دیکشنری تخصصی مهندسی نفت - نسخه آنلاین

the resistance to initial flow of a fluid or stress required to start fluid moving.

The stress on a material at which the first significant permanent or plastic deformation occurs without an increase in stress (NACE).

n: a measure of the force needed to deform tubular goods to the extent that they are permanently distorted.

The stress in which the stress-strain relation of material changing.

the stress at which a material exhibits a specified deviation from the proportionality of stress to strain. The deviation is expressed in terms of strain by either the offset method (usually at a strain of 0.2%) or the total-extension-under-load method (u

The stress that must be applied to a material to make it begin to flow (or to yield). Yield stress is a parameter in the Herschel-Bulkley rheological model.

n: the resistance to initial flow, or the stress required to start fluid movement. This resistance is caused by electrical charges located on or near the surfaces of the particles. The values of the yield point and thixotropy, respectively, are measurements of the same fluid properties under dynamic and static states. The Bingham yield value, reported in pounds/100 square foot, is determined from a directindicating viscometer by subtracting the plastic viscosity from the 300-rpm reading. Also called yield point.

Also called movable shear stress. The viscosity dont change along with the shear stress when shear stress arrive a given value,now shear stress and rate of shearing present direct ratio relation, the value of crossing point of this direct ratio relation

the critical shear stress that must be exceeded before flow can be initiated.

stress over strain. A measure of stiffness or Modulus of Elasticity. Rocks are ½ to 12 x 106 psi and mild steel is 30 x 106 psi.

yield point, the point at which a fluid shears.

stream function or value of a streamline.