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fcolomb

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  1. fcolomb

    Springback result far from experiment

    Hello @Ivan, thank you very much for the reply. It is really helpful, even after reading the guides and Radioss book, it is still difficult to evaluate how accurate a model is or is there are mistakes. About the Dynamic relaxation with explicit method from the Example 24, I just missed it because actually this 90º test was a validation model for a much more complex springback study case (after single point incremental forming). So we wanted to use the same simulation method now and later. But of course I will give a try to it. Regarding the boundary conditions, I will take another look, but this image was only made to explain how the measures were taken. In any case, have you take a look at the model? Did you see any significant mistake on it? I will play around with these cards related to the dynamic effects. Thank you very much indeed Ivan.
  2. Hello guys, I am trying to validate a springback model to be used in a more complex forming simulation. For now I am performing some 90º bend experiment on a lab and trying to compare the results with my model. Unfortunately I am getting more than 25% error, while I see on literature that the result for simple cases like that should be much better. What am I doing wrong? I already tried a bunch of tips and different parameters. Please, find the results and the model attached. Could someone please take a look and give me some hints? Is there a way to "turn off" or "reduce" dynamic/impact effects? I could notice the sheet body bouncing and waving. I am not sure if it also happens in reality but our eyes can't capture. Thank you in advance. Springback_standard3_0000.rad Springback_standard3_0001.rad Springback_standard3_0002.rad
  3. Yes @Andy, when I reduce yield stress (or increase sheet thickness) the wrinkles disappear, but only in a level that is too far from reality. I believe too that the problem can also be related to element size. The problem is that I can`t reduce it due run time, and I can`t increase it due geometry. Maybe you can help me on an suggestion: My whole simulation path, if displacement were to be imposed in seconds, is taking 591s, what with a timestep of 1e-6 will take 10 days to run (which is kind of a problem here). The problem is if I increase element to a huge size (like 15mm lenght), I can only reduce the time step to I would say 2.5e-6, then it takes 5 days. So, still doesn`t help a lot (and we loose all the precision). Another thing I am noticing, is that even when I don`t use DT/NODA, with zero mass added, I always have 99.9% error. Maybe because my simulation is too long? What can be the reason? Do you think its possible to imposed the displacement in milli seconds? What do you think about the dynamic effects on the Single point incremental forming? I need to find a way to run it faster.... As always, thank you very much for the help.
  4. Thank you very much the answers guys. Yes @Ivan, that was exactly my doubt. Now I understand it, its good to know that I can use small elements attached to Rbody without increasing running time. And also, very useful information about the relation between stiffness and contact, I wasn't aware of that. About adding mass to the Rbody, if I am using impdisp on this specific Rbody the whole time, does the mass on it affect time step too? I mean, the inertia effect are controlled by my impdisp, right?
  5. Hello @Prakash, thank you for the reply. Yes, I am aware of the two kinds of time step and I know the courant condition that dictate the time step too. But my doubt is for example whether elements attached to a Rigidbody that is totally constrained, will also play a hole on this count or no. Because since they won't have any stress/strain, there should be no calculation on them. But I don't know if the software "thinks" like that. If the solver "choose" this time step as the one to be used, can I reduce the young modulus of these elements (the ones attached to the RB) to reduce their timestep? I know is not good to add mass to rbody, but what about reducing stiffness on it's slave elements, since I don't care about them?
  6. Hello, I am running an explicit simulation and I have a forming tool that due to its geometry requires a small mesh, much smaller than the part of interest. Since I don't want to investigate anything that happens with the tool, all its elements are linked to a Rigid body. My "element check tool" is showing that the timestep for these elements will be really small. Will the solver use this related timestep as the minimum of my run? I don't think it will be counted, but just being sure, because I couldn't find this information elsewhere. Thank you.
