HYPERFOAM Model Issue

Viertelstein · September 23, 2026, 11:12am

Hi All,
We discussed my set-up with latex foam in https://prepomax.discourse.group/. Same setting works well in ABAQUS, but not with CalculiX, thus, I have been asked to open an additional discussion here, the more so, I would like to share some data to support this community to find a solution.
Best,
Viertelstein
PS: I assume uploads of ASCII files will be possible once the topic is published?

Here are some basics about the samples tested from Kunststoffzentrum Leipzig (Original German, English translation):

Druckspannungswert (Stauchhärte) CV40 nach DIN EN ISO 3386-1:2015-10
Latexschaum Probekörper 50 mm × 50 mm × 25 mm
Das Probenmaterial wurde vor Beginn der Prüfungen mehr als 24 h bei Normklima 23/50 Klasse 2 nach DIN EN ISO 291:2008-08 gelagert.
Druckspannungswert (Stauchhärte) CV40 nach DIN EN ISO 3386-1:2015-10
Prüfeinrichtung: Universalprüfmaschine Zwicki Z2,5 TH, Zwick GmbH & Co. KG|
Probekörper: 50 mm × 50 mm × 25 mm , Anzahl: 7
Prüfgeschwindigkeit: Setzzyklus: 100 mm/min, Messzyklus: 100 mm/min, Prüftemperatur: 23°C

Compressive stress value (indentation hardness) CV40 according to DIN EN ISO 3386-1:2015-10;
latex foam test specimens 50 mm × 50 mm × 25 mm.
Prior to testing, the sample material was conditioned for more than 24 hours in a standard atmosphere (23/50, Class 2) according to DIN EN ISO 291:2008-08.
Compressive stress value (indentation hardness) CV40 according to DIN EN ISO 3386-1:2015-10;
testing equipment: Zwicki Z2.5 TH universal testing machine (Zwick GmbH & Co. KG);
test specimens: 50 mm × 50 mm × 25 mm, quantity: 7;
testing speed: pre-loading cycle: 100 mm/min, measurement cycle: 100 mm/min; test temperature: 23°C.

Viertelstein · September 23, 2026, 11:16am

Calc_em · September 23, 2026, 12:10pm

Most importantly, I’d like to add that I’ve noticed a potential bug with this material model and I would appreciate if someone could confirm it:

hyperfoam ccx

Here’s the input deck: Dropbox

Viertelstein · September 23, 2026, 12:24pm

I can fully confirm, since 2 days this happen to me. However all other conditions are, the edges stay fixed.

Calc_em · September 23, 2026, 12:39pm

It seems to be a fault of the hyperfoam material model. It doesn’t seem to happen with hyperelasticity. And it works normally with the same input deck in Abaqus:

Viertelstein · September 23, 2026, 12:44pm

I heard/saw that before. With ABAQUS it looks pretty well, but NOT with CALCULIX. Someone mentioned it is an internal error (bug?).

Calc_em · September 23, 2026, 12:48pm

Yeah, it’s for the CalculiX community to show that the hyperfoam model seems to have some issues. Looks like a bug, but should be confirmed by someone. And we may need a minimum reproducible example like a small cube.

Viertelstein · September 23, 2026, 12:51pm

Calc_em · September 23, 2026, 1:11pm

@Viertelstein For the next time, it would be good if you could also share the CalculiX .inp file exported from the PrePoMax file (since many users here work in other preprocessors). But I’ve already shared the model showing the bug above (via Dropbox) so no worries for now.

Btw. to clarify, I’m FEAnalyst from the PrePoMax forum.

