Dear all,
I am working on a buckling problem of a long cylindrical shell under bending moment. One end is fixed and the other one is free to move. A bending moment is acting on free end. I calculated the critical moment from a Linear buckling analysis in Abaqus as first step. Then I used Riks method to trace the buckling behaviour and I took as imperfection the 1% of thickness of critical mode. After bifurcation point is reached convergence is hard to achieved and the post buckling behaviour cannot be traced. I was expected the load factor to decrease but such a thing wasn't happened. I run the same without including any imperfections and things seem more normal since I got a degradation in load factor as I was expected. Any ideas abou this?
Note: Figures below are from the case where imperfections are included.
You should find other theories that relate buckling and bending moment.
Also, formulate your theory and test it.
Hi Bashir,
Are you using the displacement control method (RIKS) ? If no, then you should.
Sirous Yasseri why should I use a displacement control method in RIKS method , by applying displacement load and not force load? Could you explain?
In a load-controlled procedure, the software increases the load until the system becomes unstable (the stiffness vanishes), and thus the software cannot converge and stop. This is the ultimate load. Since the software crushes you cant capture the post ultimate capacity behaviour.
By reaching the ultimate capacity, systems have undergone either buckling or gross plastic deformation (probably both). Such a system may still be stable under a lower load but more deformation. A load-control procedure cannot unload the system. In a displacement-controlled approach, displacement can grow, but software reduces the load to attain equilibrium. In this way, you can capture the post-bucking behaviour.
Sirous Yasseri But in arc-length method (called RIKS in Abaqus) it doesnt matter if use a load displacement or a force since it upgrades bot of them , right?
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