• 제목/요약/키워드: Strain-rate hardening

검색결과 194건 처리시간 0.022초

CF8M 스테인리스 강 저주기 환경피로 실험의 주기적 변형률 경화 특성 (Characteristics of the Cyclic Hardening in Low Cycle Environmental Fatigue Test of CF8M Stainless Steel)

  • 정일석;하각현;김태룡;전현익
    • 대한기계학회논문집A
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    • 제32권2호
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    • pp.177-185
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    • 2008
  • Low-cycle environmental fatigue tests of cast austenitic stainless steel CF8M at the condition of fatigue strain rate 0.04%/sec were conducted at the pressure and temperature, 15MPa, $315^{\circ}C$ of a operating pressurized water reactor (PWR). The used test rig was limited to install an extensometer at the gauge length of the cylindrical fatigue specimen inside a small autoclave. So the magnet type LVDT#s were used to measure the fatigue displacement at the specimen shoulders inside the high temperature and high pressure water autoclave. However, the displacement and strain measured at the specimen shoulders is different from the one at the gauge length for the geometry and the cyclic strain hardening effect. Displacement of the fatigue specimen gauge length calculated by FEM (finite element method) used to modify the measured displacement and fatigue life at the shoulders. A series of low cycle fatigue life tests in air and PWR conditions simulating the cyclic strain hardening effect verified that the FEM modified fatigue life was well agreed with the simulating test results. The process and method developed in this study for the environmental fatigue test inside the small sized autoclave would be so useful to produce reliable environmental fatigue curves of CF8M stainless steel in pressurized water reactors.

중탄소강의 동적 재결정에 관한 연구 (Dynamic Recrystallization of Medium Carbon Steels)

  • 김성일;한창훈;유연철;이덕락;주웅용
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2000년도 추계학술대회 논문집
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    • pp.33-36
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    • 2000
  • The dynamic recrystallization (DRX) of medium carbon steels (SCM 440 and POSMA45) was studied with torsion test in the temperature range of $900-1100^{\circ}C$ and the strain rate range of $5.0x10^{-2}\;-\;5.0x10^0/sec$. To establish the quantitative equations for DRX, the evolution of flow stress curve with strain was analyzed. The critical strain (${\varepsilon}_c$) and strain for maximum softening rate ( ${\varepsilon}^{*}$) could be confirmed by the analysis of work hardening rate ($d{\sigma}/d{\varepsilon}\;=\; \theta$). The volume fraction of dynamic recrystallization ($X_{DRX}$) as a function of processing variables, such as strain rate ( $\dot{\varepsilon}$ ), temperature (T), and strain ( $\varepsilon$ ) were established using the ${\varepsilon}_c$ and ${\varepsilon}^{*}$. For the exact prediction, the ${\varepsilon}_c$, ${\varepsilon}^{*}$ and Avrami' exponent (m') were quantitatively expressed by dimensionless parameter, Z/A respectively. The transformation-effective strain-temperature curve for DRX could be composed. It was found that the calculated results were agreed with the experimental data for the steels at any deformation conditions.

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강소성 유한요소법을 이용한 알루미늄 7075합금강의 국부화 현상에 대한 연구 (A Study of Localization with Al7075 By Using Rigid-Plastic Finite Element Method)

  • 이병섭
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2000년도 춘계학술대회논문집
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    • pp.9-12
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    • 2000
  • The importance of the role of plastic spin in the rate-dependent response of materials at large deformations is the main objective of this work. After a brief presentation of a general consitutive framework for visco-rigid plasticity at large strains an isotropic/kinematic hardening and a visco-rigid plastic model are used to analyze the stress-strain response under simple shear. A clear understanding of the role of plastic spin is achieved by obtaining numerical analyzed results for different stress values in which the plastic spin consititutive parameters interrelaste with the strain rate and other more conventional model constants, Especially this paper is concerned with introducing behaviors of Al7075

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변형률속도 민감성을 고려한 요크 코킹공정의 해석에 의한 품질 평가 (Quality Assessment by Analysis of Yoke Caulking Process Considering Strain Rate Sensitivity)

  • 박문식;강경모;한덕수
    • 한국정밀공학회지
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    • 제20권6호
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    • pp.37-46
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    • 2003
  • This paper is to predict quality deterioration resulting from a caulking process of yoke which is a part of automotive steering system. The caluking is a plastic deformation process involving such as impact of high speed tool, contacts between part and fixtures and strain rate sensitivity of the part material. Elaborate application of finite element method is neccesary to calculate changes of part dimensions because they fall into a level of tolerances. Simple work hardening and strain rate sensitive model is proposed fur the material and applied for the simulation by using Abaqus which is able to cater for elastoplastic rate sensitive material and contacts. Numerical results of test models that represent tensile bar and tensile plate are compared with material data inputs. Dimensional changes for the yoke are calculated from simulations and compared to the mesurements and they show good agreement. The method presented here with the material model proved to be valuable to assess quality deterioration for similar metal forming processes.

