Plastic behavior

[flyforever85]

I'm analyzing a component that can be yield but cannot reach ultimate stress (AISI 4340). I initialize the elastic behavior with E and V and in the plastic section I put the yield stress and 0 plastic deformation and then the ultimate stress with the relative plastic deformation. Now the model stopped converging and I cannot think of anything to fix it

 

[FEA way]

Apparently your model was on the edge of nonconvergence before you added plasticity. But it’s rather unusual that including plastic behavior makes things worse (usually it’s the opposite). Did you get any warnings regarding plasticity calculations from Abaqus ? Are you sure that units are correct ? Try adding more stress-strain pairs to the plasticity definition. That’s because when load goes beyond the end of defined curve then Abaqus extrapolates the curve with horizontal line (perfect plasticity) and convergence issues may occur. Also reduce initial time increment and consider using stabilization.

 

[flyforever85]

I think the non-convergence was not related to the plasticity effect but to the change of other boundary conditions.

On a side note: I want to be sure I implement the "plasticity" effect in the right way. I'm using AISI 4130 and I found in matweb that yield strength is 65,000 psi and ultimate is 95,000 ksi. Elogantion at break is 25% so when I implement these data in ABAQUS through Plasticity tab, shall I put 0 deformation at 65,000 psi and 0.25 at 95,000 psi?

 

[FEA way]

Yes, that’s correct. Of course you always have to be careful with units and if you use data from mechanical tests remember that you must input true stress-strain values (not nominal).