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# how to calculate CPRESS (in Abaqus)2

## how to calculate CPRESS (in Abaqus)

(OP)
Hello everyone,

I was wondering how Abaqus calculate the CPRESS in the contact formulation ?
Let take an example of pure sliding between 2 deformable blocks (say block A is placed above block B), consisted of solid elements. Slave/master surface is used for the contact between these blocks. The bottom nodes of block A are set to have always the same displacement, so that the bottom elements of block A would have the constant vertical stress. I also give the horizontal restraint at the bottom-middle node of block A, so that the total contact shear force would be zero (the distribution of contact shear stress is not zero)
Next when I applied vertical pressure (DLOAD) on top of surface of block A, I expected the constant distribution of contact pressure (CPRESS) at the slave/master surface, but infact I got the nonlinear parabolic distribution of CPRESS. Does anybody know the reason ?

Any opinion would be appreciated and thank you for your time in responsing this post.

### RE: how to calculate CPRESS (in Abaqus)

I'm not sure of your fixed displacements but in general if you have two solids in contact then the stiffness at the free edges is not the same as in the centre, hence you'd get a non uniform contact pressure distribution. The same applies when you look at interference fit between two different lengths of annular rings and you see this effect at the free edge of the shorter ring.

corus

### RE: how to calculate CPRESS (in Abaqus)

I think the contact problem you mentioned is similar to compressing one rectangular block having the bottom edge fully constrained (i.e., u1=u2=0 for all nodes on the bottom edge) while the upper edge is compressed (by imposing u2=-x). This problem will result in a non-linear stress distribution along the bottom edge.

### RE: how to calculate CPRESS (in Abaqus)

(OP)
xerf, Yes I did just exactly like you said. Thank you for the confirmation.
corus, thank you for the sentence about the difference of stiffness matrix at free edge and in the centre.

regards,
Sendy.

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