I have modelled a heavily welded structure in LS-DYNA and I am using implicit method to solve it as the problem is static. Which is the correct command (keyword) in LS-DYNA in order to model initial stresses such as the residuals from the welding procedure? I am using the keyword: “*Initial_Stress_Shell_Set” and I am introducing the tensile and compressive stresses at the respective shells. However, this command seems that it doesn’t work as the results do not make sense. It looks like this keyword affects only the first step of the solution. Is there any respective command such as: “inistate” that is used in Ansys?
hello dear friend
in my opinion about modeling the residual stress in LS-DYNA your selected software is not good for this issue
but if you want to do it carefully its better to modelling it in Abaqus or Ansys.
DYNA is good for blast modeling
i had write some codes in matlab for residual stress welding in FSW wellding if it related to your work will send it to you.
Thank you very much for your reply. Unfortunately, Abaqus or Ansys are not an option now. You are right about DYNA and blast modelling. It is more suitable for highly dynamic problems such as blasts, crash tests, metal forming etc. However, I am trying to solve my problem as a static one using implicit analysis and compare it with an explicit one. My problem is that I just want to introduce initial stresses at some shells in order to model the residual welding stresses. I know both the values of these residual stresses and the shells at which they have to be implemented. I just don’t know which is the correct command that I have to introduce. To make it more general, if I had any kind of problem where preload had to be implemented at shells, which would be the correct keyword to do it? I mean, imagine a plate comprised of 50 shells. If I want to introduce initial tensile stresses at 10 of them, what should I do? It seems that the keyword *Initial_stress_shell_set doesn’t work. For the latter keyword, according to LS-DYNA manual, I quote: “Define as many shell elements or shell element sets in this section as desired. The input is assumed to terminate when a new keyword is detected. It is not …”. The second sentence might be the reason that this keyword affects only the first step of the implicit analysis but I am not sure.
Dear Droutsas,
I don't know if you found a solution already, but had some difficulty using *initial_stress for incorporating residual stresses and found better to include them as a thermal load using the card *LOAD_THERMAL_VARIABLE. In newer versions of ls-dyna you can add two load curves, one for the "dynamic relaxation" step and another for the explicit step, LCID and LCIDR, which allows you to initialise the residual stresses and keep it constant throughout the explicit step (in my case during the impact of the object).
Kind regards,
Rodolfo
Dear Radolfo,
I have found a solution through *Initial_Stress_Shell_Set. Nonetheless, thank you for your comment. It may be useful for the rest that are interested in the topic.
Kind regards,
Athanasios
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