I have a thin walled cylindrical tube to be analysed at high temperature around 1000 C, and I want to simulate the ballooning (bulge at a particular point) due to plastic instability. The software I am using is ABAQUS. And the material is Stainless Steel. Could anybody throw some light on this?
Thank you
It sounds like a bifurcation problem. Though i'm not aware of the material you are using, but from continuum mechanics point of view I suggest you to perform some bifurcation analysis using the tangent stiffness tensor at material point level.
The following reference might be of your interest: Y. B. Fu and Y. X. Xie
Effects of imperfections on localized bulging in inflated membrane tubes
Phil Trans R Soc A 2012 370: 1896-1911.
@Arghya Das
Thank you for the reference you have given. I will study about the bifurcation. Kindly suggest how to perform the analysis in Abaqus.
I have modeled buckling of stinger ribs on sheet metal during plastic deformation and compared it to experiments.
I used Abasuqs Standard and Explicit and since it is a forming analysis also the Dynamic Implicit solver with moderate dissipation.
I found that you don't need to add mperfections to the model in order to see buckling, as the simulation accuracy is "imperfect" enaugh (at least when using an unstructuresd mesh). My experiments buckle slightly more quickly than the simulations, so imperfections might help. However since the difference is not very large and all influences of geometrical and material parameters are predicted nicely, I don't think you need them unless you need to bee very very accurate.
However, the problem is very mesh sensitive and in case of an explicit solver mass scaling can be an issue. If the mass is too high or the process is run to quickly buckling is damped to the point where no buckling will occur in the simulation when it does in the experiment.
It is a thin walled tube. I have to give the plastic instability in Abaqus so that I will observe the sudden bulge in the tube. I observed the inflation in the tube experimentally, i want to observe the same using abaqus. I expect help to know how to incorporate this plastic instability in Abaqus.
Try to simulate the similar test in Abaqis as you did in the experiment. In addition you may add some imperfection (a weak element i.e. slightly lower yield than the rest of the specimen) to observe the bulging in a specific location. However, as the previous author (Frederic) says unstructured may be enough to trigger the instability. One important issue is about the regularization of the model material as the results will be highly mesh dependent upon the instability. In Abaqus regularized model materials can be constructed through UMAT (for Abaqus standard) subroutine.
It’s a thin stainless steel tube at 1000 deg C but what is causing ballooning (inflation during experiment)….is tube constrained or subjected to internal pressure or some other load…...
As you are using explicit solver so you will capture it correctly if you apply load very slowly at the onset of instability ……such problems show convergence issues or wrong simulation due to large deflection with small load increase…..you can also try deflection control loading to simulate in case of convergence issues….
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