차체용 고장력 강판의 동적 인장 특성 평가 (Dynamic Tensile Characteristics of the High Strength Steel Sheet for an Auto-body)

  • 김석봉;허훈;신철수;김효균
    • 한국자동차공학회논문집
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    • 제15권1호
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    • pp.171-176
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    • 2007
  • An important challenging issue in the automotive industry is the light-weight, safe design and enhancement of crash response of an auto-body structures. These objectives lead to increasing adoption of high strength steel sheet for inner and outer auto-body members. This paper evaluates the dynamic tensile characteristics of high strength steel sheets, HS45R, TRIP60, DP60 and DP100, along the rolling direction and transverse direction. Static tensile tests were carried out at the strain rate of 0.003/sec using the static tensile machine (Instron 5583). Dynamic tensile tests were carried out at the range of strain rate from 0.1/sec to 200/sec using a high speed material testing machine developed. The tensile tests acquire stress-strain relation and strain rate sensitivity of each material. The experimental results show two important aspects for high strength steels: the flow stress increases as strain rate increases; the strain hardening decreases as the tensile stress increases. The experiments also produce interesting results that the elongation does not decrease even when the strain rate increases.

일반 등방경화 구성관계에 대한 내재적인 음력적분 : 1. 정식화 (Implicit Stress Integration of the Generalized Isotropic Hardening Constitutive Model : 1. Formulation)

  • 오세붕;이승래
    • 한국지반공학회지:지반
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    • 제12권4호
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    • pp.145-156
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    • 1996
  • 연약한 지반의 거동을 적절하게 표현할 수 있는 일반 등방경화 규칙에 근거한 비등방경화 구성모델을 비선형 유한요소해석에 적용하기 위하여 내재적인 응력적분기법을 정식화하였다. 정식화된 응력적분기법은 비선형 해석시에 필요한 응력을 일반 사다리꼴규칙에 의하여 내재적으로 적분하고 응력변형률 접선계수를 비선형 해법에 일관되게 도출할 수 있다. 이러한 알고리즘을 통하여 해의 정확도 및 수렴도를 확보할 수 있으므로, 비등방경화 구성 관계를 적용한 비선형 해석을 정확하고 효율적으로 수행할 수 있는 토대를 구축할 수 있었다.

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INFLUENCE OF ALLOY COMPOSITION ON WORK HARDENING BEHAVIOR OF ZIRCONIUM-BASED ALLOYS

  • Kim, Hyun-Gil;Kim, Il-Hyun;Park, Jeong-Yong;Koo, Yang-Hyun
    • Nuclear Engineering and Technology
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    • 제45권4호
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    • pp.505-512
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    • 2013
  • Three types of zirconium base alloy were evaluated to study how their work hardening behavior is affected by alloy composition. Repeated-tensile tests (5% elongation at each test) were performed at room temperature at a strain rate of $1.7{\times}10^{-3}s^{-1}$ for the alloys, which were initially controlled for their microstructure and texture. After considering the yield strength and work hardening exponent (n) variations, it was found that the work hardening behavior of the zirconium base alloys was affected more by the Nb content than the Sn content. The facture mode during the repeated tensile test was followed by the slip deformation of the zirconium structure from the texture and microstructural analysis.

지반재료의 비등방경화 구성모델에 대한 응력적분 알고리즘 (Stress Integration Algorithm for an Anisotropic Hardening Constitutive Model of Geomaterials)

  • 오세붕;이진구;김태경
    • 한국전산구조공학회:학술대회논문집
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    • 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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    • pp.343-350
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    • 2005
  • A constitutive model was implemented in ABAQUS code. The constitutive equation can model the behavior for overall range of strain level from small to large deformation, which is based on anisotropic hardening rule and total stress concept. The formulation includes (1) finite strain formulation on the basis of Jaumann rate, (2) implicit stress integration and (3) consistent tangent moduli. Therefore the mathematical background was established in order that large deformation analysis can be performed accurately and efficiently with the anisotropic constitutive model. In the large deformation analyses, geometric nonlinearity was considered and the result of analyses with the proposed model was compared with that of Mises model for the overall strain range behavior.

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구형석출물을 갖는 무한 고체에 전수압이 가해지는 경우에 대한 탄소성해 (An elasto-plastic solution for infinite solid containing a spherical precipitate under hydrostatic pressure)

  • 최병익;엄윤용
    • 대한기계학회논문집
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    • 제5권2호
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    • pp.122-130
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    • 1981
  • Equation of equilibrium is derived and solved for an infinite isotropic solid under applied hydrostatic stress which is uniform at large distance, and disturbed by a spherical precipitate which has isotropoc elastic constants dirrerent form those of the matrix. A linear strain hardening behavior of the matrix is assumed, and an elasto-plastic sloution is obtained. The difference of the total strain energy stored inthe infinite solid with and without a precipitate is computed, and compared with that for purely elastic case. Finally the effect of the ratio of the bulk modulus of the precipitate to that of the matrix and the effct of linear strain hardening rate on the plastic zone size and the energy difference are discussed.

TiAl 금속간 화합물의 미세조직에 따른 고온변형특성 (High Temperature Deformation Behavior of Ti-Al Intermetallic Compound - Microstructure Effect)

  • 하태권;정재영;이광석;장영원
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2003년도 춘계학술대회논문집
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    • pp.295-298
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    • 2003
  • High temperature deformation behavior of a Ti-Al intermetallic compound has been investigated. Specimens with a near gamma and a lamella structures were obtained by performing heat treatment at 1200 and 1330$^{\circ}C$, respectively, for 24 hr and stabilized at 900$^{\circ}C$ for 4 hr followed by air cooling. A series of load relaxation tests has been conducted on these samples at temperatures ranging from 850 to 950$^{\circ}C$ to construct flow curves in the strain rate range from 10$\^$-6//s to 10$\^$-3//s. Strain hardening was observed even at the temperature of 950$^{\circ}C$ in both the near gamma and the lamella structures. Further aging treatment for 12 hr at test temperatures has found to cause no softening in both microstructures.

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