• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.352-355
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• 2007

Polycrystalline materials such as steels(BCC) and aluminum alloys(FCC) show the strain hardening and the strain rate hardening during the plastic deformation. The strain hardening is induced by deformation resistance of dislocation glide on some crystallographic systems and increase of the dislocation density on grain boundaries or inner grain. However, the phenomenon of the strain rate hardening is not demonstrated distinctly. In this paper, tensile tests for various strain rates are performed in the rage of $10^{-2}$ to $10^2s^{-1}$ then, specimens are extracted on the same strain position to investigate the microscopic behavior of deformed materials. The extracted specimen is investigated by using the electron backscattered diffraction(EBSD) and transmission electron microscopy(TEM) results which contain grain size, grain shape, aspect ratio and dislocation substructure.

• 대한기계학회논문집A
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• 제32권6호
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• pp.488-495
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• 2008

In order to achieve long fatigue lifetimes for cyclically pressurized thick cylinders, multi-layered compound cylinder has been proposed. Such compound cylinder involves a shrink-fit procedure incorporating a monobloc tube which has previously undergone autofrettage. The basic autofrettage theory assumes elastic-perfectly plastic behaviour. Because of the Bauschinger effect and strain-hardening, most materials do not display elastic-perfectly plastic properties and consequently various autofrettage mo dels are based on different simplified material strain-hardening models, which is assumed that combination of linear strain-hardenig and power strain-hardening model. This approach gives a more accurate prediction than the elastic-perfectly plastic model and is suitable for different strain-hardening materials. In this paper, a general autofrettage model that incorporates the material strain-hardening relationship and the Bauschinger effect, based upon the actual tensile-compressive stress-strain curve of a material was proposed. The model was obtained using the von Mises yield criterion and plane strain condition. The tensile-compressive stress-strain curve was obtained by experiment. The parameters needed in the model were determined by fitting the actual tensile-compressive curve of the material. Finally, strain- hardening model was compared with elastic-perfectly plastic model.

• 소성∙가공
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• 제17권1호
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• pp.46-51
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• 2008

Polycrystalline materials such as steels(BCC) and aluminum alloys(FCC) show the strain hardening and the strain rate hardening during the plastic deformation. The strain hardening is induced by deformation resistance of dislocation glide on some crystallographic systems and increase of the dislocation density on grain boundaries or inner grain. However, the phenomenon of the strain rate hardening is not demonstrated distinctly in the rage of $10^{-2}$ to $10^2/sec$ strain rate. In this paper, tensile tests for various strain rates are performed in the rage of $10^{-2}$ to $10^2/sec$ then, specimens are extracted on the same strain position to investigate the microscopic behavior of deformed materials. The extracted specimens are investigated by using the electron backscattered diffraction(EBSD) and transmission electron microscopy(TEM) results which show the effect of texture orientation, grain size and dislocation behavior on the strain rate hardening.

• 소성∙가공
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• 제12권5호
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• pp.504-512
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• 2003

The plastic strain ratios(R-values) of low carbon steel sheets were determined by the automatic strain measurement method using two extensometers, the indirect photo method for the same tensile specimen during tensile test and the indirect method for the specimen after tensile test. The experimental results showed that the measured plastic strain ratios from the automatic strain measurement method using two extensometers coincided with those from the indirect photo method and the indirect method for all tensile specimens. In addition, the strain dependence of plastic strain ratios could be continuously recorded and the anisotropy of the strength coefficient, K, and strain hardening exponent, n, could be automatically calculated in three directions by computer through the use of two extensometers. The experimental results showed that the strain dependence of R-value was related to the anisotropy of strain hardening exponent in low carbon steel sheets.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.153.1-156
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• 1999

Based upon the experimental data from multi-stage tensile loading at angles to the rolling direction of steel sheets, anisotropic hardening rules are proposed. Experiments show that orthotropic anisotropy is maintained and the orientations of orthotropy axes are changed during tensile loading. A phenomenological model is proposed which includes the rotations of orthotropy axes, work hardening and kinematic hardening. Using the model, uniaxial tensile stress, R-value and tensile necking strain are predicted and compared with the experimental data.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.439-440
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• 2010

고인성 복합재료에서 공기량은 인장변형성능에 중요한 영향을 끼치는 인자이다. 공기량에 따른 인장 특성의 변화를 실내실험을 통하여 검토하였다.

• International Journal of Precision Engineering and Manufacturing
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• 제1권1호
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• pp.91-97
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• 2000

Anisotropic work hardening of cold rolled low carbon steel sheets is studied. The experiments consist of two stage tensile prestraining and tensile tests. At the first prestraining, steel sheets are streteched along the rolling direction by 3% and 6% tensile strains. The second prestrains are at 0${\cric}$, 30${\cric}$, 60${\cric}$to the rolling directions by varying degrees. Tensile tests are performed on the specimens cut from the sheets after the two stage prestraining. A theoretical framework on anisotropic hardening is proposed which includes Hill's quadratic yield function, ziegler's kinematic hardening rule, and Kim and Yin's assumption on the rotation of orthotropy axes. The predicted variations of R-values with second stage tensile strain are compared with the experimental data.

• Computers and Concrete
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• 제21권3호
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• pp.231-237
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• 2018

A strain-hardening highly ductile composite based on an alkali-activated slag binder and synthetic fibers is a promising construction material due to its excellent tensile behavior and owing to the ecofriendly characteristics of its binder. This study investigated the effect of different types of synthetic fibers and water-to-binder ratios on the compressive strength and tensile behavior of slag-based cementless composites. Alkali-activated slag was used as a binder and water-to-binder ratios of 0.35, 0.45, and 0.55 were considered. Three types of fibers, polypropylene fiber, polyethylene (PE) fiber, and polyparaphenylene-benzobisethiazole (PBO) fiber, were used as reinforcing fibers, and compression and uniaxial tension tests were performed. The test results showed that the PE fiber series composites exhibited superior tensile behavior in terms of the tensile strain capacity and crack patterns while PBO fiber series composites had high tensile strength levels and tight crack widths and spacing distances.

• Food Science and Biotechnology
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• 제18권4호
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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.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.325-328
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• 2008

In recent years, developments of light weight vehicle are one of the most important issues in automotive industry. It is important to know the variations of the mechanical properties in the hydro forming process for the safe and durable design purposes. Generally, tube hydroforming process consists of three main processes such as bending, preforming, and hydroforming. It means that the strain hardening histories of final products are nonlinear. In this study, strain hardening behavior during hydroforming has been investigated by hydroforming of engine cradle as a model process. The variation of mechanical properties such as local hardness and strength were used as an index of strain hardening during respective processes. The correlationship between strength and hardness obtained from tensile test has been equivalently converted into correlation between hardness and measured strain.