• Title, Summary, Keyword: 변형률 속도

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Influence of strain rate on the acoustic emission signal characteristics in corrosive environment (부식환경하에서 음향방출신호 특성에 미치는 변형률속도의 영향)

  • Yu, Hyo-Seon;Jeong, Se-Hui
    • Korean Journal of Materials Research
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    • v.5 no.1
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    • pp.12-21
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    • 1995
  • The study was performed to study the effects of strain rate on acoustics emission( AE) during bulging test in corrosive environmentsynthetic sea water. The strain rates used were in the range $4 \times 10^{-6}S^{-1}$ to $1 \times 10^{-4} \times S^{-1}$ and the parameters used to evaluate AE signal characteristics were AE hit and amplitude. It can be observed that the cumulative AE hit and average amplitude during fracture process increase highly at decreasing strain rates while the equivalent fracture strain and the crack length of circumferencial direction become decrease. The peak point of AE signal characteristic parameters approach to the first half of test. When the average amplitude per unit equivalent fracture strain was above 20dB, it was definitly observed stress corrosion cracking phenomena. Additional, we knew that the AE test had the possibility to evaluate SCC susceptibility with various strain rates.

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Finite Strain and Nonlinear Consolidation Analysis Considering the Effect of Strain Rate Dependency on Clay (점토의 변형률 속도 의존성을 고려한 비선형 유한변형 압밀해석)

  • Lee, Bongjik;Lee, Heunggil;Kwon, Youngcheul
    • Journal of the Korean GEO-environmental Society
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    • v.9 no.6
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    • pp.53-60
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    • 2008
  • In recent years, finite strain consolidation theories including a mechanical nonlinearity and a reasonable coordinate system have been proposed and used in educations and practical consolidation problems. However, despite their reasonable ability to predict the consolidation behavior, their failure in the field can be attributed to the complexity of estimating and selecting proper parameters for simulating the consolidation phenomenon. In this study, therefore, the application of a piecewise-linear method was proposed to solve such problems including the assumption of the uniqueness in compressibility. Especially, the concept of reference curve was introduced to define the effect of strain rate dependency of clay. The applicability of the methodology is verified by several tests. It was found that the proposed method is applicable in restrictive ranges of study carried out in the laboratory. Finally it is expected that the verification in field consolidation problem has to be carried out through future study.

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Non-Quadratic Anisotropic Strain Rate Potential Defined in Plane Stress State (평면 응력 조건에서 정의된 비이차 비등방 변형률 속도 포텐셜)

  • Kim, D.;Kim, J.H.;Lee, Y.S.;Barlat, Frederic;Chung, K.
    • Transactions of Materials Processing
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    • v.20 no.5
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    • pp.369-376
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    • 2011
  • A non-quadratic anisotropic strain rate potential was introduced as a conjugate potential of the yield stress potential Yld2000-2d to describe anisotropic behavior of sheet metals, in particular, aluminum alloy sheets under plane stress state. This strain-rate potential takes into account the anisotropic yield stresses and R-values measured along the directions measured at 0, 45 and 90 degrees from the rolling direction, as well as the balanced biaxial yield stress and strain-rate ratio. The convexity of the strain-rate potential was completely proven. The strain-rate potential was applied for two anisotropic aluminum alloy sheets, AA6022-T4 and AA2090-T3. The results verified that the strain rate potential properly described the anisotropic behavior of aluminum alloy sheets and was closely conjugate of Yld2000-2d under the plane stress state.

Dynamic Simulation of Rail Strain and Vibration Changes According to Track Irregularity (선로 궤도틀림에 따른 레일 변형률과 진동 변화 동역학 시뮬레이션)

  • Kim, Ju Won;Kim, Yong Hwan
    • Journal of the Korea Society for Simulation
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    • v.30 no.1
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    • pp.127-137
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    • 2021
  • The method of utilizing the strain and vibration values of rails is primarily used to diagnose the condition of wheels and railroad facilities. The dynamic load is measured under the assumption that the strain of the rail and the load of the railroad vehicle are proportional. Wheel condition is measured under the assumption that the magnitude of the defect and the magnitude of the rail vibration are proportional. However, environmental factors affecting the strain and vibration of the rail such as vehicle speed, wheel load, climate, and track conditions are not reflected, many errors occur depending on the measurement conditions. In this study, the effect of track distortion, which is a major indicator of the track condition among the environmental factors that affect the strain and vibration of the rail, on the strain and vibration of the rail, was examined through dynamic simulation. As a measure to reduce the measurement deviation, the effect of securing additional measurement points was analyzed.

Effects of Various Stress Histories Including Creep Loading on Strength of a Geogrid (크리프 하중을 포함한 응력이력이 지오그리드 강도에 미치는 영향)

  • Park, Young-Kon;Fumio Tatsuoka
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.441-444
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    • 2001
  • PVC로 코팅된 폴리에스테르 섬유로 만들어진 지오그리드 보강재에 대해 변형률을 달리하여 단일 또는 다단 크리프 하중단계를 포함한 하중을 연속적으로 작용시킴으로써 그 인장파괴강도를 검토하였다. 연구결과, 동일한 변형률에서 지오그리드의 인장파괴강도는 극한인장파괴가 되기 전에 작용된 웅력이력에 의해서 거의 영향을 받지 않는다. 또한 지오그리드의 설계파단강도는 적정한 변형률하에서 정의되어야 하며, 변형률 속도가 빠른 인장시험을 통해 지오그리드의 설계파단강도를 얻을 경우 이에 대한 보정이 필요할 것으로 사료된다.

