Which statement correctly contrasts yield strength and offset yield in steel?

Which statement correctly contrasts yield strength and offset yield in steel?

• A. Offset yield uses a defined strain offset (commonly 0.2%) to locate a practical yield point on the stress-strain curve.
• B. Yield strength is the same as ultimate tensile strength.
• C. Offset yield is the stress at which necking begins.
• D. Yield strength depends on temperature while offset yield does not.

Answer: (A)

The key idea is how a practical yield value is defined on the stress-strain curve. In many steels, there isn’t a sharp, easily identifiable yield point, so engineers use the 0.2% offset method to mark when plastic (permanent) deformation begins. You draw a line parallel to the initial elastic portion of the curve, offset by a fixed strain amount (commonly 0.2%). The stress corresponding to the intersection of this line with the actual stress-strain curve is the offset yield strength. This provides a repeatable, conservative measure of when the material starts to yield. Yield strength and ultimate tensile strength are not the same: yield strength signals the onset of permanent deformation, while ultimate tensile strength is the maximum stress the material can withstand before necking and failure. The notion that offset yield is the stress at which necking begins is incorrect; necking occurs after yield, during the portion leading to failure. Finally, both yield strength and offset yield can depend on temperature; the idea that one does not is not accurate.

The key idea is how a practical yield value is defined on the stress-strain curve. In many steels, there isn’t a sharp, easily identifiable yield point, so engineers use the 0.2% offset method to mark when plastic (permanent) deformation begins.

You draw a line parallel to the initial elastic portion of the curve, offset by a fixed strain amount (commonly 0.2%). The stress corresponding to the intersection of this line with the actual stress-strain curve is the offset yield strength. This provides a repeatable, conservative measure of when the material starts to yield.

Yield strength and ultimate tensile strength are not the same: yield strength signals the onset of permanent deformation, while ultimate tensile strength is the maximum stress the material can withstand before necking and failure. The notion that offset yield is the stress at which necking begins is incorrect; necking occurs after yield, during the portion leading to failure. Finally, both yield strength and offset yield can depend on temperature; the idea that one does not is not accurate.