Learning Forum

[helen.durand]

Hello!

BACKGROUND: I am using some nonlinear temperature-dependent stress-strain data in an ANSYS Transient Structural simulation, entered as a multilinear model in a command object as APDL. The data I am using contains of a series of curves, one for each temperature. I am using the TB, TBTEMP, and TBPT commands to enter in plastic strain versus true stress data for each temperature, and I am using the MPTEMP and MPDATA to enter in the elastic modulus data.

The issue is that there is not a clear yield point, and I am not sure what the best way to determine this in a systematic way. 

Should I use a 0.2% offset as shown in the following plot? The red line is one of the stress-strain curves I am using, and the blue line represents the 0.2% offset. I am concerned about this because, to me, it looks like plastic deformation is already occurring before this yield point.

Previously, I was representing the stress-strain curve with a series of line segments (something like what is shown below, in green). This follows the stress-strain curve more nicely but it also means that yielding starts at a much lower stress. Is this a better method? 

Thank you!

 

[peteroznewman]

I would do what you did previously and choose the first point on the line segments as the yield point.

Do you also use that point to compute the value of Young's Modulus?

[mjmiddle]

This is more of a general engineering question than a question directed at Ansys software. So there should be plenty of other sources that address such a material. From my basic engineering instruction, I remember that the most linear portion should deternine the yield point when it appears to start deviating significantly from this linear portion. So your second graph is most accurate, and you could use typically a multilinear isotropic or kinematic material property.

The 0.2% cutoff seems to cut off too much of the behavior's curvature.

[helen.durand]

Yes, I used the point to find Young's Modulus.

Thank you both for the helpful replies.