Differences in the size of the elements ahead of and behind the crack tip/front affect the accuracy of
the energy-release rat e calculation. While the program uses a correction algorithm, it may be inadequate
to produce an accurat e solution. Instead, use equal sized meshes for elements along the predefined
crack path. For more information, see Numerical Evaluation of Fracture Mechanics Parameters (p. 350).
12.1.1.2. Step 2. Perform the Energy-Release Rat e Calculation
For VCCT-based crack-growth simulation, it is necessary to perform the energy-release rat e calculation
first.
To calculate the energy-release rates, issue the CINT,TYPE,VCCT command. Issue subsequent CINT
commands to specify other options such as the crack tip node component and crack plane/edge normal.
The VCCT calculation uses the following assumptions:
- The strain energy released when a crack advances by a small amount is the same as the energy required
to close the crack by the same amount. - The crack tip field/deformation at the crack tip/front location is similar to when the crack ext ends by a
small amount.
The assumptions do not apply when crack growth approaches the boundary or when the two cracks
approach each other; therefore, use the VCCT calculation with care and examine the analysis results.
For further information, see VCCT Energy-Release Rat e Calculation (p. 356).
12.1.1.3. Step 3. Perform the Crack Growth Calculation
The crack growth calculation occurs in the solution phase after stress calculation. To perform the crack
growth calculation, you must define a crack growth set, then specify the crack path, fracture criterion,
and crack growth solution controls. The solution command CGROW defines all necessary crack growth
calculation parameters.
Perform the crack growth calculation as follows:
12.1.1.3.1. Step 3a. Initiate the Crack Growth Set
12.1.1.3.2. Step 3b. Specify the Crack Path
12.1.1.3.3. Step 3c. Specify the Crack-Calculation ID and Fracture Criterion
12.1.1.3.4. Step 3d: Specify Solution Controls for Crack Growth12.1.1.3.1. Step 3a. Initiate the Crack Growth Set
To define a crack growth set, issue the CGROW,NEW,n command, where n is the crack growth set
number.
12.1.1.3.2. Step 3b. Specify the Crack Path
To define the crack path, issue the CGROW,CPATH,cmname command, where cmname is the component
name for the interface elements.
12.1.1.3.3. Step 3c. Specify the Crack-Calculation ID and Fracture Criterion
Specify the crack-calculation ID via the CGROW,CID,n command, where n is the crack-calculation (CINT)
ID for energy-release rat e calculation with VCCT. ( The CINT command defines parameters associated
with fracture parameter calculations.)
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationVCCT-Based Crack Growth Simulation