For constitutive models that require a stress integration algorithm, ensure that the algorithm is accurate. Exercise the user-defined material in simple simulations to determine if it is producing accurate stress results for the types of simulations that will use the user-defined material routine. The accuracy of the stress update directly affects the accuracy of the finite element solution.

The material tangent returned by the user-defined material routine should be the algorithmic tangent in the co-rotated frame. For a Newton-Raphson solution, the material tangent affects the convergence rate and an algorithmic material tangent will generally give a quadratic convergence rate for iterations that are close to the solution.