role in the study of plastic working of a sheet because it governs the plastic deformation properties of the sheet during plastic forming process. In this paper, we propose a novel anisotropic yield function useful for describing the plastic behavior of various anisotropic sheets. The proposed yield function includes the anisotropic version of the second stress invariant J2 and the third stress invariant J3. The anisotropic yield function newly proposed in this study is as follows. F(J2)+ αG(J3)+ βH (J2 × J3) = km The proposed yield function well explains the anisotropic plastic behavior of various sheets by introducing the parameters α and β, and also exhibits both symmetrical and asymmetrical yield surfaces. The parameters included in the proposed model are determined through an optimization algorithm from uniaxial and biaxial experimental data under proportional loading path. In this study, the validity of the proposed anisotropic yield function was verified by comparing the yield surface shape, normalized uniaxial yield stress value, and Lankford's anisotropic coefficient R-value derived with the experimental results. Application for the proposed anisotropic yield function to aluminum sheet shows symmetrical yielding behavior and to pure titanium sheet shows asymmetric yielding behavior, it was shown that the yield curve and yield behavior of various types of sheet materials can be predicted reasonably by using the proposed new yield anisotropic function.

Enhanced Spherical Indentation Techniques for Rubber Property Evaluation (향상된 구형압입 고무 물성평가법)

  • Hwang, Kyu-Min;Oh, Jopng-Soo;Lee, Hyung-Yil
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.33 no.12
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    • pp.1357-1365
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    • 2009
  • In this study, we enhance the numerical approach of Lee et al.$^{(1)}$ to spherical indentation technique for property evaluation of hyper-elastic rubber. We first determine the friction coefficient between rubber and indenter in a practical viewpoint. We perform finite element numerical simulations for deeper indentation depth. An optimal data acquisition spot is selected, which features sufficiently large strain energy density and negligible frictional effect. We then improve two normalized functions mapping an indentation load vs. deflection curve into a strain energy density vs. first invariant curve, the latter of which in turn gives the Yeoh-model constants. The enhanced spherical indentation approach produces the rubber material properties with an average error of less than 3%.

Development and Verification of Micro-indentation Technique for Material Property Evaluation of Hyper-elastic Rubber (초탄성고무 물성평가용 미소압입시험법 개발 및 검증)

  • Lee, Hyung-Il;Lee, Jin-Haeng
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.132-137
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    • 2004
  • In this work, effects of hyper-elastic rubber material properties on the indentation load-deflection curve and subindenter deformation are first examined via [mite element (FE) analyses. An optimal data acquisition spot is selected, which features maximum strain energy density and negligible frictional effect. We then contrive two normalized functions. which map an indentation load vs. deflection curve into a strain energy density vs. first invariant curve. From the strain energy density vs. first invariant curve, we can extract the rubber material properties. This new spherical indentation approach produces the rubber material properties in a manner more effective than the common uniaxial tensile/compression tests. The indentation approach successfully measures the rubber material properties and the corresponding nominal stress.strain curve with an average error less than 3%.

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A Study on the Crack Tip Plastic Region for Stable Crack Growth -304 Stainless Steel- (안정군열성장에 대한 군열선단 소성역에 관한 연구 -304 스테인리스 강-)

  • 황갑운
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.6
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    • pp.1183-1192
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    • 1989
  • 본 논문에서는 평면변형률 상태하에서 안정하게 성장하는 균열선단에 집중 되어있는 강소성역의 해석에 역점을 두어 재결정법과 탄.소성유한요소법을 도입하여 안정 성장균열 선단에 형성되는 균열 성장저항에 직접적인 영향을 미치고 있는 소성 역의 크기나 형태에 대한 실험 및 해석을 하였다.

3D stress-fractional plasticity model for granular soil

  • Song, Shunxiang;Gao, Yufeng;Sun, Yifei
    • Geomechanics and Engineering
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    • v.17 no.4
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    • pp.385-392
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    • 2019
  • The present fractional-order plasticity models for granular soil are mainly established under the triaxial compression condition, due to its difficult in analytically solving the fractional differentiation of the third stress invariant, e.g., Lode's angle. To solve this problem, a three dimensional fractional-order elastoplastic model based on the transformed stress method, which does not rely on the analytical solution of the Lode's angle, is proposed. A nonassociated plastic flow rule is derived by conducting the fractional derivative of the yielding function with respect to the stress tensor in the transformed stress space. All the model parameters can be easily determined by using laboratory test. The performance of this 3D model is then verified by simulating multi series of true triaxial test results of rockfill.

Asymmetric Yield Functions Based on the Stress Invariants J2 and J3(II) (J2 와 J3 불변량에 기초한 비대칭 항복함수의 제안(II))

