MEMS Module Updates
For users of the MEMS Module, COMSOL Multiphysics® version 5.2a brings upgraded piezoresistivity interfaces, a new Magnetostriction interface for modeling sensors and actuators, the ability to model adhesion and decohesion, and more. Review all of the MEMS Module updates in more detail below.
New Magnetostriction Interface
A new Magnetostriction interface has been introduced. With this functionality, you can model a wide range of sensors and actuators based on the principles of magnetostriction. One magnetostrictive effect, the Joule effect, describes the change in length due to a change in the magnetization state of the material. This effect is used in transducers for applications in sonar, acoustic devices, active vibration control, position control, and fuel injection systems. The inverse effect accounts for the change in magnetization due to mechanical stress in a material. This effect is known as the Villari effect and is useful for sensors.
When the Magnetostriction interface is added to a model, a Solid Mechanics interface; Magnetic Fields interface; and Magnetostriction multiphysics coupling, or series of nodes, are created. In the Solid Mechanics interface, a new material model, Magnetostrictive Material, has been added with three different formulations: Linear, Nonlinear isotropic, and Nonlinear cubic crystal. In the Magnetic Fields interface, the new Ampère’s law, Magnetostrictive feature is used when modeling a magnetostrictive material.
NOTE: In order to model magnetostrictive behavior, you need the AC/DC Module along with either the Structural Mechanics Module, MEMS Module, or Acoustics Module.
Application Library path for an example that uses the new Magnetostriction interface with the Nonlinear isotropic material model:
Piezoresistivity Physics Interfaces Upgraded to Multiphysics Couplings
The three dedicated physics interfaces for the piezoresistive effect — the Piezoresistivity, Domain Currents interface, the Piezoresistivity, Boundary Currents interface, and the Piezoresistivity, Shell interface — have all been upgraded to corresponding Multiphysics nodes. The "Select Physics" tree view in the Model Wizard looks the same as before; the three multiphysics couplings, with the same names, remain in the same location under Structural Mechanics > Piezoresistivity.
The new multiphysics couplings provide you with the flexibility to enable/disable each constituent physics interface and/or the coupling between the physics. Since the piezoresistive effect is a one-way coupling, from the mechanical stress to the electrical conductivity, a new Piezoresistive Material node has been added under the Electric Currents node by default for each case.
Harmonic Perturbation for Prescribed Velocity and Acceleration
The Prescribed Velocity and Prescribed Acceleration features have been augmented with a Harmonic Perturbation subnode. These boundary conditions can thus be used as a fixed constraint in a stationary study step and then provide a harmonic vibration in a subsequent prestressed frequency-domain study. This new functionality is available in the Solid Mechanics interface.
Modeling Adhesion and Decohesion
Using the new Adhesion subnode under the Contact node, you can analyze various manufacturing processes that involve parts sticking together and pulling apart. The contacting boundaries will stick together when a certain criterion has been fulfilled. This criterion can either be a contact pressure, a gap distance, or an arbitrary user-defined expression. The latter can, for example, be based on the temperature from a heat transfer study. You can also specify the elastic properties of the virtual adhesive layer.
Two boundaries that are joined by adhesion can separate again if a decohesion law is specified. Also found within the new Adhesion subnode, and as part of its Settings window, is the ability to choose Decohesion. There are three different decohesion laws that are included in this subnode: Linear, Polynomial, and Multilinear. The decohesion laws allow mixed-mode decohesion with independent properties for the normal and tangential directions, a technique also known as a cohesive zone model (CZM).
Application Library path for an example that shows the modeling of decohesion: Structural_Mechanics_Module/Contact_and_Friction/cohesive_zone_debonding
Elements of the so-called Serendipity type have been added to the Solid Mechanics and Membrane interfaces to complement the Lagrangian type. For models with predominantly hexahedral elements, using serendipity elements will provide significant performance improvements, run faster, and use less memory. Using serendipity elements is now the default when adding new physics interfaces.
New Methods for Entering Thermal Expansion Data
There are now three different ways in which thermal expansion material data can be entered:
- As a Secant coefficient of thermal expansion. This is the default and the only method available in previous versions.
- As a Tangent ("thermodynamic") coefficient of thermal expansion.
- By explicitly specifying the Thermal strain as a function of temperature.
By selecting the appropriate option, you can use different types of measured data without conversions. The new options are available in the Solid Mechanics, Membrane, and Truss interfaces.
The Secant coefficient of thermal expansion option is used to compute a total change in strain when the temperature is changed from a certain reference temperature, . The Tangent coefficient of thermal expansion option provides information on the sensitivity of thermal strain with respect to the temperature: . At the reference temperature, the two values coincide.
Thermal Expansion of Constraints
You can now augment constraint conditions, such as Fixed Constraint and Prescribed Displacement, using a Thermal Expansion subnode. This makes it possible to relieve the stresses induced by constraints when the surrounding structure, idealized by the constraints, is not held at a fixed temperature. Similarly, a Thermal Expansion subnode has been added to the Rigid Connector and Attachment nodes, allowing for the thermal expansion of these otherwise rigid objects.
When using this feature, you specify the thermal expansion coefficient and temperature distribution of the nonmodeled surroundings of the structure. The thermal strains caused by these factors are integrated to obtain a displacement field, which is added to the constraint.
You can now use the Terminal feature in the Electric Currents and Electrostatics physics interfaces on the domain level. This is convenient for geometrically complex electrodes that would involve the selection of a large number of boundaries when using a terminal at the boundary level. The unknowns for the electric potential inside the terminal's domain selection are not solved for, but rather replaced by a variable. This is useful when modeling electrodes with a finite thickness that is respected by the geometry.