• Title, Summary, Keyword: 변형률 속도

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Plasticity and Fracture Behaviors of Marine Structural Steel, Part I: Theoretical Backgrounds of Strain Hardening and Rate Hardening (조선 해양 구조물용 강재의 소성 및 파단 특성 I: 변형률 경화 및 변형률 속도 경화의 이론적 배경)

  • Choung, Joon-Mo;Shim, Chun-Sik;Kim, Kyung-Su
    • Journal of Ocean Engineering and Technology
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    • v.25 no.2
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    • pp.134-144
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    • 2011
  • In this paper, the global study trends for material behaviors are investigated regarding the static and dynamic hardenings and final fractures of marine structural steels. In particular, after reviewing all of the papers published at the 4th and 5th ICCGS (International Conference on Collision and Grounding of Ship), the used hardening and fracture properties are summarized, explicitly presenting the material properties. Although some studies have attempted to employ new plasticity and fracture models, it is obvious that most still employed an ideal hardening rule such as perfect plastic or linear hardening and a simple shear fracture criterion with an assumed value of failure strain. HSE (2001) presented pioneering study results regarding the temperature dependency of material strain hardening at various levels of temperature, but did not show strain rate hardening at intermediate or high strain rate ranges. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature hardening and softening at multiple steps of strain rates and temperatures. The main goal of this paper is to provide the theoretical background for strain and strain rate hardening. In addition, it presents the procedure and methodology needed to derive the material constants for the static hardening constitutive equations of Ludwik, Hollomon, Swift, and Ramberg-Osgood and for the dynamic hardening constitutive equations of power from Cowper-Symonds and Johnson-Cook.

Laboratorial Study for Mechanical Prosperities of Intermediate Soils (중간토의 역학적 특성에 관한 실험적 연구)

  • 박중배;전몽각
    • Geotechnical Engineering
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    • v.11 no.3
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    • pp.113-122
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    • 1995
  • The purposes of this study are to investigate the mechanical prospeities of the inter mediate soils through consolidation tests and triaxial compression shear tests. The intermediate soils used in this study are artificial soils which are composed of sea clay, sand and it's crushed component. The relationship between plastic index and mechanical prosperties (permeability and compressibility) is investigated through series of consoli dation tests. Strain hardening phenomenon under shearing is explored based on several overconsideration ratios and strain rates in undrained shear tests. To make a comparative study difference of drain condition and strain rate, drain shear tests are performed with overconsolidation ratio.

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Determination of True Stress-Strain Curves of Auto-body Plastics Using FEGM (FEGM을 이용한 자동차용 플라스틱의 진응력-변형률 선도 도출)

  • Park, C.H.;Kim, J.S.;Huh, H.;Ahn, C.N.;Choi, S.J
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.223-226
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    • 2009
  • The plastics are widely utilized in the inside of vehicles. The dynamic tensile characteristics of auto-body plastics are important in a prediction of deformation mode of the plastic component which undergoes the high speed deformation during car crash. This paper is concerned with the dynamic tensile characteristics of the auto-body plastics at intermediate strain rates. Quasi-static tensile tests were carried out at the strain rate ranged from 0.001/sec to 0.01/sec using the static tensile machine(Instron 5583). Dynamic tensile tests were carried out at the strain rate ranged from 0.1/sec to 100/sec using the high speed material testing machine developed. Conventional extensometry method is no longer available for plastics, since the deformation of plastic is accompanied with localized deformation. In this paper, quasi-static and dynamic tensile tests were performed using ASTM IV standard specimens with grids and images from a high speed camera were analyzed for strain measurement. True stress-strain relations and the actual strain rates at each deformation step were obtained by processing load data and deformation images, assuming the plastics to deform uniformly in each grid.

