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Basics II

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. Download is available in the download section of this document

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?

Keywords

*BOUNDARY_PRESCRIBED_MOTION_NODE
*BOUNDARY_SPC_NODE
*CONTROL_IMPLICIT_AUTO
*CONTROL_IMPLICIT_GENERAL
*CONTROL_IMPLICIT_SOLUTION
*CONTROL_IMPLICIT_SOLVER
*CONTROL_SHELL
*CONTROL_TERMINATION
*DATABASE_BINARY_D3PLOT
*DATABASE_ELOUT
*DATABASE_EXTENT_BINARY
*DATABASE_GLSTAT
*DATABASE_HISTORY_SHELL
*DATABASE_NODAL_FORCE_GROUP
*DATABASE_NODFOR
$*DEFINE_CURVE
*DEFINE_CURVE
*ELEMENT_SHELL
*END
*KEYWORD
*LOAD_NODE_POINT
*MAT_TRANSVERSELY_ANISOTROPIC_ELASTIC_PLASTIC
*NODE
*PART
*SECTION_SHELL
*SET_NODE_LIST
*TITLE

Reduced Input

  *KEYWORD
  *TITLE
  implicit tensile test, elastic-plastic material 
  $
  $ test coupon, 200 mm long, 20 mm width, 2.67 mm thickness, 50.8 mm gauge length
  $ 
  $ units; mm, s, ton, N
  $
  $ By A. Tabiei
  $
  $---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
  $
  *CONTROL_TERMINATION
      1.0000
  $
  $========1=========2=========3=========4=========5=========6=========7=========8
  $
  *CONTROL_IMPLICIT_GENERAL
  $   imflag       dt0      iefs   nstepsb      igso
           1      0.01         0         0         0
  $
  *CONTROL_IMPLICIT_SOLUTION
  $  nlsolvr    ilimit    maxref     dctol     ectol     rctol     lstol
           0         0         0       0.0       0.0         0         0
  $    dnorm   divflag   inistif   nlprint
           0         0         0         0
  $
  *CONTROL_IMPLICIT_SOLVER
  $   lsolvr   prntflg    negeig
           0         0         0
  $
  *CONTROL_IMPLICIT_AUTO
  $    iauto    iteopt    itewin     dtmin     dtmax
           0         0         0       0.0       0.0
  $        1       200         0       0.0      0.05
  $
  $========1=========2=========3=========4=========5=========6=========7=========8
  $
  *DATABASE_BINARY_D3PLOT
      0.0100
  *DATABASE_EXTENT_BINARY
  $    neiph     neips    maxint    strflg    sigflg    epsflg    rltflg    engflg
                                         1         1                                  
  $   cmpflg    ieverp    beamip
                      
  $
  *DATABASE_GLSTAT
      0.0001
  $
  *DATABASE_NODFOR
      0.0001
  *DATABASE_NODAL_FORCE_GROUP
          2
  *SET_NODE_LIST
          2
  30,31,32,33,38,39
  $
  $
  *DATABASE_ELOUT
      0.0001
  *DATABASE_HISTORY_SHELL
  71,72,73,74,75,76,77,78
  79,80
  $
  $---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
  *CONTROL_SHELL
  $   WRPANG    ITRIST     IRNXX    ISTUPD    THEORY       BWC     MITER      PROJ
           0         0         0         0         0         0         1         0
  $
  *SECTION_SHELL
  $       ID    elform      
           1        16
  $       t1        t2        t3        t4
   2.670E-00 2.670E-00 2.670E-00 2.670E-00
  $
  *PART
  shell tensile strip
           1         1         1
  $
  $---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
  $
  *MAT_TRANSVERSELY_ANISOTROPIC_ELASTIC_PLASTIC
  $      MID        RO         E        PR      SIGY      ETAN         R     HLCID
           1 0.780E-08 0.207E+06 0.280E+00 0.200E+03 0.572E+03 0.140E+01        13
  $
  $ hardening curve: effective stress vs. effective plastic strain
  *DEFINE_CURVE
          13
            0.00000000               200.0
            0.00006657               200.5
            0.00013650               201.1
            0.00020990               201.6
            0.00028690               202.2
            0.00036780               202.7
            0.00045280               203.2
            0.00054200               203.8
            0.00091670               205.8
            0.00136600               207.9
            0.00190600               210.0
            0.00255300               212.1
            0.00472900               217.2
            0.00654700               220.3
            0.00891000               223.4
            0.03259000               250.8
            0.04616000               270.5
            0.06516000               291.5
            0.09176000               313.8
            0.13830000               342.4
            0.20810001               373.2
            0.31279999               406.2
            0.46990001               441.6
            0.70560002               479.7
  $
  $---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
  $
  *LOAD_NODE_POINT
         204         1         3         1
         205         1         3         1
         206         1         3         1
         207         1         3         1
         212         1         3       0.5
         213         1         3       0.5
  *DEFINE_CURVE
           3
                  0.00                0.00
                  1.00             2000.00
                  2.00             2000.00
  $
  $---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
  $
  $*BOUNDARY_PRESCRIBED_MOTION_NODE
  $       204         1         2         4      1.00
  $       205         1         2         4      1.00
  $       206         1         2         4      1.00
  $       207         1         2         4      1.00
  $       212         1         2         4      1.00
  $       213         1         2         4      1.00
  $*DEFINE_CURVE
  $         4
  $                0.00                0.00
  $                1.00                7.00
  $                2.00                7.00
  $---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
  $
  *BOUNDARY_SPC_NODE
          30         0         1         1         1         1         1         1
          31         0         1         1         1         1         1         1
          32         0         1         1         1         1         1         1
          33         0         1         1         1         1         1         1
          38         0         1         1         1         1         1         1
          39         0         1         1         1         1         1         1
         204         0         0         1         1         0         0         0
         205         0         0         1         1         0         0         0
         206         0         0         1         1         0         0         0
         207         0         0         1         1         0         0         0
         212         0         0         1         1         0         0         0
         213         0         0         1         1         0         0         0
  $
  $---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
  $
  *END

Figures

image01.gif

image02.gif

Animated Result

Result