• 제목/요약/키워드: Deformation Hardening

검색결과 392건 처리시간 0.025초

Deformation Analysis of Micro-Sized Material Using Strain Gradient Plasticity

  • Byon S.M.;Lee Young-Seog
    • Journal of Mechanical Science and Technology
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    • 제20권5호
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    • pp.621-633
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    • 2006
  • To reflect the size effect of material $(1\sim15{\mu}m)$ during plastic deformation of polycrystalline copper, a constitutive equation which includes the strain gradient plasticity theory and intrinsic material length model is coupled with the finite element analysis and applied to plane strain deformation problem. The method of least square has been used to calculate the strain gradient at each element during deformation and the effect of distributed force on the strain gradient is investigated as well. It shows when material size is less than the intrinsic material length $(1.54{\mu}m)$, its deformation behavior is quite different compared with that computed from the conventional plasticity. The generation of strain gradient is greatly suppressed, but it appears again as the material size increases. Results also reveal that the strain gradient leads to deformation hardening. The distributed force plays a role to amplify the strain gradient distribution.

액상화 해석을 위한 간단한 구성모델 (A Simple Constitutive Model for Soil Liquefaction Analysis)

  • 박성식;김영수;;김대만
    • 한국지반공학회논문집
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    • 제21권8호
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    • pp.27-35
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    • 2005
  • 액상화에 따른 지반의 과도한 변형으로 인한 피해가 자주 발생되고 있다. 그에 따른 지반의 움직임을 예측하기 위해서는 유효응력 개념에 기초한 수치해석 기법이 요구되어 진다. 본 연구에서는 지진 및 유사한 반복 하중에 따른 수압의 상승을 예측할 수 있는 연성(fully coupled) 유효응력 구성모델인 UBCSAND를 제안하였다. 제안된 모델은 간단한 완전탄소성모델인 Mohr-Coulomb을 변형한 형태로 마찰각(friction angle)과 팽창각(dilation angle)을 점진적으로 증가시킴으로써, 기존의 파괴상태내에서도 연속적인 소성변형 발생을 표현할 수 있다. 항복함수는 전단응력과 평균응력의 비인 $(\sigma'_1-\sigma'_3)/(\sigma'_1-\sigma'_3)$로 나타내며, 응력도의 원점에서 시작하는 무한개의 방사선을 의미한다. 따라서, Mohr-Coulomb의 파괴면과 같은 형태의 무수한 항복면을 가진다. 소성 경화법칙은 등방경화(isotropic hardening)와 이동경화(kinematic hardening)를 혼합한 형태를 이루고 있다. 재하(loading) 및 재재하(reloading)시에는 연속적인 소성 변형이 일어나나, 제하(unloading)시에는 탄성변형을 가정하였다. 제안된 모델은 느슨한 Fraser River 모래를 이용한 직접단순전단시험(Direct simple shear test)결과와 비교하여 검증하였다.

비선형 이동경화를 고려한 점소성 모델의 내연적 적분 (A Semi-Implicit Integration for Rate-Dependent Plasticity with Nonlinear Kinematic Hardening)

  • 윤삼손;이순복
    • 대한기계학회논문집A
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    • 제27권9호
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    • pp.1562-1570
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    • 2003
  • The prediction of the inelastic behavior of the structure is an essential part of reliability assessment procedure, because most of the failures are induced by the inelastic deformation, such as creep and plastic deformation. During decades, there has been much progress in understanding of the inelastic behavior of the materials and a lot of inelastic constitutive equations have been developed. The complexity of these constitutive equations generally requires a stable and accurate numerical method. The radial return mapping is one of the most robust integration scheme currently used. Nonlinear kinematic hardening model of Armstrong-Fredrick type has recovery term and the direction of kinematic hardening increment is not parallel to that of plastic strain increment. In this case, The conventional radial return mapping method cannot be applied directly. In this investigation, we expanded the radial return mapping method to consider the nonlinear kinematic hardening model and implemented this integration scheme into ABAQUS by means of UMAT subroutine. The solution of the non-linear system of algebraic equations arising from time discretization with the generalized midpoint rule is determined using Newton method and bisection method. Using dynamic yield condition derived from linearization of flow rule, the integration scheme for elastoplastic and viscoplastic constitutive model was unified. Several numerical examples are considered to demonstrate the efficiency and applicability of the present method.

나노구조재료의 소성변형 성질의 변형률속도 의존성 (Strain Rate Dependence of Plastic Deformation Properties of Nanostructured Materials)

  • 윤승채;김형섭
    • 소성∙가공
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    • 제14권1호
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    • pp.65-70
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    • 2005
  • A phase mixture model was employed to simulate the deformation behaviour of metallic materials covering a wide grain size range from micrometer to nanometer scale. In this model a polycrystalline material is treated as a mixture of two phases: grain interior phase whose plastic deformation is governed by dislocation and diffusion mechanisms and grain boundary 'phase' whose plastic flow is controlled by a boundary diffusion mechanism. The main target of this study was the effect of grain size on stress and its strain rate sensitivity as well as on the strain hardening. Conventional Hall-Petch behaviour in coarse grained materials at high strain rates governed by the dislocation glide mechanism was shown to be replaced with inverse Hall-Petch behaviour in ultrafine grained materials at low strain rates, when both phases deform predominantly by diffusion controlled mechanisms. The model predictions are illustrated by examples from literature.

