• 제목/요약/키워드: stress and strain

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고온 구조물의 한계응력강도 결정을 위한 크리프 일-시간 관계식의 유용성 (Usefulness of Creep Work-Time ]Relation for Determining Stress Intensity Limit of High-Temperature Components)

  • 김우곤;이경용;류우석
    • 대한기계학회논문집A
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    • 제27권5호
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    • pp.750-757
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    • 2003
  • In order to determine creep stress intensity limit of high-temperature components, the usefulness of the creep work and time equation, defined as W$\_$c/t$\^$p/ = B(where W$\_$c/ = $\sigma$$\varepsilon$ is the total creep work done during creep, and p and B are constants), was investigated using the experimental data. For this Purpose, the creep tests for generating 1.0% strain for commercial type i16 stainless steel were conducted with different stresses; 160 MPa, 150 MPa, 145 MPa, 140 MPa and 135 MPa at 593$^{\circ}C$. The plots of log W$\_$c/ - log t showed a good linear relation up to 10$\^$5/ hr, and the results of the creep work-time relation for p, B and stress intensity values showed good agreement to those of isochronous stress-strain curves (ISSC) presented in ASME BPV NH. The relation can be simply obtained with only several short-term 1% strain data without ISSC which can be obtained by long-term creep data. Particularly, this relation is useful in estimating stress intensity limit for new and emerging class of high-temperature creeping materials.

마그네슘 합금 판재의 변형률, 변형률 속도 및 온도 환경을 고려한 유동응력 모델에 대한 연구 (Evaluation of Strain, Strain Rate and Temperature Dependent Flow Stress Model for Magnesium Alloy Sheets)

  • 송우진;허성찬;구태완;강범수;김정
    • 소성∙가공
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    • 제20권3호
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    • pp.229-235
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    • 2011
  • The formability of magnesium alloy sheets at room temperature is generally low because of the inherently limited number of slip systems, but higher at temperatures over $150^{\circ}C$. Therefore, prior to the practical application of these materials, the forming limits should be evaluated as a function of the temperature and strain rate. This can be achieved experimentally by performing a series of tests or analytically by deriving the corresponding modeling approaches. However, before the formability analysis can be conducted, a model of flow stress, which includes the effects of strain, strain rate and temperature, should be carefully identified. In this paper, such procedure is carried out for Mg alloy AZ31 and the concept of flow stress surface is proposed. Experimental flow stresses at four temperature levels ($150^{\circ}C$, $200^{\circ}C$, $250^{\circ}C$, $300^{\circ}C$) each with the pre-assigned strain rate levels of $0.01s^{-1}$, $0.1s^{-1}$ and $1.0s^{-1}$ are collected in order to establish the relationships between these variables. The temperature-compensated strain rate parameter which combines, in a single variable, the effects of temperature and strain rate, is introduced to capture these relationships in a compact manner. This study shows that the proposed concept of flow stress surface is practically relevant for the evaluation of temperature and strain dependent formability.

다짐 풍화토의 Duncan & Chang 모델 매개변수-초기접선계수와 극한축차응력 산정에 관한 연구 (Study on the Estimation of Duncan & Chang Model Parameters-initial Tangent Modulus and Ultimate Deviator Stress for Compacted Weathered Soil)