Calc_em · September 23, 2026, 1:41pm

Issue shown with just two elements:

Input file:

*Node
1, 0.00000000E+000, 0.00000000E+000, 0.00000000E+000
2, 0.00000000E+000, 0.00000000E+000, 1.00000000E+001
3, 0.00000000E+000, 1.00000000E+001, 0.00000000E+000
4, 0.00000000E+000, 1.00000000E+001, 1.00000000E+001
5, 1.00000000E+001, 0.00000000E+000, 0.00000000E+000
6, 1.00000000E+001, 0.00000000E+000, 1.00000000E+001
7, 1.00000000E+001, 1.00000000E+001, 0.00000000E+000
8, 1.00000000E+001, 1.00000000E+001, 1.00000000E+001
9, 0.00000000E+000, 0.00000000E+000, 1.00000000E+001
10, 0.00000000E+000, 0.00000000E+000, 2.00000000E+001
11, 0.00000000E+000, 1.00000000E+001, 1.00000000E+001
12, 0.00000000E+000, 1.00000000E+001, 2.00000000E+001
13, 1.00000000E+001, 0.00000000E+000, 1.00000000E+001
14, 1.00000000E+001, 0.00000000E+000, 2.00000000E+001
15, 1.00000000E+001, 1.00000000E+001, 1.00000000E+001
16, 1.00000000E+001, 1.00000000E+001, 2.00000000E+001
17, 5.00000000E+000, 5.00000000E+000, 2.00000000E+001
18, 5.00000000E+000, 5.00000000E+000, 2.00000000E+001
*Element, Type=C3D8, Elset=Solid_part-1
1, 4, 2, 1, 3, 8, 6, 5, 7
*Element, Type=C3D8, Elset=Solid_part-2
2, 12, 10, 9, 11, 16, 14, 13, 15
*Nset, Nset=Top_part
9, 10, 11, 12, 13, 14, 15, 16
*Nset, Nset=Internal-1_Contact_top
9, 11, 13, 15
*Nset, Nset=Internal-1_Contact_bot
2, 4, 6, 8
*Nset, Nset=Fixed_bot
1, 3, 5, 7
*Nset, Nset=Reference_Point-1_Ref_161
17
*Nset, Nset=Reference_Point-1_Rot_171
18
*Elset, Elset=Internal-1_Contact_top_S5
2
*Elset, Elset=Internal-1_Contact_bot_S3
1
*Elset, Elset=Top_part_elset
2
*Elset, Elset=Bot_part_elset
1
*Surface, Name=Contact_top, Type=Element
Internal-1_Contact_top_S5, S5
*Surface, Name=Contact_bot, Type=Element
Internal-1_Contact_bot_S3, S3
*Material, Name=Steel
*Elastic
210000, 0.3
*Material, Name=Foam
*HYPERFOAM, N=1
0.02, 3.0, 0.05
*Solid section, Elset=Top_part_elset, Material=Steel
*Solid section, Elset=Bot_part_elset, Material=Foam
*Rigid body, Nset=Top_part, Ref node=17, Rot node=18
*Surface interaction, Name=Surface_Interaction-1
*Surface behavior, Pressure-overclosure=Hard
*Friction
0.1
*Contact pair, Interaction=Surface_Interaction-1, Type=Surface to surface
Contact_bot, Contact_top
*Step, Nlgeom
*Static, Solver=Pardiso
*Boundary, op=New
*Boundary
Fixed_bot, 1, 6, 0
*Boundary
17, 1, 1, 0
17, 2, 2, 0
17, 3, 3, -4
18, 1, 1, 0
18, 2, 2, 0
18, 3, 3, 0
*Node file
RF, U
*El file
S, E, NOE
*End step

Calc_em · September 23, 2026, 1:45pm

But it can be even shown with one element too (so nothing to do with contact or rigid body, just the material model):

