A new feature, Test Material, has been added to the Solid Mechanics interface. With this feature, it is possible to set up single-element tests for various scenarios like uniaxial or biaxial tension. The purpose is to test and verify the behavior of a material model for a given set of material properties. For material models with an explicit time dependence, the test study can be time dependent.

In the Solid Mechanics interface, a new feature called Thin Layer has been introduced. You can use it to add material models on interior and exterior boundaries. Most domain material models that would also be relevant for a thin layer are available. With the Composite Materials Module, a thin layer can itself be multilayered. There are different formulations of the thin layer materials, depending on the assumed kinematics.

Two new multiphysics interfaces for modeling thin-film damping have been added: Solid Thin-Film Damping and Shell Thin-Film Damping. They combine a Thin-Film Flow interface with a Solid Mechanics or Shell interface, respectively. The couplings are made through the new Structure Thin-Film Flow Interaction and Shell Thin-Film Flow Interaction multiphysics couplings.

As an effect of this more general approach, the Thin-Film Damping feature in the Solid Mechanics interface has been retired. It will still appear if you open an old model that contains such a feature, but you can no longer add it. Consider replacing it using the new modeling paradigm, since it will only be available for a few more releases and is no longer actively maintained.

In a linearized buckling study, you can now separate the loads into those that are assumed to be independent of the load factor (dead loads) and those that are proportional to the load factor (live loads). To mark a certain load as being a dead load, you go to the Linear Buckling section in the settings for that load feature. This section is only shown when Advanced Physics Options is enabled. There are also special settings in the Linear Buckling study step to control the different load cases.

In the Shell and Membrane interfaces, the Thickness and Offset node has been augmented by a subnode called Thickness Change. There, it is possible to enter a rate of thickness change. The purpose is to model phenomena like wear, corrosion, and electrodeposition.

A new Wear subnode has been added to the Contact node in the Shell and Membrane interfaces. With this feature you can model thickness reduction and corresponding changes in contact force distribution caused by wear. The functionality is similar to what was already available in the Solid Mechanics interface.

When the offset-based wear formulation is used, you can now select the type of shape function that is used to describe the offset field. This is done in the new Discretization section in the Wear node.

In the Continuity node in the Solid Mechanics and Multibody Dynamics interfaces, you can now select between three different methods for enforcing the continuity conditions. In addition to using pointwise or weak constraints, a new formulation based on Nitsche’s method is also available. The main advantage with the new method is that there is no need for constraint elimination, since it only adds terms to the stiffness matrix.

A new search method for finding the distance between contacting boundaries has been implemented. It is significantly faster than the previous methods, in particular for large 3D models. The new method, Hierarchical, is now the default search method in the settings for a Contact Pair. The old search methods have been renamed to better reflect their properties. The performance has been improved for these methods as well.

For contact between solid objects, it is now possible to select Nitsche as Contact method. This method does not suffer from the introduction of an arbitrary stiffness, as in the penalty method, and still no extra degrees of freedom are required. The Nitsche method is robust but can be more costly because it produces a nonsymmetric stiffness matrix.

The formulation for the contact equations has been improved for all contact methods. In particular, a reduced Jacobian is now used by default. You can control the assembly of the Jacobian through the Jacobian contribution control in the Advanced section of the Contact settings. Select Legacy to revert to the version 6.0 behavior.

If you make the same selection for the source and destination in a Contact Pair node, a formulation of the contact conditions that is fully symmetric between source and destination boundaries is used.

The Trigger Cutback section is now available for all contact methods. By setting an appropriate cutback criterion, you can force the solver to go back and start with a smaller parameter or time step, rather than spending many iterations on a solution that is far from convergence.

A new node at the global level, Base Excitation, has been added to the structural mechanics interfaces. The purpose is to handle the case where all support points experience a common acceleration history. Base excitation can be used for any dynamic study type, but it is most important for the modal-based procedures where it is not possible to directly prescribe a nonzero acceleration of displacement.

The Gravity node has been changed to be a global feature in all structural mechanics interfaces. The reason is that gravity is almost always applied to the entire structure. A new node, Linearly Accelerated Frame, makes it possible to prescribe nonuniform inertial loads.

For a Boundary Load or Point Load, it is now possible to give the total load as a force and moment resultant. To use such a load, select Resultant from the Load type list. This option is available in the Solid Mechanics, Multibody Dynamics, and Layered Shell interfaces.

For Point Load, there is now also the possibility to set Load type to either Force per point or Total force.

By adding a Local System Results node in a Solid Mechanics, Multibody Dynamics, or Solid Rotor interface, you can get access to a number of result variables expressed in a given coordinate system. This includes displacements, velocities, accelerations, stresses, strains, and material properties.

When two boundaries with shell elements are joined using the Edge to Edge connection in the Shell interface, it is possible to define the connection as a weld and to evaluate weld-specific stress results. Three types of welds can be defined: single-sided fillet weld, double-sided fillet weld, and butt weld.

In the Beam interface, a capability to draw moment and shear force diagrams has been included. Such section force diagrams can be added from the Add Predefined Plot window. The section force diagrams take the load distribution into account, so that even with a very coarse mesh, the diagrams are more or less exact.

A set of new section force variables, called distributed section forces has been added to facilitate this. The variable names are the same as for the standard section forces but appended by _d, for example, beam.Myl_d.

In the Truss interface, the Cross-Section Data node has been augmented by an option for defining the element cross section by geometrical properties. The available cross sections are the same as in the Beam interface, that is, Rectangle, Box, Circular, Pipe, H-profile, U-profile, T-profile, C-profile, and Hat.

