[destroy]

Hi everyone,

I am solving a quite simple problem of pipe undergoing pressurizing up to about 10 kPa. Static structural. The model is solved succesfully even with 1 substep when large deflection=off:


However, setting large deflection=on, cause non-convergence, with a standard warning "The solver engine was unable to converge on a solution for the nonlinear problem as constrained". I tried auto time stepping with many substeps on the level of 1000 without success.
Below I listet what I tried:
- changing mesh number of elements through thickness, as 1, 2, 3 or 4 - no effect on convergence,
- changing mesh density through the pipe length, as the higher gradients are in the endings regions - no effect,
- changing the pressure boundary condition, as if it linearly increases from the endings to the final value (depicted below) - didnt help



- trying to use tetrahedral mesh instead, with Nonlinear Adaptive Region option activated - without success,
- activating Semi-implicit option - I just putted command "SEMIIMPLICIT" i.e. without editing this utility' options. This allowed me to solve greater part of the load, however with the extreme deformations which were growing rapidly within the last solved steps, as depicted below on the true-scale deformation field and the charts:



- tuning settings of the Analysis settings ->nonlinear controls -> stabilization; to my suprise this got completely no effect, no matter what option of stabilization I choose or what values of constants I put, I can even completely turn off stabilization and have the same substeps number solved, as for stabilization=program controlled (or some option manually chosen)

I am aware, that in such problems the issue might be simply, the relation between the Young modulus and loads. In my model, I got very small pipe (diameters about 0.3 milimeters), Young modulus about 21 kPa and inside pressure 10 kPa. I can succesfully solve the large-deflection model for decreased pressure to max 2.5 kPa, or with pressure unchanged (10 kPa) but increased Young modulus, up to 100 kPa, if I remember correctly.
Hovever, in my opinion I got correct model, geometry and material properties, which I concluded based on three things: 1) large deflection=off model results, 2) analytical model results, 3) experimental results. All three results are similar. Therefore I still think, that this is the issue of stabilizing the solver, which I am trying to do.

Please guide me, what I might also try to solve the issue,
Kind regards

[Renata98]

In Ansys Mechanical, significant deflection convergence troubles are frequently caused by inadequate mesh refinement or incorrect solver parameters. To overcome this, fine-tune the mesh in important locations and modify solver settings to increase stability and convergence in large deflection studies.
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[evcelica]

A few additional details would help us out.
Diameter and wall thickness?
Elastic material properties?
Young's modulus and Poisson's ratio?
How are you constraining the ends?