## General Mechanical

#### contact pressure

• m.caragiuli
Subscriber

Hi,

Do you know how to compute the contact pressure between two bodies without using the contact tootl? This because I've used a shared topology to connect the mesh thus, the contact tool is not available. I've tried to retrieve the reaction force in the imprinted face involved in the connection and divide it by the contact area, but making some trials comparing this method to the contact tool method in a simplified geometry the two values are different.

So do you have any idea?

Thanks

• peteroznewman
Subscriber

Insert a Coordinate system at the location where you want to extract the internal "contact pressure" so that the Z axis is normal to the plane you want to cut through.

Insert a Construction Geometry and insert a Surface.

Insert a Normal Stress result, scope it to the Surface, using the coordinate system in step 1 and ask for the Z axis component of stress.

• m.caragiuli
Subscriber

Hi Peter,

thanks for answearing! The procedure is clear, but what if I have two rounded contact surface like in the picture?

This is exploded view to let you know that I want to know the pressure at the contact surface between the sphere and the box, that is a convex or concave interface. Should I put the coordinate system at the central bottom of the sphere in order to insert a surface that interfaces with the sphere only at one point?

• peteroznewman
Subscriber

You can only use planes to slice a body to extract stress.

Go back to SpaceClaim and Unshare the geometry, then insert Contact in Mechanical and obtain the Contact Pressure using the Contact Tool.

• m.caragiuli
Subscriber

Ok Peter,

however, can you explain to me why it is not correct to evaluate the pressure at the interface between the two bodies as the ratio between the reaction force in the contact surface and the contact area? Wha is instead the difference between the pressure and the stress as outputs?

Thanks

• peteroznewman
Subscriber

Stress has six components: three normal stresses and three shear stresses.

Pressure is generally concerned with only the stress normal to the surface, which ignores the other five stresses.

If you have a fluid that carries zero shear stress, then it can only provide a normal stress to a solid body.

If you have  solid body in contact with another solid body and there is friction at the interface, then it is possible to transmit a normal contact stress and two shear stresses at the surface, but that ignores three other stresses.

It is only if you have continuous material that you can transmit all six components of stress across an imaginary plane.

• m.caragiuli
Subscriber

ok thank you!