Introduction

LS-DYNA Implicit Workshop

Problem #4: Elastic-Plastic Tensile Test

Objectives
* Learn how to observe convergence behavior of nonlinear
equilibrium iterations.
* Learn to use automatic time step control for nonlinear
problems.
* Learn the benefits of force vs. displacement controlled
simulations.

Problem Description
A static tensile test is simulated using shell elements and
a nonlinear, elastic-plastic material model. One end of the
specimen is constrained, while concentrated nodal loads are
applied at the other end. Uniform stresses develop in the
narrowed center section.

Input Filename: tensile2.k

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

1. Which material model is used? What is the yield stress?
2. How is load applied?
3. How many steps are used to apply the load?

Run the input deck. Does the job run to completion?

4. At what time does the solution begin to struggle?

Using the postprocessor, plot the X-displacement of an end
node vs. time.

5. What is happening at the time shown above?

6. max end displacement max eff. stress
max eff. strain

Activate the nonlinear print flag to get more information
about the nonlinear solution process, and repeat the simulation.

7. What two methods are available for this?

8. How many cycles are used in the simulation?

Switch from load control to displacement control, and repeat
the simulation (Hint: helpful keywords are commented out in
the original input deck). Using the postprocessor, again
plot the X-displacement of an end node.

9. max end displacement max eff. stress
max eff. strain

10. Why is this problem easier to solve?

Return to the original input deck, and activate automatic time
step control (IAUTO=1 on the keyword *CONTROL_IMPLICIT_AUTO).
Use 200 as the optimum iteration count, and set the maximum
step-size to 0.050. Repeat the simulation.

11. What happens?

12. max end displacement max eff. stress
max eff. strain

Using the ASCII menu, load the GLSTAT database and plot the
step size vs. time.

13. When does the step size change? Why?