ABSTRACT
Y Y Yeast: Any of a number of species of single-celled fungus. Most important are the Saccharomyces spp., which are used in bread making and beer brewing. Y (Growth Rate): See Growth rate. Yield: The quantity of petroleum product derived from a process, based on the specic weights of raw materials. Yield (Drilling Fluid): A measurement applied to clay dealing with the number of barrels of a set viscosity ¤uid that can be made from a given quantity of clay. Yield Point: The point at which a ¤uid shears. Yield Point (Drilling Point): The resistance to initial ¤ow of a ¤uid or stress required to start ¤uid moving. Yield Point (Metal): The stress on a material at which the rst signicant permanent or plastic deformation occurs without an increase in stress (NACE). Yield Strength (Metal): The stress at which a material exhibits a specied 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-underload method (usually at a strain of 0.5%). Yield Value (Fluids): The critical shear stress that must be exceeded before ¤ow can be initiated. Young’s Modulus (E): Stress over strain. A measure of stiffness or modulus of elasticity. Rocks are ½ to 12 × 106 psi and mild steel is 30 × 106 psi. YP: See Yield point.
