Just to endorse the statements below and to confirm that there is nothing unusual in finding that many grades of steel (and most other metals) do not have a defined yield point and we take the 0.2% proof stress as being 'yield' for design purposes. One exception is pipeline steels (many of which do not have clear yield point) but where we follow US practice and take as 'yield' the intercept with the stress strain curve corresponding to the 0.5% total strain. However if in doubt take the 0.2% proof stress as defined in Mohan Ananthanarayanan's email below.
Alan
Alan Denney
AKD Materials Consulting Ltd
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Mohanananthanarayanan KR
Sent: 02 November 2015 04:33
To: materials-welding@googlegroups.com
Subject: Re: [MW:23843] Tensile testing
Dear all,
In order to get the 0.2% yield or proof stress, in the load vs extension curve take a point on x-axis at 0.2% of gauge length ( if 50 is GL then this point is 0.1mm on the x-axis ie along the extension). From this point draw a parallel line to the curve obtained by tensile test. This line would meet the curve at a point. Load corresponding to this is the 0.2% proof load and the stress based on this will give 0.2% Proof stress. Since some alloy steel unlike mild steel does not have a specific point of yield, this method is suggested for estimating the yield strength allowing a permanent yield of 0.2%. Software will have this but you have to verify that 0.2% of GL marked is taken for getting the value.
With warm regards
Mohan Ananthanarayanan
DGM QC VSSC
On Fri, 30 Oct 2015 20:28:50 +0400, Harish Kannepalli wrote
> Did u use extensometer or not?
> You have to construct 0.2% offset on the strain axis and get the 0.2% yield strength. Probably ur software would have that option!
>
> 2015-10-29 19:13 GMT+04:00 Padmasanker S <padmasanker87@gmail.com>:
>
> Dear all,
> Please refer to attached stress -strain graph obtained during tensile testing of SA 106 Gr B pipe.
> While performing tensile testing of SA 106 pipes for Div 1 vessels ,we were not getting yield point even though required tensile strength is obtained.
> The specimen were taken in both transverse and longitudinal direction from half thickness.
> Kindly share your experience in finding the root cause..
> Please inform if any further details is required for clarity.
>
> Best regards,
> Padmasanker,
> Quality coordinator,
> Bilfal heavy industries ltd.
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> Mr. Harish.
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