• Title/Summary/Keyword: strain sensitivity

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The Influence of Temperature and Strain Rate on the Mechanical Behavior in Uranium

  • Lee, Key-Soon;Park, Won-Koo
    • Nuclear Engineering and Technology
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    • v.10 no.2
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    • pp.73-78
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    • 1978
  • The effect of temperature and strain rate on the deformation behavior of $\alpha$-uranium was investigated in the temperature ranged 300$^{\circ}$ to 55$0^{\circ}C$ by strain, rate change test. Strain rate sensitivity, activation volume, strain rate sensitivity exponent and dislocation velocity exponent were determined. The strain rate sensitivity exponent and dislocation velocity exponent were determined. The strain rate sensitivity exponent increases with strain below 40$0^{\circ}C$, while the exponent decreases with strain above 50$0^{\circ}C$. It is believed that the increase of strain rate sensitivity exponent with strain below 40$0^{\circ}C$ can be attributed to an increase in internal stress as a result of work hardening while decrease of the exponent with strain above 50$0^{\circ}C$ is due to predominance of thermal softening over work hardening because more slip, system are active in deformation above about 50$0^{\circ}C$.

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Modeling on the Nonlinear Rate Sensitivity of Flow Stress (유동응력의 비선형 속도 민감도에 대한 모델링)

  • Ho, Kwang-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.6
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    • pp.670-676
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    • 2004
  • Most metallic materials and alloys show rate independence or negative rate sensitivity in some temperature region when dynamic strain aging occurs. It is generally recognized that negative rate sensitivity is an essential feature of dynamic strain aging that can depend on strain and/or strain rate. The unified viscoplasticity theory based on overstress is applied to reproduce a change of rate sensitivity type that depends on strain or strain rate. This is accomplished through the introduction of a single new term in the growth law of the equilibrium stress, which is a tensor valued state variable of the model. It is also shown that the new term can be used to reproduce a dramatic increase of rate sensitivity in dynamic plasticity.

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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    • 2005.10a
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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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A Study on the Strain-Rate Sensitivity According to the Temperature for Steel Sheets of an Auto-Body (차체용 강판의 온도에 따른 변형률속도 민감도 연구)

  • Lee, H.J.;Song, J.H.;Cho, S.S.;Park, S.H.;Huh, H.
    • Transactions of Materials Processing
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    • v.15 no.2 s.83
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    • pp.132-137
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    • 2006
  • This paper is concerned with the thermo-mechanical behavior including 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 at environmental temperatures varied 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. Experimental results show that the strain-rate sensitivity increases at low temperature. It represents that as the strain-rate increases, the variation of flow stress becomes sensitive on the temperature. The results indicate that the flow stress of SPRC35R is more dependent on the changes of strain-rate and temperature than those of SPRC45E.

The Study of the Variation of Strain Rate Sensitivity Index depending on the Strain and Microstructural Observations of AZ31 Mg Alloy Sheet (변형율에 따른 AZ31 합금의 변형율 속도 민감도 지수 변화와 미세조직 특성에 관한 연구)

  • Kim, D.O.;Kang, C.W.;Lee, S.Y.
    • Transactions of Materials Processing
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    • v.20 no.7
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    • pp.498-503
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    • 2011
  • The strain rate sensitivity index, m, plays an important role in plastic deformation at elevated temperatures. It is affected by strain rate, temperature, and the microstructure of the material. The strain rate sensitivity index has been used as a constant in numerical analysis of plastic forming at a specified strain rate and temperature. However, the value of m varies as deformation proceeds at an elevated temperature and a certain strain rate. Thus, in this present study, the value of m has been characterized as a function of strain by multiple tensile jump tests for AZ31 magnesium alloy sheet, and the variation of m has been discussed in conjunction with the microstructural observations before and after deformation. The experimental results show that the variation of m is dependent on the temperature and strain rate. Grain growth with dynamic recrystallization also affects the variation of m.

Improvement of Sensitivity to In-plane Strain/Deformation Measurement by Micro-ESPI Technique (마이크로 ESPI 기법에 의한 면내 변형 측정 민감도 향상)

  • Kim D.I.;Huh Y.H.;Kee C.D.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.06a
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    • pp.1442-1445
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    • 2005
  • Several test methods, including micro strain/deformation measurement techniques, have been studied to more reliably measure the micro properties in micro/nano materials. Therefore, in this study, the continuous measurement of in-plane tensile strain in micro-sized specimens of thin film materials was introduced using the micro-ESPI technique. TiN and Au thin films 1 and $0.47\;\mu{m}$ thick, respectively, were deposited on the silicon wafer and fabricated into the micro-sized tensile specimens using the electromachining process. The micro-tensile loading system and micro-ESPI system were developed to measure the tensile strain during micro-tensile test. The micro-tensile stress-strain for these materials was determined using the algorithm for continuous strain measurement. Furthermore, algorithm for enhancing the sensitivity to measurement of in-plane tensile strain was suggested. According to the algorithm for enhancement of sensitivity, micro-tensile strain data between interfringe were calculated. It is shown that the algorithm for enhancement of the sensitivity suggested in this study makes the sensitivity to the in-plane tensile strain increase.

