Learning Forum

[helen.durand]

Hello!

Consider: Denlinger, Erik R., Jarred C. Heigel, and Panagiotis Michaleris. "Residual stress and distortion modeling of electron beam direct manufacturing Ti-6Al-4V." Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 229.10 (2015): 1803-1813.

In this work, the authors are performing a 3D thermal and mechanical analyses of an additive manufacturing process using one-way coupled transient thermal and quasi-static structural analyses. 

The authors state that: "The thermo-elasto-plastic model presented accounts for the observed stress relaxation by resetting both stress and plastic strain to 0 when the temperature exceeds a prescribed stress relaxation temperature."

I was wondering how this might be accomplished. How would I set stress and plastic strain to zero when the temperature exceeds a value? 

I am implementing my simulation in transient thermal and transient structural utilizing APDL command blocks. Is there an APDL command that can set stresses and plastic strains to zero? I already have code that is capable of finding the temperature of each element by looking at the nodal temperatures. 

Thank you!

[Ashish Khemka]

Hi Helen,

Try the following commands for the material input. The commands below define a multilinear isotropic hardening model where for temperature of 66 degree C, the plastic strain is zero and stress is 1e-6MPa. Other data is for 22 and 44 degree C.

TB,PLAS,1,3,3,MISO
TBTEMP,22
TBPT,,0,100
TBPT,,0.1,200
TBPT,,0.2,300
TBTEMP,44
TBPT,,0,100
TBPT,,0.1,200
TBPT,,0.2,300
TBTEMP,66
TBPT,,0,1e-06

Regards,

Ashish Khemka

[helen.durand]

Thank you for the reply! 

For the 66 °C data, you have only listed a value of true stress of 1e-6 for a plastic strain of 0. Does this mean that ANSYS will continue to use a true stress value of 1e-6 for larger plastic strain values at 66 °C?

Could you explain how this corresponds to resetting both stress and plastic strain?

How does this ensure a plastic strain of 0? It seems like the plastic strain could still be a larger number at 66 °C, and doing what you suggested will just ensure that the stress remains low at 1e-6.