The nonlinear spring does not behave properly

1

I tried to compute spring2.inp from the test cases. I only modified the force-displacement curve, but the displacement result becomes Infinity. What could be the possible reason？Any help is appreciated.

The input is,

**
** Structure: spring.
** Test objective: static calculation of a nonlinear spring.
**
*NODE,NSET=NALL
1,0.,0.,0.
2,1.,0.,0.
*ELEMENT,TYPE=SPRINGA,ELSET=EALL
1,1,2
*BOUNDARY
1,1,3
2,2,3
*SPRING,ELSET=EALL,NONLINEAR

0.,0.
1.,1.
20.,2.
*STEP,NLGEOM
*STATIC
*CLOAD
2,1,11.
*NODE PRINT,NSET=NALL
U
*END STEP

And the output is:
displacements (vx,vy,vz) for set NALL and time 0.1000000E+01

     1  0.000000E+00  0.000000E+00  0.000000E+00
     2     -Infinity  0.000000E+00  0.000000E+00
2

imagen
imagen685×505 13.7 KB

A very sharp kink for default convergence parameters, try with:

*STEP,NLGEOM
*STATIC
0.01,1.0
3

It works. Thank you.