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Improvement of Sensitivity to In-plane Strain/Deformation Measurement by Micro-ESPI Technique (마이크로 ESPI 기법에 의한 면내 변형 측정 민감도 향상)

  • Kim Dong-Iel;Kee Chang-Doo;Huh Yong-Hak
    • Journal of the Korean Society for Precision Engineering
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    • v.23 no.8 s.185
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    • pp.54-63
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    • 2006
  • Enhancement methods of sensitivity to in-plane strain measurement by micro-ESPI(Electronic Speckle Pattern Interferometry) technique were proposed using TiN and Au thin films. Micro-tensile strain over the micro-tensile specimens, prepared in micro-scale by those films, was measured by micro-tensile loading system and micro-ESPI system developed in this study. The subsequent measurement of in-plane tensile strain in the micro-sized specimens was introduced using the micro-ESPI technique, and the micro-tensile stress-strain curves for these films were determined. To enhance the sensitivity to measurement of in-plane tensile strain, algorithms of the phase estimation by using curve fitting of inter-fringe and the discrete Fourier Transform with object-induced dynamic phase shifting were developed. Using these two algorithms, the micro-tensile strain-stress curves were generated. It is shown that the algorithms for enhancement of the sensitivity suggested in this study make the sensitivity to measurement of the in-plane tensile strain increase.

Strain Sensitivity of Fiber Optic Bragg Grating Sensor (광섬유 브래그 격자 센서의 변형률 감지도)

  • Kwon, Il-Bum;Choi, Man-Yong;Kim, Min-Soo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.3 no.3
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    • pp.237-243
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    • 1999
  • Recently, there has been considerable interest in the development of fiber-optic sensors based on fiber Bragg gratings (FBGs), which can be made into Ge-doped fiber's core by UV phase mask or holographic methods. A good sensitivity and small size of this sensor make it an ideal candidate for distributed sensing in smart structures or other structural monitoring applications. In this study, fiber optic Bragg grating sensor, which could be applied to measure the absolute strains, was constructed and the strain sensitivity of this sensor was investigated in order to apply to the structural health monitoring. Fiber Fabry-Perot (FFP) filter has been used to detect the optical signals instead of optical spectrum analyzer. It has been convenient to determine the structural strains from the output signal of FBGs. The fiber optic Bragg grating sensor was attached on the aluminum beam near the electrical strain gage to measure the same strain. The relationship between strain and fiber signal was linearly fitted. The strain sensitivity of the fiber optic Bragg grating sensor was determined as $l.57{\mu}{\varepsilon}/{\mu}sec$ from the aluminum beam test.

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Dynamic Constitutive Equations of Auto-Body Steel Sheets with the Variation of Temperature (I) - Dynamic Material Characteristics with the Variation of Temperature - (차체용 강판의 온도에 따른 동적 구성방정식에 관한 연구 (I) - 온도에 따른 동적 물성 특성 -)

  • Lee, Hee-Jong;Song, Jung-Han;Park, Sung-Ho;Huh, Hoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.2 s.257
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    • pp.174-181
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    • 2007
  • This paper is concerned with the thermo-mechanical behavior of steel sheet for an auto-body including temperature dependent strain rate sensitivity. In order to identify the temperature-dependent strain rate sensitivity of SPRC35R, SPRC45E and TRIP60, uniaxial tensile 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 from the static tensile test and that at the intermediate strain rate is obtained from the high speed tensile test. Experimental results show that the variation of the flow stress and fracture elongation becomes sensitive to the temperature as the strain rate increases. It is observed that the dynamic strain aging occurs with TRIP60 at the temperature above $150^{\circ}C$. Results also indicate that the flow stress and tincture elongation of SPRC35R are more dependent on the changes of strain rates and temperature than those of SPRC45E and TRIP60.

Influence of Strain Rate on Tensile Properties and Dynamic Strain Aging of an Fe-24.5Mn-4Cr-0.45C Alloy (변형률 속도에 따른 Fe-24.5Mn-4Cr-0.45C 합금의 인장 특성과 동적 변형시효)

  • Lee, Seung-Yong;Hwang, Byoungchul
    • Korean Journal of Materials Research
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    • v.26 no.5
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    • pp.281-286
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    • 2016
  • In the present study, the tensile properties and dynamic strain aging of an Fe-24.5Mn-4Cr-0.45C alloy were investigated in terms of strain rate. During tensile testing at room temperature, all the stress-strain curves exhibited serrated plastic flows related to dynamic strain aging, regardless of the strain rate. Serration appeared right after yield stress at lower strain rates, while it was hardly observed at high strain rates. On the other hand, strain-rate sensitivity, indicating a general relationship between flow stress and strain rate at constant strain and temperature, changed from positive to negative as the strain increased. The negative strain-rate sensitivity can be explained by the Portevin Le Chatelier effect, which is associated with dynamic strain aging and is dependent on the strain rate because it is very likely that the dynamic strain aging phenomenon in high-manganese steels is involved in the interaction between moving dislocations and point-defect complexes.