# Nonlinear patch test, hex8

A unit cube of 3 × 3 × 3 hex8 elements whose non-corner nodes are moved off the lattice, so no
element is a parallelepiped. Every boundary node is prescribed u = (F − I) X with
F = [[1.3, 0.2, -0.1], [-0.15, 0.9, 0.25], [0.05, -0.2, 1.1]] (stretch, shear and rotation, J = 1.389000); the eight inner nodes are free. The neo-Hookean
material (E = 100, ν = 0.3) must take the homogeneous deformation: the inner node 22 moves by
(F − I) X and the Cauchy stress is uniform.