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Andy

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Andy last won the day on September 8

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  1. Hi @fcolomb Sorry for the late reply. Concerning run time,, you can try applying the load faster then the actual forming. This is often still valid if the kinetic energy doesn't get too high. Next, to increase the time step you could use /DT/NODA/CST and define a higher timestep which will add mass in the model. Alternatively, you can artificially increase the density of the whole part to increase the time step. Last instead of using /DT/NODA/CST or increasing the density, you could try using advanced mass scaling. /DT/AMS in the engine and /AMS in the starter. Using AMS you can normally increase the timestep by a factor of 10 - 20 time your original timestep. The AMS method requires more computations so your simulation will run approximately 4-10 time faster. With all these methods, I would recommend running the model a short amount of time with and without these options and compare the results to make sure these options give good results. The amount of mass add using /DT/NODA/CST or using the AMS is model dependent so you have to validate using these options. Last concerning the energy error. I suspect that is coming from the friction which is included in the contact energy. If you have high contact energy relative to your total energy you can get a larger error. Plot the contact energy and compare to the TTE: Translational total energy. If this is true then it is OK to ignore the energy error. Thanks, Andy
  2. Hi, Sorry for the late reply. I agree it seems the material could have too high of a yield stress. Ideally you would have a stress strain test done on the actual material used to make the part and then use that data in your simulation. If you are unable to do that, then you could try using LAW2 and reducing the yield stress to see if that helps. I also wonder if a finer mesh would change the deformation and buckling behavior of the model. Thanks, Andy
  3. Andy

    Density in material PLAS_JOHNS

    Hi, I doubt this is an issue with the time step. Radioss calculates the highest timestep based on the desnity, modulus and mesh size as mentioned by Nachiket Kadu. The change in density/mass could cause the part to fail sooner. It depends how much mass you were adding before and how close the part was to failing. As already suggest check the kinetic energy in both models. If it is a quasi static test then the kinetic energy should remain low in both models. The importance of mass in the simulation is the same as the importance of mass in the test. In both the test and the simulation if the mass is different the physic and energy will be different which can cause a difference in the results. Thanks, Andy
  4. Andy

