Contact I

The rear bumper of a truck is modeled using shell elements. A solid, rigid bar is displaced into the bumper, causing plastic buckling of the support. Post-buckling response is determined.

LS-DYNA Implicit Workshop

Problem #6: Truck Bumper

Objectives
* Learn the behavior of contact interfaces in static implicit simulations.
* Learn how to set input parameters for implicit contact problems.

Problem Description
The rear bumper of a truck is modeled using shell elements. A solid, rigid
bar is displaced into the bumper, causing plastic buckling of the support.
Post-buckling response is determined.

Input Filename: bumper.k

Procedure
Copy the input file to your local directory. Using an editor, view the input
file and answer the following questions:

1. What type of contact interface is used?

2. Is the thickness of the shell elements considered?

Run the simulation and postprocess the results.

3. Why does the simulation stop?

Temporarily increase the default displacement convergence tolerance to
DCTOL=0.005 using keyword *CONTROL_IMPLICIT_SOLUTION, and repeat the simulation.
Stop the job after about 10 steps using the interactive command stop.
Postprocess the results, and magnify the displacements 10x.

4. What is wrong with the contact interface?

Activate the flag IGAPF=2 on optional card C in the *CONTACT_ keyword. Repeat the simulation.

5. Does the job run? Why?

To reduce the severity of the initial contact, decrease the contact penalty scale
factor using SLSFAC=0.01 on *CONTROL_CONTACT. Rerun the simulation.

6. Does the interface separate cleanly?

Plot the resultant interface force for the slave side of the interface.
Save the curve data.

7. Why is the curve not smooth?

Restore the convergence tolerance DCTOL to it's default value of 0.001, and repeat
the simulation. Compare the new interface force with the saved data.

Is the new curve smoother? Why?

*BOUNDARY_PRESCRIBED_MOTION_RIGID
*CONTACT_SURFACE_TO_SURFACE
*CONTROL_CONTACT
*CONTROL_IMPLICIT_AUTO
*CONTROL_IMPLICIT_GENERAL
*CONTROL_IMPLICIT_SOLUTION
*CONTROL_IMPLICIT_SOLVER
$*CONTROL_SHELL
*CONTROL_TERMINATION
*DATABASE_BINARY_D3PLOT
*DATABASE_GLSTAT
*DATABASE_RCFORC
*DEFINE_CURVE
*ELEMENT_SHELL
*ELEMENT_SOLID
*END
*KEYWORD
*MAT_PLASTIC_KINEMATIC
*MAT_POWER_LAW_PLASTICITY
*MAT_RIGID
*NODE
*PART
*SECTION_SHELL
*SECTION_SOLID
*TITLE

  *KEYWORD
  *TITLE
  truck rear bumper
  $
  $ units: in,lbf,sec
  $
  *CONTROL_TERMINATION
   0.0500000
  $
  $========1=========2=========3=========4=========5=========6=========7=========8
  $
  *CONTROL_IMPLICIT_GENERAL
  $   imflag       dt0      iefs   nstepsb      igso
           1    0.0001         0         0         0
  $
  *CONTROL_IMPLICIT_SOLUTION
  $  nlsolvr    ilimit    maxref     dctol     ectol     rctol     lstol
  $        0         0         0       0.0       0.0         0       0.0
           0         0         0     0.001       0.0         0       0.0
  $    dnorm   divflag   inistif   nlprint
           0         0         0         1
  $   arcctl    arcdir    arclen    arcmth    arcdmp
           0         0       0.0         0         0
  $
  *CONTROL_IMPLICIT_SOLVER
  $   lsolvr   prntflg    negeig
           0         0         0
  $
  *CONTROL_IMPLICIT_AUTO
  $    iauto    iteopt    itewin     dtmin     dtmax
           1       100         0    0.0001     0.001
  $
  $========1=========2=========3=========4=========5=========6=========7=========8
  $
  $ displace bumper 5 inches
  $
  *BOUNDARY_PRESCRIBED_MOTION_RIGID
           4         2         2         1 1.0000000         0 0.0000000 0.0000000
  *DEFINE_CURVE
           1         0 1.0000000 1.0000000 0.0000000 0.0000000
        0.00000000E+00      0.00000000E+00
        0.50000000E-01      5.00000000E+00
        2.00000000E-01      5.00000000E+00
  $ 
  $========1=========2=========3=========4=========5=========6=========7=========8
  $
  *CONTROL_CONTACT
  $   SLSFAC    RWPNAL    ISLCHK    SHLTHK    PENOPT    THKCHG     ORIEN
  $      0.0         0         0         1         0         0         0
        0.01         0         0         1         0         0         0
  $ (second card blank)
  
  $
  *CONTACT_SURFACE_TO_SURFACE                      
           4         3         3         3
   0.0000000 0.0000000 0.0000000 0.0000000 0.0000000         0 0.0000000 0.0000000
   0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000
  $
  $ optional card A
  $     soft
           0
  $
  $ optional card B
  $   penmax    thkopt    shlthk     snlog
         0.0         0         0         0
  $
  $ optional card C 
  $    igapf  1=sticky (DEFAULT), 2=no-stick
  $        0
           2
  $ 
  $========1=========2=========3=========4=========5=========6=========7=========8
  $
  *DATABASE_GLSTAT
        1e-4
  *DATABASE_RCFORC
        1e-4
  *DATABASE_BINARY_D3PLOT
        1e-4
  $ 
  $========1=========2=========3=========4=========5=========6=========7=========8
  $
  $ material properties
  $
  *MAT_PLASTIC_KINEMATIC
  $ 1020 steel bilinear material model
           1 7.30000-4 3.00000+7 0.3000000 30000.000 1.25000+5 0.0000000
   0.0000000 0.0000000 0.0000000
  *MAT_RIGID
           2 7.30000-4 3.00000+7 0.3000000 0.0000000 0.0000000 0.0000000          
  $ constrain all dof of frame
   1.0000000 7.0000000 7.0000000
   0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000
  *MAT_PLASTIC_KINEMATIC
  $ 1020 steel bilinear material model
           3 7.30000-4 3.00000+7 0.3000000 30000.000 1.25000+5 0.0000000
   0.0000000 0.0000000 0.0000000
  *MAT_RIGID
           4 7.30000-4 3.00000+7 0.3000000 0.0000000 0.0000000 0.0000000          
  $ allow only y dof of impactor
   1.0000000 6.0000000 7.0000000
   0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000
  *MAT_POWER_LAW_PLASTICITY
  $ alternate 1020 steel material model
           5 7.30000-4 3.00000+7 0.3000000     91353     .1911 
           0         0
  *SECTION_SHELL
           1         6 0.0000000 5.0000000 0.0000000 0.0000000         0
   0.2500000 0.2500000 0.2500000 0.2500000
  *SECTION_SHELL
           2         6 0.0000000 5.0000000 0.0000000 0.0000000         0
   0.2500000 0.2500000 0.2500000 0.2500000
  *SECTION_SHELL
           3         6 0.0000000 5.0000000 0.0000000 0.0000000         0
   0.1875000 0.1875000 0.1875000 0.1875000
  *SECTION_SOLID
           4
  $*CONTROL_SHELL
  $0,0,0,0,0,0,2
  $
  *PART
  support
           1         1         1
  *PART
  frame
           2         2         2
  *PART
  bumper
           3         3         3
  *PART
  impactor
           4         4         4
  $ 
  $ ---------------------------------------------------------------
  $
  *END