  • 유건선
    • 한국지반환경공학회 논문집
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    • 제19권12호
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    • pp.47-58
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    • 2018
  • Duncan & Chang(1970)는 던컨-창 모델을 제안하면서 흙시료의 초기 접선계수와 극한 축차응력을 구하기 위하여 쌍곡선이론을 사용하여 삼축압축시험의 응력-변형률의 비선형관계를 변환된 변형률/축차응력-변형률의 선형관계로 재구성하였다. 그러나 변환된 응력-변형률 관계는 이론적으로 선형관계를 나타내지만, 실제로는 시험이 시작되는 변형률이 작은 구간과 시료가 파괴에 이르는 변형률이 큰 구간에서는 비선형관계를 보인다. 이러한 현상은 삼축압축시험의 응력-변형률 곡선이 완전한 쌍곡선 형태가 아님을 나타낸다. 따라서 변환된 응력-변형률 곡선의 전 구간에 대하여 선형 회귀분석을 실시하여 직선의 식을 구하게 되면, 비선형관계를 나타내는 구간의 범위에 따라 선형관계식의 산정에 편차가 발생하게 된다. 이러한 편차를 줄이기 위하여 본 연구에서는 변환응력-변형률 관계에서 비선형을 나타내는 초반과 종반 구간을 제외한 구간에 대하여 선형회귀분석을 실시함으로써 초기접선계수와 극한 축차응력을 산정하는 수정회귀분석법을 제안하였다. 수정회귀분석법을 검증하기 위하여, 풍화토의 다짐시료에 대하여 압밀-배수 삼축압축시험을 실시하였다. 삼축압축시험의 응력-변형률 곡선으로부터 구한 변환응력-변형률 관계에 대해서 수정회귀분석을 실시하여 Duncan et al.(1980)이 제안한 2점법으로 구한 결과와 비교하였다. 분석결과 수정회기분석법에 비해 Duncan의 2점법으로 산정한 초기 접선계수는 4.0% 크게, 그리고 극한 축차응력은 2.9% 작게 평가되었다.

횡구속 콘크리트의 압축 응력-변형률 모델 : Part II. 사각단면 부재 (Stress-Strain Model for Laterally Confined Concrete : Part II. Rectangular Sectional Members)

  • 선창호;정혁창;김익현
    • 한국지진공학회논문집
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    • 제21권1호
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    • pp.59-67
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    • 2017
  • Due to a lack of the hoop action of lateral reinforcements the effective confining force in rectangular sections reduces compared to circular ones. Therefore, the stress-strain model obtained from the experimental data with circular sections overestimates the lateral confinement effect in rectangular sections, which evaluates seismic safety margin of overall structural system excessively. In this study experiments with laterally-confined square sections have been performed and the characteristic values composing stress-strain model have been analyzed. With introduction of section coefficients, in addition, the new unified stress-strain model applicable to square sections as well as circular ones has been proposed.

Theoretical analysis of stress-strain behavior of multi-layer RC beams under flexure

  • Ertekin Oztekin
    • Structural Engineering and Mechanics
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    • 제90권5호
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    • pp.505-515
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    • 2024
  • In this study, obtaining theoretical stress-strain curves and determining the parameters defining the equivalent rectangular stress block were aimed for 3 and 4-layered rectangular Reinforced Concrete (RC) cross-sections subjected to flexure. For these aims, the analytical stress-strain model proposed by Hognestad was chosen for the concrete grades (20 MPa≤fck≤60 MPa) used in this study. The tensile strength of the concrete was neglected and the thickness of the concrete layers in the compression zone of the concrete cross-section was taken as equal. In addition, while concrete strength was kept constant within each layer, concrete strengths belonging to separate layers were increased from the neutral axis towards the outer face of the compression zone of the concrete cross-section. After the equivalent rectangular stress block parameters were determined by numerical iterations, variations of these parameters depending on concrete strength in layers and layer numbers were obtained. Finally, some analytical equations have been proposed to predict the equivalent stress block parameters for the 3 and 4-layered RC cross-sections and validities of these proposed equations were shown by different metrics in this study.

조선 해양 구조물용 강재의 소성 및 파단 특성 II: 파단의 이론적 배경 (Plasticity and Fracture Behaviors of Marine Structural Steel, Part II: Theoretical Backgrounds of Fracture)

  • 정준모;심천식;김경수
    • 한국해양공학회지
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    • 제25권2호
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    • pp.92-100
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    • 2011
  • The main goal of this paper is to provide the theoretical background for the fracture phenomena in marine structural steels. In this paper, various fracture criteria are theoretically investigated: shear failure criteria with constant failure strain and stress triaxiality-dependent failure strain (piecewise failure and Johnson-Cook criteria), forming limit curve failure criterion, micromechanical porosity failure criterion, and continuum damage mechanics failure criterion. It is obvious that stress triaxiality is a very important index to determine the failure phenomenon for ductile materials. Assuming a piecewise failure strain curve as a function of stress triaxiality, the numerical results coincide well with the test results for smooth and notched specimens, where low and high stress triaxialities are observed. Therefore, it is proved that a failure criterion with reliable material constants presents a plastic deformation process, as well as fracture initiation and evolution.