In the Edge to Edge, Edge to Boundary, and Boundary to Boundary connections in the Shell interface, it is now possible to select a through-thickness location (top, bottom, or midsurface) as the reference for the connection.

In the Linear Elastic Material and Layered Linear Elastic Material nodes, there are new input options for material properties:

For the Piezoelectric Material, a new formulation has been implemented in which the inelastic (piezoelectric) strains under geometric nonlinearity are removed from the total strains through multiplicative decomposition. The formulation is controlled by the Use multiplicative formulation check box. When selected, any study will be forced to be geometrically nonlinear.

When you select Average stress as Periodicity Type in Cell Periodicity, it is now possible to create an average compliance matrix. This is an effect of the Linear Elastic Material setting now allowing input to be included on the compliance form.

The built-in Structural Steel material has been augmented so that material properties are temperature dependent. There is also material data for a wide range of nonlinear material models.

In the Part Library, a new folder called Representative Volume Elements has been added to the COMSOL Multiphysics branch. It contains a number of parameterized geometries for common microstructures, like fiber and particulate composites. These geometries can, for example, be used to compute effective material properties using the representative volume element (RVE) method. The Cell Periodicity node in the Solid Mechanics interface is designed for this.

It is now possible to specify that there is no connection in a certain direction for a rigid connector. The direction can be specified in a local coordinate system, so that it, for example, can be the radial direction from a certain point. You specify this behavior in the new Released Degrees of Freedom in the settings for the Rigid Connector node.

When a rigid connector has a selection that consists of only two points, it is now possible to add a spring type condition to suppress the rotational singularity that could occur. The setting for this is in the Advanced section in the settings for the Rigid Connector. The Add rotational stiffness for two-point selection check box is shown when the Include consistency checks check box is cleared.

In the Prescribed Displacement node in the Truss interface, there is a new option, Limited Displacement. This type of boundary condition limits the displacement in a certain direction to a given maximum value. The Prescribed Displacement node has been redesigned in order to accommodate this.

In the Pipe Mechanics interface, you can now specify correction factors for stiffness and stress evaluation in pipe bends. To do so, you add the Bend subnode under Pipe Cross Section.

When specifying a Pipe Cross Section in the Pipe Mechanics interface, you can now enter a reduced pipe thickness for the stress evaluation. This can be used when, for example, taking corrosion allowance into account.

In the Part Library, the content of the Pipes folder in the COMSOL Multiphysics branch has been augmented. The folder now contains parameterized geometries for the following common piping parts: straight pipe, bend, reducer, and T-junction. These geometries can be used for detailed analysis using the Solid Mechanics or Shell interface. Such a part can be inserted into a pipe system modeled using the Pipe Mechanics interface, through the Structure-Pipe Connection multiphysics coupling.

Because the new parts are more general in scope, the old straight_pipe and bent_pipe parts have been removed.

The Rigid Domain material model has been renamed to Rigid Material in all physics interfaces. The purpose is to emphasize that this is a material model with the same status as other material models.

With the introduction of the new concept of predefined plots, the number of default plots that are always produced by the structural mechanics interfaces has been reduced significantly. Several plots that were default plots are now instead optional and can be added from Add Predefined Plot window. There are also several new useful predefined plots.

In the Damping, Layered Damping, and Mechanical Damping nodes, it is now possible to create a preview plot that shows the damping as a function of frequency when data for Rayleigh damping has been given.

In the Thickness and Offset nodes in the Shell and Membrane interfaces, it is now possible to create a preview plot that shows how the given inputs are interpreted.

When creating material data from a Cell Periodicity node, you can now choose between the two actions Create Material by Reference and Create Material by Value. The new second option makes it possible to store material data in a file that can be used in other models.

In each Rigid Connector and Attachment node, a set of ordinary differential equation (ODE) degrees of freedom are created, representing the translation and rotation. Up to version 6.0, each of these nodes would add two or three nodes under Dependent Variables in the solver sequence. For models with many such features, this list could become long. From version 6.1, the default is that such variables are grouped together instead.

You can control whether or not to use the grouping. This can be done in two places. The default behavior can be controlled from the Advanced Settings section in the settings for the physics interface. This section is visible if Advanced Physics Options is active.

The default behavior can, however, be overridden for each individual Rigid Connector or Attachment node, by using a selection in the Advanced section in the feature itself.

When opening an old model, the grouping will be turned off in order to maintain full compatibility with the previous version. When building a model using the API, the new default will be used. This is true even if, for example, a Java® file created from an older version is used. If you want to achieve full backward compatibility using the API, you need to add two lines similar to

When connecting a shell or membrane boundary to a solid domain boundary, using the Solid-Thin Structure Connection multiphysics coupling, you can now select for which physics interface the constraints are generated. If the Connection type is Shared boundaries or Parallel boundaries, you can make this selection in the new Advanced section.

When one of the three reduced-order model studies (Frequency Domain, Modal Reduced-Order Model; Time Dependent, Modal Reduced-Order Model; or Frequency Domain, AWE Reduced-Order Model) is selected, the generated studies have a structure that differs from previous releases. One study (Frequency Domain or Time Dependent) is no longer needed. Instead, subnodes with the same names are created under the Model Reduction study step.

In the Advanced Settings section in the Shell interface, you can now select whether the constraints on the rotation around the normal are added as nodal or elemental constraints.

The Reference Point for Moment Computation section has been removed from the settings for all structural mechanics interfaces. The values of the properties are now always set in the feature under Results where they are used.