Energy-Based
Use the Energy-Based node to define the fatigue model selection and parameters for energy-based fatigue evaluation. The Energy-Based feature can be applied to domains, boundaries, edges, or points.
Model Input
See Common Physics Interface and Feature Settings and Nodes for information about the Model Input.
Solution Field
From the Physics interface list select the physics interface where the load cycle is simulated.
Fatigue Model Selection
Select a Criterion — Morrow or Darveaux. This specifies the fatigue model to be evaluated. See Morrow Model and Darveaux Model for details about these models.
The Darveaux criterion is only available at the domain level in 3D, 2D axisymmetric, and 2D components.
Select an Energy type — None or User defined. This specifies the energy quantity that controls the fatigue life. The list of the Energy type is populated with additional options when nonlinear materials are used. If the material has been modeled with Plasticity, also Plastic dissipation density is selectable. If the material has been modeled with Creep, also Creep dissipation density is selectable. If the material has been modeled with Viscoplasticity, also Viscoplastic dissipation density is selectable. If the material has been modeled with two of the above material types than also Total dissipation density is selectable.
The results cannot be obtained unless Calculate dissipated energy is selected under Energy Dissipation in the Linear Elastic Material, Nonlinear Elastic Material, or Hyperelastic Material node. This is because the dissipated energy depends on the load and strain history and must be calculated at the same time as the simulation of the load cycle. This adds additional degrees of freedom to the model. See Energy Dissipation in the Structural Mechanics Module User’s Guide.
The energy-based models depend on the dissipated energy. Energy dissipation means that the energy is consumed by the material and cannot be restored. This behavior is exhibited by inelastic materials and can be modeled with the Nonlinear Structural Materials Module or Geomechanics Module.
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Energy Dissipation
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Energy-Based Fatigue Models
If the User defined option has been selected as the Energy type, two additional inputs are required. First, you need to specify the Energy dissipation density Wd. You can use any combination of energy quantities from the physics interface used for the stress analysis. Use the pattern <interface>.<variable_name>. Second, you need to provide the integration order that was used to compute this energy dissipation density.
Evaluation Settings
This section is available if Darveaux is selected as the Criterion. Select a Volume average method — Individual domains or Entire selection. This parameter determines how the volume average of the dissipated energy is calculated in the selected volume.
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For Individual domains one value is calculated for each geometrical domain.
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For Entire selection the average is calculated over the entire selection.
If the selection consists of only one geometrical domain, then both options give the same result. See Individual Domains versus Entire Selection for details.
Fatigue Model Parameters
If Morrow is selected as the Criterion, then the Fatigue energy coefficient Wf and Fatigue energy exponent m by default take values From material. For User defined enter other values or expressions in the fields as needed.
If Darveaux is selected as the Criterion, enter a value for the Crack size a. By default, it is set to 0. By default, the following parameters, Crack initiation energy coefficient K1, Crack initiation energy exponent k2, Crack propagation energy coefficient K3, Crack propagation energy exponent k4, and Reference energy density Wref, take values From material. For User defined enter other values or expressions in the fields as needed for these parameters.