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Analysis of Buried Pipelines Using Ground Strain Input from Seismic Waves (지반변형률에 의한 매설관의 지진차 거동 해석)

  • Kim, Moon-Kyum;Cho, Woo-Yeon;Eo. Jun;Lee, Kang-Won
    • Journal of the Earthquake Engineering Society of Korea
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    • v.4 no.4
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    • pp.15-26
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    • 2000
  • 지진파 전파로 인한 매설관에 작용하는 지진하중은 지진특성 및 지반조건에 따른 지반변형률로부터 산정되어야 한다. 그러나. 기존에 사용되고 있는 경험적인 방법에 의해 계산된 지반변형률 모형은 지진 및 지반의 지역적 특수성을 고려할 수 없는 문제점을 내포하고 있다. 따라서, 본 연구에서는 이러한 문제점을 개선하기 위하여 지진특성 및 지반조선을 반영할 수 있는 수정된 지반변형률 모형을 제안하고 개발된 모형을 매설관로의 지진해석에 지진하중으로 적용하였다. 여기서, 지반변형률을 예측하기 위한 지진판 전파속도는 지반조건을 고려할 수 있도록 파 에너지분포에 근거한 분산곡선을 제안하여 산정하였다. 이러한 과정을 통해 얻어진 지반변형률 산정방법에 타당성을 파악하기 위해 예측한 지반변형률과 과거 지진으로 실측된 지반변형률을 비교하였다. 타당성이 입증된 지반변형률 모형을 매설관의 하중으로 적용하여 지진해석을 실시하였으며, 계산결과는 범용 유한요소해석을 통한 동해석 및 응답변위법에 의한 결과와 비교하였다. 이를 통해 지반 변형률 모형을 적용한 매설관 지진해석의 타당성을 검증하였다. 또한, 지진 및 지반환경이 다른 다양한 관의 특성을 반영하기 위해, 지진 지반 및 관의 영향 인자에 대해 매개변수 해석에 실시되었으며, 이로써 본 연구의 활용성을 검토하였다.

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Experimental Studies on Tension, Compression JC Constitutive Equation Parameter of Strain Rate Effect for AISI-4340 (AISI-4340 변형률 속도 변화에 따른 인장, 압축형 JC 구성방정식 변수에 관한 연구)

  • Woo, Sanghyun;Lee, Changsoo;Park, Leeju
    • Journal of the Korea Institute of Military Science and Technology
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    • v.20 no.4
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    • pp.520-527
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    • 2017
  • In this study, the experimental methods are compared for obtaining the parameters of the Johnson-Cook constitutive model. The parameters used for numerical simulation are very important in making an accurate estimation of numerical simulation. So, the testing method of obtaining the parameters is also very important. We compared the difference of conventional method, compression method and tensile method of AISI-4340 steel at various strain rate by using MTS, SHPB and SHTB. Taylor impact test and M&S were carried out to compare differences among these three types of JC constitutive parameter.

Fatigue Life Prediction and Ratcheting behavior of the Elbrodur-NIB under Fatigue loading with mean stress (평균응력을 포함한 피로하중 하에서 Elbrodur-NIB의 피로수명예측 및 Ratcheting 거동)

  • Lim, Chang-Bum
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.7
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    • pp.612-617
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    • 2011
  • An experimental study was carried out for the Elbrodur-NIB(copper alloy) at room temperature under stress-controlled uniaxial fatigue loading with and without mean stress. As a result, the effects of stress amplitude, mean stress and stress rate on ratcheting behavior were investigated. The ratcheting strain increased with increasing stress amplitude for a given mean stress, and with mean stress for a given stress amplitude. But, the ratcheting strain decreased as the stress rate increased. The three mean stress models were investigated and the mean stress models of Smith-Watson-Topper and Walker yielded good correlation of fatigue lives in the life range of $10^2-10^5$cycles.

