• Computers and Concrete
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• 제4권2호
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• pp.101-117
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• 2007

A new model predicting the nonlinear basic creep behaviour of concrete structures subjected to high multi-axial stresses is proposed. It combines a model based on the thermodynamic framework of the elasto-plastic continuum damage theory for time-independent material behaviour and a rheological model describing phenomenologically the long-term delayed deformation. Strength increase due to ageing is regarded. The general 3D solution for the creep theory is derived from a rate-type form of the uniaxial formulation by the assumption of associated creep flow and a theorem of energy equivalence. The model is able to reproduce linear primary creep as well as secondary and tertiary creep stages under high compressive stresses. For concrete in tension a simple viscoelastic formulation is applied. The material law is then incorporated into a finite element solution procedure for analysis of reinforced concrete structures. Numerical examples of uniaxial creep tests and concrete members show excellent agreement with experimental results.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 추계학술대회논문집
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• pp.69-75
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• 1995

The deformation behavior of stainless steel-clad aluminum sheet metals under uniaxial tension has been investigated. The differences in mechanical properties such as elastic modulus, flow stress and plastic strain ratio, of component layers of the composite sheet gave rise to warping of the tensile specimens. The warping has been analyzed by FEM and the total force and momentum equilibria. The analyzed radii of curvature of the warped specimens were smaller than the measured data possibly due to elastic recovery during unloading. The differences in mechanical properties may also give rise to transverse stresses in the component layers. The transverse stresses have been analyzed on the assumption of isostrain and by the FEM in which the warping has been taken into account. The transverse stresses calculated by the FEM were lower than those by the isostrain hypothesis due to stress relaxation by the warping and turned out to be negligible compared with the longitudinal stresses. Consequently, the flow stresses of the composite sheets follow the rule of mixtures.

• Journal of the Optical Society of Korea
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• 제17권5호
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• pp.399-404
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• 2013

This article proposes a digital image correlation (DIC) strain measurement method based on a finite element (FE) algorithm. A two-step digital image correlation is presented. In the first step, the gradient-based subpixels technique is used to search the displacements of a region of interest of the specimen, and then the strain fields are obtained by utilizing the finite element method in the second step. Both simulation and experiment processing, including tensile strain deformation, show that the proposed method can achieve nearly the same accuracy as the cubic spline interpolation method in most cases and higher accuracy in some cases, such as the simulations of uniaxial tension with and without noise. The results show that it also has a good noise-robustness. Finally, this method is used in the uniaxial tensile testing for Dahurian Larch wood specimens with or without a hole, and the obtained strain values are close to the results which were obtained from the strain gauge and the cubic spline interpolation method.

• Computers and Concrete
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• 제4권1호
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• pp.19-32
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• 2007

This paper is concentrated on the behaviors of five different types of fiber reinforced concrete (FRC) in uniaxial tension and flexural impact. The complete stress-strain responses in tension were acquired through a systematic experimental program. It was found that the tensile peak strains of concrete with micro polyethylene (PEF) fiber are about 18-31% higher than that of matrix concrete, those for composite with macro polypropylene fiber is 40-83% higher than that of steel fiber reinforced concrete (SFRC). The fracture energy of composites with micro-fiber is 23-67% higher than that of matrix concrete; this for macro polypropylene fiber and steel fiber FRCs are about 150-210% and 270-320% larger than that of plain concrete respectively. Micro-fiber is more effective than macro-fiber for initial crack impact resistance; however, the failure impact resistance of macro-fiber is significantly larger than that of microfiber, especially macro-polypropylene-fiber.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.64-68
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• 2005

In recent years, there has been a growth of the manufacture and application of magnesium products because of its small specific gravity as well as its relatively high strength. However, there are so many studies to assure good formability because magnesium sheet alloy is difficult to form. In this study, uniaxial tensile and biaxial tensile test of AZ31 magnesium sheet alloy with thickness of 1.2mm were performed at room temperature. Uniaxial tensile test were performed until $7\%$ of engineering strain. R-values and stress-strain curve were obtained. Biaxial tensile tests with cruciform specimen were performed until the breakdown of the specimen occurs. The yield loci are made by application of plastic work theory. The results are compared with the theoretical predictions based on the Hill and Logan-Hosford model. However, next study will be performed at warm-temperature because the specimens are broken under the $0.5\%$ of equivalent strain at biaxial tensile test.

