Nonlinear Structural Materials Module Updates

For users of the Nonlinear Structural Materials Module, COMSOL Multiphysics® version 5.3 brings new Perzyna and Chaboche viscoplastic material models and a new tutorial model that demonstrates the Lemaitre-Chaboche viscoplasticity constitutive law. See all of the new Nonlinear Structural Materials Module features below.

New Framework for Inelastic Strains in Geometrically Nonlinear Analyses

A new framework and more rigorous handling of decomposition into elastic and inelastic deformations has been implemented for cases of geometric nonlinearity. Previous versions of the COMSOL® software used an additive decomposition approach, with a few exceptions such as for large-strain plasticity analyses, which use a multiplicative decomposition approach.

Multiplicative decomposition is now also available for:

  • Thermal Expansion
  • Hygroscopic Swelling
  • Initial Strain
  • External Strain
  • Viscoplasticity
  • Creep

Multiplicative decomposition of deformation gradients is now the default option for all inelastic contributions in studies where geometric nonlinearity is active. The main advantage is that it is possible to handle several large inelastic strain contributions in a material. Furthermore, linearization will be more consistent as, for example, it is now possible to accurately predict the shift in eigenfrequencies caused by pure thermal expansion. If you want to switch to the behavior of previous versions of the COMSOL Multiphysics® software, the new Additive strain decomposition check box can be selected in the Settings window for the respective material models.


As part of this improvement, the External Strain attribute under the Linear Elastic Material and Nonlinear Elastic Material nodes has been expanded with several new options. These options allow for supplying inelastic strains in several forms and you can also transfer inelastic strains from other physics interfaces to this attribute. Additionally, an External Strain attribute with similar properties has been added to the Hyperelastic Material.


New Viscoplastic Material Models

Two new viscoplastic material models have now been included: Perzyna and Chaboche. These models are suitable for cases where the yield stress has a significant dependence on the strain rate. The previously available viscoplastic material model has also been augmented such that material properties can be obtained from a Material node.

A surface plot of the new viscoplastic material model. Viscoplastic strains are shown in a test specimen, calculated with the new viscoplastic material model. Viscoplastic strains are shown in a test specimen, calculated with the new viscoplastic material model.

Porous Plasticity Models

Porous plasticity models are important when simulating, for example, powder compaction. As opposed to classic plasticity models, where plastic deformation is assumed to not change the volume, porosity is an important parameter in porous plasticity models. Five such models are now available:

  1. Shima-Oyane
  2. Gurson
  3. Gurson-Tvergaard-Needleman
  4. Fleck-Kuhn-McMeeking
  5. FKM-GTN

Associated Flow Rule for the Tresca Yield Function

An associated flow rule has been added to the Tresca yield function in plasticity analyses. As before, the default flow rule uses the von Mises yield surface as plastic potential, but this can be changed in the Settings window.

Anisotropic Thermal Expansion and Hygroscopic Swelling for Hyperelastic Materials

The Thermal Expansion feature in the Hyperelastic Materials feature has been augmented with the option to provide orthotropic and anisotropic coefficients of thermal expansion. Similarly, you can now use orthotropic and anisotropic coefficients of hygroscopic swelling in the Hygroscopic Swelling node.

New Tutorial Model: Lemaitre-Chaboche Viscoplastic Model

Most metals and alloys undergo viscoplastic deformation at high temperatures. In case of cyclic loading, a constitutive law with both isotropic and kinematic hardening is necessary to describe effects such as ratcheting, cyclic softening/hardening, and stress relaxation. The Lemaitre-Chaboche viscoplastic model combines isotropic hardening with nonlinear kinematic hardening to model these effects. This viscoplastic model is commonly used in areas such as additive manufacturing, laser welding, laser cutting, and thermal processing of metals and alloys at high temperatures. The tutorial model demonstrates the Lemaitre-Chaboche viscoplastic constitutive law on a test specimen.

A tutorial featuring the new Lemaitre-Chaboche viscoplastic model in the Nonlinear Structural Mechanics Module. Viscoplastic strains, calculated using the Lemaitre-Chaboche viscoplastic model, in a test specimen after four load cycles with a strain rate of 0.001 s-1. Viscoplastic strains, calculated using the Lemaitre-Chaboche viscoplastic model, in a test specimen after four load cycles with a strain rate of 0.001 s-1.

Application Library path:
Nonlinear_Structural_Materials_Module/Viscoplasticity/lemaitre_chaboche_viscoplastic_model