• Title, Summary, Keyword: 변형률 속도

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Study on the Strain-Rate Dependent Constitutive Equation using Elastoplastic-Viscoplastic Constitutive Model (Bounding Surface 모델을 이용한 변형율속도 의존적인 구성 관계식에 관한 연구)

  • Lee, Ki-Sun;Kim, Dae-Kyu;Lee, Woo-Jin
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.207-214
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    • 2001
  • 응력-변형률 관계의 모델링에 있어서 creep, stress relaxation, strain rate effect 등의 묘사는 중요한 지반거동중의 하나인 시간 의존적 거동에 대한 simulation은 있어서 대단히 중요한 요소라 할 수 있다. 특히 지반은 변형률 속도에 대하여 때로는 매우 다른 거동 특성을 보이기 때문에 지반의 모델링에 있어서 변형율 속도를 고려한 구성방정식의 제시는 큰 비중을 차지한다 하겠다. 본 연구에서는 변형율에 따라 변화하는 지반의 거동특성을 보다 현실에 가갈게 묘사하기 위한 시간 의존적 구성모델을 제시하는데 있다. Bounding Surface Model의 Stress Invariant 부분을 Perzyna(1966)와 Adachi and Oka(1982)의 변형율 속도 의존적인 구성관계 이론을 이용하여 발전시켰다 제안된 구성모델은 다양한 변형율 속도에 적용에 있어서 기존의 방식보다 간단히 모델 정수들을 결정 할 수 있다. 지반거동의 수치적인 해석을 위하여 기존의 Bounding Surface Model에 사용되었던 Program Code를 발전 시켜 사용하였으며, 엄격히 시행된 실내시험의 결과와 비교/검증하였다.

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Fracture Prediction in Drawing Processes of AZ31 alloy Sheet by the FEM combined with a Ductile Fracture Criterion considering Strain Rate Effect (변형률 의존성 연성파괴이론과 유한요소법에 의한 AZ31합금 판재의 드로잉 성형공정시 파단발생 예측)

  • Kim, Sang-Woo;Lee, Young-Seon;Kim, Dae-Yong
    • Proceedings of the KAIS Fall Conference
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    • pp.614-616
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    • 2011
  • 본 연구에서는 유한요소법과 변형률 의존성 연성파괴이론을 이용하여 드로잉 공정에서의 AZ31 마그네슘 합금 판재의 파단 발생을 예측 하였다. 다양한 온도에서의 사각컵 드로잉 실험을 수행하여, 각 온도조건에서의 파단깊이를 측정하였으며, 고온 인장시험을 통해 연성파괴상수를 온도 및 변형률 속도에 의존적인 값으로 표현하고, 실험과 동일하게 모사된 유한요소해석을 수행하였다. 해석결과 얻어진 각 요소의 온도 및 변형률 속도에 따른 연성파괴상수를 이용하여 파단발생을 예측하였으며, 실험결과와 검증하였다.

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Limit Analysis of Plane Strain Drawing (평면 변형 인발의 극한 해석)

  • 김병민;최인근;최재찬;이종수
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1407-1416
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    • 1991
  • 본 연구에서는 Liu의 수식화를 바탕으로 가공 경화성을 고려하여 수식화를 재 구성하고, 유한요소 프로그램을 개발하여 평면 변형 인발문제를 극한 해석함으로써, 성형에 필요한 한계 하중 및 최적 속도장을 직접적으로 구하였다.수렴되어진 최적 속도장으로 각 요송에서의 변형률 속도, 변형률 및 격자 변형등을 수치적으로 계산함 으로써 가공에 따른 변형 특성도 파악하였다. 한계 하중은 항공기 구조용 소재인 알 루미늄 6061 재료를 이용하여 판재 인발 실험을 행함으로써 얻은 결과치와 비교 검토 하였으며, 유동 특성을 관찰하기 위하여 격자 왜곡(grid distortion) 실험을 하여 얻 은 변형 패턴과 수치 계산에서 구한 격자변형 패턴을 상호 비교하였다.

Modeling Strain Rate-dependent Behavior in Consolidation of Natural Clay (자연점토의 변형률속도 의존적인 압밀거동의 해석)

  • ;Leroueil, S.
    • Journal of the Korean Geotechnical Society
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    • v.15 no.6
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    • pp.17-28
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    • 1999
  • In order to analyze effects of strain rate on consolidation of natural clay, this paper presents a nonlinear elasto viscoplastic model in which viscoplastic behavior is modeled by a unique effective stress-strain-strain rate relationship (equation omitted). The predicted values using numerical analysis are compared with measured ones in several laboratory tests such as creep test, multistage load test, and relaxation test for Berthierville clay. It is possible to estimate consolidation behavior of natural clay with reasonable accuracy using the proposed nonlinear viscoplastic model.

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Compressive Behavior of Carbon/Epoxy Composites under High Pressure Environment-Strain Rate Effect (고압환경에서 탄소섬유/에폭시 복합재의 압축거동에 대한 연구-변형률 속도 영향)

  • 이지훈;이경엽
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.4
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    • pp.148-153
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    • 2004
  • It is well-known that the mechanical behavior of fiber-reinforced composites under hydrostatic pressure environment is different from that of atmospheric pressure environment. It is also known that the mechanical behavior of fiber-reinforced composites is affected by a strain rate. In this work, we investigated the effect of strain rate on the compressive elastic modulus, fracture stress, and fracture strain of carbon/epoxy composites under hydrostatic pressure environment. The material used in the compressive test was unidirectional carbon/epoxy composites and the hydrostatic pressures applied was 270㎫. Compressive tests were performed applying three strain rates of 0.05%/sec, 0.25%/sec, and 0.55%/sec. The results showed that the elastic modulus increased with increasing strain rate while the fracture stress was little affected by the strain rate. The results also showed that the fracture strain decreased with increasing strain rate.

