• 제목/요약/키워드: Yield Criterion

검색결과 282건 처리시간 0.024초

소결분말금속의 항복함수 (A Yield Function for Sintered Porous Metals)

  • 박종진
    • 대한기계학회논문집
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    • 제17권5호
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    • pp.1115-1122
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    • 1993
  • Several yield criteria for porous materials are compared with each other, defining the apparent yield stress as the yield stress of the porous material in simple compression. It was found that the plastic Poisson's ratio is the parameter needed to define the yield criterion, rather than the relative density. The plastic Poisson's ratio is regarded as a material characteristic that is obtained from a simple compression test. A new form of yield criterion was suggested, and it was applied to hydrostatic compression as well as uniaxial strain compression of sintered Al-2024 powder. The crossover point in the mean stress vs volume change curves of the processes was predicted. It is presented that the flow stress of the fully densed material can be obtained from that of the porous material using relations obtained from the yield criterion.

폴리머 폼 재료의 정수압 종속 항복조건 결정에 관한 연구 (Determination of pressure-Dependent Yield . Criterion for Polymeric Foams)

  • 김영민;강신일
    • 소성∙가공
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    • 제11권1호
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    • pp.69-74
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    • 2002
  • In addition to lightweight and moldable characteristics, polymeric foams possess an excellent energy absorbing capability that can be utilize for a wide range of commercial applications, especially in the crashworthiness of the automobiles. The purpose of the present study is to develop experimental methodology to characterize the pressure dependent yield behavior of the energy absorbing polymeric foams. For the compression test in a triaxial stress sate, a specially designed device was placed in a hydraulic press to produce and control oil pressure. For the test material, the polyurethane foams of two different densities were used. The displacement of the specimen, the load subjected to the specimen, and oil pressure applied to the specimen were measured and controlled. Stress strain curves and yield stresses for the four different oil pressure were obtained. It was found from the present experiments that the polyurethane foams exhibited significant increases in yield stress with applied pressure or mean normal stress. Based on this observation, a yield criteria which included the effect of the stress invariant were established for the polymeric foams. The obtained experimental constants which constituted the pressure-dependent yield criterion were verified.

Influence of pressure-dependency of the yield criterion and temperature on residual stresses and strains in a thin disk

  • Alexandrov, S.;Jeng, Y.R.;Lyamina, E.
    • Structural Engineering and Mechanics
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    • 제44권3호
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    • pp.289-303
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    • 2012
  • Existing plane stress solutions for thin plates and disks have shown several qualitative features which are difficult to handle with the use of commercial numerical codes (non-existence of solutions, singular solutions, rapid growth of the plastic zone with a loading parameter). In order to understand the effect of temperature and pressure-dependency of the yield criterion on some of such features as well as on the distribution of residual stresses and strains, a semi-analytic solution for a thin hollow disk fixed to a rigid container and subject to thermal loading and subsequent unloading is derived. The material model is elastic-perfectly/plastic. The Drucker-Prager pressure-dependent yield criterion and the equation of incompressibity for plastic strains are adopted. The distribution of residual stresses and strains is illustrated for a wide range of the parameter which controls pressure-dependency of the yield criterion.

탄소성 구성 방정식을 이용한 삼차원 브레이드 복합재료의 역학적 해석 (Mechanical Analysis of 3D Circular Braided Glass Fiber Reinforced Composites Using Elastic-Plastic Constitutive Equations)

  • 류한선;이명규;김지훈;정관수
    • 한국복합재료학회:학술대회논문집
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    • 한국복합재료학회 2004년도 추계학술발표대회 논문집
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    • pp.147-150
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    • 2004
  • In order to describe the mechanical behavior of highly anisotropic and asymmetric materials such as fiber­reinforced composites, the elastic-plastic constitutive equations were used here based on the recently developed yield criterion and hardening laws. As for the yield criterion, modified Drucker-Prager yield surface was used to represent the orthotropic and asymetric properties of composite materials, while the anisotropic evolution of back­stress was accounted for the hardening behavior. Experimental procedures to obtain the material parameters of the hardening laws and yield surface are presented for 3D Circular Braided Glass Fiber Reinforced Composites. For verification purpose, comparisons of finite element simulations using the elastic-plastic constitutive equations, anisotropic elastic constitutive equations and experiments were performed for the three point bending tests. The results of finite element simulations showed good agreements with experiments, especially for the elastic-plastic constitutive equations with yield criterion considering anisotropy as well as asymmetry and anisotropic back stress evolution rule.

