C3D8I fails patch test

[victorkemp]

Errors in stress and strain of around 50%. The paper it's based on (Taylor, Beresford, Wilson 1976) says it passes this test so it must be a bug in the implementation.

Solution Description of patch test Input file

*NODE
1,0.249,0.342,0.192
2,0.826,0.288,0.288
3,0.85,0.649,0.263
4,0.273,0.75,0.23
5,0.32,0.186,0.643
6,0.677,0.305,0.683
7,0.788,0.693,0.644
8,0.165,0.745,0.702
9,0,0,0
10,0,1,0
11,1,1,0
12,1,0,0
13,0,0,1
14,1,0,1
15,1,1,1
16,0,1,1
*ELEMENT,TYPE=C3D8I,ELSET=DEFAULT
1,1,2,3,4,5,6,7,8
2,1,4,3,2,9,10,11,12
3,5,6,7,8,13,14,15,16
4,1,2,6,5,9,12,14,13
5,2,3,7,6,12,11,15,14
6,3,4,8,7,11,10,16,15
7,4,1,5,8,10,9,13,16
*MATERIAL,NAME=MATERIAL
*ELASTIC,TYPE=ISOTROPIC
1000000,0.25
*SOLID SECTION,ELSET=DEFAULT,MATERIAL=MATERIAL
*STEP
*STATIC
*BOUNDARY
9,1,,0
9,2,,0
9,3,,0
10,1,,0.0005
10,2,,0.001
10,3,,0.0005
11,1,,0.0015
11,2,,0.0015
11,3,,0.001
12,1,,0.001
12,2,,0.0005
12,3,,0.0005
13,1,,0.0005
13,2,,0.0005
13,3,,0.001
14,1,,0.0015
14,2,,0.001
14,3,,0.0015
15,1,,0.002
15,2,,0.002
15,3,,0.002
16,1,,0.001
16,2,,0.0015
16,3,,0.0015
*EL FILE
S,E
*END STEP

[OliverKunc]

Original source: https://doi.org/10.1016/0168-874X(85)90003-4