*Node
1, 0.00000000E+000, 0.00000000E+000, 0.00000000E+000
2, 0.00000000E+000, 0.00000000E+000, 1.00000000E+001
3, 0.00000000E+000, 1.00000000E+001, 0.00000000E+000
4, 0.00000000E+000, 1.00000000E+001, 1.00000000E+001
5, 1.00000000E+001, 0.00000000E+000, 0.00000000E+000
6, 1.00000000E+001, 0.00000000E+000, 1.00000000E+001
7, 1.00000000E+001, 1.00000000E+001, 0.00000000E+000
8, 1.00000000E+001, 1.00000000E+001, 1.00000000E+001
*Element, Type=C3D8, Elset=Solid_part-1
1, 4, 2, 1, 3, 8, 6, 5, 7
*Nset, Nset=Fixed_bot
1, 3, 5, 7
*Nset, Nset=Loaded_top
2, 4, 6, 8
*Elset, Elset=Foam_cube_elset
1
*Material, Name=Foam
*HYPERFOAM, N=1
0.02, 3.0, 0.05
*Solid section, Elset=Foam_cube_elset, Material=Foam
*Step, Nlgeom
*Static, Solver=Pardiso
*Boundary
Fixed_bot, 1, 6, 0
*Boundary
Loaded_top, 1, 1, 0
Loaded_top, 2, 2, 0
Loaded_top, 3, 3, -4
Loaded_top, 4, 4, 0
Loaded_top, 5, 5, 0
Loaded_top, 6, 6, 0
*Node file
RF, U
*El file
S, E, NOE
*End step

fgr · September 23, 2026, 2:39pm

@Viertelstein It seemed to be a bug in ccx. A quick workaround for you could be just to add the material parameters twice like this:

*Material, Name=Latexschaum
*HYPERFOAM, N=2
0.02, 3.0, 0.02, 3.0, 0.05, 0.05

It should give you this result.

JuanP74 · September 23, 2026, 2:42pm

I run the calculix test example beamhf.inp using your material model and it runs with the example material model HY but not with Latexschaum material model so could be a mix of both problems, in ccx and in the material model.

