• Title/Summary/Keyword: Stress/Strain Effect

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

  • Sun, Chang Ho;Jeong, Hyeok Chang;Kim, Ick hyun
    • Journal of the Earthquake Engineering Society of Korea
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    • v.21 no.1
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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.

A Study on Nonlinear Analysis of Reinforced Concrete Structures (철근(鐵筋)콘크리트 구조물(構造物)의 비선형(非線型) 해석(解析)에 관한 연구(硏究))

  • Chang, Dong Il;Kwak, Kae Hwan
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.7 no.2
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    • pp.69-77
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    • 1987
  • A finite element method has been developed to study the material nonlinear analysis of reinforced concrte structures. Concrete behavior under the biaxial state of stress is represented by a nonlinear constitutive relationship which incorporates tensile cracking, tensile stiffening effect between cracks and the strain-softening phenomenon beyond the maximum compressive strength. The concrete model used is based upon nonlinear elasticity by assuming concrete to be an orthotropic material and modeled as equivalent uniaxial stress-strain constitutive relationship using equivalent uniaxial strain. The streel reinforcement is assumed to be in a uniaxial stress state and is modeled as a bilinear, elasto-plastic material with strain hardening approximating the Bauschinger effect. In plane stress state, R.C. beams is modeled as a quadratic element that has two degrees of freedom in each node. And this results of finite element analysis are compared with the experimential results of midspan deflection, stresses and strains.

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Rheological Properties of Cooked Noodles with Different Starch Content Using Tensile Tests

  • Kim, Su-Kyoung;Lee, Seung-Ju
    • Food Science and Biotechnology
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    • v.18 no.4
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    • pp.1013-1018
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    • 2009
  • Several rheological terms were introduced to estimate the properties of cooked noodles with different starch content using tensile tests. Ring-shaped specimens were prepared by connecting both ends of the noodle strip before cooking. Hencky strain and rate, as well as true stress were applied in constant deformation tests. The elastic region on the curves of strain vs. stress was not clearly identified. Strain hardening in the subsequent plastic region was more prominent in low-starch noodles. Elongational viscosities at lower strain rates were used to differentiate noodles with different starch content, representing the dominant effect of protein content in the range of lower strain rates. In stress relaxation tests, the reciprocal of Peleg's constant $K_1$ (initial decay rate) and $K_2$ (asymptotic level) increased and decreased respectively, with an increase in starch content. This indicated that addition of starch contributed to the noodles becoming viscous liquid rather than elastic solid.

Consolidation Characteristics at the Constant Rate of Strain(CRS) Test (일정변형률(CRS) 시험에서의 압밀특성)

  • Lee, Dal-Won;Kim, Si-Jung
    • Korean Journal of Agricultural Science
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    • v.37 no.3
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    • pp.491-499
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    • 2010
  • This study was carried out to investigate the consolidation characteristics of the remolded clay by the oedometer and the constant rate of strain(CRS) consolidation tests. As the rate of strain increases, the settlement rapidly decreased. As the ratio of the sand in the specimen increases, its effect on the rate of strain to the settlement was reduced. As the effective stress increased, the void ratio decreased, while the rate of strain increased, it did not show a clear variation. The reduction of the void ratio was shown to be less than the oedometer test. The coefficient of vertical consolidation with effective stress showed very large variation around preconsolidation stress, but the rate of strain did not provide significant effects. The rate of strain with effective stress gradually decreased at all tests and mixed ratio of sand. The rate of strain at the constant rate of strain tests showed smaller than in the oedometer test. The coefficient of consolidation at the constant rate of strain tests showed much more increase than in the oedometer test. The ratio of the vertical coefficient of consolidation by the odometer and the constant rate of strain tests showed a large difference according to various tests method and mixing ratio. Therefore, it is recommended that careful attention should be paid to designing the soft ground improvement.

A Study on the Axial Behavior of the Concrete Cylinders Confined by Carbon Fiber Sheets (탄소섬유쉬트로 횡구속된 콘크리트 공시체의 압축 거동에 관한 연구)

  • Hwang, Jin-Seog
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.4 no.4
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    • pp.141-148
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    • 2000
  • Recently the Carbon Fiber Sheet(CFS) is widely used for strengthening damaged RC structures. Strengthening compression members such as column can increase ductility and strength due to the confinement effect. In this experiment, the behavior of concrete cylinders confined by CFS was examined. The confinement pressure is increased linearly as axial stress is increased in low axial stress, and the confinement effect of CFS was rapidly developed after near maximum axial stress, thus axial strength and ductility was improved. As the ratio of CPS is increased, concrete cylinders failed due to local fracture of CFS. The confinement effect of circular section is more efficient than that of rectangular section. And significant improvement of axial strength, axial strain, transverse strain at failure is observed in circular section. This is because in rectangular section the local fracture of CFS near corner may be occured, thus the strain efficiency ratio must be considered for RC structures with CFS.

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Effect of Strain Rate and Material Hardness on Residual Stress in Multiple Impact Shot Peening (다중충돌 쇼트피닝에서 변형률 속도와 소재 경도가 잔류응력에 미치는 영향에 관한 연구)

  • Kim, Tae-Woo;Yang, Zhao-Rui;Na, Doo-Hyun;Lee, Young-Seog
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.11
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    • pp.1369-1375
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    • 2011
  • Shot ball impacts to materials cause residual compressive stress on their surfaces. Improving the fatigue strength of a material that has this residual compress stress is the purpose of the shot peening process. A numerical study was performed to evaluate the effect of the strain rate sensitivity and hardness of the shot ball on the residual compressive stress. We calculated the residual compressive stress due to multiple impact shot peening using ABAQUS 6.9-1. AISI 4340 steel was the material used in this study. We compared the effects of high strain rate sensitivities and low strain rate sensitivities and found that when the material's sensitivity to the strain rate increased, the residual compressive stress decreased. In addition, the residual compressive stress of low-hardness material is higher than that of high-hardness material.

