Learning Forum

[Kirtan Sahu]

Hello everyone,

I am unable to understand the stress behaviour when the column gets buckled. I am performing the structural nonlinear analysis (Buckling) and I have observed that when stress goes beyond the yield strength, the stress develop in the column show a zig-zag behaviour as shown below figure.

This is the buckled column with stress variation

This is stress w r t time

Please help me to understand this behaviour.

[peteroznewman]

Does the material model for this part have Plasticity defined?

[Kirtan Sahu]

Yes, I have defined the plasticity considering it as binlear isotrpic hardening with defualt nonlinear properties of structural steel (E = 200 GPa and Poissions ratio = 0.3, yield strength = 360 Mpa, and Tangent modulus = 1.45 GPa).

[peteroznewman]

The plot shows the stress anywhere in the model so the maximum value jumps to different locations during the solution.

Create a stress plot scoped to a vertex in the model, that should show a smoother curve.

[Kirtan Sahu]

Thank you Mr. Peteroznewman for your responses, now it is clear to me.

I want to clear one more doubt.

I am performing nonlinear buckling for two different case of misalignment of a stepped column, first, when rod is inclined by 1 degree from its axial axis and, second, when rod is inclined by 5 degree from it axial axis, the buckling load is more in case of 5 degree in comparison to 1 degree inclination.

As we knwo that if any column have imperfection or mislaignmnet then its stability or buckling load capacity become reduced, so why I am getting more buckling load in case of 5 degree inclination in comparsion to 1 degree inclination?

[peteroznewman]

Kirtan,

I assume you have turned on Large Deflection under the Analysis Settings.

Please show the loads and supports that were used in these models.

Please show the force vs deflection substep points with lines connecting the points for these two models on the same plot with a legend and labeled axes with units.

Regards,

Peter

[Kirtan Sahu]

Yes, I have turned on large deflection.

Remote displacment A

Ux=Uy=Uz=0,

Rx=Rz=0, Ry = free

Remote displacement B

Uy=Uz=0, Ux= -10 mm

Rx=Rz=0, Ry = free

[Kirtan Sahu]

I want to add one more point, actually it is a hydraulic cylinder. Please see the below figure.

The cylinder and piston rod have the frictional contact with frictional coefficient of 0.3 and interface treatment between them is "Adjust to touch".

A gap is also there between rod and gland.