Nonlinear Structural Materials Module Updates

For users of the Nonlinear Structural Materials Module, COMSOL Multiphysics® version 6.2 provides new functionality for parameter estimation, new material models for polymer viscoplasticity, and an update to the kinematic hardening model that enables it to handle large plastic strains. Read more about the updates below.

Parameter Estimation

In this version, enhanced parameter estimation capabilities have been introduced, including improvements to the Levenberg–Marquardt and interior point optimizer (IPOPT) solvers. These additions can significantly enhance the performance of parameter estimation of experimental data, including uniaxial, biaxial, and cyclic load cases. Three new tutorial models in the Application Gallery demonstrate this new functionality:

The COMSOL Multiphysics UI showing the Model Builder with a Global Least-Squares Objective node highlighted, the corresponding Settings window, and a 1D plot in the Graphics window.
Parameter estimation of a hyperelastic Ogden material, using a combination of uniaxial, pure-shear, and equibiaxial data.

Polymer Viscoplasticity

In order to accurately analyze structures made of solid polymer materials, new material models for polymer viscoplasticity have been added. These include the Bergstrom–Boyce, Bergstrom–Bischoff, and parallel network models. This new framework can handle large viscoplastic strains, and it is based on the multiplicative decomposition of deformation gradients. You can see these new additions in the following tutorial models:

The small punch test is designed to assess mechanical properties of very small samples.

Fiber Enhancements

Version 6.2 introduces several improvements to the Fiber feature, including:

  • Compressible fibers within the Holzapfel–Gasser–Ogden hyperelastic material model
  • The Thermal Expansion feature for fibers embedded in hyperelastic materials
  • The Uniaxial data material model for handling nonlinear stress–strain relationships for fibers within the Linear Elastic Material and Nonlinear Elastic Material features

These new improvements can be seen in the new Tire Inflation tutorial model.

An aortic valve prosthesis model showing the fiber reinforcement.
Fiber reinforcement on an aortic valve prosthesis.

Shape Memory Alloy Enhancements

The updates for shape memory alloys include:

  • Enhanced flexibility in specifying material parameters for phase transformation, allowing inputs to be entered as start and finish stresses or start and finish temperatures
  • Introduction of a new predefined plot showing the stress–temperature phase diagram, which illustrates the austenite-to-martensite transition
  • Significantly improved penalty method for enforcing upper bounds on transformation strains
  • Inclusion of the Prager–Lode yield surface, enabling the modeling of anisotropic deformation for tension or compression
  • Introduction of large-strain plasticity capabilities

You can see these enhancements in the new Uniaxial Loading of Shape Memory Alloy Using Souza–Auricchio Model tutorial model.

The COMSOL Multiphysics UI showing the Model Builder with the Shape Memory Alloy node highlighted, the corresponding Settings window, and a 1D plot in the Graphics window.
Martensite volume fraction in a stress–temperature phase diagram for the pseudoelastic effect in a single load cycle.

Viscoplastic Material Model for Lithium

A new material model, Anand–Narayan, has been added to the Viscoplasticity feature. This material model specifically targets the properties of lithium in battery applications.

The COMSOL Multiphysics UI showing the Model Builder with the Viscoplasticity node highlighted, the corresponding Settings window, and a 1D plot in the Graphics window.
Stress versus true-strain curves (at different temperatures and strain rates) for a lithium specimen obtained with the Anand–Narayan model.

New Phase-Field Damage Multiphysics Interface

The new Phase-Field Damage multiphysics interface combines a Solid Mechanics interface with the new Phase-Field in Solids interface through a Phase-Field Damage bidirectional multiphysics coupling. The stress or the strain energy density drives the evolution of the phase field, and the phase field determines the degree of damage to the elastic material model.

Phase-field modeling of ductile damage evolution in an elastoplastic compact tension specimen.

New Tutorial Models

COMSOL Multiphysics® version 6.2 brings several new tutorial models to the Nonlinear Structural Materials Module.