Creep behaviour of mudstone in the tertiary Duho Formation at Pohang basin (포항분지 제3기 두호층 이암의 크리프 거동)

  • 김광식;김교원
    • The Journal of Engineering Geology
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    • v.13 no.2
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    • pp.227-238
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    • 2003
  • Understanding of a creep behavior in rocks under a constant load, due to visco-elastic properties of rock, is an essential element to predict a long term ground deformation. In order to clarify the creep characteristics of the mudstone in Duho formation at Pohang basin, deposited during Tertiary, a series of laboratory tests including physical properties, unconfined compressive strength and uniaxial creep tests, was performed. The mudstone showed a higher creep potential due to 26% of clay minerals such as illite and chlorite. The unconfined compressive strength of the rock was $462{\;}kg/\textrm{cm}^2$ in average, and four creep tests were performed under constant stress of 40 to 70 % of the strength. The creep constants in the empirical and theoretical equations were deduced from the time-strain curves obtained from the tests. Among the several equations, the empirical equation proposed by Griggs and theoretical equation of Burger’s model are appreciated as the best one to express the creep behavior of the mudstone. Instantaneous elastic strain was linearly increased with stress level but strain velocity during the first creep is decreased with a similar pattern by time lapse regardless the stress level.

Experimental Evaluation of Seismic Performance of Laminated Elastomeric Bearing and Lead-Rubber Bearing (적층고무베어링과 납-고무베어링의 내진 성능에 관한 실험적 평가)

  • 김대곤;이상훈;김대영;박칠림
    • Journal of the Earthquake Engineering Society of Korea
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    • v.2 no.4
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    • pp.53-62
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    • 1998
  • Experimental studies for the laminated elastomeric bearing and the lead-rubber bearing, those are often used to improve the seismic capacity of the structures recently, are conducted to evaluate the seismic capacity of the bearings. The shear stiffness of the bearings decreases as the shear strain amplitude or the constant axial load level increases, but not sensitive to the strain rates effect. Bearings are strong for the axial compression but weak for the axial tension.

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Effect of Loading Rate on the Deformation Behavior of SA508 Gr.1a Low Alloy Steel and TP316 Stainless Steel Pipe Materials at RT and 316℃ (상온과 316℃에서 SA508 Gr.1a 저합금강 배관과 TP316 스테인리스강 배관의 변형거동에 미치는 하중속도의 영향)

  • Kim, Jin Weon;Choi, Myung Rak
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.4
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    • pp.383-390
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    • 2015
  • This study conducted tensile tests on SA508 Gr.1a low alloy steel and SA312 TP316 stainless steel piping materials under various strain rates at room temperature (RT) and $316^{\circ}C$ to investigate the effects of loading rate on the deformation behavior of nuclear piping materials. At RT, the deformation behavior for both pipe materials showed a typical loading rate dependence, i.e., the strength increased and the ductility decreased as the loading rate increased. At $316^{\circ}C$, however, the strength and elongation of SA508 Gr.1a low alloy steel decreased as the loading rate increased, and its reduction of area non-linearly varied with the loading rate. For SA312 TP316 stainless steel, the strength, elongation, and reduction of area at $316^{\circ}C$ were almost the same regardless of the loading rate. At both temperatures, the strain hardening capacity was nearly independent of the loading rate for SA508 Gr.1a low alloy steel, while it decreased with increasing loading rate for SA312 TP316 stainless steel.

A study on the strain rate sensitivity according to the temperature for steel sheets of an auto-body (차체용 강판의 온도에 따른 변형률 속도 민감도 연구)

  • Lee H. J.;Song J. H.;Cho S. S.;Kim S. B.;Huh H.;Park S. H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.148-151
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    • 2005
  • This paper is concerned with the thermo-mechanical behavior and temperature dependent strain rate sensitivity of steel sheet for an auto-body. In order to Identify the temperature dependent strain rate sensitivity of SPRC35R and SPRC45E, uniaxial tension tests are performed with the variation of the strain rates from 0.001/sec to 200/sec, and the variation of environmental temperatures from $-40^{\circ}C\;to\;200^{\circ}C$. The thermo-mechanical response at the quasi-static state is obtained with the static tensile test and at the intermediate strain rate is from the high speed tensile test. The experimental results show that the strain rate sensitivity increases at low temperature and it decreases at high temperature. It means that as the strain rate getting increasing, the variation of flow stress is more sensitive on the temperature. The results also indicates that the material properties of SPRC35R is more depend on the changes of strain rates and temperature than those of SPRC45E.

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