beamhf.inp

**
** Structure: cantilever beam.
** Test objective: hyperfoam material (N=2) under tension.
**
*HEADING
Model: beam Date: 10-Mar-1998
*NODE
1, 0.000000, 0.000000, 0.000000
2, 1.000000, 0.000000, 0.000000
3, 1.000000, 1.000000, 0.000000
4, 0.000000, 1.000000, 0.000000
5, 0.000000, 0.000000, 8.000000
6, 1.000000, 0.000000, 8.000000
7, 1.000000, 1.000000, 8.000000
8, 0.000000, 1.000000, 8.000000
9, 0.250000, 0.000000, 0.000000
10, 0.500000, 0.000000, 0.000000
11, 0.750000, 0.000000, 0.000000
12, 1.000000, 0.250000, 0.000000
13, 1.000000, 0.500000, 0.000000
14, 1.000000, 0.750000, 0.000000
15, 0.750000, 1.000000, 0.000000
16, 0.500000, 1.000000, 0.000000
17, 0.250000, 1.000000, 0.000000
18, 0.000000, 0.750000, 0.000000
19, 0.000000, 0.500000, 0.000000
20, 0.000000, 0.250000, 0.000000
21, 0.250000, 0.000000, 8.000000
22, 0.500000, 0.000000, 8.000000
23, 0.750000, 0.000000, 8.000000
24, 1.000000, 0.250000, 8.000000
25, 1.000000, 0.500000, 8.000000
26, 1.000000, 0.750000, 8.000000
27, 0.750000, 1.000000, 8.000000
28, 0.500000, 1.000000, 8.000000
29, 0.250000, 1.000000, 8.000000
30, 0.000000, 0.750000, 8.000000
31, 0.000000, 0.500000, 8.000000
32, 0.000000, 0.250000, 8.000000
33, 1.000000, 0.000000, 0.500000
34, 1.000000, 0.000000, 1.000000
35, 1.000000, 0.000000, 1.500000
36, 1.000000, 0.000000, 2.000000
37, 1.000000, 0.000000, 2.500000
38, 1.000000, 0.000000, 3.000000
39, 1.000000, 0.000000, 3.500000
40, 1.000000, 0.000000, 4.000000
41, 1.000000, 0.000000, 4.500000
42, 1.000000, 0.000000, 5.000000
43, 1.000000, 0.000000, 5.500000
44, 1.000000, 0.000000, 6.000000
45, 1.000000, 0.000000, 6.500000
46, 1.000000, 0.000000, 7.000000
47, 1.000000, 0.000000, 7.500000
48, 0.000000, 0.000000, 7.500000
49, 0.000000, 0.000000, 7.000000
50, 0.000000, 0.000000, 6.500000
51, 0.000000, 0.000000, 6.000000
52, 0.000000, 0.000000, 5.500000
53, 0.000000, 0.000000, 5.000000
54, 0.000000, 0.000000, 4.500000
55, 0.000000, 0.000000, 4.000000
56, 0.000000, 0.000000, 3.500000
57, 0.000000, 0.000000, 3.000000
58, 0.000000, 0.000000, 2.500000
59, 0.000000, 0.000000, 2.000000
60, 0.000000, 0.000000, 1.500000
61, 0.000000, 0.000000, 1.000000
62, 0.000000, 0.000000, 0.500000
63, 1.000000, 1.000000, 0.500000
64, 1.000000, 1.000000, 1.000000
65, 1.000000, 1.000000, 1.500000
66, 1.000000, 1.000000, 2.000000
67, 1.000000, 1.000000, 2.500000
68, 1.000000, 1.000000, 3.000000
69, 1.000000, 1.000000, 3.500000
70, 1.000000, 1.000000, 4.000000
71, 1.000000, 1.000000, 4.500000
72, 1.000000, 1.000000, 5.000000
73, 1.000000, 1.000000, 5.500000
74, 1.000000, 1.000000, 6.000000
75, 1.000000, 1.000000, 6.500000
76, 1.000000, 1.000000, 7.000000
77, 1.000000, 1.000000, 7.500000
78, 0.000000, 1.000000, 0.500000
79, 0.000000, 1.000000, 1.000000
80, 0.000000, 1.000000, 1.500000
81, 0.000000, 1.000000, 2.000000
82, 0.000000, 1.000000, 2.500000
83, 0.000000, 1.000000, 3.000000
84, 0.000000, 1.000000, 3.500000
85, 0.000000, 1.000000, 4.000000
86, 0.000000, 1.000000, 4.500000
87, 0.000000, 1.000000, 5.000000
88, 0.000000, 1.000000, 5.500000
89, 0.000000, 1.000000, 6.000000
90, 0.000000, 1.000000, 6.500000
91, 0.000000, 1.000000, 7.000000
92, 0.000000, 1.000000, 7.500000
93, 0.500000, 0.250000, 0.000000
94, 0.250000, 0.500000, 0.000000