  • Kim, Y.S;Nguyen, P.V.;Ahn, J.B.;Kim, J.J.
    • Transactions of Materials Processing
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    • v.31 no.6
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    • pp.351-364
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    • 2022
  • The yield criterion, or called yield function, plays an important role in the study of plastic working of a sheet because it governs the plastic deformation properties of the sheet during plastic forming process. In this paper, we propose a modified version of previous anisotropic yield function (Trans. Mater. Process., 31(4) 2022, pp. 214-228) based on J2 and J3 stress invariants. The proposed anisotropic yield model has the 6th-order of stress components. The modified version of the anisotropic yield function in this study is as follows. f(J20,J30) ≡ (J20)3 + α(J30)2 + β(J20)3/2 × (J30) = k6 The proposed anisotropic yield function well explains the anisotropic plastic behavior of various sheets such as aluminum, high strength steel, magnesium alloy sheets etc. by introducing the parameters α and β, and also exhibits both symmetrical and asymmetrical yield surfaces. The parameters included in the proposed model are determined through an optimization algorithm from uniaxial and biaxial experimental data under proportional loading path. In this study, the validity of the proposed anisotropic yield function was verified by comparing the yield surface shape, normalized uniaxial yield stress value, and Lankford's anisotropic coefficient R-value derived with the experimental results. Application for the proposed anisotropic yield function to AA6016-T4 aluminum and DP980 sheets shows symmetrical yielding behavior and to AZ31B magnesium shows asymmetric yielding behavior, it was shown that the yield locus and yielding behavior of various types of sheet materials can be predicted reasonably by using the proposed anisotropic yield function.

Creep Properties of Squeeze Infiltrated AS52 Mg/Al18B4O33w Composite (용탕가압침투 AS52 Mg/Al18B4O33w 복합재료의 크리프 특성)

  • Choi, Kye-Won;Park, Yong-Ha;Park, Bong-Gyu;Park, Yong-Ho;Park, Ik-Min;Cho, Kyung-Mox
    • Korean Journal of Metals and Materials
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    • v.46 no.7
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    • pp.412-419
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    • 2008
  • Creep behavior of the squeeze infiltrated AS52 Mg matrix composites reinforced with 15 vol% of aluminum borate whiskers($Al_{18}B_4O_{33}w$) fabricated squeeze infiltration method was investigated. Microstructure of the composites was observed as uniformly distributed reinforcement in the matrix without any particular defects of casting pores etc.. Creep test was carried out at the temperature of 150 and $200^{\circ}C$ under the applied stress range of 60~120 MPa. The creep resistance of the composite was significantly improved comparing with the unreinforced AS52 Mg alloy. The creep behavior of composites might be interpreted with the substructure invariant model successfully for the composite. Threshold stress of the composite exist for the creep deformation of the composite. The analysis of the creep behavior of the composite with threshold stress indicated that creep deformation was controlled by the lattice diffusion process of AS52 Mg matrix at given effective stresses and temperatures. Activation energy was also calculated to check lattice diffusion controlled creep behavior of the composite.

Effect of shear deformation on adhesive stresses in plated concrete beams: Analytical solutions

  • Touati, Mahmoud;Tounsi, Abdelouahed;Benguediab, Mohamed
    • Computers and Concrete
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    • v.15 no.3
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    • pp.337-355
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    • 2015
  • In this scientific work, an improved analytical solution for adhesive stresses in a concrete beam bonded with the FRP plate is developed by including the effect of the adherend shear deformations. The analysis is based on the deformation compatibility approach where both the shear and normal stresses are assumed to be invariant across the adhesive layer thickness. The shear stress distribution is supposed to be parabolic across the depth of the adherends in computing the adhesive shear stress and Timoshenko's beam theory is employed in predicting adhesive normal stress to consider the shear deformation. Numerical results from the present analysis are presented both to demonstrate the advantages of the present solution over existing ones and to illustrate the main characteristics of adhesive stress distributions.

Software and Hardware Development of Micro-indenter for Material Property Evaluation of Hyper-Elastic Rubber (초탄성고무 물성평가용 미소압입시험기의 소프트웨어 및 하드웨어 개발)

  • Lee, Hyung-Yil;Kim, Dong-Wook;Lee, Jin-Haeng;Nahm, Seung-Hoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.6
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    • pp.816-825
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    • 2004
  • In this work, effects of hyper-elastic rubber material properties on the indentation load-deflection curve and subindenter deformation are examined via finite element (FE) analyses. An optimal location for data analysis is selected, which features maximum strain energy density and negligible frictional effect. We then contrive two normalized functions, which map an indentation load vs. deflection curve into a strain energy density vs. first invariant curve. From the strain energy density vs. first invariant curve, we can extract the rubber material properties. This new spherical indentation approach produces the rubber material properties in a manner more effective than the common uniaxial tensile/com-pression tests. The indentation approach successfully measures the rubber material properties and the corresponding nominal stress-strain curve with an average error less than 3%.

Numerical Approach Technique of Spherical Indentation for Material Property Evaluation of Hyper-elastic Rubber (초탄성 고무 물성평가를 위한 구형 압입시험의 수치접근법)

  • Lee, Hyung-Yil;Lee, Jin-Haeng;Kim, Dong-Wook
    • Elastomers and Composites
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    • v.39 no.1
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    • pp.23-35
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    • 2004
  • In this work, effects of hyper-elastic rubber material properties on the indentation load-deflection curve and subindenter deformation are first examined via finite element (FE) analyses. An optimal data acquisition spot is selected, which features maximum strain energy density and negligible frictional effect. We then contrive two normalized functions, which map an indentation load vs. deflection curve into a strain energy density vs. first invariant curve. From the strain energy density vs. first invariant curve, we can extract the rubber material properties. This new spherical indentation approach produces the rubber material properties in a manner more effective than the common uniaxial tensile/compression tests. The indentation approach successfully measures the rubber material properties and the corresponding nominal stress-strain curve.