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Applying a stress tensor to a model

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I posted a question recently about trying to apply a distributed torque density to a model, but to no avail. Since then, I've come up with a way to potentially apply the load, but I'm not sure if it's possible to use the inputs I want.

I'm able to convert my torque load into an applied stress tensor which includes only shear stress terms. Since there are no boundary conditions on my stress element, it's not in static equilibrium and so has imaginary eigenvectors and values. If I could calculate them, I would just find the appropriate body load to simulate the tensor.

I was wondering if it's possible to input a stress tensor as an boundary/initial condition. The torque is always present, so COMSOL would need to calculate the stress produced because of the boundary conditions.

If my description above was not clear, here's the idea:
1. Make a shaft that's fixed somewhere.
2. Apply a torque about an arbitrary axis using the stress tensor (which may be spatially or time dependent). For a non-fixed geometry, the stress tensor has components sigma_xy=-sigma_yx=(torque about z-axis), -sigma_xy=sigma_zx=(torque about y-axis), sigma_yz=-sigma_zy=(torque about x-axis)
3. Calculate the steady-state stress/strain/deflection of the model.

3 Replies Last Post 2015年9月7日 GMT-4 03:40
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Hello Joseph Boales

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Montassar Aidi Sharif

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Posted: 9 years ago 2015年9月6日 GMT-4 01:16
Hi
please do you have the model for applying torque
thanks
Hi please do you have the model for applying torque thanks

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 9 years ago 2015年9月6日 GMT-4 18:16
Hi

you can add a rigid constraint on a boundary and then add a torque as a sub node, but your boundary becomes really "rigid"!
Else try a search on the Forum for "Torque" I 'm sure I have already given the formula a few times, I believe it's even in the Model Exchange, but that might be an old v3.3 version
--
Good luck
Ivar
Hi you can add a rigid constraint on a boundary and then add a torque as a sub node, but your boundary becomes really "rigid"! Else try a search on the Forum for "Torque" I 'm sure I have already given the formula a few times, I believe it's even in the Model Exchange, but that might be an old v3.3 version -- Good luck Ivar

Henrik Sönnerlind COMSOL Employee

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Posted: 9 years ago 2015年9月7日 GMT-4 03:40
Hi,

Mathematically, it is only possible to prescribe three components (out of six) as boundary condition. These are (in a local coordinate system oriented along the normal to the boundary) one normal stress and two shear stresses in the plane of the boundary.

Regards,
Henrik
Hi, Mathematically, it is only possible to prescribe three components (out of six) as boundary condition. These are (in a local coordinate system oriented along the normal to the boundary) one normal stress and two shear stresses in the plane of the boundary. Regards, Henrik

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