    Friction in RADIOSS

    Hi, In the 2018.0.1 which is scheduled to be released soon, we will have a new /FRICTION option which can to the same thing as *DEFINE_FRICTION. At this time we do not have any way to define friction in two principal directions. What is the use case for this? Thanks, Andy
  5. Hi, I reviewed your files and ran them a little while. I think the motion is caused by the lack of contact and deformation of the plane. The tool doesn't seem to be hitting the plate very much. The contact gap between your tool and sheet is defined as a constant value of Gapmin=0.01 because Igap=1000. Is the location of tool correct for that small of a contact gap? I would suggest changing to Igap=1 and then the half the thickness of the tool and sheet (more like the actual physical part) will be used to calculate the contact gap between the parts. The initial motion of the tool doesn't cause any plastic strain which seems strange to me. Is this correct? For more accurate stress results set /PROP/SHELL, N=5, I_thick=1 and I_plas=1. You can also make a 2nd contact where the tool is the master and the sheet is the slave. We call this a symmetric contact and with these two contact you basically have a suface to surface contact. Last, I would recommend making your sheet mesh more coarse which will increase the time step of the model and reduce the run time. This will allow you to confirm motion of the tool and contact and get approximate results in a shorter amount of time. Then once those are correct you can go back to your original mesh. Thanks, Andy
  6. Hi, I am glad it is working. There are a few different ways to do the spring back calculation in Radioss. I would suggest running HyperForm and looking at the options in the engine files it creates and using those same commands. There is a tutorial HF-3070: Springback Analysis. It looks like they are saving a state file (*.sta) at the end of the first simulation and then creating a second analysis and include the *.sta file from the first analysis. To create a state file see the /STATE/DT help and comments. You can either rerun your simulation with the state file outputs included or if you still have your *.rst files created at the end of the simulation you could create a second engine file with the state outputs in it and then run the simulation for a short amount of time. This is how to continue a simulation with a second engine file. How to create a second engine file. If the first engine file is named runname_0001.rad. When creating a second engine file the number is increased by 1 for the next engine file to a maximum of 9999 engine files. So, the second engine file would be named runname_0002.rad. To avoid a warning message, the engine file number should also match the Run Number listed in the keyword, /RUN. Example: First Engine file, TensileTest_0001.rad /RUN/TensileTest/1 5.0 /TFILE 0.005 /ANIM/DT 0. 0.5 /ANIM/TENS/STRESS/MEMB /PRINT/-1000 /DT/NODA/CST 0.9 1e-6 Example: Second Engine file TensileTest_0002.rad with changed options. /RUN/TensileTest/2 10.0 /TFILE 0.0005 /ANIM/DT 0. 0.05 /ANIM/TENS/STRESS/MEMB /PRINT/-10 /DYREL 1.00 0.002 /DT/NODA/CST 0.9 1e-7
  7. I was referring to /IMPDISP. /IMPDISP/FGEO moves a set of nodes from a start location to an end location linearly. Your motion doesn't sound linear so I am guessing /IMPDISP/FGEO would not work. My assumption is that the ball for SPF would be rigid so you could create a /RBODY of the ball mesh. Then on the master node of the /RBODY define 3 /IMPDISP and 3 /FUNCT one for each direction (x, y, z). Each /FUNCT would be a be displacement versus time. Like this, /IMPDISP/1 x displacement # Ifunct DIR Iskew Isensor Gnod_id Frame Icoor 224 X 0 0 2858 0 0 # Scale_x Scale_y Tstart Tstop 1 1 0 0 /IMPDISP/2 Y displacement # Ifunct DIR Iskew Isensor Gnod_id Frame Icoor 225 Y 0 0 2858 0 0 # Scale_x Scale_y Tstart Tstop 1 1 0 0 /IMPDISP/1 Z displacement # Ifunct DIR Iskew Isensor Gnod_id Frame Icoor 226 Z 0 0 2858 0 0 # Scale_x Scale_y Tstart Tstop 1 1 0 0 /GRNOD/NODE/2858 IMPDISP_group_2860_of_NODE 3235 /FUNCT/224 X displacment # Time displacement 0 0 1 0.5 2 1.5 3 3.5 ..... /FUNCT/225 Y displacment # Time displacement 0 0 1 0.5 2 1.5 5 5.5 .... /FUNCT/226 Z displacment # Time displacement 0 0 1 0.5 2 1.5 2.6 4.5 ....
  8. Hi, If you can export your x, y, z data as a function of time. Then you could define 3 /IMPDISP, one for each direction with a time versus displacement function for each direction. Does the ball also need to rotate while translating in the x, y, z? Is this for Incremental sheet forming (or ISF, also known as Single Point Forming) ? Thanks, Andy
  9. Hi, /TRANSFORM/ROT will rotate the initial model but that will not make the ball have an imposed movement during the simulation. I believe in /IMPDISP you need to set Icoor=1 and define a local /SKEW Now the x, y, z DIR are. x= radial direction (r), y= azimuthal angular direction ( θ ) z= longitudinal direction (Z) So you need reorient your local system so that the local z direction is the axis you rotate about. Then set DIR=Y to get rotation. I have attached a sample model. Thanks, Andy rotate_0000.rad rotate_0001.rad
  10. Using LAW42, The Mooney Rivlin parameters C10 and C01 can be used to calculate mu and alpha, mu1=2*C10 mu2=-2*C01 alpha1=2 alpha2=-2 For Neo-Hooken use. mu1=2*C10 mu2=0.0 alpha1=2 alpha2=0.0 Last as suggested by Prakash for Yeoh use LAW94 which was added in RADIOSS 2017.2. Thanks, Andy
  11. Andy

