Here’s a much simpler file showing the problem. It’s a block with no loads but it spontaneously rolls itself up.
Is there some way to restrict the contact search as @mdsimulationgroup suggested?
![selfcontact](https://canada1.discourse-cdn.com/free1/uploads/calculix/original/2X/6/6af49611dd92bb419520612948d47343dbd82e37.png)
*NODE
1,0.4,0,0
2,0.2,0,0.4
3,0.2,0,0.2
4,0.2,0.1,0.4
5,0,0,0
6,0.4,0,0.2
7,0,0.1,0
8,0,0,0.2
9,0.2,0.1,0.2
10,0,0.1,0.4
11,0.2,0.1,0
12,0.4,0.1,0
13,0.4,0.1,0.2
14,0.4,0.1,0.4
15,0.2,0,0
16,0,0,0.4
17,0,0.1,0.2
18,0.4,0,0.4
*ELEMENT,TYPE=C3D8,ELSET=FILM
1,3,6,13,9,2,18,14,4
2,5,15,11,7,8,3,9,17
3,15,1,12,11,3,6,13,9
4,8,3,9,17,16,2,4,10
*SURFACE,NAME=CONTACT_FACES(6)
1,S3
3,S3
2,S3
4,S3
*SURFACE,NAME=CONTACT_FACES
1,S5
3,S5
2,S5
4,S5
*MATERIAL,NAME=FILM
*ELASTIC,TYPE=ISOTROPIC
2500000000,0.333
*DENSITY
1300
*SOLID SECTION,ELSET=FILM,MATERIAL=FILM
*BOUNDARY
5,1,3,0
7,1,3,0
8,1,3,0
10,1,3,0
16,1,3,0
17,1,3,0
*CONTACT PAIR,INTERACTION=SI_1,TYPE=SURFACE TO SURFACE
CONTACT_FACES(6),CONTACT_FACES
*SURFACE INTERACTION,NAME=SI_1
*SURFACE BEHAVIOR,PRESSURE-OVERCLOSURE=LINEAR
1000000000000,1
*STEP,NLGEOM=YES
*STATIC
0.01,1,0,0
*NODE FILE,GLOBAL=YES
U
*END STEP