Hi, there,
I am writing to ask for help in contact simulation.
I am simulating a punch process. A disc, resting on a ring
die(rigid), is pressed down at the center by 2mm by a ball(rigid). This
simulation should include elastic and plastic and contact
behaviour. I have run a few simulations with different
friction coefficients to see the influence of the friction
on the process. The simulations with friction coefficients
of 0.2-0.5 were finished with no warning or error message.
But the simulations with friction coefficients of 00 and 0.1
produced some warning messages, though the computation were finished.
The messages from the simulation with a friction of 0.0
were:
1. Overclosure of contact surfaces, sdiskl and sball is too
servere, cutback will result...(No. of warning: 1)
2. The system matrix has 18 nagetive eigenvalues....(1)
3. Elements 801, 405 and 606 are distorting so much that
they turn inside out...(3)
The messages from the simulation with a friction of 0.1 were
1. Overclosure of contact surfaces, sdiskl and sball is too
servere, cutback will result...(1)
2. The system matrix has 18 nagetive eigenvalues....(3)
3. Elements 801, 1201 1602 and 1801 are distorting so much
that they turn inside out...(5)
4. The strain increment has exceeded fifty times the strain
to cuase first yield at 14(12) points (2)
5. Convergence judged unlikely. Increment will be attempted
again with a time increment of 0.12500
For overclosure problem, it is usually induced by incorrect definition
of the contact surfaces, i.e. the normals of the surface point inwards
(of the surface). However I have checked the surface normals, which were
fine.
The input files for all 6 simulations are exactly the same
except the friction coefficients, which has been attached below.
I would appreciate greatly for any advice and suggestion to
explain the causes of the warnings and the effect on the results,
and to overcome these warnings.
Thank you very much for all your help in advance.
Best regards.
Tian
==============================================================
*HEADING
CASE STUDY , friction=0, dir_corner=0.005mm
** CASE : (disk: r=0.015m, thickness=0.001m, rigid_ball_
** head_r=0.003m, die_hole_r=0.01m, die_out_r=0.017m, die=rigid)
** edges of disk rest on the die, pressing down by 2mm, 10 layers of, **
total 1200 CAX4R elements
*PREPRINT, MODEL=NO, HISTORY=NO
*NODE
1, 0.0, 0.0
41, 0.005, 0.0
81, 0.01, 0.0
121, 0.015, 0.0
2001, 0.0, 0.001
2041, 0.005, 0.001
2081, 0.01, 0.001
2121, 0.015, 0.001
10000, 0.0, 0.004
20000, 0.0135, -0.0025
*NGEN, NSET=LEFT
1, 2001, 200
*NGEN, NSET=MID
41, 2041, 200
*NGEN, NSET=RIGHT
81, 2081, 200
*NGEN, NSET=FRIGHT
121, 2121, 200
*NFILL, NSET=NLEFT, BIAS=0.98
LEFT, MID, 40
*NFILL, NSET=NRIGHT, BIAS=1.020408
MID, RIGHT, 40
*NFILL, NSET=NFRIGHT, BIAS=0.98
RIGHT, FRIGHT, 40
*NSET, NSET=NALL
NLEFT, NRIGHT, NFRIGHT
*NSET, NSET=MIDLAYER, GENERATE
1001, 1121
*ELEMENT, TYPE=CAX4R
1, 1, 2, 202, 201
*ELGEN, ELSET=EDISK
1, 10, 200, 200, 120, 1, 1
*ELSET, ELSET=TOP
1801, 1920
*ELSET, ELSET=ELEFT, GENERATE
1801, 1840, 1
*ELSET, ELSET=ERIGHT, GENERATE
70, 120, 1
*SURFACE DEFINITION, NAME=SDISKL
ELEFT,
*SURFACE DEFINITION, NAME=SDISKR
ERIGHT,
*RIGID SURFACE, NAME=SBALL, TYPE=SEGMENTS, REF NODE=10000, FILLET
RADIUS=0.0005
START, 0.003, 0.004
CIRCL, 0.0, 0.001, 0.0, 0.004
*RIGID SURFACE, NAME=SDIE, TYPE=SEGMENTS, REF NODE=20000, FILLET
RADIUS=0.0005
START, 0.01, -0.003
LINE, 0.01, 0.0
LINE, 0.016, 0.0
*CONTACT PAIR, INTERACTION=ROUGH
SDISKL, SBALL
*CONTACT PAIR, INTERACTION=ROUGH
SDISKR, SDIE
*SURFACE INTERACTION, NAME=ROUGH
*FRICTION
0.0
*SOLID SECTION, ELSET=EDISK, MATERIAL=STEEL
*MATERIAL, NAME=STEEL
*ELASTIC
206.8E9, 0.3
*PLASTIC
400.E6, 0.0E-2
420.E6, 2.0E-2
500.E6, 20.0E-2
600.E6, 50.E-2
** first step,
*RESTART, W, F=20
*STEP, INC=10, NLGEOM, UNSYMM=YES
let the die contact with the disk
*STATIC
1., 1.
*BOUNDARY
LEFT, XSYMM
10000, 1, 1
10000, 2, 2
10000, 6, 6
20000, 1, 1
20000, 2, 2, 0.00000001
20000, 6, 6
MIDLAYER, 2, 2
*PRINT, RESIDUAL=NO, F=10
*EL PRINT, F=0
*NODE FILE, F=1000
U, RF,CF
*END STEP
** second step
STEP, INC=10, NLGEOM, UNSYMM=YES
let the punch contact with the disk
STATIC
1., 1.
BOUNDARY, OP=NEW
LEFT, XSYMM
1000, 1, 1
1000, 2, 2,-0.00000001
1000, 6, 6
2000, 1, 1
2000, 2, 2, 0.00000001
2000, 6, 6
**MIDLAYER, 2, 2
**END STEP
** third step
*STEP, INC=10, NLGEOM, UNSYMM=YES
remove the constraints on the midplane of the disk
*STATIC
1., 1.
*BOUNDARY, OP=NEW
LEFT, XSYMM
10000, 1, 1
10000, 2, 2, 0.00000001
10000, 6, 6
20000, 1, 1
20000, 2, 2, 0.00000001
20000, 6, 6
*END STEP
** fourth step
*STEP, INC=9999, NLGEOM, UNSYMM=YES
push punch down by 2 mm
*STATIC
0.05, 100.,,0.5
*BOUNDARY, OP=NEW
LEFT, XSYMM
10000, 1, 1
10000, 2, 2, -0.002
10000, 6, 6
20000, 1, 1
20000, 2, 2, 0.00000001
20000, 6, 6
**DLOAD
** TOP, P3, 78.0
*MONITOR, NODE=10000, DOF=2
*EL PRINT, F=200
PEEQ, PE
*NODE PRINT, F=200
U
*EL FILE,ELSET=EDISK
*NODE FILE, F=10
U, RF,CF
*END STEP
==============================================
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