The Creep Behavior of Shale in Daegu Area (대구지역 셰일의 크리프 특성)

  • 김영수;정성관;차주석;방인호
    • Tunnel and Underground Space
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    • v.13 no.2
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    • pp.100-107
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    • 2003
  • Deformation is found by an external force in the rock which has internal stress. So, deformation is increased in time what is stressed under constant load. Rock materials collapse suddenly in a long period when the creep rate increases slightly. So mechanical deformability of the ground is an essential condition for determination of long term safety in structures. The result of analysis in 40%, 50%, 60%, 70% of constant load in creep test, strain velocity constants $\alpha$ and ${\gamma}$ increase with load increasement. Griggs equation is more exact than Li and Xia, Singh equation, and G$_2$of a flow constant by Burger's model decreases with stress increasement, but η$_1$$_2$and G$_1$ manifest irregularly in this study.

Axisymmetric Simulation of Nonpremixed Counterflow Flames - Effects of Global Strain Rate on Flame Structure - (비예혼합 대향류 화염의 축대칭 모사 - 변형률이 화염구조에 미치는 영향 -)

  • Park Woe-Chul
    • Journal of the Korean Institute of Gas
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    • v.8 no.2
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    • pp.42-47
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    • 2004
  • The axisymmetric methane-air counterflow flame in microgravity was simulated to investigate effects of the global strain rate on the flame structure. The flame shapes and profiles of temperature and the axial velocity for the mole fraction of methane in the methane-nitrogen fuel stream, Xm= 20, 50, $80\%$, and the global strain rate, ag= 20, 60, 90 $s^{-1}$ each mole fraction were compared. The profiles of the temperature and axial velocity of the axisymmetric simulations were in good agreement with those of OPPDIF, an one-dimensional flamelet code. It was confirmed that the flame is stretched more and the flame radius increases and the flame thickness decreases as the global strain rate increases.

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Temperature-Dependent Viscoplastic-Damage Constitutive Model for Nonlinear Compressive Behavior of Polyurethane Foam (폴리우레탄 폼 비선형 압축 거동 해석용 온도 의존 손상 점소성 구성방정식)

  • Lee, Jeong-Ho;Kim, Seul-Kee;Lee, Jae-Myung
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.29 no.5
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    • pp.437-445
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    • 2016
  • Recently, polyurethane foam has been used in various industry fields to preserve temperature environment of structures, and a wide range of loads from the static to the dynamic are imposed on the material during a life period. The biggest characteristic of polyurethane foam is porosity as being polymeric material, and it is generally known that insulation performance of the material strongly depends on internal void size. In addition, polyurethane foam's mechanical behavior has high dependence on strain rate and temperature as well as being highly non-linear ductile for compression. In the non-linear compressive behavior, volume fraction of voids and elastic modulus decrease as strain increases. Therefore, in this study, temperature-dependent viscoplastic-damage constitutive model was developed to describe the non-linear compressive behavior with the aforementioned features of polyurethane foam.

An analysis of deformation behavior on dynamic bulging in the high speed continuous casting (고속 연속주조에 있어서 동적 벌징의 변형거동 해석)

  • 강충길;윤광식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.6
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    • pp.1217-1226
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    • 1988
  • This paper shows an deformation behavior of steel cast slabs, which is used to prevent internal cracks of a slab in an unbending zone, in case of hot charge rolling(HCR) and hot direct rolling(HDR). The value of moving strand shell bulging between two supporting rollers under ferrostatic pressure has been computed in terms of creep and elastic-plasticity and for high strand surface temperature and high casting speed V=1.4-2.2m/min. The strain and strain rate distributions in solidified shell undergoes a series of bulging are calculated with boundary condition a very closed to continuous steel cast slabs productions.

A Study on Consolidation Characteristics of Remolded Clay due to the Liquid Limit (액성한계에 따른 재성형 점토의 압밀특성에 관한 연구)

  • Lim, Hyeongmin
    • Journal of the Korean GEO-environmental Society
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    • v.15 no.5
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    • pp.67-74
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    • 2014
  • In this study, a constant rate of strain test (CRS) and oedometer test was performed in order to study the consolidation characteristics to the liquid limit using a re-shaped clay which was preconsolidated at a constant pressure. Consolidation samples were made of kaolinite which was mixed with bentonite of 6 %, 9 %, 12 % and 15 % of it by weight and the test value of liquid limit of samples were appeared in 77 %, 84 %, 88 % and 91 % respectively. And then consolidation samples which were agitated sufficiently adding distilled water 2 times of liquid limit were preconsolidated in the condition of a constant pressure of 0.2 MPa. The oedometer test which is commonly used recently and the consolidation test of constant rate of strain which were applied in 0.001 %/min, 0.004 %/min, 0.01 %/min rate of strain according to ASTM, D4186-82 were performed and the preconsolidation pressures were compared and analyzed at 0.2 MPa preconsolidated pressure. As a result, in the case of low value of liquid limit, preconsolidation pressure was appeared same as 0.2 MPa preconsolidated pressure at the high speed strain rate, and in the case of high value of liquid limit, preconsolidation pressure was appeared same as 0.2 MPa preconsolidated pressure at the low speed strain rate.