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평균수직응력에 민감한 모재를 가진 기공체의 구성식과 기공생성모델 (A Constitutive Law for Porous Solids with Pressure-Sensitive Matrices and a Void Nucleation Model)

  • 정현용
    • 대한기계학회논문집A
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    • 제24권2호
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    • pp.472-480
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    • 2000
  • A macroscopic yield criterion for porous solids with pressure-sensitive matrices modeled by Coulomb's yield criterion was obtained by generalizing Gurson's yield criterion with consideration of the hydrostatic yield stresses for a spherical thick-walled shell and by fitting the finite element results of a voided cube. The macroscopic yield criterion is valid for negative mean normal stresses as well as for positive mean normal stresses. From the yield criterion, a plastic potential function for the porous solids was derived either for plastic normality flow or for plastic non-normality flow of pressure- sensitive matrices. In addition, the elastic relation, an evolution equation of the plastic flow stress of the matrices and an evolution equation of the void volume fraction were presented to complete a set of constitutive relations. The set of constitutive relations was implemented into a finite element code ABAQUS to analyze the material behavior of rubber-toughened epoxies. The cavitation and the deformation behavior were analyzed around a crack tip under three-point bending and around notch tips under four-point bending. In the numerical analyses, the cavitation of rubber particles was considered via a stress-controlled nucleation model. The numerical results indicate that a reasonable cavitation zone can be obtained with void nucleation controlled by the macroscopic mean normal stress, and a plastic zone is smaller around a notch tip under compression than under tension. These numerical results agree well with corresponding experimental results on the cavitation and plastic zones.

고준위폐기물 처분장치 및 완충장치에 대한 탄소성해석 : 비대칭 암반력 (An Elastoplastic Analysis for Spent Nuclear Fuel Disposal Container and Its Bentonite Buffer: Asymmetric Rock Movement)

  • 권영주;최석호
    • 소성∙가공
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    • 제12권5호
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    • pp.479-486
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    • 2003
  • This paper presents an elastoplastic analysis for spent nuclear fuel disposal container and its 50 cm thick bentonite buffer to predict the collapse of the container while the horizontal asymmetric sudden rock movement of 10 cm is applied on the composite structure. This sudden rock movement is anticipated by the earthquake etc. at a deep underground. Elastoplastic material model is adopted. Drucker-Prager yield criterion is used for the material yield prediction of the bentonite buffer and von-Mises yield criterion is used for the material yield prediction of the container. Analysis results show that even though very large deformations occur beyond the yield point in the bentonite buffer, the container structure still endures elastic small strains and stresses below the yield strength. Hence, the asymmetric 50 cm thick bentonite buffer can protect the container safely against the 10 cm sudden rock movement by earthquake etc.. Analysis results also show that bending deformations occur in the container structure due to the shear deformation of the bentonite buffer. The finite element analysis code, NISA, is used for the analysis.

천공판재의 항복거동 (Plastic yield behaviour of perforated sheets)

  • 백승철;이동녕;오규환
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 1994년도 춘계학술대회 논문집
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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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A fracture criterion for high-strength steel cracked bars

  • Toribio, J.
    • Structural Engineering and Mechanics
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    • 제14권2호
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    • pp.209-221
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    • 2002
  • In this paper a fracture criterion is proposed for cracked cylindrical samples of high-strength prestressing steels of different yield strength. The surface crack is assumed to be semi-elliptical, a geometry very adequate to model sharp defects produced by any subcritical mechanism of cracking: mechanical fatigue, stress-corrosion cracking, hydrogen embrittlement or corrosion fatigue. Two fracture criteria with different meanings are considered: a global (energetic) criterion based on the energy release rate G, and a local (stress) criterion based on the stress intensity factor $K_I$. The advantages and disadvantages of both criteria for engineering design are discussed in this paper on the basis of many experimental results of fracture tests on cracked wires of high-strength prestressing steels of different yield strength and with different degrees of strength anisotropy.

압축-인장 비대칭을 고려한 AZ31 튜브의 압괴해석 (FE Simulation of Axial Crushing Test for AZ31 Tube Considering Tension-Compression Asymmetry)

  • 윤종헌;이정환
    • 대한기계학회논문집A
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    • 제36권9호
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    • pp.997-1002
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    • 2012
  • 수송기기의 연비향상과 에너지 절감을 위하여 자동차 업계를 비롯한 각종 산업 전반에 마그네슘 합금의 적용이 확대되고 있는 추세이다. 조밀육방 격자 구조(HCP)를 갖는 마그네슘 합금의 경우, 낮은 성형성과 강한 소성 비대칭성 및 소성 이방성으로 인하여 실제 부품의 적용에 많은 제약조건이 수반되고 있다. 본 논문에서는 CPB06 항복함수를 이용하여 AZ31의 인장-압축 비대칭성을 모델링하고 이를 이용하여 AZ31 튜브의 압괴해석을 수행하고자 하였다.

Description of reversed yielding in thin hollow discs subject to external pressure

  • Alexandrov, Sergei E.;Pirumov, Alexander R.;Jeng, Yeau-Ren
    • Structural Engineering and Mechanics
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    • 제58권4호
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    • pp.661-676
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    • 2016
  • This paper presents an elastic/plastic model that neglects strain hardening during loading, but accounts for the Bauschinger effect. These mathematical features of the model represent reasonably well the actual behavior of several materials such as high strength steels. Previous attempts to describe the behavior of this kind of materials have been restricted to a class of boundary value problems in which the state of stress in the plastic region is completely controlled by the yield stress in tension or torsion. In particular, the yield stress is supposed to be constant during loading and the forward plastic strain reduces the yield stress to be used to describe reversed yielding. The new model generalizes this approach on plane stress problems assuming that the material obeys the von Mises yield criterion during loading. Then, the model is adopted to describe reversed yielding in thin hollow discs subject to external pressure.