95, 0.500000, 0.500000, 0.000000
96, 0.750000, 0.500000, 0.000000
97, 0.500000, 0.750000, 0.000000
98, 0.500000, 0.250000, 8.000000
99, 0.250000, 0.500000, 8.000000
100, 0.500000, 0.500000, 8.000000
101, 0.750000, 0.500000, 8.000000
102, 0.500000, 0.750000, 8.000000
103, 0.500000, 0.000000, 0.500000
104, 0.250000, 0.000000, 1.000000
105, 0.500000, 0.000000, 1.000000
106, 0.750000, 0.000000, 1.000000
107, 0.500000, 0.000000, 1.500000
108, 0.250000, 0.000000, 2.000000
109, 0.500000, 0.000000, 2.000000
110, 0.750000, 0.000000, 2.000000
111, 0.500000, 0.000000, 2.500000
112, 0.250000, 0.000000, 3.000000
113, 0.500000, 0.000000, 3.000000
114, 0.750000, 0.000000, 3.000000
115, 0.500000, 0.000000, 3.500000
116, 0.250000, 0.000000, 4.000000
117, 0.500000, 0.000000, 4.000000
118, 0.750000, 0.000000, 4.000000
119, 0.500000, 0.000000, 4.500000
120, 0.250000, 0.000000, 5.000000
121, 0.500000, 0.000000, 5.000000
122, 0.750000, 0.000000, 5.000000
123, 0.500000, 0.000000, 5.500000
124, 0.250000, 0.000000, 6.000000
125, 0.500000, 0.000000, 6.000000
126, 0.750000, 0.000000, 6.000000
127, 0.500000, 0.000000, 6.500000
128, 0.250000, 0.000000, 7.000000
129, 0.500000, 0.000000, 7.000000
130, 0.750000, 0.000000, 7.000000
131, 0.500000, 0.000000, 7.500000
132, 1.000000, 0.500000, 0.500000
133, 1.000000, 0.250000, 1.000000
134, 1.000000, 0.500000, 1.000000
135, 1.000000, 0.750000, 1.000000
136, 1.000000, 0.500000, 1.500000
137, 1.000000, 0.250000, 2.000000
138, 1.000000, 0.500000, 2.000000
139, 1.000000, 0.750000, 2.000000
140, 1.000000, 0.500000, 2.500000
141, 1.000000, 0.250000, 3.000000
142, 1.000000, 0.500000, 3.000000
143, 1.000000, 0.750000, 3.000000
144, 1.000000, 0.500000, 3.500000
145, 1.000000, 0.250000, 4.000000
146, 1.000000, 0.500000, 4.000000
147, 1.000000, 0.750000, 4.000000
148, 1.000000, 0.500000, 4.500000
149, 1.000000, 0.250000, 5.000000
150, 1.000000, 0.500000, 5.000000
151, 1.000000, 0.750000, 5.000000
152, 1.000000, 0.500000, 5.500000
153, 1.000000, 0.250000, 6.000000
154, 1.000000, 0.500000, 6.000000
155, 1.000000, 0.750000, 6.000000
156, 1.000000, 0.500000, 6.500000
157, 1.000000, 0.250000, 7.000000
158, 1.000000, 0.500000, 7.000000
159, 1.000000, 0.750000, 7.000000
160, 1.000000, 0.500000, 7.500000
161, 0.500000, 1.000000, 0.500000
162, 0.750000, 1.000000, 1.000000
163, 0.500000, 1.000000, 1.000000
164, 0.250000, 1.000000, 1.000000
165, 0.500000, 1.000000, 1.500000
166, 0.750000, 1.000000, 2.000000
167, 0.500000, 1.000000, 2.000000
168, 0.250000, 1.000000, 2.000000
169, 0.500000, 1.000000, 2.500000
170, 0.750000, 1.000000, 3.000000
171, 0.500000, 1.000000, 3.000000
172, 0.250000, 1.000000, 3.000000
173, 0.500000, 1.000000, 3.500000
174, 0.750000, 1.000000, 4.000000
175, 0.500000, 1.000000, 4.000000
176, 0.250000, 1.000000, 4.000000
177, 0.500000, 1.000000, 4.500000
178, 0.750000, 1.000000, 5.000000
179, 0.500000, 1.000000, 5.000000
180, 0.250000, 1.000000, 5.000000
181, 0.500000, 1.000000, 5.500000
182, 0.750000, 1.000000, 6.000000
183, 0.500000, 1.000000, 6.000000
184, 0.250000, 1.000000, 6.000000
185, 0.500000, 1.000000, 6.500000
186, 0.750000, 1.000000, 7.000000
187, 0.500000, 1.000000, 7.000000
188, 0.250000, 1.000000, 7.000000
189, 0.500000, 1.000000, 7.500000
190, 0.000000, 0.500000, 0.500000
