scholarly journals The determination of static and dynamic yield stresses using a steel ball

1949 ◽  
Vol 197 (1050) ◽  
pp. 416-432 ◽  
Keyword(s):  
Mild Steel ◽  
Yield Stress ◽  
Plane Surface ◽  
Steel Ball ◽  
Polished Surface ◽  
Normal Velocity ◽  
Chrome Steel ◽  
Static Yield ◽  
Von Mises ◽  
Static Yield Stress

The static and dynamical yield stress of the material of a thick steel plate may be estimated by pressing and by dropping a hard steel ball on a plane surface of the plate which has been ground and then polished. Under these conditions, the first appearance of an indentation on the polished surface can be detected with good accuracy, either by an optical interference method, or by an optical reflexion method. The statical experiment consists in finding the least force which must be applied to the steel ball to produce a permanent indentation, whilst the dynamical experiment consists in finding the least normal velocity of impact which gives similarly a permanent indentation. Using either the Guest-Mohr principal-stress difference or the von Mises shear strain energy hypotheses as criteria of failure, combined with an analysis of the stresses in the plate, it is shown how the appropriate yield stress can be calculated from the experimental data. Tests were made on a specimen of mild steel, two specimens of homogeneous armour plate and a very hard nickel-chrome steel of the type used for ball and roller bearings. The ratio of the dynamic value of the yield stress to the static value was found to increase as the hardness number decreases; the ratio was practically unity for the nickel-chrome steel, about 1⋅1 for the armour plate and about 2 for the mild steel. The values of the static yield stress found by the ball method and by an ordinary tensile or compression test are different; this is probably due partly to the inaccuracy of the criteria of plastic flow, partly to the difference in work-hardening in the two experiments, and partly to changes in the structure of the surface due to polishing. This discrepancy is without effect on the ratio of the dynamic to static yield stress as determined by the ball method, since the stress distributions in the static and dynamic ball experiments are identical.

LANTHANUM TITANATE NANOPARTICLES ER FLUIDS WITH HIGH PERFORMANCE

2012 ◽  
Vol 26 (13) ◽  
pp. 1250079 ◽  
Author(s):  
DE WANG ◽  
RONG SHEN ◽  
SHIQIANG WEI ◽  
KUNQUAN LU
Keyword(s):  
Yield Stress ◽  
Silicone Oil ◽  
Heating Temperature ◽  
Hydroxyl Group ◽  
Lanthanum Titanate ◽  
Different Temperatures ◽  
Static Yield ◽  
Er Fluids ◽  
Er Fluid ◽  
Static Yield Stress

A new type of electrorheological (ER) fluid consisting of lanthanum titanate (LTO) nanoparticles is developed. The ER fluids were prepared by suspending LTO powder in silicone oil and the particles were fabricated by wet chemical method. This ER fluid shows excellent ER properties: The static yield stress reaches over 150 kPa under 5 kV/mm with linear dependence on the applied DC electric field, and the current density is below 10 μA/cm2. In order to investigate the affect factor on the ER behavior, the LTO powder were heated under different temperatures. The ER performances of two particles treated under different temperatures were compared and the composition changes for those particles were analyzed with TG-FTIR technique. It was found that the static yield stress of the suspensions fell from over 150 kPa to about 40 kPa and the current densities decreased prominently as the rise of the heating temperature. TG-FTIR analysis indicated that polar groups remained in the particles such as alkyl group, hydroxyl group and carbonyl group etc., contribute to the ER effect significantly. The experimental results are helpful to understand the mechanism of the high ER effect and to synthesize better ER materials.

scholarly journals A study of the static yield stress in a binary Lennard-Jones glass

2004 ◽  
Vol 120 (6) ◽  
pp. 2788-2801 ◽  
Author(s):  
F. Varnik ◽  
L. Bocquet ◽  
J.-L. Barrat
Keyword(s):  
Yield Stress ◽  
Lennard Jones ◽  
Static Yield ◽  
Static Yield Stress

Static yield stress of ER fluids and the role of electric current

1997 ◽  
Vol 40-41 ◽  
pp. 699-704
Author(s):  
T. Sakai ◽  
K. Kobayashi ◽  
M. Sato
Keyword(s):  
Electric Current ◽  
Yield Stress ◽  
Static Yield ◽  
Er Fluids ◽  
Static Yield Stress

scholarly journals Effects of Volume Fraction and Surface Area of Aggregates on the Static Yield Stress and Structural Build-Up of Fresh Concrete

2020 ◽  
Author(s):  
Irina Ivanova ◽  
Viktor Mechtcherine
Keyword(s):  
Rheological Properties ◽  
Yield Stress ◽  
Surface Area ◽  
Cement Paste ◽  
Volume Fraction ◽  
Fresh Concrete ◽  
Total Surface Area ◽  
Rheological Parameters ◽  
Static Yield ◽  
Static Yield Stress

