Welding Inspection & Metallurgy API ICP Self Study Notes

R e 0.2%
Yield strength is the amount of stress at which plastic deformation becomes
noticeable and significant. Fig.1 is an engineering stress-strain diagram in
tensile test. Because there is no definite point on the curve where elastic
strain ends and plastic strain begins, the yield strength is chosen to be that
strength when a definite amount of plastic strain has occurred. For the
general engineering structural design, the yield strength is chosen when 0,2
percent plastic strain has taken place. The 0.2% yield strength or the 0.2%
offset yield strength is calculated at 0.2% offset from the original crosssectional
area of the sample (s=P/A).