Yield Stress V 0.2% Proof Stress 1

[sammcc]

Hi All, I am looking at a material cert to find the 0.2% proof stress of the material.
Trouble is, the field is empty but the cert gives a value for Yield stress.
Are these one in the same thing? If not could someone explain them to me as I am rather confused by it.

Thanks in Advance,

 

[mp87]

For certain materials such as low carbon steels in annealed conditions, yielding can be clearly seen in a stress-strain curve and it is even possible to define an upper and lower yield strength.

For other materials there is not a clear transition from the elastic to the plastic region and it is in such cases that the 0.2% proof strength comes into play. It represents a stress level below which the material can be considered macroscopically elastic.

This is a possible explanation for the information reported in your material certificate.

 

[metengr]

http://www.kobelco-welding.jp/education-center/abc/ABC_2005-04.html

 

[sammcc]

Thanks guys for the quick responses.