High stress concentration in fillet radius

[crigido3d]

Hi guys!
I have made a FEM analysis of a roller and the results show below.
The forces acting are flexion and torsion. The diameter max. of the roller is 330 mm and 5000 mm of total length.
I do not like high stress values in the fillet zone. I tried refine mesh but the values increase even more. Also I tried increase fillet radius but there is not change.
Is something wrong? Or only generates a hardening for localized plastic deformation and i can ignored this?
I would like to know what you think
Thanks
Sebastian.

Zoom image:

"Persistence prevails, like a stream that is temporarily blocked by boulders and then collects force enough to overflow onward."

 

[lopessilva]

Hello,

As I understand, you are applied a force (A) which is equivalent to a bending moment. As you are applying the load relatevely far from the support, the critical zone is the zone near the support. However, on geometric discontinuities, such as holes, or in your case, fillets, stress values may reach pretty high values in relation to the overall behaviour of the object. If your aim is to study fatigue after the static test, i´m pretty sure the fillet zone will have the lowest life of the entire object. This can be a problem in terms of design, and can invalidate any attempts of design for infinite life. If you only want to perform a static study, I would not care much about it. I understand that you may need to check mesh refinement, as your results changed a lot when you refined it. The way I suggest to improve the stress concentration is to redefine the geometry for the less sharp geometric transitions as possible. Anyway, no matter what you do, the fillet zone will always be a preferential stress concentration zone.

I hope I have helped,

Regards,
Hugo Silva
Mechanical Eng. PhD student
Materials Eng. MSc.

 

[crigido3d]

Hello Hugo. Your point of view is very interest, even, I think same as you. However finally I have solved my problem changing boundary conditions. In one support I have restrained in translation along x,y,z, but allowed to pivot around x,y,z and of other side restrained in translation along x,y,z, pivot around y,z but restrained pivot around x axis. Such conditions are closer to real behavior of the type of bearings to use in this machine. Now, the stress distribution is in all length of roller. The maximum values of stress also occur in filet but with one value of 190 MPA. It's not bad.
Thanks you very much for your response.
Sebastián

Before (with zoom scale)

After

"Persistence prevails, like a stream that is temporarily blocked by boulders and then collects force enough to overflow onward."

 

[lopessilva]

Hello,

It is in fact very interesting that you could solve the problem by changing the constraints. If in this way the DOF constraints are closer to the real behaviour, that´s very good news. Thanks for sharing the solution

regards,


Regards,
Hugo Silva
Mechanical Eng. PhD student
Materials Eng. MSc.