In this problem, a 3D, large-deformation, hyperelastic user-defined material is developed and implemented. The constitutive model is the Neo-Hookean hyperelastic model, which closely reproduces the Neo-Hookean model already available as a standard material within the program.

To demonstrate the user-defined material model, the shearing of a 1 x 1 x 1 block is simulated, and the effective stress versus effective strain is reported. The model is recast in the co-rotated frame (required by the user-defined material subroutine), and an algorithm for the determination of the co-rotated frame rotation vis polar decomposition of the deformation gradient is also presented. The stress, material tangent, and change of basis operations from are converted from full tensor form to Voigt notation.