• Journal of Magnetics
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• 제21권2호
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• pp.244-248
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• 2016

Aiming to improve the shear yield stress of magnetorheological fluid, magnetorheological fluids with different particle characteristics are prepared, and the influence rules of particle mass fraction, particle size, nanoparticles content and application temperature on shear yield stress are investigated. Experimental results indicate that shear yield stress increases approximate linearly with the enhancement of particle mass fraction. Particle size and the nanoparticles within 10% mass fraction can improve the shear yield stress effectively. When the application temperature is higher than $100^{\circ}C$, the shear yield stress decreases rapidly because of thermal expansion and thermal magnetization effect.

• Journal of Pharmaceutical Investigation
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• 제37권3호
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• pp.137-148
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• 2007

Using a strain-controlled rheometer [Rheometrics Dynamic Analyzer (RDA II)], the steady shear flow properties of a semi-solid ointment base (vaseline) have been measured over a wide range of shear rates at temperature range of $25{\sim}60^{\circ}C$. In this article, the steady shear flow properties (shear stress, steady shear viscosity and yield stress) were reported from the experimentally obtained data and the effects of shear rate as well as temperature on these properties were discussed in detail. In addition, several inelastic-viscoplastic flow models including a yield stress parameter were employed to make a quantitative evaluation of the steady shear flow behavior, and then the applicability of these models was examined by calculating the various material parameters (yield stress, consistency index and flow behavior index). Main findings obtained from this study can be summarized as follows : (1) At temperature range lower than $40^{\circ}C$, vaseline is regarded as a viscoplastic material having a finite magnitude of yield stress and its flow behavior beyond a yield stress shows a shear-thinning (or pseudo-plastic) feature, indicating a decrease in steady shear viscosity as an increase in shear rate. At this temperature range, the flow curve of vaseline has two inflection points and the first inflection point occurring at relatively lower shear rate corresponds to a static yield stress. The static yield stress of vaseline is decreased with increasing temperature and takes place at a lower shear rate, due to a progressive breakdown of three dimensional network structure. (2) At temperature range higher than $45^{\circ}C$, vaseline becomes a viscous liquid with no yield stress and its flow character exhibits a Newtonian behavior, demonstrating a constant steady shear viscosity regardless of an increase in shear rate. With increasing temperature, vaseline begins to show a Newtonian behavior at a lower shear rate range, indicating that the microcrystalline structure is completely destroyed due to a synergic effect of high temperature and shear deformation. (3) Over a whole range of temperatures tested, the Herschel-Bulkley, Mizrahi-Berk, and Heinz-Casson models are all applicable and have an almostly equivalent ability to quantitatively describe the steady shear flow behavior of vaseline, whereas the Bingham, Casson,and Vocadlo models do not give a good ability.

• Journal of Welding and Joining
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• 제8권3호
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• pp.79-88
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• 1990

Welded joint often contains soft or softened regions such as the HAZ of TMCP steel welded with high heat input. In this study, the equivalent yield strength of plate structure containing softened region was predicted by FEM analysis, and its incremental behavior was explained with the results of the analysis. The calculated results of yield strength indicated the following for the plate structures. 1) As the softened region starts to yield, shear stress begins to build up along the boundary between base metal and softened region. This results in multi-axial stress condition which gives restraint on the softened region. 2) Restraint effect has a significant influence on the distribution of the shear stress, the nominal stress, and the strain. 3) The yielding behavior of softened region becomes the same as that of base metal when both ratios of length to width and thickness to width of softened region are larger than 30 and 13 respectively.

• 산업식품공학
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• 제13권1호
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• pp.70-73
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• 2009

The yield stress of stirred yogurt was measured by the vane viscometer at different pre-shearing conditions, such as pre-shear speed, pre-shear time, and wait time, and temperature (12-38${^{\circ}C}$). The yield stress ranged from ~17.6 to 10 Pa and from 34.2 to 11.9 Pa, depending on the pre-shearing conditions and temperature, respectively. The preshear speed and the wait time significantly affected the yield stress. The temperature dependence of the yield stress was described by the Eyring's kinetic model. The linear function of the temperature on the yield stress was limited at the 22${^{\circ}C}$, and at the above 22${^{\circ}C}$, the yield stress was maintained to be a constant (~12.5 Pa).

