Convergence problem

[Delirium80]

Hello,
I'm starting to use Abaqus program.
I have already exercised a lot of tutorials but now I have a strange problem.
I'm training to design a steel beam subjected to a line load and a pre-initial stress.
This beam is inclined by 45 °. I'm using the mesh of beam elements.
When I go to submit the job can not complete the analysis because I have convergence problems and do not understand why.
this is my input file :

*Heading
** Job name: Job-1 Model name: Model-1
** Generated by: Abaqus/CAE 6.9-EF1
*Preprint, echo=NO, model=NO, history=NO, contact=NO
**
** PARTS
**
*Part, name=Beam
*Node
1, -1144.5, -1161., 0.
2, -1088.67078, -1104.36584, 0.
3, -1032.84143, -1047.73169, 0.
4, -977.012207, -991.097534, 0.
5, -921.182922, -934.46344, 0.
6, -865.353638, -877.829285, 0.
7, -809.524414, -821.195129, 0.
8, -753.695129, -764.560974, 0.
9, -697.865845, -707.926819, 0.
10, -642.03656, -651.292664, 0.
11, -586.207336, -594.658508, 0.
12, -530.378052, -538.024414, 0.
13, -474.548767, -481.390259, 0.
14, -418.719513, -424.756104, 0.
15, -362.890259, -368.121948, 0.
16, -307.060974, -311.487793, 0.
17, -251.231705, -254.853653, 0.
18, -195.402435, -198.219513, 0.
19, -139.573166, -141.585373, 0.
20, -83.7439041, -84.9512177, 0.
21, -27.9146347, -28.3170738, 0.
22, 27.9146347, 28.3170738, 0.
23, 83.7439041, 84.9512177, 0.
24, 139.573166, 141.585373, 0.
25, 195.402435, 198.219513, 0.
26, 251.231705, 254.853653, 0.
27, 307.060974, 311.487793, 0.
28, 362.890259, 368.121948, 0.
29, 418.719513, 424.756104, 0.
30, 474.548767, 481.390259, 0.
31, 530.378052, 538.024414, 0.
32, 586.207336, 594.658508, 0.
33, 642.03656, 651.292664, 0.
34, 697.865845, 707.926819, 0.
35, 753.695129, 764.560974, 0.
36, 809.524414, 821.195129, 0.
37, 865.353638, 877.829285, 0.
38, 921.182922, 934.46344, 0.
39, 977.012207, 991.097534, 0.
40, 1032.84143, 1047.73169, 0.
41, 1088.67078, 1104.36584, 0.
42, 1144.5, 1161., 0.
*Element, type=B31
1, 1, 2
2, 2, 3
3, 3, 4
4, 4, 5
5, 5, 6
6, 6, 7
7, 7, 8
8, 8, 9
9, 9, 10
10, 10, 11
11, 11, 12
12, 12, 13
13, 13, 14
14, 14, 15
15, 15, 16
16, 16, 17
17, 17, 18
18, 18, 19
19, 19, 20
20, 20, 21
21, 21, 22
22, 22, 23
23, 23, 24
24, 24, 25
25, 25, 26
26, 26, 27
27, 27, 28
28, 28, 29
29, 29, 30
30, 30, 31
31, 31, 32
32, 32, 33
33, 33, 34
34, 34, 35
35, 35, 36
36, 36, 37
37, 37, 38
38, 38, 39
39, 39, 40
40, 40, 41
41, 41, 42
*Nset, nset=_PickedSet2, internal, generate
1, 42, 1
*Elset, elset=_PickedSet2, internal, generate
1, 41, 1
*Nset, nset=_PickedSet3, internal, generate
1, 42, 1
*Elset, elset=_PickedSet3, internal, generate
1, 41, 1
** Section: Section-1 Profile: Profile-1
*Beam Section, elset=_PickedSet2, material=Steel, temperature=GRADIENTS, section=RECT
50., 3.
0.,0.,-1.
*End Part
**
**
** ASSEMBLY
**
*Assembly, name=Assembly
**
*Instance, name=Beam-1, part=Beam
*End Instance
**
*Nset, nset=_PickedSet4, internal, instance=Beam
1, 42
*Nset, nset=_PickedSet5, internal, instance=Beam, generate
1, 42, 1
*Elset, elset=_PickedSet5, internal, instance=Beam, generate
1, 41, 1
*End Assembly
**
** MATERIALS
**
*Material, name=Steel
*Elastic
210000, 0.3
*No Compression
*INITIAL CONDITIONS,TYPE=STRESS
_PickedSet5, 523.4653, 523.4653
** STEP: Load
**
*Step, name=Load, nlgeom=YES
*Static
1., 1., 1e-05, 1.
**
** BOUNDARY CONDITIONS
**
** Name: Fix Type: Displacement/Rotation
*Boundary
_PickedSet4, 1, 1
_PickedSet4, 2, 2
_PickedSet4, 3, 3
**
** LOADS
**
** Name: Carico Type: Line load
*Dload
_PickedSet5, PZ, -25.0767
**
** OUTPUT REQUESTS
**
*Restart, write, frequency=0
**
** FIELD OUTPUT: F-Output-1
**
*Output, field, variable=PRESELECT
**
** HISTORY OUTPUT: H-Output-1
**
*Output, history, variable=PRESELECT
*End Step

Could you help me?
thank you

 

[rb1957]

geez ... please don't post your model in the message, attach the file using the attachment tool at the bottom of the screen.

posting the FE or ABAQUS

is "picked set 4" a single node, 42 ?
it looks like you're constraining only XYZ at one node ? which is insufficient, yes?

 

[Delirium80]

I'm sorry rb1957,
I do not know why but I was not able to attach the file.
However the _PickedSet4 contains nodes 1 and 42, this set fact to apply the boundary conditions.
I also tried to constrain all degrees of freedom, but I have the same problem.
The strange thing is that if the beam is arranged horizontally I get a solution

 

[JoshPlumSE]

When performing a non-linear analysis there are many ways in which a program can diverge. I don't know abaqus at all, so I can't review your model.

However, there is one piece of advice that I can give. Try starting with a much lower load... like 10% or 1% of your total load. If that converges then keep increasing the load until the program stops converging. That way you can determine the point at which the structure is on the verge of divergence. Reviewing the results for this loading can really help you understand why divergence happens.

I understand that's probably a pain in the rear to do with Abaqus. But, it is a simple rule of thumb for investigating complex solutions.

 

[fcu45]

Try the convergence of your problem if the "pre-initial stress" is omitted.

If it works, that means either you need to know your mistake in applying this stress.
Or you maybe need to add your loads in steps, first place your "pre-initial stress"
Then in another step apply your load(s).

 

[Delirium80]

fcu45
I have already tried the convergence without pre-stress but I have the same problem: negative eigenvalues ​​and the error of too many attempts.