riks - critical load 1

[gwena]

Hello,
There is something that I don't understand about the determination of the critical buckling load.
The method is :
1) Perform a linear analysis to have an idea of the critical load and its associated mode.
2) Introduce a perturbation in the geometry (*IMPERFECTION)
3) Perform a postbuckling analysis with the RIKS method. Then I plot the reaction force versus displacment in order to identify the real critical load.
My question is : Why the Abaqus documentation specify that the Riks algorithm cannot obtain a solution at a given load or displacement value since these are treated as unknows ?
This means that the reaction force that I read as critical load is wrong ?
Is the load factor necessary to determine the critical load ?
Thanks a lot for any explanation !

 

[mrgoldthorpe]

gwena,

As I understand, the Riks method in ABAQUS adjusts the load
factor in such a way as to ensure that the displacements do
not increase by more than given amounts at each increment.
It does this because you are dealing with a nonlinear,
possibly non-convergent problem where there may not be a
solution for an arbitrary value of applied load.

The load applied in any increment is the load you specified
multiplied by the load factor. So the critical load would
be the maximum load factor achieved times your applied load.

 

[gwena]

ok. This means that applying a displacment condition, the reaction force that I will read will be the real critical load.
Thanks !