Rupture simulation of a spring retainer
Rupture simulation of a spring retainer
(OP)
Hello
I am simulating the push-through test on a spring retainer and I would like to determine the maximal load that I can apply. The idea is, basically, to simulate the rupture of the part under an increasing load.
I have defined the spring retainer material to be bilinear isotropic hardening, using the strain at rupture to determine the tangential modulus. My idea is to apply increasing loads until the von Mises stress at any point is higher than the ultimate tensile stress. However, I am having problems with convergence at loads which result in stresses well under the UTS (although big sections of the retainer are already plastic) which I tried to avoid by reducing the element size. Additionally, I have tried with a modified definition of the material, with a higher tangential modulus. Although this solution worked, I am not too pleased with this "faking" of the material properties.
Any ideas?
Thanks in advance and have a nice weekend!
Fernando
I am simulating the push-through test on a spring retainer and I would like to determine the maximal load that I can apply. The idea is, basically, to simulate the rupture of the part under an increasing load.
I have defined the spring retainer material to be bilinear isotropic hardening, using the strain at rupture to determine the tangential modulus. My idea is to apply increasing loads until the von Mises stress at any point is higher than the ultimate tensile stress. However, I am having problems with convergence at loads which result in stresses well under the UTS (although big sections of the retainer are already plastic) which I tried to avoid by reducing the element size. Additionally, I have tried with a modified definition of the material, with a higher tangential modulus. Although this solution worked, I am not too pleased with this "faking" of the material properties.
Any ideas?
Thanks in advance and have a nice weekend!
Fernando





RE: Rupture simulation of a spring retainer
You need much smaller time steps (or whatever your program calls them) when the material becomes plastic. Some solvers are much better than others on this type of problem.
Sometimes applying prescribed displacements can help, although I tend to avoid this if I can. Some programs offer an option of specifying maximum displacements on collapse type problems with a load/displacement algorithm which I find work can very well.
RE: Rupture simulation of a spring retainer
corus
RE: Rupture simulation of a spring retainer
However, I have figured out that the convergence problem was not in the plastic material but on the contact area between the spring retainer and the tool used to apply the press-through force. Sorry about that
Another question: what do you think of the rupture criteria? Is it correct to consider it breaks once it reaches UTS in a certain point? I had also thought about modelling it with a multilinear isotropic which would have the same first two "lines" as the bilinear described above and a final horizontal line at the UTS, to model that with this stress, it can take any displacement on this point (break).
Regards
RE: Rupture simulation of a spring retainer
Technically it would be more accurate for the third line to be vertical (down to zero stress) or to include rupture within the material model, but these will make convergence much more difficult at the final stages.
RE: Rupture simulation of a spring retainer
crisb, what do you mean with true stresses/engineering stresses and not mixing them up? If I can correctly remember, engineering stresses are determined over the undeformed cross-section and true stresses over the deformed one. I suppose that when I plot the stresses, they are engineering stresses, right? Can I obtain the true stresses from ANSYS?
I had also thought about the vertical line in the multilinear model, but discarded it for the expected convergence problems.
Thanks again
Fernando
RE: Rupture simulation of a spring retainer
I dont know Ansys. I have the option of plotting "FE effective stresses" or "effective stresses" in Adina, and have to plot FE effective stresses if I want to compare results with the material (property) input data. I also like to plot plastic strains on this type of analysis.
RE: Rupture simulation of a spring retainer
Ed.R.
RE: Rupture simulation of a spring retainer
comparison of the von Mises stress with the UTS as rupture criterion should be a good approximation for steels. It is something I learnt from my old boss but can not confirm nor demonstrate it. Maybe someone with more experience than I could bring some light here.
Regards
Fernando