36.6. Analysis and Solution Controls

Because crack-growth is typically a nonlinear phenomenon, a nonlinear static analysis is performed. For a VCCT-based crack-growth simulation, it is also necessary to perform both of the following tasks at each crack tip:

For more detailed information, see VCCT Energy-Release Rate Calculation in the Fracture Analysis Guide and VCCT-Based Crack-Growth Simulation in the Fracture Analysis Guide.

 

36.6.1. Energy Release-Rate Calculation Setup

The following commands initiate the new energy-release rate calculation:

CINT,NEW,1 -- Assigns an energy-release rate calculation ID of 1 (Par1 = 1).
CINT,TYPE,VCCT -- Specifies a VCCT-based energy-release-rate calculation (Par1 = VCCT).

VCCT calculation requires the finite element mesh to be in the crack-extension direction. The crack tip component, normal of crack plane, and crack-extension direction provide the data necessary for the calculation:

CINT,CTNC,CRACK_RIGHTR -- Assigns the crack tip component name (Par1 = CRACK_RIGHTR).
CINT,NORM,0,2 -- Specifies the global Cartesian coordinate system (Par1 = 0 [default]) and the Cartesian Y axis of the coordinate system (Par2 = 2 [default]).

Crack-plane and crack-extension directions are defined in relation to the global Cartesian coordinate system by assuming the flat crack plane.

 

36.6.2. Crack-Growth Calculation Setup

The following commands initiate the crack-growth calculation:

CGROW,NEW,1 -- Assigns a crack-growth data set ID of 1.
CGROW,CID,1 -- The contour-integral calculation ID, the same value specified for CGROW,NEW.
CGROW,CPATH,CPATH_RIGHTR -- The interface element component name for the crack path.
CGROW,FCOPTION,MTAB,6 -- Specifies the linear fracture criterion for crack-growth (as defined in the material table by TB,CGCR,,,,LINEAR) and material ID 6.

The following commands specify the solution controls for crack-growth:

CGROW,DTIME,1E-3 -- Initial time step when crack-growth is detected.
CGROW,DTMIN,1E-4 -- Minimum time step allowed when crack-growth is detected.
CGROW,DTMAX,2E-2 -- Maximum time step allowed when crack-growth is detected.
CGROW,FCRAT,1 -- Fracture-criterion ratio (fc, generally around 1).
 

36.6.3. Input for Defining Energy-Release Rate and Crack-Growth

The following example input defines the energy-release rate and crack-growth simulation set for crack tip 1:

! Energy Release Rate
CINT,NEW,1
CINT,TYPE,VCCT
CINT,CTNC,CRACK_RIGHTR
! Define a local coordinate system. Use neighboring nodes.
CS,21,0,229,228,1171
! Use the y axis the crack normal.
CINT,NORM,22,2

! Crack-Growth Simulation Set
CGROW,NEW,1
CGROW,CID,1
CGROW,CPATH,CPATH_RIGHTR
CGROW,FCOP,MTAB,6					! Crack-growth fracture criterion used with the 
                   				!    material data table
CGROW,DTIME,1E-3   				! Initial time step when crack-growth is detected 
CGROW,DTMIN,1E-4   				! Minimum time step allowed when crack-growth is 
                   				!    detected
CGROW,DTMAX,2E-2   				! Maximum time step allowed when crack-growth is 
                   				!    detected
CGROW,FCRAT,1      				! Fracture-criterion ratio