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High Strain Rate Tensile Test of Composite Material for Automotive Front End Module Carrier (자동차 프론트엔드모률 캐리어용 경량 복합소재의 고속인장 시험)

  • Kang, Woo-Jong;Kim, Sung-Tae
    • Composites Research
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    • v.24 no.3
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    • pp.12-16
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    • 2011
  • High strain rate tensile tests were performed to measure the strain rate sensitivity of fiber reinforced composite material. The composite material was developed for the light weight design of an automotive FEM(front end module) carrier. Standard specimens for quasi-static tests of fiber reinforced composites can be found in ASTM D3039. However, in case of high strain rate tests, it was hard to find standard specimen shapes. In this study, three kinds of tensile specimens designed based on ASTM D638 were investigated to determined the adequate gauge width of tensile specimen for fiber reinforced composite. A drop tower type of high speed tensile apparatus was developed for strain rates of about 15/s and 100/s. Gauge width of 6mm, 8mm and 10mm were investigated. Test results showed the specimen of 8mm width was adequate for the high strain rate tensile tests of fiber reinforced composite. It was found the strength of the composite material increased as the strain rate increased.

Dynamic Deformation Behavior of Rubber Under High Strain-Rate Compressive Loading by Using Plastic SHPB Technique (플라스틱 SHPB기법을 사용한 고무의 고변형률 하중 하에서의 동적변형 거동)

  • 이억섭;김경준
    • Journal of the Korean Society for Precision Engineering
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    • v.20 no.11
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    • pp.158-165
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    • 2003
  • A specific experimental method, the Split Hopkinson pressure bar (SHPB) technique has been widely used to determine the dynamic material properties under the impact compressive loading conditions with strain rate of the order of 10$^3$/s∼l0$^4$/s. In this paper, dynamic deformation behaviors of rubber materials widely used for the isolation of vibration from structure under varying dynamic loading are determined by using plastic SHPB technique. A transition point to scope with the dynamic deformation behavior of rubber-like material is defined in this paper and used to characterize the specifics of the dynamic deformation of rubber materials.

Impact Response Behaviors of Laminated Composite Plates Subjected to the Transversely Impact of a Steel Ball (강구에 의한 횡방향 충격을 받는 적층복합판의 충격 응답 거동)

  • 김문생;김남식;박승범;백인환
    • Journal of Ocean Engineering and Technology
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    • v.7 no.2
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    • pp.44-56
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    • 1993
  • The purpose of this paper is to analyze the impact response behaviors of glass/epoxy laminated composite plates subjected to the transversely impact of a steel ball. For this purpose, dynamic finite element analysis based on the higher-order shear defomation plate theory is used to compute the contact forces, rebound velocity of a steel ball, and dynamic strain response histories. And low-velocity and high-velocity impact experiments were conducted to compare the results and compute the wave propagation velocities. The results obtained from impact experiments are in good agreement with those of dynamic finite element analysis. Also the wave propagation velocities obtained from high-velocity impact experiments and wave propagation theory agree well, and wave velocities were higher in the smaller radius of steel ball.

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Failure Time Prediction by Nonlinear Least Square Method with Deformation Data (계측 자료의 비선형최소자승법을 이용한 파괴시간 예측)

  • Yoon, Yong-Kyun;Kim, Byoung-Chul;Jo, Young-Do
    • Tunnel and Underground Space
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    • v.19 no.6
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    • pp.558-566
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    • 2009
  • Time-dependent behavior is a basic mechanical property of rocks. Predicting the failure time of rock structures by analyzing the time-dependent characteristic is important and problematic. It is tried to predict the failure time of tunnel, slope & laboratory creep test specimen from measured displacement(or strain) and rate with relationship suggested by Voight($\ddot{\Omega}=A\dot{\Omega}^\alpha$, where $\Omega$ is a measurable quantity such as strain & displacement and A & $\alpha$ are constants). A & $\alpha$ are estimated through applying the nonlinear least square method to the single and double integrated Voight's equations and utilized to predict the failure time. Predicted failure time is in accordance with real one except minor error. Linear inverse rate method applied to creep strain and rate yields a poor linear correlation of data and precision of predicted failure time is not better than methods using strain and rate.

An Investigation of the Formability of Thermoplastic Composite in Biaxial Stretch Forming (열가소성 복합재료의 2축 인장성형시 성형성에 관한 연구)

  • 이중희
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.10
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    • pp.127-134
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    • 1997
  • 열가소성 복합재료는 고상 성형법에 의해 저렴한 가격으로 부피가 튼 제품의 제조에 널리 사용될 수 있어 아주 좋은 전망을 가지고 있다. 그러나, 이러한 재료의 성형성에 대해선 아직 잘 알려지지 않았다. 본 연구의 첫번때 주안점은 2축 인장성형시 성형성에 대한 연구에 두었다. 실험에 사용된 재료는 임의의 방향으로 위치한 유리 섬유를 중량비로 20, 35, 40% 함유한 폴리프로필렌이다. 성형시험은 75 .deg. C 에서 150 .deg. C 사이의 온도에서 행했으며, 펀치 속도는 0.01cm/sec 와 1cm/sec 에서 행했다. 2축 인장성형에서 측정된 한계 변형률(Limiting Strain)은 Marciniak 불완전성 (Imperfection) 이론에 근거한 예견치외 비교되었다. 이론치와 실험치가 잘 일치함을 보였으며, 성형한계선도(Forming Limit Diagram) 로써 결과들을 요약하였다. 성형한계 변형률은 성형온도와 성형속도에 의해 크게 영향을 받는다는 것을 보인다. 이러한 결과들은 적절한 성형조건이 선택된다면 열가소성 복합재료의 인장성형은 실제 상업적으로 이용하기에 충분한 성형성을 갖는다는 것을 보인다.

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