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A brief description of the example.
LS-DYNA Implicit Workshop

Problem #6: Truck Bumper

* 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

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?