  7. Hello @Andy, as always your tips were really helpful and made a lot of sense. That was indeed wrong and together with some other changes solved the problem of the small vibrations. I found out that the tool was probably approaching too fast, building up some inertia or dynamic effect. Now, as it seems to never reach an end, I am facing another problem. I hope, if not asking too much, that you can help me again with your valuable hints. I am pretty confident that it is related to the material formulation. After certain level of strains, some wrinkles start to pop up on the sheet, a behavior that we didn't see in the real test. The model is acting as if the sheet is still too elastic, even after a great amount of plastic strain had developed. I am using all the materials properties we have here and that I found on internet (for Aluminium 2024 T3). I was initially trying with Johnson Cook (Law2) formulation, now I tried with Elastic Plastic Tabulated Material (Law36), also got the same results. I plotted the stress and strain over time and it seems coherent, but I can`t figure exactly what is wrong. Do you have some ideas or directions I should look for? Please, find video of the wrinkling and the plot. Thank you very much. Animation_wrinkling.mp4
  8. Hi @Andy, thank you very much for the help and hints. I followed your steps and tried with a mass scaled model. It ran fine, but there was no significant springback, only stress dissipation. I guess because my material properties were wrong (I used false density to learn the displacement). So I decided running a new model, using all the real mechanical properties for the Johnson Cook model... I don`t know what is happening with this new model now, but I keep getting this weird vibrations and buckling modules. I believe the time step is small enough, and I double checked the cards, and everything seems fine. Could you give me some cues about what could be wrong? My doubts are: Am I using the right impdisp time input (seconds vs. mm) for a "mm, s, Mg" model? Are my contact setup right? Are the units of the material properties right? Please, find a animation of the problem I mentioned, a picture about my current run and the .rad files. Again, thank you for the help. I hope I am not taking too much of your time. Animation.avi Spif_5_0000.rad Spif_5_0001.rad
  9. Thank you so much @Andy, I did in this way and its working now. I've been struggling with this for days. I was taught initially to control displacements always from the IMPDISP card, not from the function. Now it makes much more sense, its working perfectly. Sorry for abusing, but may be you can help me with this too. The next phase will be to calculate spring back. I know from hyperform that we can add a second step and release the clamps to see the springback behavior. How can I do this on Radioss for my SPIF? Is it possible? Thank you again, your help has been essential
  10. Thank you for the reply @Andy, yes this is exactly for SPF and the tool will be rotating around its own axis while translating. As I said, this is only one of the shapes, the other shape will be a cone. When you say /IMPDISP, do you mean the normal one or the /IMPSDISP/FGEO? I am not sure how to input time versus displacement functions on IMPDISP. The only way I know, I define a curve (0;0) to (1;1), and then scale it as for the dimensions I need. Should I do this input using the standard console or directly in the starter deck?
  11. Hi @Andy, Your help was really helpful for me to understand the method, but it also showed me that will be impossible to perform my task using the console Impdisp tool. To work around this problem I am trying to generate the path I want using hypergraph and now I would like to export this coord. data (x,y,z) and use it as the /IMPDISP points. I heard its possible to do, but I don't know how to input the data in the starter deck. Please, find attached a simplified version of my path. Could you give me some hints, please? Thank you very much.
  12. Hi Andy, thank you very much for the hint. Now it is working perfectly, its rotating around the axis I wanted. Only one question about the movement, should I be able to do this linking the ball elements to a rigid body and imposing the disp. to this rigid body? Because I tried so, but then the radios (x coordinate) is increasing and I am getting a spiral. I want only one lap, returning to the original position after 360°.
  13. Hello Prakash, Thank you for the reply. Well, I've never done /TRANSFORM/ROT before, but I went through the guidelines and tried it. Still doesn't work. Keep spinning around it's own axis. May I share my model with you? I already attached the .hm Ball_impact3.hm
  14. Hi there, hope someone can help me. I am trying to make this ball rotate around the Z axis of the local coord. system created by me (skew in the middle of the plate). I don't know why, but the ball keep spinning around its own Z axis. I already tried creating RBody, cylindrical system, changing from /Skew to /Frame... nothing of that worked, it always rotates around its own axis. What am I doing wrong? Thank you.
  15. Hello James, thank you for your message. Well, as I said, I am not used to incremental analysis. I was told briefly once that I should use the impose displacement method to create this conic path (see picture below). Then I was following this...but please, let me know if it makes no sense. I don't know a method in Radioss or Hyperform to input this displacement. Do you have any hints?
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