Temperature-Dependent Material Data
Many material properties, such as Young’s modulus, coefficient of thermal expansion, and yield stress, can have a significant dependence on temperature. In many cases, materials supplied in the material libraries and databases have such dependencies incorporated.
Materials in the COMSOL Multiphysics Reference Manual
If a material property under the Materials branch has a temperature dependence, you have to input the temperature to be used in the Model Input section in the settings window for the node in the physics interface that references the property. It is possible that not all aspects of a material are defined in the same node in the Model Builder tree. For example, if a problem is run with thermal expansion and plasticity, then:
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Young’s modulus, Poisson’s ratio, and density are given in the Linear Elastic Material node.
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Yield stress and hardening function are given in the Plasticity node.
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Coefficient of thermal expansion is given in the Thermal Expansion (for Materials) subnode.
The Plasticity node is available as a subnode to the Linear Elastic Material node when you have either the Nonlinear Structural Materials Module or the Geomechanics Module.
For each of these nodes, there is a Model Input section in the Settings window. Some of these sections may be empty if none of the properties given in that node has a temperature dependence. In general you have to supply the temperature in all the Model Inputs sections. This can be done either by explicitly giving a temperature or by selecting a temperature variable from another physics interface.
If there is a Temperature Coupling node under the Multiphysics branch, then you cannot change the temperature input under Model Inputs. The temperature is automatically taken from the connected Heat Transfer in Solids interface.
Mass Density and Volume Reference Temperature
All structural mechanics interfaces are formulated on the material frame. This means that the equations of motion are written for a certain volume in its initial configuration.
The preservation of mass requires that the mass density is constant. In a structural mechanics problem this means that the mass density must not change. If you are using a material in which the density has a temperature dependence, you must specify a specific temperature at which the value is evaluated. This is the volume reference density. Conceptually, you can consider this as the temperature at which the domain has the size in which it is drawn. In practice, the choice of reference temperature is seldom an issue, unless your application requires extreme precision. The density of a solid material has a rather slow variation with temperature, so in most cases it is sufficient to use room temperature as reference.
If any material in the model has a temperature dependent mass density, the Volume reference temperature list will appear in the Model Input section of the material settings. As a default, the value of Tref is obtained from a Common model input. You can also select User defined to enter a value or expression for the reference temperature locally.
When using Common model input, you can see or modify the value of the volume reference temperature by clicking the Go To Source button (). This will move you to the Common Model Inputs node under Global Definitions in the Model Builder. The default value is room temperature; 293.15 K.
If you want to create a model input value which is local to your current selection, click the Create Model Input button . This will create a new Model Input node under Definitions in the current component, having the same selection as in the current node.
All effects of volume change with temperature are incorporated through the thermal expansion effects.