    Reaction Force at Time Zero

    I believe this is caused by using the imposed displacement. If you differentiate your imposed displacement curve you will get a non-zero velocity curve at T=0. Thus RADIOSS has to apply a force to get that initial velocity. You could try an imposed velocity and see if that gives you the zero force at t=0. If not and you have contact then maybe the issue is initial penetrations. Usually the initial force caused by imposed displacements does not change the results later in the simulation as compared to using an imposed velocity.
  12. Andy

    Issue with Mat Law 42

    Hi Jonas, For solid parts using LAW42 it is recommended to use Ismtr=10 in /PROP/SOLID. Is is written in the comments in /PROP/SOLID. This probably won't fix the tied contact problem though. The 1157 warning means that there are slave nodes of your tied contact that are not able to be projected to a master surface so they are removed from the tied contact. Please check and see which nodes this happens with to see if these are the nodes that are not being tied correctly. Thanks, Andy
  13. Andy

    Failure /FAIL/JOHNSON and /FAIL/TAB1

    Hi, No, you do not need to use /fail/johnson and fail/tab1 together to get the effect of the lode angle. The /FAIL/TAB1 includes the effect of stress triaxiality and lode angle. This is Card 3 in /FAIL/TAB1 from the manual and there is an example for solids in the /FAIL/TAB1 manual. To use /FAIL/TAB1 with lode angle you need test data showing the plastic failure strain at different triaxiality values and different lode angles. Do you have this kind of test data? If you only have plastic failure strain versus triaxiality data and no lode angle then you can still use /FAIL/TAB1 with only defining of plastic strain versus triaxiality. The /FAIL/TAB1 manual has an example for shells without lode angle which could also still be used for solids. It really depends on what failure data you have available. For years engineers got reasonable results by just entering one plastic strain at failure in a material law and it didn't matter the stress triaxality or lode angle (for solids). Now there are more advanced methods with the /FAIL options. Going from most basic to more complex, I would rank the failure models like this: Enter 1 plastic strain at failure value in a material law like /MAT/LAW2 or /MAT/LAW36 /FAIL/JOHNSON /FAIL/BIQUAD (nice balance of easy with advanced features) /FAIL/TAB1 To use more advanced failure models you need to have data to use with them. Even so I would start basic and make sure your simulation is reasonable and then move to a more complex model if you have data for that model. Thanks, Andy
  14. Andy

    Issue with Mat Law 42

    I assume the LAW42 material is the disc that is colored and Vertebrae is grey. Are there any warning messages in your *0.out file? Which is part is slave and which part is master? Is there other TYPE7 contact? What material is the vertebrae and what element (they look like tetra) but are they 1st or 2nd order? Thanks, Andy
  15. Andy

    Failure /FAIL/JOHNSON and /FAIL/TAB1

    Hi, /FAIL/JOHNSON and /FAIL/TAB1 are very similar and work on the same basic idea where a plastic failure strain versus stress triaxility curve has to be defined. In /FAIL/JOHNSON the plastic failure strain versus stress triaxility is created by defining the D1, D2 , D3 parameters which are used in the Johnson-Cook equation. In /FAIL/TAB1, the user defines a /FUNCT which represents the plastic failure strain versus stress triaxility curves. In /FAIL/TAB1 you can define different /FUNCT which represent different plastic failure strain versus stress triaxility curves at different strain rates. In /FAIL/JOHNSON the strain rate affect is defined via the D4 parameter input. So you should not need to use both /FAIL/TAB1 and /FAIL/JOHNSON in the same model since they do the same thing. If you have a plastic strain at failure for compresion (trixaility= -1/3) shear ((trixaility= 0) and tension (trixaility= 1/3) then you can do a curve fit to calculate the D1, D2, and D3 paramters. You could also look at /FAIL/BIQUAD which uses two quadratic equations to define the plastic failure strain versus stress triaxility curves and has some built in starting values for some different materials. Thanks, Andy
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