UMAT4COMSOL: An Abaqus user material (UMAT) subroutine wrapper for COMSOL

TL;DR

This work tackles the limitation of COMSOL in directly utilizing Abaqus UMAT material models by introducing UMAT4COMSOL, a C-based wrapper that enables Abaqus Fortran UMATs to be used as COMSOL External Materials. It details the required input/output transformations between COMSOL and Abaqus conventions for both small-strain and finite-strain constitutive laws, and demonstrates accuracy and convergence parity through elastoplasticity, hyperelasticity, crystal plasticity, and a coupled hydrogen diffusion–deformation benchmark. The results show exact or near-exact agreement with Abaqus across multiple complex material models, validating the wrapper’s ability to extend COMSOL’s multiphysics capabilities with Abaqus-era material physics. By enabling this nonintrusive integration, UMAT4COMSOL broadens the practical impact of advanced material modelling in multi-physics contexts, with the code freely available to the community.

Abstract

We present a wrapper that allows Abaqus user material subroutines (UMATs) to be used as an External Material library in the software COMSOL Multiphysics. The wrapper, written in C language, transforms COMSOL's external material subroutine inputs and outputs into Fortran-coded Abaqus UMAT inputs and outputs, by means of a consistent variable transformation. This significantly facilitates conducting coupled, multi-physics studies employing the advanced material models that the solid mechanics community has developed over the past decades. We exemplify the potential of our new framework, UMAT4COMSOL, by conducting numerical experiments in the areas of elastoplasticity, hyperelasticity and crystal plasticity. The source code, detailed documentation and example tutorials are made freely available to download at www.empaneda.com/codes.

Figures (10)

• Figure 1: Flow chart of UMAT4COMSOL
• Figure 2: Mechanical response of an elastoplastic holed plate: contour plots of the equivalent plastic strain. Results obtained: (a) with Abaqus, using an elastoplastic UMAT, and (b) with COMSOL, using the same UMAT and UMAT4COMSOL. The deformation has been scaled by a factor of 20.
• Figure 3: Mechanical response of an elastoplastic holed plate: (a) Force versus displacement response, predicted with Abaqus (+UMAT) and with COMSOL (+UMAT and UMAT4COMSOL); and (b) convergence plots for both COMSOL and Abaqus solvers, showing the magnitude of the residual for each iteration as a function of the load increment. In (b), iterations are represented with equispaced subdivisions within each increment interval.
• Figure 4: Mechanical response of a twisted neo-Hookean cube: contour plots of the displacement field magnitude (L2 norm). Results obtained: (a) with Abaqus, using a non-linear hyperelastic UMAT, and (b) with COMSOL, using the same UMAT and UMAT4COMSOL.
• Figure 5: Convergence plots of twisting cuboid simulation using a neo-Hookean UMAT material in both solvers, Abaqus and COMSOL. Subfigure (a) shows the residual evolution in 10 pseudo-time increments, while subfigure (b) provides convergence plots for 1 pseudo-time increment. In (a), iterations are represented with equispaced subdivisions within each increment interval.