191, 0.000000, 0.750000, 1.000000
192, 0.000000, 0.500000, 1.000000
193, 0.000000, 0.250000, 1.000000
194, 0.000000, 0.500000, 1.500000
195, 0.000000, 0.750000, 2.000000
196, 0.000000, 0.500000, 2.000000
197, 0.000000, 0.250000, 2.000000
198, 0.000000, 0.500000, 2.500000
199, 0.000000, 0.750000, 3.000000
200, 0.000000, 0.500000, 3.000000
201, 0.000000, 0.250000, 3.000000
202, 0.000000, 0.500000, 3.500000
203, 0.000000, 0.750000, 4.000000
204, 0.000000, 0.500000, 4.000000
205, 0.000000, 0.250000, 4.000000
206, 0.000000, 0.500000, 4.500000
207, 0.000000, 0.750000, 5.000000
208, 0.000000, 0.500000, 5.000000
209, 0.000000, 0.250000, 5.000000
210, 0.000000, 0.500000, 5.500000
211, 0.000000, 0.750000, 6.000000
212, 0.000000, 0.500000, 6.000000
213, 0.000000, 0.250000, 6.000000
214, 0.000000, 0.500000, 6.500000
215, 0.000000, 0.750000, 7.000000
216, 0.000000, 0.500000, 7.000000
217, 0.000000, 0.250000, 7.000000
218, 0.000000, 0.500000, 7.500000
219, 0.500000, 0.500000, 0.500000
220, 0.500000, 0.250000, 1.000000
221, 0.250000, 0.500000, 1.000000
222, 0.500000, 0.500000, 1.000000
223, 0.750000, 0.500000, 1.000000
224, 0.500000, 0.750000, 1.000000
225, 0.500000, 0.500000, 1.500000
226, 0.500000, 0.250000, 2.000000
227, 0.250000, 0.500000, 2.000000
228, 0.500000, 0.500000, 2.000000
229, 0.750000, 0.500000, 2.000000
230, 0.500000, 0.750000, 2.000000
231, 0.500000, 0.500000, 2.500000
232, 0.500000, 0.250000, 3.000000
233, 0.250000, 0.500000, 3.000000
234, 0.500000, 0.500000, 3.000000
235, 0.750000, 0.500000, 3.000000
236, 0.500000, 0.750000, 3.000000
237, 0.500000, 0.500000, 3.500000
238, 0.500000, 0.250000, 4.000000
239, 0.250000, 0.500000, 4.000000
240, 0.500000, 0.500000, 4.000000
241, 0.750000, 0.500000, 4.000000
242, 0.500000, 0.750000, 4.000000
243, 0.500000, 0.500000, 4.500000
244, 0.500000, 0.250000, 5.000000
245, 0.250000, 0.500000, 5.000000
246, 0.500000, 0.500000, 5.000000
247, 0.750000, 0.500000, 5.000000
248, 0.500000, 0.750000, 5.000000
249, 0.500000, 0.500000, 5.500000
250, 0.500000, 0.250000, 6.000000
251, 0.250000, 0.500000, 6.000000
252, 0.500000, 0.500000, 6.000000
253, 0.750000, 0.500000, 6.000000
254, 0.500000, 0.750000, 6.000000
255, 0.500000, 0.500000, 6.500000
256, 0.500000, 0.250000, 7.000000
257, 0.250000, 0.500000, 7.000000
258, 0.500000, 0.500000, 7.000000
259, 0.750000, 0.500000, 7.000000
260, 0.500000, 0.750000, 7.000000
261, 0.500000, 0.500000, 7.500000
*ELEMENT, TYPE=C3D20R , ELSET=B1
1, 1, 10, 95, 19, 61, 105, 222, 192, 9, 93,
94, 20, 104, 220, 221, 193, 62, 103, 219, 190
2, 10, 2, 13, 95, 105, 34, 134, 222, 11, 12,
96, 93, 106, 133, 223, 220, 103, 33, 132, 219
3, 19, 95, 16, 4, 192, 222, 163, 79, 94, 97,
17, 18, 221, 224, 164, 191, 190, 219, 161, 78
4, 95, 13, 3, 16, 222, 134, 64, 163, 96, 14,
15, 97, 223, 135, 162, 224, 219, 132, 63, 161
5, 61, 105, 222, 192, 59, 109, 228, 196, 104, 220,
221, 193, 108, 226, 227, 197, 60, 107, 225, 194
6, 105, 34, 134, 222, 109, 36, 138, 228, 106, 133,
223, 220, 110, 137, 229, 226, 107, 35, 136, 225
7, 192, 222, 163, 79, 196, 228, 167, 81, 221, 224,
164, 191, 227, 230, 168, 195, 194, 225, 165, 80
8, 222, 134, 64, 163, 228, 138, 66, 167, 223, 135,
162, 224, 229, 139, 166, 230, 225, 136, 65, 165
9, 59, 109, 228, 196, 57, 113, 234, 200, 108, 226,
