Stress Strain Curve Super Duplex BPVC Section VIII, Division 2 ANNEX 3-D

[SiggiN]

Hi!

I'm new to the BPVC and have some questions regarding the Stress Strain Curve generated by Annex 3-D

I've enclosed my mathcad sheet. My motivation is to generate stress strain values I can use in nonlinear FEA

1)the "m2" parameter states: "curve fitting exponent for the stress-strain curve equal to the true strain at the true ultimate stress"

Does this mean that the value for m2 is the strain at fracture? I'm getting 0.18, but comparing with material certificates I expect >0.25

2) the "m1" paramter states: "curve fitting exponent for the stress-strain curve equal to the true strain at the proportional limit and the strain hardening coefficient in the large strain region"

Looking at the graph I have generated I expected the strain at the proportional limit to equal m1 (0.08 in my case), but this is not the case. What strain value should be at proportional limit?

3)the "sigma_utst" value is way larger than I expected, comparing with material certificates the Rm is >750MPa, i'm getting 960MPa.

Regards
Sigurd

 

[TGS4]

You are mixing up true stress with engineering stress. Your material certificate will present Engineering Stress, but your FEA will need true stress.

Also, remember to start your plastic curve at a strain of epsilon_P.

Remember to keep the plastic strain and total strain separate.

 

[MagBen]

either your engineering curve or your true strain curve is wrong! true curve must be always higher than engineering curve, but you used the same set of stress for both curves.