• Title/Summary/Keyword: Strain test

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A Study on the Measurement Methods of Plastic Strain Ratio in Automotive sheet steel (자동차용 강판의 소성변형비 측정 방법 연구)

  • 김인수;김인수
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1996.10a
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    • pp.85-92
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    • 1996
  • The Measurement method of the plastic strain ratio is various in Automotive sheet steel. In this paper, the measurement of the plastic strain are used two different methods, ASTM E 517 method and the automatic strain measurement tensile specimen during the tensile test, and compared the plastic strain ratios from the two methods. The experimental results showed that the measured plastic strain ratios from the automatic strain measurement method are coincide with that from the ASTM E 517 standard measurement in various specimens. Therefore, automatic strain measurement method by two extensometers shows good accuracy. Also, the strain dependance of plastic strain ratios could be recorded by the computer continuously and anisotropy of the strength coefficient, K, and strain hardening exponent, n ,could be compared with each direction automatically through the use of automatic strain measurement system.

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Effect of Strain Path on Lattice Strain Evolution during Monotonic and Cyclic Tension of Magnesium Alloy

  • Yoon, Cheol;Gharghouri, Michael A.;Lee, Soo Yeol
    • Korean Journal of Materials Research
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    • v.25 no.5
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    • pp.221-225
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    • 2015
  • In-situ neutron diffraction has been employed to examine the effect of strain path on lattice strain evolution during monotonic and cyclic tension in an extruded Mg-8.5wt.%Al alloy. In the cyclic tension test, the maximum applied stress increased with cycle number. Lattice strain data were acquired for three grain orientations, characterized by the plane normal to the stress axis. The lattice strain in the hard {10.0} orientation, which is unfavorably oriented for both basal slip and {10.2} extension twinning, evolved linearly throughout both tests during loading and unloading. The {00.2} orientation exhibited significant relaxation associated with {10.2} extension twinning. Coupled with a linear lattice strain unloading behavior, this relaxation led to increasingly compressive residual strains in the {00.2} orientation with increasing cycle number. The {10.1} orientation is favorably oriented for basal slip, and thus showed a soft grain behavior. Microyielding occurred in the monotonic tension test and in all cycles of the cyclic test at an applied stress of ~50 MPa, indicating that strain hardening in this orientation was not completely stable from one cycle to the next. The lattice strain unloading behavior was linear in the {10.1} orientation, leading to a compressive residual strain after every cycle, which, however, did not increase systematically from one cycle to the next as in the {00.2} orientation.

A Study on the Equi-biaxial Tension Test of Rubber Material (고무재료의 등 이축 인장시험에 관한 연구)

  • 김완두;김동진;김완수;이영신
    • Transactions of the Korean Society of Automotive Engineers
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    • v.11 no.5
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    • pp.95-104
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    • 2003
  • The material properties of rubber was determined by the experiments of uniaxial tension, uniaxial compression, planer tension, equi-biaxial tension and volumetric compression. In compression test, it is difficult to obtain the pure state of compression stress and strain due to friction force between the specimen and compression platen. In this study, the stress and strain data from the equi-biaxial tension test were converted to compression stress and strain and compared to a pure state of simple compression data when friction was zero. The compression test device with the tapered platen was proposed to overcome the effect of friction. It was fumed out that the relationship of the stress and strain using the tapered platen was in close agreement with the pure compressive state.

Dynamic characteristics of combined isolation systems using rubber and wire isolators

  • Lee, Seung-Jae;Truong, Gia Toai;Lee, Ji-Eon;Park, Sang-Hyun;Choi, Kyoung-Kyu
    • Nuclear Engineering and Technology
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    • v.54 no.3
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    • pp.1071-1084
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    • 2022
  • The present study aims to investigate the dynamic properties of a novel isolation system composed of separate rubber and wire isolators. The testing program comprised pure compressive, pure-shear, compressive-stress dependence, and shear-strain dependence tests that used full-scale test specimens according to ISO 22762-1. A total of 22 test specimens were fabricated and investigated. Among the tests, the pure compressive test was a destructive test that reached up to the failure stage, whereas the others were nondestructive tests before the failure stage. Similar to the pure-shear test, at each compressive-stress level in the compressive dependence test or at each shear-strain level in the shear-strain dependence test, the cyclic loading was conducted for three cycles. In the nondestructive tests, examination of the dynamic shear properties in the X-direction was independent of the Y-direction. The test results revealed that the increase in the shear strain increased the energy dissipation but decreased the damping ratio, whereas the increase in the compressive stress increased the damping ratio. In addition, a macro model was developed to simulate the load-displacement response of the isolation systems, and the prediction results were consistent with the experimental results.

