How to make Von Mises Stress look better

General
10

VTXWriter and VTKFile supports arbitrary order continuous and discontinuous Lagrange spaces, and should be used for outputting these variables.

If you want to show the von Mises stresses on the deformed geometry, I would interpolate the displacement into the same DG-1 space, i.e.

V_DG = dolfinx.fem.functionspace(mesh, ("DG", degree, (mesh.geometry.dim,)))
stresses = dolfinx.fem.Function(V_DG, name="VonMises")
u_dg = dolfinx.fem.Function(V_DG, name="u")
bp_vonmises = dolfinx.io.VTXWriter(mesh.comm, output / "von_mises.bp", [stresses, u_dg])
s = sigma(u, mu, lmbda) - 1.0 / 3 * ufl.tr(sigma(u, mu, lmbda)) * ufl.Identity(len(u))
von_Mises = ufl.sqrt(3.0 / 2 * ufl.inner(s, s))
stress_expr = dolfinx.fem.Expression(von_Mises, V_DG.element.interpolation_points())
stresses.sub(0).interpolate(stress_expr)
u_dg.interpolate(u)
bp_vonmises.write(0.0)
bp_vonmises.close()
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