Dynamic Stress/Strain Measurement and Analysis of the Aluminum Alloy Road Wheel through F1 Circuit Ultimate Driving Test (F1 서킷 극한주행시험을 통한 알루미늄 알로이 휠의 동응력/변형률 계측 및 분석)

  • Lee, Chang Soo;Park, Cheol Soon;Park, Hyung Bae;Jung, Sung Pil;Chung, Won Sun
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2014.10a
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    • pp.612-617
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    • 2014
  • It is generally known that the automotive road wheel involves the non-proportional multiaxial loading condition, therefore the measuring dynamic stress and strain in driving state is very important to predict an endurance characteristic of the automotive road wheel. In this study, the ultimate driving test using F1 circuit with respect to 2 kinds of velocity conditions have been carried out in order to measure dynamic stress, strain of the wheel and acceleration of a vehicle. Based on the measured results, the characteristics of dynamic stress generation have been analyzed, and factors which have effect on the dynamic stress generation have been studied.

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Elimination of the effect of strain gradient from concrete compressive strength test results

  • Tabsh, Sami W.
    • Computers and Concrete
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    • v.3 no.6
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    • pp.375-388
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    • 2006
  • Poor strength test results are sometimes not an indication of low concrete quality, but rather inferior testing quality. In a compression test, the strain distribution over the ends of the specimen is a critical factor for the test results. Non-uniform straining of a concrete specimen leads to locally different compressive stresses on the cross-section, and eventual premature breaking of the specimen. Its effect on a specimen can be quantified by comparing the compressive strength results of two specimens, one subjected to uniform strain and another to a specified strain gradient. This can be done with the help of a function that relates two parameters, the strain ratio and the test efficiency. Such a function depends on the concrete strength and cross-sectional shape of the specimen. In this study, theoretical relationships between the strain ratio and test efficiency are developed using a concrete stress-strain model. The results show that for the same strain ratio, the test efficiency is larger for normal strength concrete than for high strength concrete. Further, the effect of the strain gradient on the test result depends on the cross-sectional shape of the specimen. Implementation of the results is demonstrated with the aid of two examples.

Analysis of the Strain Rate Effect in Electro-Magnetic Forming (전자기 성형에서의 변형률 속도 효과 해석)

  • 곽신웅;신효철;이종수
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.5
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    • pp.1043-1058
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    • 1990
  • The Strain rate effect in electro-magnetic forming, which is one of the high velocity forming methods, is studied by the finite element method in this paper. The forming process is simplified by neglecting the coupling between magnetic field and work-piece deformation, and the impulsive magnetic pressure is regarded as inner pressure load. A rate-dependent elasto-plastic material model, of which tangential modulus depends of effective strain rate, is proposed. The model is shown to well describe the transient increase of yield stresses, the decreases of the final displacement and yield stress, the decrease of the difference in the distribution of deformation along the axial direction, and the change of deformation mechanism due to strain rate effect. As a result, displacement, final deformed shape, radial velocity, deformation energy, and the changes of effective stress, effective strain and effective strain rate through plastic working are given. Based on the results, the effectiveness of this model and the strain rate effect of the deformation process of the work-piece are discussed.

Viscoelastic Properties of Fruit Flesh(I) - Stress Relaxation Behavior - (과실(果實)의 점탄성(粘彈性) 특성(特性)(I) - 응력이완거동(應力弛緩擧動) -)

  • Kim, M.S.;Park, J.M.;Choi, D.S.
    • Journal of Biosystems Engineering
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    • v.17 no.3
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    • pp.260-271
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    • 1992
  • Fruits are generally subjected to mechanical forces during harvesting, handling, and transportation that may cause damage in the form of bruises, punctures, and cracks. In order to prevent damage, and insure better quality fruits for consumers, it is very essential to study physical properties of these materials. The studies were conducted to examine the effect of storage period, storage condition, and other factors, such as loading rate and initial strain, on the stress relaxation behavior of the fruit flesh, and develop nonlinear viscoelastic models to represent its stress relaxation behavior. The following results were obtained from the study : 1. Since the viscoelastic behavior of the fruits flesh was nonlinear, the behavior was satisfactorily modelled as follows ; $${\delta}({\varepsilon},\;t)={\varepsilon}^A[B\;{\exp}(-Ct)+D\;{\exp}(-Ft)+G(-Ht)]$$ But, for the every strain applied, the stress relaxation behavior of the fruit flesh, such as apple and pear, could be well described by the Generalized Maxwell model, respectively. 2. The effect of loading rate on the stress relaxation behavior was remarkable. The higher loading rate resulted in the higher initial stress, and the faster stress relaxation. 3. The higher initial strain resulted in the higher initial stress, and stress relaxed at the large initial strain was also much higher than at the small initial strain. 4. Stress relaxation rate and quantity stored in the fruits at the low temperature storage were much higher than those at the normal temperature storage in the same storage period. Also, in all fruits tested, the longer storage period was the more relaxation rate and quantity were shown. These trends in the normal temperature condition was the more significant than in the low temperature condition.

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