• 한국초전도ㆍ저온공학회논문지
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• 제20권4호
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• pp.31-35
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• 2018

When REBCO coated conductors (CCs) are applied to superconducting devices such as coils and magnets, they are subjected to deformation in various modes such as compression/tension bending, uniaxial/transverse tension and torsion. Despite outstanding performances by REBCO CC tapes, their electromechanical properties have been evaluated primarily under uniaxial tension, therefore data about the critical current ($I_c$) response in the compressive strain region are lacking. In this study, the characteristic responses of $I_c$ in REBCO CC tapes under bending strains in the range from tensile to compressive were evaluated. The springboard bending beam was used, wherein the CC tape sample was soldered onto the surface of the springboard. A Goldacker-type bending test rig, which lacks a support holding the sample during testing, was used as a comparator. Degradation in $I_c$ behaviors, including strain sensitivity, in differently processed REBCO CC tapes were examined based on the test rig used.

• 한국소음진동공학회논문집
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• 제13권2호
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• pp.132-143
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• 2003

Viscoelastic components for vibration isolation or shock absorption in automobiles, machines and buildings are often subject to a high level of static deformation. From the dynamic design point of view, it is requisite to predict dynamic complex stiffness of viscoelastic components accurately and efficiently. To this end, a systematic procedure for complex modulus measurement of the viscoelastic material under large static deformation is often required in the industrial fields. In this paper, dynamic test conditions and procedures for the viscoelastic material under small oscillatory load superimposed on large static deformation are discussed. Various standard test methods are investigated in order to select an adequate test methodology. The influence of fixed boundary condition in the compression tests upon complex stiffness are investigated and an effective correction technique is proposed. Then the uniaxial tension and compression tests are performed and its results are compared with analysis results from conventional constitutive models.

• 한국지반공학회지:지반
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• 제5권2호
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• pp.57-77
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• 1989

본고는 팽장성 암석들의 시간의존적변형의 측정을 위한 실험장치와 실험고과에 관해서 설명한다. 새로운 실험장치들은 개선된 일축벽축하의 팽난시험, 일축 인장하의 인창시험과 이축 응력하의 팽 복시험을 위해서 제작하였다. 본 실험장치들은 암반파착시 지반에 작용하는 단순화된 헌력상태하에 있는 암반의 시간의존적 변형을 제 수직방향에서 측정한다. 지난 몇년간에 걸쳐서 얻은 실험결과에 의하면 본 실험장치들은 세공적으로 작동하는 것으로 나타났다. 실험결과로 보면, 퀸스톤 체일(Queenston shale)의 자유변형조건하에서의 시간의존적 변형 거동은 층리면과 수직인 방향에서는 층리면과 평행인 방향에서보다 약간 더 많은 역접이 일어나는 이방성적 거동을 보인다. 한 방향에 응력을 받을 때에는 응력이 작용하는 방향은 물론 그와 수직되는 방향의 역장성변형이 억제된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.475-478
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• 1999

A numerical tool for predicting the behavior of reinforced concrete structures under uniaxial loads is proposed. Concrete is considered as quasi-brittle material, and for a reinforcing bar, an elastic-perfectly plastic constitutive relationship is adopted. In this study, the behavior of reinforced concrete according to the interface properties between the concrete and steel is analyzed. Comparisons between the numerical predictions and the experimental results show good agreements in the load-deflection behaviors and ultimate loads of reinforced concrete structures.

• Computers and Concrete
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• 제9권1호
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• pp.35-50
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• 2012

The 2D representative volume element (RVE) for softening quasi-brittle materials like concrete is determined. Two alternative methods are presented to determine a size of RVE in concrete subjected to uniaxial tension by taking into account strain localization. Concrete is described as a heterogeneous three-phase material composed of aggregate, cement matrix and bond. The plane strain FE calculations of strain localization at meso-scale are carried out with an isotropic damage model with non-local softening.