5.5.5.1. SMART Crack Growth Application

Insert a SMART Crack Growth object into the Outline by right-clicking on the Fracture object and selecting Insert > SMART Crack Growth from the context menu. Alternatively, you can select the SMART Crack Growth option on the Fracture Context Tab or right-click in the Geometry window and select Insert > SMART Crack Growth. Once inserted, the Initial Crack and Material properties highlight.

Select the crack or Crack Initiation object that you have already created from the drop-down list of the Initial Crack property. Once selected, the application automatically assigns the Material of the object specified by the Initial Crack property.

Specify the Crack Growth Option property. The setting of this property is based on the desired type of crack growth propagation. Select Fatigue (default) or Static.

Fatigue

If you set the Crack Growth Option property to Fatigue, your structure is subject to constant amplitude cyclic load.

The following other properties are available in the category:

Failure Criteria Option: This is a read-only property that is set to Material Data Table.
Material: The application uses the material that is assigned to the geometry used to define the crack selected in the Initial Crack property. You can change the material using the property's fly-out menu. The application automatically selects the default material of scoped crack bodies. Any material that you select must include a Crack Growth Law, such as Paris’ Law. Supported Crack Growth Law selections include Paris’ Law, Walker Equation, Forman Equation, Tabular Fatigue Law, NASGRO Equation V3, and NASGRO Equation V4.
Crack Growth Law: This read-only property displays the Crack Growth Law that was defined in the Engineering Data workspace and selected in the above Material property, such as Paris' Law. In the Engineering Data workspace, you can also include a fatigue crack-closure function with either Paris’ Law or the Tabular Fatigue Law. Supported functions include Elber Crack-Closure, Schijve Crack-Closure, Newman Crack-Closure, or Polynomial Crack-Closure. When specified, the function's name is automatically appended to the crack growth law displayed in this property. If the specified Material does not include an associated Crack Growth Law, this property displays the entry None.
For more information about crack growth laws and crack-closure functions, see the Fatigue Crack-Growth Mechanics topic in the MAPDL Fracture Analysis Guide for more information.
Crack Growth Methodology: Fatigue crack growth can be modeled using either Life Cycle Prediction (default) or Cycle By Cycle methodologies. If you specify Cycle By Cycle, the property Incremental Number of Cycles displays. Use this property to specify the incremental number of cycles during a substep. The default setting is 10.
Stress Ratio: You use this property to specify the stress ratio. The default value is 0. The entry range is less than 1.

Static

If you set the Crack Growth Option property to Static, crack growth modeling is based on selected fracture parameters and criteria.

Failure Criteria Option: When you set the Crack Growth Option property to Static you also need to specify the Failure Criteria Option property. Options include Stress Intensity Factor (default) and J-Integral. Each option requires you to also specify a value in the dependent property Critical Rate. The default value for the Critical Rate property is 0 for either property option. The unit system of the Critical Rate property varies based on your selection. The property can be parameterized.

Note: Either the Stress Intensity Factor or J-Integral fracture parameter can be computed in one solution. Additionally, you can compute Equivalent SIFS Range fracture result and related time history results on any crack front node (Fracture Probes).

Furthermore, when you set the Crack Growth Option property to Static, an additional category displays for the object: Step Controls for Crack Growth. The properties for this category include:

Auto Time Stepping: Property options include Program Controlled (default) or Manual. Setting the property to Manual enables you to modify the following time step properties, otherwise they are read-only.
Initial Time Step: Defines the initial time step to initiate crack growth.
Minimum Time Step: Minimum time step for subsequent crack growth.
Maximum Time Step: Maximum time step for subsequent crack growth.

Equivalent SIF Method: This property is applicable only when the SIFS property (Analysis Settings > Fracture Controls) is set to Yes and all other Fracture Controls are set to No. For mixed mode fracture problems, you must include the Mode II stress intensity factor- SIFS (K2) and Mode III stress intensity factor- SIFS (K3), to calculate the Equivalent Stress Intensity Factor (SIF) and Kink Angle. The application supports certain Equivalent SIF calculation methods through this property. Specify the Equivalent SIF calculation method and the related property definitions/options. This property includes the following options:

Program Controlled (default): The application uses the solver default Max Tangential Stress Criterion calculation method.
Max Tangential Stress Criterion: According to this criterion, a crack tends to extend to a radial direction corresponding to the maximum tangential stress on a finite circle around the crack tip. This method does not include Stress Intensity Factor K3 from Mode III fracture in the Equivalent SIF calculation.
Richard Function: This option calculates the Equivalent SIF using the approximation function proposed by Richard.
Pook Criterion: This option calculates the Equivalent SIF using the Pook's Criterion function.
Empirical Function: This option is based on customizable multiplicative factors for the Equivalent SIF calculation.

