Learning Forum

[lis29]

Hi, I'm new to Ansys and having trouble with this sim.

• The model consists of multiple parts held together by solid body bolts with simplified cylindrical shafts and T-nuts

  • Realistic contacts:

    • Nuts are bonded to bolt shafts with a tiny gap in between

    • Bolt head contacts with gussets are frictional, 0.2 coefficient

    • Nut contact with beam is frictional, 0.2 coefficient

    • Bolt shafts to gusset and beam walls is frictionless (basically the bolt hole)

    • Parts held together by physically modeled bolts have frictional contacts between them if they’re directly connected by a fastener and frictionless otherwise

  • All parts without physically modeled bolts are bonded

• Boundary conditions are two fixed supports where the model is cut off, plus a planar symmetry boundary condition

• 500N force upward

• Fixes attempted

  • Gradual load stepping from 50N to 500N over 10 steps

  • Increased substeps to 250 initial, 100 minimum, 500 max

  • Removing mesh controls and using a very fine mesh

  • Fixed red contacts in contact tool

  • Large deflection on and off

Any advice would be greatly appreciated!

Bolt geometry example (bolt head, gusset, nut, and 80/20 extrusion beam)

Failed convergence result

Original mesh

Meshing with no controls, 5 or 10 mm element size

Bolt locations shown using bolt pretensions, which I turned off at some point

[Dennis Chen]

Honestly, I doubt anyone can just see a few images and your description and figure out what's causing convergence issues lol.   There are a few steps you can take

1) turn on NR residual under solution information (set number to 2 or 4 instead of 0 at default), this allows you to narrow into where the convergence issues have occurred, which provides you with clues if it's related to contact or other factors

2) maybe copy paste your solve.out file's last few lines before the job terminated, that may provide some clues. 

Best of Luck

[lis29]

I turned NR residual to 4 and the simulation still crashed, but got much further than it did before. I'm attaching the solutions branch contact tool here, as well as the last few lines of the solver output file. What's the best way to evaluate what's causing the convergence issue? 

 

    EQUIL ITER  22 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.1951E-01
     DISP CONVERGENCE VALUE   =  0.1951E-01  CRITERION=  0.7500E-02
     LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC =  0.1951E-01
     FORCE CONVERGENCE VALUE  =   1.808      CRITERION=   4.455     <<< CONVERGED
    Writing NEWTON-RAPHSON residual forces to file: file.nr001
    EQUIL ITER  23 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.2220E-01
     DISP CONVERGENCE VALUE   =  0.2220E-01  CRITERION=  0.8610E-02
     LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC =  0.2220E-01
     FORCE CONVERGENCE VALUE  =   1.954      CRITERION=   4.546     <<< CONVERGED
    Writing NEWTON-RAPHSON residual forces to file: file.nr002
    EQUIL ITER  24 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.2525E-01
     DISP CONVERGENCE VALUE   =  0.2525E-01  CRITERION=  0.9872E-02
     LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC =  0.2525E-01
     FORCE CONVERGENCE VALUE  =   7.778      CRITERION=   4.638   
    Writing NEWTON-RAPHSON residual forces to file: file.nr003
    EQUIL ITER  25 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.2590E-01
     DISP CONVERGENCE VALUE   =  0.2590E-01  CRITERION=  0.1113E-01
     LINE SEARCH PARAMETER =   1.000     SCALED MAX DOF INC =  0.2590E-01
     FORCE CONVERGENCE VALUE  =   6.809      CRITERION=   4.647   
    Writing NEWTON-RAPHSON residual forces to file: file.nr004
    EQUIL ITER  26 COMPLETED.  NEW TRIANG MATRIX.  MAX DOF INC=  0.2953E-01

 *** ERROR ***                           CP =   15009.078   TIME= 08:13:14
 Solution not converged at time 4.14475 (load step 5 substep 5).        
  Run terminated.   

 

 

After this, there were a number of summary for contact pairs, and then this:

         R E S T A R T   I N F O R M A T I O N

 REASON FOR TERMINATION. . . . . . . . . .UNCONVERGED SOLUTION                   
 FILES NEEDED FOR RESTARTING . . . . . . .  file0.Rnnn
                                            file.ldhi
                                            file.rdb
 TIME OF LAST SOLUTION . . . . . . . . . .  4.1437   
    TIME AT START OF THE LOAD STEP . . . .  4.0000   
    TIME AT END OF THE LOAD STEP . . . . .  5.0000   
 NOTE: FOR CONVERGING SOLUTIONS, ADDITIONAL EQUILIBRIUM ITERATIONS MAY BE
       ADDED IN THE RESTART (NEQIT COMMAND) USING THE RESTART FILE file0.Rnnn                                                                                                                                                                                                                                                         

 ALL CURRENT MAPDL DATA WRITTEN TO FILE NAME= file.db
  FOR POSSIBLE RESUME FROM THIS POINT

 

 NUMBER OF WARNING MESSAGES ENCOUNTERED=         17
 NUMBER OF ERROR   MESSAGES ENCOUNTERED=          4

 

 ***** PROBLEM TERMINATED BY INDICATED ERROR(S) OR BY END OF INPUT DATA *****

[Dennis Chen]

under solution information, there should be contours that let you know where the convergence issue occurred.  From there, you can further troubleshoot. 

[lis29]

Do you mean visual contours like in the total deformation results or some information in the solver output text file? The total deformation result looked like this:

In the animation, the deformation looks really good until the part highlighted in orange and red just detaches upward from the rest of the body at time step 5.