What is Bingham yield stress?
The Bingham plastic model is the most common rheological model used in the drilling industry. This model is a two parameter model that includes yield stress and plastic viscosity of the fluid. As it is shown in Figure 2-15, the fluid initially resists flowing until the shear stress exceeds a certain value.
Is Bingham plastic shear thinning?
Both the Bingham plastic and the pseudoplastic are shear thinning, since the viscosity decreases with increasing shear rate, whereas the dilatant fluid is shear thickening.
What do you mean by Bingham plastic fluid?
Bingham plastic is a material that behaves as rigid body at low stresses but flows as a viscous fluid at high stress. This behaviour is exhibited by slurries, suspensions of solids in liquids, paints, emulsions, foams, etc.
What is yield stress in rheology?
A yield stress in rheology is defined as the applied stress at which irreversible plastic deformation is first observed across the sample. It is usually represented as σy. Figure 1 depicts some “theoretical ideal” flow models with a yield stress.
Are Bingham plastics Newtonian?
Among many viscoplastic fluids, there is a special class called Bingham plastics. For Bingham plastic fluid, the shear stress beyond the yield stress is linearly proportional to the shear rate. If the yield stress approaches zero, the Bingham plastic fluid can be approximately treated as a Newtonian fluid.
What is Bingham viscosity?
A Bingham plastic is a viscoplastic material that behaves as a rigid body at low stresses but flows as a viscous fluid at high stress. It is named after Eugene C. Bingham who proposed its mathematical form.
Is blood a Bingham plastic?
Blood is considered as Bingham plastic fluid. The analytical results such as pressure drop, resistance to flow and wall shear stress have been obtained.
What causes yield stress?
This occurs typically by introducing defects such as impurities dislocations in the material. To move this defect (plastically deforming or yielding the material), a larger stress must be applied. This thus causes a higher yield stress in the material.
How do you calculate yield stress in rheology?
One of the most extensively used method to determine the yield stress is probably the continuous shear stress or shear rate ramp, from low to high stress or rate. The yield stress is usually determined by fitting the stress/rate curves with Bingham, Casson or Herschel-Bulkley models.
What is the difference between Bingham plastic and Newtonian fluid?
As before, the Newtonian fluid flows and gives a shear rate for any finite value of shear stress. However, the Bingham plastic again does not exhibit any shear rate (no flow and thus no velocity) until a certain stress is achieved.
Is toothpaste a Bingham plastic?
Toothpaste is a Bingham Plastic. Pseudo-plastics (shear thinning) decrease in viscosity when more force is applied. Example of pseudo-plastics include: nail polish, lava, ketchup, and whipped cream. Dilatants (shear thickening) increases in viscosity as more force is applied.
What is the difference between yield stress and yield strength?
For materials that have a yield point, the yield stress (also called yield strength) is the stress at the yield point. The symbol for yield stress (yield strength) is σy . Yield stress is a particular value of stress and is therefore expressed in the same units, psi or MPa.
Why yield stress is important?
In design applications, the yield strength is often used as an upper limit for the allowable stress that can be applied to a material. It is especially important in material applications that require precise dimensional tolerances to be maintained in the presence of high stresses and loads.
What does a high yield stress mean?
A metal that has a high yield strength can withstand high stress without permanent deformation. The yield strength of a bar of material is the maximum stress that can be applied along its axis before it begins to change shape.
Why is yield stress important?
An understanding and knowledge of a material’s yield strength is vital when designing and manufacturing components, as it represents the upper load limit for that substance. Consequently, yield strength is very important in the production processes used for many materials such as pressing, rolling, or forging.
What is yield point plastic viscosity?
The plastic viscosity (PV) of the drilling fluid is calculated by subtracting the 300-rpm shear stress (R300) from the 600-rpm shear stress (R600). The yield point of the drilling fluid (YP) is calculated by subtracting the PV from the R300 reading. Multiplying the rpm by 1.7 changes the units to re- ciprocal seconds.
What is the yield stress of Bingham fluid?
Regarding the flow of the Bingham fluid, the stress varies in space and time. There can be regions in the fluid where the yield stress is exceeded, and other regions where it is not. The boundaries between the two regions are the yield surfaces.
What is the shear stress in Bingham plastic?
In the Bingham plastic model, the shear stress should exceed a certain value to break the gelation bonding of the drilling fluid and allow it to flow. This behavior enables drilling fluid to suspend the drilling cuttings and solids within the drilling fluid when the circulation stops.
What is a Bingham plastic?
A Bingham plastic is a viscoplastic material that behaves as a rigid body at low stresses but flows as a viscous fluid at high stress. It is named after Eugene C. Bingham who proposed its mathematical form.
Is Bingham plastic model suitable for sediment-laden flows?
The Bingham plastic model is well suited to sediment-laden flows with large concentrations of fine particles (Wan and Wang, 1994; Julien, 1995 ). 4. The yield stress of hyperconcentrated mixture is generally formulated as a function of sediment concentration.