Based on the method you select, specify the following additional properties:

Multiplicative Factors: Available when you set the Equivalent SIF Method property to Richard Function. Options include Program Controlled (default) and Manual. Use the Manual option to specify the desired entries for the Factor Alpha 1 and Factor Alpha 2 properties.
Factor Alpha 1: Available when the Equivalent SIF Method is set to Richard Function or Empirical Function. Specify the positive multiplicative factor for the K2 term in the Equivalent SIF calculation function. The default value is 1.155 for the Richard Function option. This property can be parameterized when the Multiplicative Factors property is set to the Manual option or if the Equivalent SIF Method property is set to the Empirical Function.
Factor Alpha 2: Available when the Equivalent SIF Method property is set to Richard Function or Empirical Function. Specify the positive multiplicative factor for the K3 term in the Equivalent SIF calculation function. The default value is 1 for the Richard Function option. This property can be parameterized when the Multiplicative Factors property is set to Manual or if the Equivalent SIF Method property is set to the Empirical Function.
Kink Angle Method: Available when the Equivalent SIF Method property is set to any option other than Program Controlled. Use this property to specify the method for the kink angle calculation. Options include Max Tangential Stress Criterion (default) and Richard Function. The Richard Function option is only supported when the Equivalent SIF Method property is set to the Richard Function or the Empirical Function. The Max Tangential Stress Criterion setting can be used with all the options of the Equivalent SIF Method property except the Richard Function option.
Richard Coefficients: Displayed when the Kink Angle Method property is set to Richard Function. Options include Program Controlled (default) and Manual. Use Manual option to specify the desired inputs for Coefficient A and Coefficient B properties.
Coefficient A: Available when the Kink Angle Method property is set to Richard Function. Specify the coefficient of the first order term in the Richard Function for the kink angle calculation. The default value is 140°. The valid entry range for this property is -180° to 180°. This property can be parameterized when the Richard Coefficients property is set to Manual.
Coefficient B: Available when the Kink Angle Method property is set to Richard Function. Specify the coefficient of the second order term in the Richard Function for the kink angle calculation. The default value is -70°. The valid range for this property is -180° to 180°. This property can be parameterized when the Richard Coefficients property is set to Manual.
Note: The specified values for the Coefficient A and the Coefficient B properties are always in degrees, irrespective of the Angle units.

Note: See the Mechanical APDL commands CGROW,SOPT,KEQV and CGROW,SOPT,KANG for more information.

Min Increment of Crack Extension: This property specifies the minimum crack extension increment value. The options include Program Controlled (default) and Manual. The Program Controlled option uses the default minimum increment value. If you set the property to Manual, additional properties display:

Min Increment Value Treatment: Specify how to treat the value. Options include Absolute (default) and Multiplier.
Min Increment Value: This property displays when you set the Min Increment Value Treatment property to Absolute. This enables you to specify a minimum crack increment value. The default value is 0. This property can be parameterized.
Min Multiplier Value: This property displays when you set the Min Increment Value Treatment property to Multiplier. The specified value is treated as a multiplier of the reference element size at the crack front (determined by the application). This property can be parameterized.
Min Increment Control: Options include Default and Set Small Increments to Zero. When you set the property to Default, the application internally sets the crack increments which are less than the value specified for the Min Increment Value property to a value set for Min Increment Value. When you set the property to Set Small Increments to Zero, the application sets the crack increments, which are less than the specified value of the Min Increment Value property, to zero.

Max Increment of Crack Extension: This property specifies the maximum crack extension increment value. The options include Program Controlled (default) and Manual. The Program Controlled option uses the default maximum increment value. If you set the property to Manual, additional properties display:

Max Increment Value Treatment: Specify how to treat the value. Options include Absolute (default) and Multiplier.
Max Increment Value: This property displays when you set the Max Increment Value Treatment property to Absolute. It enables you to specify a maximum crack increment value. The default value is 0. This property can be parameterized.
Max Multiplier Value: This property displays when you set the Max Increment Value Treatment property to Multiplier. The specified value is treated as a multiplier of the reference element size at the crack front (determined by the application). This property can be parameterized.

Note: For a SMART Crack Growth solved model with multiple load steps or substeps, if a Force, Pressure, or Displacement boundary condition is modified or deactivated at any load step, the restart point is set to Initial point instead of the Last solved load step and sub step. This is because the SMART Crack Growth associated re-meshing will not apply the load to the re-meshed model.

You can avoid this automatic change by applying the load using a node-based Named Selection with the Preserve During Solve property set to Yes. This applies the load to the updated nodal component. Ensure that the nodes of the node-based Named Selection are included in a single face.

As needed, specify the Stop Criterion property. Options include None (default), Max Crack Extension, Free Boundary, Max Stress Intensity Factor, and Max Total Number of Cycles (displayed when the Crack Growth Option property is set to Fatigue).

When you select the Max Crack Extension, Max Stress Intensity Factor, or the Max Total Number of Cycles, the --Stop Value property displays. This property requires you to enter a value for the selected Stop Criterion option. Once the maximum stop criterion limit is reached, the application stops the solution process. In this instance, the solution is incomplete and the Solution folder will not be in solved state because the solution is not complete for all time points. If the maximum stop criterion limit is not reached during solution, then the solution process completes normally.

Specify the Mesh Coarsening property. You use this property to define a desired level of coarsening of the excessively fine mesh surrounding the crack front during the SMART crack growth remeshing processing. Options include:

Conservative (default): This option performs the least amount of mesh coarsening and creates a larger number of nodes and elements after a substantial amount of crack-growth. This options offers the greatest remeshing success rate.
Moderate: This option modestly reduces the number of nodes and elements and offers a satisfactory remeshing success rate.
Aggressive: This option quickly coarsens the mesh in the region behind crack front and offers the largest reduction in the number of nodes and elements following a substantial amount of crack-growth.

Repeat the steps above to define additional SMART Crack Growth objects when multiple cracks exist in the model.