Yield Strength:

A number of words have been described for the reason of identifying the stress at that plastic deformation starts. The value most general used for this reason is the yield strength.  Yield strength is described as the stress at that a predetermined amount of permanent deformation occurs. The graphical portion of the early stages of a tension test is used to evaluate yield strength.  For search yield strength, the predetermined amount of permanent strain is set along the strain axis of the graph, to the right of the origin (zero).  It is denoted in above Figure as Point (D).

A direct line is drawn by Point (D) at the similar slope as the initial portion of the stress-strain curve. A point of intersection of the new line and the stress- strain curve is projected to the stress axis. A stress value, in pounds per square inch, is the yield strength.  That is denoted in Figure as Point. That method of plotting is completed for the reason of subtracting the elastic strain from the total strain and leaving the predetermined "permanent offset" as a remainder.  While yield strength is reported then the amount of offset used in the determination should be stated. For instance, "Yield Strength (at 0.2% offset) = 51,200 psi."

Figure: Typical Brittle Material Stress-Strain Curve