Applying bearing forces 1

[Chebeba]

Hi All!

I am new to Abacus, so maybe this question is trivial, but anyway...

From other FEA packages I am used to being able to select faces of my geometry and apply forces to it. This force is usually distributed across all mesh nodes on the selected face(s) so that the total node forces sum up to my specified force.

I can't seem to figure the equivalent steps in Abaqus/CAE.

Concentrated loads apply only to vertices, and if I specify all vertices on the surface I want, the force is not distributed, instead it is applied in full at each point, making the total force = my specified force times the number of points. Not what I want. If I divide my specified force with the number of vertices I get the correct total force, but unnecessary high local stress around the vertices since the load is only applied at one mesh node. Not good either.

If I use a Surface Traction load I get my force distributed across mesh nodes, but now I have to calculate the surface pressure from the force I want to apply and the surface area. I know I can get the areas from Tools > Query, but it gets very cumbersome when the force is distributed across multiple faces.

Am I missing something? Is there a smarter way to do this?

/C

 

[corus]

Forces aren't applied to nodes on a face as the results would be dependent on the uniformity of the mesh. If the mesh was biased to one point, for instance, then you'd have a greater concentration of force in that region. In reality this would be wrong. Calculating a pressure on a face by dividing the known force by the area of the face is something you'll have to get used to.

corus

 

[bobthedalek]

The loading functionality you seek is needed by us all (who are trying to load our FEA models in a realistic manner) but it is not too common to find it in commercial FEA codes. In ABAQUS you could use the user subroutine DLOAD in order to specify your bearing load (as long as you have the mathematical description of the pressure load). It is good technique to apply natural face pressures where possible as this is exactly what happens in nature. Note that the ROSHAZ program (see

http://www.roshaz.com)

does exaactly what you require as this has the GENCOZ pressure distributions (typ of bearings and lugs and the like) already coded up for you. Load balances are proviuded and you'll be laughing. The GENCOZ distributions were developed by BOEING doing a host of pin and lug type stuff and I have performed my own contact simulations in order to check them out. Best of LUCK.

 

[johnsmith2]

I have the similar problem at the force applied on the surface!!!

As corus mentioned, we usually calculate the pressure on the surface by known force and area. P=F/A. But, this pressure is assumed to be applied vertically on that surface. Sometimes, if the applied force is not exactly vertical or horizontal direction, but at an angle on the surface, how can we convert the forces (F cos (alpha), F sin (alpha) ) into pressure on the same surface?

 

[brep]

Create a distributing coupling (you'll find this in the Interaction module). Then apply the concentrated load to the reference point of the distributing coupling.

Alternatively, apply a pressure load to the face, and use a python expression to define the spatial distribution of the load. (The same is achieved using the DLOAD subroutine, but the Python expression is MUCH simpler)

 

[johnsmith2]

thanks for you reply.

When I create the distributing coupling, which constraint control point should I select, any point on that surface? Also, which weighting method should I choose? uniform?

I work on the Lug hole of the casting body, the surface to be applied force is curve, should I select the point of the centre of the lug hole (How can I choose in geometry)? or any point on the curve surface.

Thanks.

 

[johnsmith2]

If I am correct, I can choose the centre point of the hole as reference point, and then distributing coupling this node.