Compression of a box

[dokken]

Please format your code using 3x` such that it is possible to copy-paste the code to an editor and run it without modifications.
Please also note that your VonMises stresses should be projected into a DG 0 space, as the displacement lives in CG 1. This has also been noted in other questions such as:

Results obtained by FEniCS mismatches Abaqus

The code you supplied is not complete, and therefore there is not much one can do to investigate this. Note that the von Mises stresses should be projected into W (the discontinuous space).