Irreversible Transformation
This subnode should be used to model thermally induced irreversible transformations in solids.
Irreversible transformation
Two models are available to define the material transformation depending on temperature, both using integral forms over time.
Select the Transformation model—Temperature threshold (the default) or Energy absorption, depending on the material properties you have access to.
For Temperature threshold, select the type of analysis—Overheating analysis (the default) or Overcooling analysis, depending on the expected temperature variations.
Overheating Analysis
Enter values for:
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Transformation temperature Tit, h to define the (high) temperature that the solid needs to reach to start getting transformed.
•
Transformation time tit, h to define the time needed for the complete transformation to happen while the temperature is above Tit, h.
•
Enthalpy change Lit, h to define the enthalpy variation associated with transformation due to overheating. The following heat source is added to the right-hand side of Equation 6-9 in Solid node:
Overcooling Analysis
Enter values for:
•
Transformation temperature Tit, c to define the (low) temperature that the solid needs to reach to start getting transformed.
•
Transformation time tit, c to define the time needed for the complete transformation to happen while the temperature is below Tit, c.
•
Enthalpy change Lit, c to define the enthalpy variation associated with transformation due to overcooling. The following heat source is added to the right-hand side of Equation 6-9 in Solid node:
For Energy absorption, define the Frequency Factor and Activation Energy to compute the degree of transformation with the Arrhenius equation.
Frequency Factor and Activation Energy
Enter values for:
•
Frequency factor A in the Arrhenius equation. Default is taken From material. For User defined enter a value or an expression.
•
Activation energy ΔE in the Arrhenius equation. Default is taken From material. For User defined enter a value or an expression.
•
Enthalpy change L to define the enthalpy variation associated with the transformation. The following heat source is added to the right-hand side of Equation 6-9 in Solid node:
Specific thermodynamics properties before and after complete transformation may be defined by selecting the check box Specify different material properties for the transformed state.
Choose a Transformed material, which can point to any material in the model. The default uses the Domain material. The properties before transformation are the ones specified in the Heat Conduction, Solid and Thermodynamics, Solid sections of the parent Solid node. The effective material properties are dynamically updated with the transformation evolution.
Heat Conduction
This section is available when the Specify different material properties for the transformed state check box is selected.
Select a Thermal conductivity kd —From material (the default) or User defined, to be used for transformed solid. For User defined choose Isotropic, Diagonal, Symmetric, or Anisotropic based on the characteristics of the thermal conductivity and enter another value or expression in the field or matrix.
Thermodynamics
This section is available when the Specify different material properties for the transformed state check box is selected.
Select a Density ρd and Heat capacity at constant pressure Cp, d —From material (the default) or User defined, to be used for transformed solid. The heat capacity describes the amount of heat energy required to produce a unit temperature change in a unit mass.
For a detailed overview of the functionality available in each product, visit http://www.comsol.com/products/specifications/
Location in User Interface
Context menus
 Heat Transfer in Solids>Solid>Irreversible Transformation
More locations are available. For example:
Heat Transfer in Fluids>Solid>Irreversible Transformation
Ribbon
Physics Tab with Solid selected in the model tree:
Attributes>Irreversible Transformation