Determination of a critical damage by experiment and analysis of tensile test (인장시험의 실험과 해석 결과를 이용한 임계손상도의 결정)

  • Jang, S.M.;Eom, J.G.;Lee, M.C.;Joun, M.S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2008.10a
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    • pp.292-296
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    • 2008
  • A new method of evaluating critical damage values of commercial materials is presented in this paper. The method is based on the previous study of the methodology [1] of acquisition of true stress-strain curves or flow stress curves over large strain from the tensile test in which the flow stress is described by the Hollomon law-like form, that is, by the strain dependent strength coefficient and the strain hardening exponent. The strain hardening exponent is calculated from the true strain at the necking point to meet the Considere condition. The strength coefficient is assumed to be constant before necking and represented by a piecewise linear function of strain after necking. With the predicted flow stress, a tensile test is simulated by a rigid-plastic finite element method with higher accuracy of less than 0.5% error between experiments and predictions. The instant when the fracture begins and thus the critical damage is obtained is determined by observing the stress variation at the necked region. It is assumed that the fracture due to damage begins when the pattern of stress around the necked region changes radically. The method is applied to evaluate the critical damage of a low carbon steel.

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Fatigue Life Evaluation of Spot Weldments of SPC Sheet Including Strain Rate Effect (변형률속도효과를 고려한 일반냉연강판 점용접부의 피로수명평가)

  • Song, Joon-Hyuk;Nah, Seok-Chan;Yu, Hyo-Sun;Kang, Hee-Yong;Yang, Sung-Mo
    • Transactions of the Korean Society of Automotive Engineers
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    • v.14 no.1
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    • pp.48-53
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    • 2006
  • A methodology is described for predicting the fatigue life of the resistance spot weldment including strain rate effect. Because it is difficult to perform a physical failure test with high strain rate, an analytical method is necessary to get the mechanical properties of various strain rate, To this end, quasi-static tensile-shear tests at several strain rate were performed on spot weldments of SPC. These test provided the empirical data with the strain rate. With these results, we formulated the function of fatigue life prediction using the lethargy coefficient which is the global material property from tensile test. And, we predicted the fatigue life of spot weldment at dynamic strain rate. To confirm this method for fatigue life prediction, analytical results were compared with the experimental fatigue data.

Effect of Pre-strain on Hydrogen Embrittlement in Intercritically Annealed Fe-6.5Mn-0.08C Medium-Mn steels

  • Sang-Gyu Kim;Young-Chul Yoon;Seok-Woo Ko;Byoungchul Hwang
    • Archives of Metallurgy and Materials
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    • v.67 no.4
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    • pp.1491-1495
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    • 2022
  • The present research deals with the effect of pre-strain on the hydrogen embrittlement behavior of intercritically annealed medium-Mn steels. A slow strain-rate tensile test was conducted after hydrogen charging by an electrochemical permeation method. Based on EBSD and XRD analysis results, the microstructure was composed of martensite and retained austenite of which fraction increased with an increase in the intercritical annealing temperature. The tensile test results showed that the steel with a higher fraction of retained austenite had relatively high hydrogen embrittlement resistance because the retained austenite acts as an irreversible hydrogen trap site. As the amount of pre-strain was increased, the hydrogen embrittlement resistance decreased notably due to an increase in the dislocation density and strain-induced martensite transformation.

Forming Limit Diagram Measurement of Tube for Tube Hydroforming Process (하이드로 포밍용 튜브의 성형 한계선도 측정)

  • Han, S.S.
    • Transactions of Materials Processing
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    • v.15 no.6 s.87
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    • pp.467-472
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    • 2006
  • The forming limit diagram of tube is required for the part design and the formability analysis of tube hydroforming. The finite element analyses of simple bulge test were done to obtain the various strain combinations on FLC. The finite element analysis results were shown that the bursting at various strain combinations could be induced by simple bulge test. The experiment oi tube bulge test was carried out according to the test condition that obtained from finite element analysis and the left hand side of forming limit diagram was built.

A Study on the Fatigue Properties of Ti-Ni Shape Memory Alloys (Ti-Ni계 형상기억 합금의 피로특성에 관한 연구)

  • S.Y Kim;S. Miyazaki
    • Journal of Advanced Marine Engineering and Technology
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    • v.21 no.5
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    • pp.482-490
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    • 1997
  • The effects of strain amplitude. test temperature and stress on the fatigue properties for Ti-Ni wires were investigated using a rotary bending fatigue tester specially designed for wires. The fatigue test results were discussed in connection with the static tensile properties. The DSC measurement was conducted after fatigue test in order to clarify the change of transformation behavior due to the progress of fatigue. Under the temperature below or near the Af, the strain amplitude($\varepsilon_a$)-failure life (Nf) curve showed to be composed of three straight lines with two turning points. Of the 2 turning points, the upper one was coincident with the elastic limit strain and the lower one with the proportional limit strain. With rising of the test temperature above Af, the pattern of $\varepsilon_a$-Nf curve changed gradually to composition of 2 straight lines. The $\varepsilon_a$-Nf curve shifted depending on test temperature. In the short and medium life zones, the higher the temperature was, the shorter the fatigue life. However, in the long life zone, above the Af temperature, the fatigue life was not affected by the temperature. The transformation enthalpy measured after fatigue test was dependent on Nf, $\varepsilon_a$, and test temperature.

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