• Journal of Magnetics
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• 제22권2호
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• pp.281-285
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• 2017

To suppress the wall slip effect and improve the yield stress measurement precision of magnetorheological fluid, measurement disks with different grooves are first manufactured. Then, the influence of groove characteristics on the yield stress of magnetorheological fluid is investigated by the method of experiments. Finally, the optimization wall grooves of measurement disks are obtained, and the yield stress of a self-prepared magnetorheological fluid is measured. Results indicate that the groove type and groove width have a slight influence on the shear yield stress, whereas the measured yield stress increases with enhanced groove density, and the optimized groove depth is 0.3 mm. The measured shear yield stress of self-prepared MR fluid can be improved by 18 % according to the optimized grooved disks, and the maximum yield stress can reach up to 65 kPa as the magnetic flux density is 0.5 T.

• 대한기계학회논문집
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• 제15권2호
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• pp.413-423
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• 1991

Multiaxial loading by combinations of tension-torsion-internal pressure have been applied to the thins-walled tubular specimens prepared from cold drawn tubes of SAE 1020 steel. Prior to the multiaxial loading, each specimen has been twisted to different shear strains. Uniaxial tensile yield stresses measured at different angles to the tube axis clearly show that the initial orthotropic symmetry is maintained during twisting. The orthotropy axes are observed to rotate with shear strains. The plane stress yield locus measured for each twisted specimens show that yield surface shape does not remain similar during twisting and thus anisotropic work hardening is not a function of only plastic work.

• 한국기계가공학회지
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• 제2권3호
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• pp.48-55
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• 2003

This study investigates the effect of temperature and electric field strength on the Bingham characteristics of Electro-Rheological(ER) fluids which change their Yield shear stress and viscosity by temperature and electric field strength. It is found that under constant temperature the Yield sheal stress and viscosity of ER fluids proportionally increase with the applied electric field strength, and under constant applied electric field strength the Yield shear stress and viscosity of ER fluids decrease with the increasing temperature. These results are considered to be applied to the fluid and pneumatic power industry.

• Tribology and Lubricants
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• 제16권5호
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• pp.341-350
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• 2000

The study reported in this paper deals with the development for parametric investigation of the influence of the rheological properties of the lubricant in the thermohydrodynamic (THD) film conditions which occur in slider and journal bearings. A parametric investigation based on a Bingham model with a shear yield stress which best fit the experimental pressure is performed for predicting the thickness of the shear Bone in lubricating films with fixed geometry between the stationary and moving surfaces. The results suggest that the shear yield stress for the lubricating film is proportional to the pressure developed in the film within the range of the investigated cases and the shear zone thickness which is of the same order of magnitude as that obtained by the empirical formula is significantly smaller than the fluid film thickness in the lubrication zone.

• Earthquakes and Structures
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• 제8권6호
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• pp.1453-1461
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• 2015

In this article the non-linear behavior of the shear wall with low yield stress retrofitted with Glass Fiber Reinforced Polymer (GFRP) is investigated under pushover loading. The models used in this study are in ${\frac{1}{2}}$ scale of one story frame and simple steel plates with low yield stress filled the frame span. The models used were simulated and analyzed using finite elements method based on experimental data. After verification of the experimental model, various parameters of the model including the number of GFRP layers, fibers positioning in one or two sides of the wall, GFRP angles in respect to the wall and thickness of the steel plate were studied. The results have shown that adding the GFRP layers, the ultimate shear capacity is increased and the amount of energy absorbed is decreased. Besides, the results showed that using these fibers in low-thickness plates is effective and if the positioning angle of the fibers on the wall is diagonal, its behavior will improve.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.178-183
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• 2000

Electrorheological(ER) effect on the dispersive system of polarizable fine powder/dielectric oil has been investigated. The electrical and rheological properties of zeolite and starch based ER fluid were reported. The ER fluids were constructed by mixing zeolite and starch power with two different dielectric oils. Yield stress of the fluids were measured on the couette cell type rheometer as a function of electric fields, particle concetrations, and temperatures. The electric field is applied by high voltage DC power supply. The outer cup is connected to positive electrode(+) and the bob becomes ground(-). And the temperatures the viscosity(or shear stress) versus shear rates were measured. In this experiment shear rates were increased from 0 to $200s^{-1}$ in 2 minutes.