Microstructural characteristics in tough pitch copper for revealing the work hardening region

  • Okayasu, Mitsuhiro;Taki, Tatsuya;Takasu, Satoshi;Takeuchi, Shuhei;Shiraishi, Tetsuro
    • Advances in materials Research
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    • 제1권4호
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    • pp.349-359
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    • 2012
  • To reveal localized plastic deformation zones in a tough pitch copper, the etching characteristics of a copper sample have been examined. The etching was carried out on a sample surface using an etchant consisting of 25 ml nitric acid solution and 75 ml water. To clarify the plastic deformation zone, the sample deformed plastically was heated to between $250^{\circ}C$ and $300^{\circ}C$ before the etching process. This is due to a change of the microstructure and crystal orientation in the plastic deformation zone producing recrystallized small grains. In this case, the plastically deformed zone is severely etched, whereas the undeformed zone is only slightly etched. Identification of the details of the deformation zone from the etching is further discussed.

V 첨가강의 고온변형시 석출 및 재결정에 관한 연구 (Precipitation and Recrystallization of V-Microalloyed Steel during Hot Deformation)

  • 조상현;김성일;유연철
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 1996년도 춘계학술대회논문집
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    • pp.48-54
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    • 1996
  • The continuous deformation , multistage deformation and stress relaxation were carried out to investigate the strain induced procipitation by torsion tests in the range of 1000∼800$^{\circ}C$, 0.05/sec∼5/sec for V-microalloyed steel. The starting temperature and time for the initiation of precipitation were determined by stress relaxation tests and the distribution of percipitates increased at higher strain rate and the mean size of precipitates was found to be about 50nm. The precipitation starting time decreased with increasing strain rate from 0.05/sec to 5 /sec and pre-strain. The effect of deformation conditions on the no-recrystallization temperature(Tnr) was determined in the multistage deformation with declining temerature. The Tnr decreased with increasing strain and strain rae. In the controlled rolling, grain refinement and precpitation hardening effects could be achieved by the alternative large pass strain at the latter half pass stage under the condition of low temperature and high strain rate.

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등방성 강판의 자동차용 Roof Panel 부품 적용 특성 해석 (FE Analysis for Application of Isotropic Steel Sheet on Auto-Roof Panel)

  • 한수식
    • 소성∙가공
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    • 제15권3호
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    • pp.241-246
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    • 2006
  • The isotropic steel sheet was developed and started to apply on the auto-body outer panel, however the characteristics of application on auto-body were not well known. In this paper the FE analysis of outer panel of auto-body was carried out to investigate the characteristics of isotropic steel sheet. For the FE analysis of the roof panel of ULSAB body the isotropic steel sheet and the bake hardening steel sheet were used. The Isotropic steel sheet shows more deformation at punch bottom area of roof panel than the bake hardening steel sheet that is most required forming properties far outer panel to obtain the shape likability of forming parts. It is shown that the isotropic steel sheet has suitable material properties far outer panels of auto-body.

모래에 대한 단일항복면 구성모델의 평가 (Evaluation of Single Hardening Constitutive Model for Sand)

  • 정진섭;박명배
    • 한국농공학회지
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    • 제40권6호
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    • pp.95-103
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    • 1998
  • Solutions of geotechnical engineering problems require calculation of deformation and stresses during various stages of loading. Powerful numerical methods are available to make such calculation even for complicated problems. To get accurate results, realistic stress-strain relationships of soil are dependent on a number of factors such as soil type, density, stress level and stress path. Attempts are continuously being made to develope analytical models for soils incorporating all such factors. The nature of stress-path dependency, the principle that governs deformations in sand, and the use of Lade's single work-hardening model for predicting sand response for a variety of stress-paths have been investigated and are examined. The test results and the analyses presented show that under some conditions sand exhibits stress-path dependent behavior. The strains calculated from Lade's single work-hardening model are in reasonable agreement with those measured, but some discrepancies occur. The largest difference between measured and calculated strains occurs for proportional loading with increasing stresses and for stress-path directions.

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A strain hardening model for the stress-path-dependent shear behavior of rockfills

  • Xu, Ming;Song, Erxiang;Jin, Dehai
    • Geomechanics and Engineering
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    • 제13권5호
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    • pp.743-756
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    • 2017
  • Laboratory investigation reveals that rockfills exhibit significant stress-path-dependent behavior during shearing, therefore realistic prediction of deformation of rockfill structures requires suitable constitutive models to properly reproduce such behavior. This paper evaluates the capability of a strain hardening model proposed by the authors, by comparing simulation results with large-scale triaxial stress-path test results. Despite of its simplicity, the model can simulate essential aspects of the shear behavior of rockfills, including the non-linear stress-strain relationship, the stress-dependence of the stiffness, the non-linear strength behavior, and the shearing contraction and dilatancy. More importantly, the model is shown to predict the markedly different stress-strain and volumetric behavior along various loading paths with fair accuracy. All parameters required for the model can be derived entirely from the results of conventional large triaxial tests with constant confining pressures.

결정의 슬립을 고려한 금속의 미시적 소성변형거동 해석(I) (Analysis of Microscopic Plastic Behaviors of metals considering slip deformation of crystals(I))

  • 김정석;정기조;김영석
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 1996년도 춘계학술대회논문집
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    • pp.55-61
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    • 1996
  • Finite element calculations are performed for crystalline solids subjected to plane strain tensile loading. Using Asaro's double slop model, shearband developments in single crystals are analyzed. The effect of various rate sensitivities and latent hardening parameters on microscopic plastic behavior was clarified. Moreover the deformation behavior of polycystals which have grain boundaries was compared to that of single crystals.

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