227, 197, 112, 232, 233, 201, 58, 111, 231, 198
10, 109, 36, 138, 228, 113, 38, 142, 234, 110, 137,
229, 226, 114, 141, 235, 232, 111, 37, 140, 231
11, 196, 228, 167, 81, 200, 234, 171, 83, 227, 230,
168, 195, 233, 236, 172, 199, 198, 231, 169, 82
12, 228, 138, 66, 167, 234, 142, 68, 171, 229, 139,
166, 230, 235, 143, 170, 236, 231, 140, 67, 169
13, 57, 113, 234, 200, 55, 117, 240, 204, 112, 232,
233, 201, 116, 238, 239, 205, 56, 115, 237, 202
14, 113, 38, 142, 234, 117, 40, 146, 240, 114, 141,
235, 232, 118, 145, 241, 238, 115, 39, 144, 237
15, 200, 234, 171, 83, 204, 240, 175, 85, 233, 236,
172, 199, 239, 242, 176, 203, 202, 237, 173, 84
16, 234, 142, 68, 171, 240, 146, 70, 175, 235, 143,
170, 236, 241, 147, 174, 242, 237, 144, 69, 173
17, 55, 117, 240, 204, 53, 121, 246, 208, 116, 238,
239, 205, 120, 244, 245, 209, 54, 119, 243, 206
18, 117, 40, 146, 240, 121, 42, 150, 246, 118, 145,
241, 238, 122, 149, 247, 244, 119, 41, 148, 243
19, 204, 240, 175, 85, 208, 246, 179, 87, 239, 242,
176, 203, 245, 248, 180, 207, 206, 243, 177, 86
20, 240, 146, 70, 175, 246, 150, 72, 179, 241, 147,
174, 242, 247, 151, 178, 248, 243, 148, 71, 177
21, 53, 121, 246, 208, 51, 125, 252, 212, 120, 244,
245, 209, 124, 250, 251, 213, 52, 123, 249, 210
22, 121, 42, 150, 246, 125, 44, 154, 252, 122, 149,
247, 244, 126, 153, 253, 250, 123, 43, 152, 249
23, 208, 246, 179, 87, 212, 252, 183, 89, 245, 248,
180, 207, 251, 254, 184, 211, 210, 249, 181, 88
24, 246, 150, 72, 179, 252, 154, 74, 183, 247, 151,
178, 248, 253, 155, 182, 254, 249, 152, 73, 181
25, 51, 125, 252, 212, 49, 129, 258, 216, 124, 250,
251, 213, 128, 256, 257, 217, 50, 127, 255, 214
26, 125, 44, 154, 252, 129, 46, 158, 258, 126, 153,
253, 250, 130, 157, 259, 256, 127, 45, 156, 255
27, 212, 252, 183, 89, 216, 258, 187, 91, 251, 254,
184, 211, 257, 260, 188, 215, 214, 255, 185, 90
28, 252, 154, 74, 183, 258, 158, 76, 187, 253, 155,
182, 254, 259, 159, 186, 260, 255, 156, 75, 185
29, 49, 129, 258, 216, 5, 22, 100, 31, 128, 256,
257, 217, 21, 98, 99, 32, 48, 131, 261, 218
30, 129, 46, 158, 258, 22, 6, 25, 100, 130, 157,
259, 256, 23, 24, 101, 98, 131, 47, 160, 261
31, 216, 258, 187, 91, 31, 100, 28, 8, 257, 260,
188, 215, 99, 102, 29, 30, 218, 261, 189, 92
32, 258, 158, 76, 187, 100, 25, 7, 28, 259, 159,
186, 260, 101, 26, 27, 102, 261, 160, 77, 189
*NSET, NSET=CN7
97, 96, 95, 94, 93, 20, 19, 18, 17, 16, 15,
14, 13, 12, 11, 10, 9, 4, 3, 2, 1
*BOUNDARY
CN7,3,3
1,1,2
2,2,2
*ELSET,ELSET=EALL,GENERATE
1,32
*NSET,NSET=NALL,GENERATE
1,261
*MATERIAL,NAME=HY
*HYPERFOAM,N=2
0.164861,8.88413,2.302e-5,-4.81798,0.,0.
**SOLID SECTION,ELSET=EALL,MATERIAL=HY
*Material, Name=Latexschaum
*HYPERFOAM, N=1
0.02, 3.0, 0.05
*SOLID SECTION,ELSET=EALL,MATERIAL=Latexschaum
*NSET,NSET=LAST
5,6,7,8,22,25,28,31,100
*NSET,NSET=GIBO
5,
6,
7,
8,
21,
22,
23,
24,
25,
26,
27,
28,
29,
30,
31,
32,
98,
99,
100,
101,
102,
*NSET,NSET=N1
100
*NSET,NSET=N2
22,25,28,31
*NSET,NSET=N3
5,6,7,8
*NSET,NSET=N4
21,23,24,26,27,29,30,32
*NSET,NSET=N5
98,99,101,102
*STEP,NLGEOM,INC=100
*STATIC
1.,1.
*CLOAD
N1,3,-0.000833333
N2,3,-0.000416666
N3,3,-0.000208333
N4,3,0.000833333
N5,3,0.001666666
*NODE PRINT,NSET=NALL
U
*EL PRINT,ELSET=EALL
S
*Node file
RF, U
*El file
S, E, NOE
*END STEP

