Nonlinear Structural Materials Module Updates

For users of the Nonlinear Structural Materials Module, COMSOL Multiphysics® version 6.0 brings 10x faster creep, performance improvements for many nonlinear materials, anisotropic hyperelastic materials, nonlocal plasticity, and improvements for viscoplastic models. Read more about these updates below.

Anisotropic Hyperelastic Materials

By adding one or more Fiber attributes under a Hyperelastic material, you can augment the stiffness by the effect of distributed fiber bundles. The new attribute includes three material models for fibers: Holzapfel-Gasser-Ogden, Linear Elastic, and User defined. You can see this new feature in the new Biventricular Cardiac Model tutorial model and the existing Arterial Wall Mechanics and Arterial Wall Viscoelasticity models.

A biventricular cardiac model showing the fiber directions in the Rainbow color table. Biventricular cardiac model. The fiber directions in the myocardium are used in the Holzapfel-Gasser-Ogden anisotropic hyperelastic material model.

Nonlocal Plasticity

Shear bands or plastic strain localization might occur when modeling plasticity in ductile materials. These zones evolve differently for different mesh sizes. The new Nonlocal Plasticity functionality has been added to the Plasticity and Porous Plasticity features and allows you to obtain a mesh-independent solution when plastic strain localization occurs. You can see this new update in the existing Necking of an Elastoplastic Metal Bar tutorial model.

Creep and Viscoplasticity Improvements

A new general framework for Creep and Anand Viscoplasticity gives large improvements in computational speed and memory usage. For larger models, a speedup by a factor of 10 or more is achieved. The inelastic strain variables are now solved with either a Backward Euler, Forward Euler, or Domain ODEs time-stepping method.

The type of equivalent stress used to determine the creep rate is now a user input. You can select von Mises, Hill Orthotropic, Pressure, or User defined to model nonisotropic creep. When more than one creep mechanism is acting, you can also add one or more Additional Creep nodes under a Creep node. You can see these improvements in the new Creep Analysis of a Turbine Stator Blade and the following existing models:

A turbine stator blade model showing the stress in the Prism color table. The Creep feature is used to demonstrate how secondary creep can cause deformation in a turbine stator blade. The creep rate is highly influenced by temperature.

New van der Waals Hyperelastic Material

A new van der Waals hyperelastic material model has been added to model rubber-like materials in solids, shells, and membranes. If the Composite Materials Module is available, the material model can also be used in multilayered shells. This material is sometimes called the Kilian model.

New Inelastic Strain Rate Node

The new Inelastic Strain Rate attribute has a similar effect to the existing External Strain feature, the difference being that you can now specify an inelastic strain rate that is then integrated in time into an inelastic strain contribution. The strain rate can be specified in terms of a strain tensor, a deformation gradient, an inverse deformation gradient, or three orthogonal stretches.

New Reduced Integration Framework

A new framework has been added for reduced integration, including hourglass stabilization. Reduced integration is particularly useful when the computational cost per integration point is high, which is true for many nonlinear material models such as Plasticity or Creep.

Reduced integration is controlled from the new Quadrature Settings section. It is available in the settings for top-level material models like Linear Elastic Material and Nonlinear Elastic Material. The selected reduced integration rule will then be inherited by any subnodes that may be added. You can see this new framework in these existing tutorial models:

New Tutorial Models

COMSOL Multiphysics® version 6.0 brings several new tutorial models to the Nonlinear Structural Materials Module.