With increasing interest in the use of additive manufacturing techniques in the construction industry, static rheological properties of fresh concrete have necessarily come into focus. In particular, the knowledge and control of static yield stress (SYS) and its development over time are crucial for mastering formwork-free construction, e.g. by means of layered extrusion. Furthermore, solid understanding of the influences of various concrete constituents on the initial SYS of the mixture and the structural build-up rate is required for purposeful material design. This contribution is concentrated on the effect of aggregates on these rheological parameters. The volume fraction of aggregates was varied in the range of 35 to 55 % by volume under condition of constant total surface area of the particles. The total surface area per unit volume of cement paste was equal to 5.00, 7.25 and 10.00 m²/l, conditioned on the constant volume fraction of aggregates. Both variations were enabled by changing the particle size distributions of the aggregates while holding the cement paste composition constant for all concrete mixtures. To characterise the SYS and the structural build-up, constant shear rate tests with a vane-geometry rotational rheometer were performed. It was found that in the ranges under investigation the variation in volume fraction had a more pronounced effect on the static rheological properties of concrete than did the variation in surface area. An accurate mathematical description of the relationship between the initial SYS of concrete and the relative volume fraction of aggregate based on the Chateau-Ovarlez-Trung model was proposed. Challenges in deriving a similar relationship for the structural build-up rate of concrete were highlighted.

scholarly journals Effects of Volume Fraction and Surface Area of Aggregates on the Static Yield Stress and Structural Build-Up of Fresh Concrete

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1551 ◽  
Author(s):  
Irina Ivanova ◽  
Viktor Mechtcherine
Keyword(s):  
Rheological Properties ◽  
Yield Stress ◽  
Surface Area ◽  
Cement Paste ◽  
Volume Fraction ◽  
Fresh Concrete ◽  
Total Surface Area ◽  
Rheological Parameters ◽  
Static Yield ◽  
Static Yield Stress

With increasing interest in the use of additive manufacturing techniques in the construction industry, static rheological properties of fresh concrete have necessarily come into focus. In particular, the knowledge and control of static yield stress (SYS) and its development over time are crucial for mastering formwork-free construction, e.g., by means of layered extrusion. Furthermore, solid understanding of the influences of various concrete constituents on the initial SYS of the mixture and the structural build-up rate is required for purposeful material design. This contribution is concentrated on the effect of aggregates on these rheological parameters. The volume fraction of aggregates was varied in the range of 35% to 55% by volume under condition of constant total surface area of the particles. The total surface area per unit volume of cement paste was equal to 5.00, 7.25 and 10.00 m²/L, conditioned on the constant volume fraction of aggregates. Both variations were enabled by changing the particle size distributions of the aggregates while holding the cement paste composition constant for all concrete mixtures. To characterise the SYS and the structural build-up, constant shear rate tests with a vane-geometry rotational rheometer were performed. It was found that in the ranges under investigation the variation in volume fraction had a more pronounced effect on the static rheological properties of concrete than did the variation in surface area. An accurate mathematical description of the relationship between the initial SYS of concrete and the relative volume fraction of aggregate based on the Chateau–Ovarlez–Trung model was proposed. Challenges in deriving a similar relationship for the structural build-up rate of concrete were highlighted.

Polar-molecules-driven enhanced colloidal electrostatic interactions and their applications in achieving high active electrorheological materials

2008 ◽  
Vol 23 (2) ◽  
pp. 409-417 ◽  
Author(s):  
L. Xu ◽  
W.J. Tian ◽  
X.F. Wu ◽  
J.G. Cao ◽  
L.W. Zhou ◽  
...  
Keyword(s):  
Yield Stress ◽  
Electrostatic Interactions ◽  
Colloidal Particles ◽  
Sol Gel ◽  
Polar Molecules ◽  
Highly Active ◽  
Static Yield ◽  
Er Fluids ◽  
Er Fluid ◽  
Static Yield Stress

We have fabricated a class of colloidal electrorheological (ER) fluids, in which suspended TiO2 particles were synthesized by a sol-gel method and modified by 1,4-butyrolactone molecules with a permanent molecular dipole moment of 4.524 D. Compared with pure TiO2 ER fluids, the quasi-static yield stress of the polar- molecules-modified ER fluid is enhanced as high as 48.1 kPa when subjected to an external electric field of 5 kV/mm. Also, it possesses other attractive characters such as low current density (<14 μA/cm2) and low sedimentation. Based on a Green’s function method, we present a first-principles approach to investigate colloidal electrostatic interactions. Excellent agreement between experiment and theory has been shown for the enhancement ratio of quasi-static yield stress, which quantitatively reveals that enough polar molecules oriented within the field-directed gap between the colloidal particles can unexpectedly enhance the interactions, thus yielding the unusual enhancement. This shows a promising and flexible direction for achieving more highly active ER materials.

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