You use the Crack Initiation feature/object to specify a criterion to determine when a crack is initiated in a specific region (or zone) of the geometry. You can also specify the location, orientation, and the size of the crack to be initiated. You insert and define a Crack Initiation object under the Fracture folder. You then assign it as an Initial Crack to the SMART Crack Growth object to study the crack growth.
Refer to the SMART Method for Crack-Initiation Simulation section of the Mechanical APDL Fracture Analysis Guide for more information.
Crack Initiation Application Recommendations
Ansys recommends the following for successful crack initiation and propagation using SMART Crack Growth:
Specify the crack initiation zone using the Geometry or Named Selection properties, such that there is enough stress concentration in the zone that meets the specified critical Criterion Value.
Make sure that the maximum stress concentration zone does not have nodes constrained using supports such as Fixed supports, Frictionless Supports, etc.
Make sure that the crack initiation zone includes a reasonably fine mesh.
Make sure that the scoped components have nodes that can be combined into a single group.
Make sure that the re-meshing zone does not have any unsupported elements, such as contact elements, surface effect (SURF) elements, etc.
Apply pressure loads using option of the property in the remeshing zone.
Manually verify the crack definition inputs, including Crack Orientation, Crack Center, and Crack Shape in case of a crack initiation failure. Consider specifying the crack center manually using the Crack Orientation or Crack Center properties.
Application
Assuming you have opened Mechanical and imported a geometry, select the Fracture option from the Model Context tab. The application inserts a Fracture folder and makes it the active object in the Outline. Alternatively, you can use the context (right-click) menu to add this object. Right-click the Model object and select > .
Select the Crack Initiation option from the Fracture Context tab. This can also be done using the context menu.
Use the properties of the Scope category in the Details pane to select geometric entities (edge, face, or body), geometry-based Named Selections (edge, face, body), or node-based Named Selections for the region of the geometry where you want to initiate the crack.
The Initiation Criteria category includes the Initiation Criterion property and the Criterion Value property. The Initiation Criterion property is read-only and set to . This specifies that the application calculates stresses at each node during the solution. Use the Criterion Value property to enter a value, that once reached during the solution process, the application will initiate a crack.
Specify additional input properties as needed. Properties include:
Crack Orientation: Options include , , and . If you select either of the manual options, an associated Coordinate System property displays. Use this property to select a desired coordinate system from the drop-down list. The list contains the options and any user-defined coordinate systems.
Crack Center: Options include and . When you select , coordinate (X, Y, Z) properties display. Use these properties to define the center of the crack.
Crack Shape: Options include and . Currently, only the elliptical shape is supported. As a result, when you select the manual option, the application displays the Major Radius and Minor Radius properties. Specify these values as needed.
Note: This feature only creates elliptical shaped cracks. The initiated crack can be completely embedded in the solid body, or it can be a surface crack intersecting one or more surfaces of the solid body, or it can be a corner crack.
Solution Contours: Specify the number of solution contours for which you want to compute the fracture result parameters. The default value is
6.
Insert a SMART Crack Growth object and select this Crack Initiation object as the option for the Initial Crack property. Complete any other entries of the SMART Crack Growth object. As needed, see the SMART Crack Growth Application section for more information.
Define remaining environmental conditions such as boundary conditions and loading.
Make sure the Fracture property of the Fracture Controls category of the Analysis Settings object is set to .
Solve the simulation.
Note: Crack Initiation may not be successful if the specified criterion value is not satisfied. In this case fracture results will be unavailable.
Insert a Fracture Tool and set the Crack Selection property to Crack Initiation.
Insert desired fracture results under the Fracture Tool.
Evaluate the fracture results.