Calc_em · September 23, 2026, 3:26pm

The constants can be mismatched too since they don’t come from any verified source. But the same model runs normally in Abaqus so I treat it as a CalculiX bug. I guess I’ll report it on GitHub then.

JuanP74 · September 23, 2026, 4:41pm

not completely sure is the case yet but might be the explanation (sorry to resort to IA ), it works and “looks” very well with the proposed change:

Calc_em · September 23, 2026, 4:47pm

In Abaqus the syntax for N=1 is:

The same syntax is used in CalculiX:

So both solvers should assume µ_1 = 0.02, α_1 = 3.0 and ν_1 = 0.05. The only question is whether these values make any sense, but Abaqus accepts them, and CalculiX should too.

Viertelstein · September 24, 2026, 12:00am

I’m attaching as screenshot. As long as this can’t be calculated in CalculiX, my only option is to upload the INP to a cloud computing service (with ABAQUS), right? That gives you 300 free hours. ABAQUS itself is prohibitively expensive.

JuanP74 · September 24, 2026, 6:10am

Are you sure that the best fit with your data is N=1 model? It seems to work pretty well in CCX with N=2.

Viertelstein · September 24, 2026, 7:03am

Calc_em · September 24, 2026, 7:12am

Some other options are:

using an equivalent hyperelastic material model
trying with different constants and N=2
switching to a different open-source solver which supports material models for such hyperelastic foams (e.g., FEBio has some advanced nonlinear elastic models meant primarily for tissue modeling, but maybe there are better options than that)

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HYPERFOAM Model Issue

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