*HEADING
Spring instability
SI units (kg, m, s, N)
*NODE,NSET=NALL
1, 0.0, 0.0
2, 1.0, 0.0
3, 0.0, 1.0
4, 0.1, 1.0
*ELEMENT,TYPE=SPRINGA,ELSET=SPRING
1,1,2
*SPRING,ELSET=SPRING

1.0E5,
*ELEMENT,TYPE=MASS,ELSET=MASS
2,2
*MASS,ELSET=MASS  
5.0,
*ELEMENT,TYPE=T2D2,ELSET=TRUSS
3,3,4
*SOLID SECTION,ELSET=TRUSS,MATERIAL=MAT1
1.0,
*MATERIAL,NAME=MAT1
*DENSITY
 10.,
*ELASTIC
 1.0E4,0.0
*NSET,NSET=N2
2,
**
*STEP
Load the truss with constant velocity
Load the spring/mass with constant force
*DYNAMIC,EXPLICIT
,2.0
*BOUNDARY, TYPE=DISPLACEMENT
NALL,2,2
1,1,3
3,1,1
*BOUNDARY, TYPE=VELOCITY
4,1,1,1
*CLOAD
2,1,1.0E3
*BULK VISCOSITY
0.0,
*MONITOR,DOF=1,NODE=2
*OUTPUT, FIELD, VARIABLE=PRESELECT, NUMBER INTERVAL=1
*OUTPUT, HISTORY, TIME INTERVAL=1.0E-3
*NODE OUTPUT,NSET=N2
U,
*ENERGY OUTPUT
ETOTAL, ALLKE, ALLIE, ALLWK
**********************************
** OUTPUT FOR ABAQUS QA PURPOSES
**********************************
*FILE OUTPUT,NUMBER INTERVAL=5
*NODE FILE
U,
*END STEP

*HEADING
Spring instability
*NODE,NSET=NALL
1, 0.0, 0.0
2, 1.0, 0.0
3, 0.0, 1.0
4, 0.1, 1.0
*ELEMENT,TYPE=SPRINGA,ELSET=SPRING
1,1,2
*SPRING,ELSET=SPRING

1.0E5,
*ELEMENT,TYPE=MASS,ELSET=MASS
2,2
*MASS,ELSET=MASS
1760.0,
*ELEMENT,TYPE=T2D2,ELSET=TRUSS
3,3,4
*SOLID SECTION,ELSET=TRUSS,MATERIAL=MAT1
1.0,
*MATERIAL,NAME=MAT1
*DENSITY
 10.,
*ELASTIC
 1.0E4,0.0
*NSET,NSET=N2
2, 
**
*STEP
Load the truss with constant velocity
Load the spring/mass with constant force
*DYNAMIC,EXPLICIT
,2.0
*BOUNDARY, TYPE=DISPLACEMENT
NALL,2,2
1,1,3
3,1,1
*BOUNDARY, TYPE=VELOCITY
4,1,1,1
*CLOAD
2,1,1.0E3
*BULK VISCOSITY
0.0,
*MONITOR,DOF=1,NODE=2
*OUTPUT, FIELD, VARIABLE=PRESELECT, NUMBER INTERVAL=1
*OUTPUT, HISTORY, TIME INTERVAL=1.0E-3
*NODE OUTPUT,NSET=N2
U,
*ENERGY OUTPUT
ETOTAL, ALLKE, ALLIE, ALLWK
**********************************
** OUTPUT FOR ABAQUS QA PURPOSES
**********************************
*FILE OUTPUT,NUMBER INTERVAL=5
*NODE FILE
U,
*END STEP