ASME VIII Div. 2 Part 5.5.4, Twice-Yield Method

[Doodler3D]

All,

I have a couple of doubts regarding the cyclic stress-strain curve.

1. Based on article PVP2008-61397 (Twice Yield Method, Dr. Kalnins), how is the value of 'stress range' incremented to generate the curve for the analysis. Is it an arbitrary increment (I think it is)? I was a bit confused with the example 5.5.4, Table E5.5.4-1 of PTB-3, where the stress range appears to be arbitrarily incremented for each corresponding value of plastic strain range.

2. What is the limiting 'stress range' or 'plastic strain range' value of this curve, if it exists?

Thank you.

 

[cbPVme]

1. The code doesn't provide any guidance on this. As the engineer it is at your discretion to enter sufficient data points into your FEA package to adequately capture the stress-strain curve.
2. My understanding is that there is no upper limit. You would eventually reach a point where your stress is so high that you don't achieve any cycles.

 

[Doodler3D]

Thank you for confirming that.

 

[IdanPV]

From my understanding of PTB-3 - It's not that stress range is arbitrarily incremented for each corresponding value of plastic strain range, but on the contrary.
The first value is basically 2*Sy (“Twice-Yield”), and then, the stress range is increased constantly in jump of 5,000psi.
The plastic strain range is increased because of the formula at the bottom of page 377 of PTB-3.
The plastic strain range is dependent on the way that the stress range is changing.

 

[Doodler3D]

@IdanPV, yes, the PTB-3 example has a defined stress range step while in the paper, its arbitrary. I thought I missed something. Now, its clear to me.

 

[Doodler3D]

@IdanPV

My software requires the cyclic stress strain curve with the elastic portion, unlike Abaqus. In that case, how is the total strain added to the cyclic stress strain curve so that it begins from the origin(0,0)? Is is appropriate to use the proportional limit, just like the monotonic stress strain curve?

 

[Doodler3D]

@all, for a software that requires the full stress-strain relationship, is the proportional limit on the twice-yield cyclic stress strain curve expressed in a method that is similar to the true monotonic stress-strain curve defined in Annex 3D of the ASME Sec VIII div 2 code?