온도보상기를 갖는 선체응력 계측용 스트레인 게이지의 개발 (Development of a strain gage with a temperature compensator for hull stress measurement)

  • 하윤수;류길수;박석주;박석배
    • 한국항해학회지
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    • 제21권3호
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    • pp.49-54
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    • 1997
  • It is very important to measure and monitor hull stress which is caused by a buoyant force and a weight of cargo for safety of ship. However, an exact measurement of hul stress, using the traditional strain gage which is made of metal or semiconductor, is very difficult, because a ship would be exposed by the severe temperature environment of $-20 ^{\circ}C$ to $80 ^{\circ}C$. This paper propose a new concept strain gage which can improve accuracy and compensage effectively affects due to temperature. The strain gage is consists of two parts. One is the Hull Deformation Amplifier which introuce several lever and link system, and another is a transducer converting distance into voltage signal. The HDA measure the amount of deformation and amplify it. And a lever and link system of the HDA is introduced for compensating temperature deformation by installing in perpendicular direction without stress. This paper also reports on the results of the experiments to verify linearity of the strain gage.

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링압축실험에 의한 유동응력 및 마찰인자의 결정 (II) (Determination of Flow Stress and Friction Factor by the Ring Compression Test (II))

  • 최영민;김낙수
    • 소성∙가공
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    • 제3권2호
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    • pp.215-228
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    • 1994
  • The purpose of this paper is to pursue a general method to determine both the flow stress of a material and the friction factor by ring compression test. The materials are assumed to obey the expanded n-power hardening rule including the strain-rate effect. Ring compression is simulated by the rigid-plastic finite element method to obtain the database used in determining the flow stress and friction factor. The Simulation is conducted for various strain hardening exponent, strain-rate sensitivity, friction factor, and compressing speed, as variables. It is assumed that the friction factor is constant during the compression process. To evaluate the compatibility of the database, experiments are carried out at room and evaluated temperature using specimens of aluminum 6061-T6 under dry and grease lubrication condition. It is shown that the proposed test method is useful and easy to use in determining the flow stress and the friction factor.

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Experiment and simulation analysis on full scale double-layer concrete shell

  • Thanh Quang Khai Lam;Thi My Dung Do
    • Computers and Concrete
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    • 제31권1호
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    • pp.9-21
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    • 2023
  • The published studies usually used analytical method, numerical methods or experimental method to determine the stress-strain state and displacement of the single-layer or multi-layer curved shell types, but with a small scale model. However, a full scale multi-layer doubly curved concrete shell roof model should be researched. This paper presents the results of the experiment and simulation analysis involving stress-strain state, sliding between layers, the formation and development of the full scale double-layer doubly curved concrete shell roof when this shell begins to crack. The results of the this study have constructed the load-sliding strain relationship; strain diagram; stress diagram in the shell layers; the Nx, Ny membrane force diagram and deflection of shell. Thisresults by experimental method on a full scale model of concrete have clarified the working of multi-layer doubly curved concrete shell roof. The experimental and simulation results are compared with each other and compared with the Sap2000 software.

반복 응력-변형률 시험을 통한 반복하중 조건에서 원전 주요 구조재료의 변형거동 평가 (Evaluation of Deformation Behavior of Nuclear Structural Materials under Cyclic Loading Conditions via Cyclic Stress-Strain Test)

  • 김진원;김종성;권형도
    • 한국압력기기공학회 논문집
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    • 제13권1호
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    • pp.75-83
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    • 2017
  • This study investigated deformation behavior of major nuclear structural materials under cyclic loading conditions via cyclic stress-strain test. The cyclic stress-strain tests were conducted on SA312 TP316 stainless steel and SA508 Gr.3 Cl.1 low-alloy steel, which are used as materials for primary piping and reactor pressure vessel nozzle respectively, under cyclic load with constant strain amplitude and constant load amplitude at room temperature (RT) and $316^{\circ}C$. From the results of tests, the cyclic hardening and softening behavior, stabilized cyclic stress-strain behavior, and ratcheting behavior of both materials were investigated at both RT and $316^{\circ}C$. In addition, appropriate considerations for cyclic deformation behavior in the structural integrity evaluation of major nuclear components under excessive seismic condition were discussed.