Problem in nonlinear analysis - boundary conditions
Problem in nonlinear analysis - boundary conditions
(OP)
I am trying to run nonlinear analysis in Abaqus under uniform traction boundary conditions. I need to find the maximum extension I can get using Abaqus for this type of problem.
I found that Abaqus can handle this problem till some specific value of the pressure magnitude and then the analysis fails. It is a simple homogeneous rectangular plate, made of neo-hookean type material, subjected to loads from both sides and constrained from rigid body motion on the corners (plane stress). I tried almost everything: using controls, defining other types of boundary conditions, adjusting increment step – nothing works. Under displacement boundary condition there is no limit – analysis completes successfully for any displacement applied, whereas under traction boundary condition the maximum extension I can get is around 1% of the plate size, which is unacceptable for my research.
Is there any bug Abaqus has for nonlinear problems of this type? Has someone tried to apply this type of boundary conditions in nonlinear analysis?
I found that Abaqus can handle this problem till some specific value of the pressure magnitude and then the analysis fails. It is a simple homogeneous rectangular plate, made of neo-hookean type material, subjected to loads from both sides and constrained from rigid body motion on the corners (plane stress). I tried almost everything: using controls, defining other types of boundary conditions, adjusting increment step – nothing works. Under displacement boundary condition there is no limit – analysis completes successfully for any displacement applied, whereas under traction boundary condition the maximum extension I can get is around 1% of the plate size, which is unacceptable for my research.
Is there any bug Abaqus has for nonlinear problems of this type? Has someone tried to apply this type of boundary conditions in nonlinear analysis?





RE: Problem in nonlinear analysis - boundary conditions
corus
RE: Problem in nonlinear analysis - boundary conditions
RE: Problem in nonlinear analysis - boundary conditions
RE: Problem in nonlinear analysis - boundary conditions
corus
RE: Problem in nonlinear analysis - boundary conditions
Thank you.
RE: Problem in nonlinear analysis - boundary conditions
RE: Problem in nonlinear analysis - boundary conditions
corus
RE: Problem in nonlinear analysis - boundary conditions
Is there a hole in your rectangular plate?
RE: Problem in nonlinear analysis - boundary conditions
RE: Problem in nonlinear analysis - boundary conditions
I don't have any holes or cracks in my plate. Initially, I tried to run analysis for heterogeneous plate - it didn't work. Then I started to simplify my model and finally came to a simple homogeneous plate under uniaxial tension. I should say that plate is constrained only on its corners and not on its edges.
Fails means analysis doesn't converge. I tried to refine mesh, but it didn't give anything. Program always reports negative eigenvalues and after sometime analysis fails.
As far as I know all stress/diplacement elements in Abaqus are based on Lagrangian description.
RE: Problem in nonlinear analysis - boundary conditions
corus
RE: Problem in nonlinear analysis - boundary conditions
RE: Problem in nonlinear analysis - boundary conditions
You mentioned negative eigenvalues and plate in tension. Since eigenvalues are typically associated with buckling and compression I would say that the negative sign is ok. (For the moment I'll ignore dynamics.)
Can you make a linear analysis work and check the stressdistribution? That might give a hint as to why nonlinear fails. Also, you say "pure elastic". Why run nonlinear at all?
Good Luck
Thomas
RE: Problem in nonlinear analysis - boundary conditions
Incidentally, how can the material be non-hookean and yet be purely elastic?
corus
RE: Problem in nonlinear analysis - boundary conditions
1) I am interested in large deformations, therefore nonlinear analysis should be on and
2)I am interested in constitutive response of an inhomogeneous plate (neo-hookean material models hyperelastic material response)
Because of the second reason I cannot use symmetry condition, although now I am considering a homogeneous case. I, actually, tried to use symmetry - force can be increased till certain level but then analysis fails again.
I tried linear analysis - it always works and creates homogeneous stress destribution inside the plate.
Also, if I have restrained the plate incorectly, analysis would fail even for small pressure magnitude which doesn't happen.
RE: Problem in nonlinear analysis - boundary conditions
RE: Problem in nonlinear analysis - boundary conditions