Mechanical APDL Structural Analysis Guide

NSEL,S,LOC,X,Xctipn

NSEL,R,LOC,Y,Yctipn

NSEL,R,LOC,Z,Zctipn

CM,CRACK_FRONT_NODE_CMn

CINT,NEW,1

CINT,TYPE,VCCT

CINT,CENC,CRACK_FRONT_NODE_CM1,,11,2

CINT,CENC,CRACK_FRONT_NODE_CM2,,11,2

CINT,CENC,CRACK_FRONT_NODE_CMn,,n,2

Example 2:

! Crack-extension node component and

! crack-extension direction specification using vectors

NSEL,S,LOC,X,Xctip1

NSEL,R,LOC,Y,Yctip1

NSEL,R,LOC,Z,Zctip1

CM,CRACK_FRONT_NODE_CM1

NSEL,S,LOC,X,Xctip2

NSEL,R,LOC,Y,Yctip2

NSEL,R,LOC,Z,Zctip2

CM,CRACK_FRONT_NODE_CM2

NSEL,S,LOC,X,Xctipn

NSEL,R,LOC,Y,Yctipn

NSEL,R,LOC,Z,Zctipn

CM,CRACK_FRONT_NODE_CMn

CINT,NEW,1

CINT,TYPE,VCCT

CINT,CENC,CRACK_FRONT_NODE_CM1,,,,Vx1,Vy1,Vz1

CINT,CENC,CRACK_FRONT_NODE_CM2,,,,Vx2,Vy2,Vz2

CINT,CENC,CRACK_FRONT_NODE_CMn,,,,Vxn,Vyn,Vzn

Local Crack-Tip Coordinate System

The VCCT calculation is based on the local crack-tip coordinate systems. To ensure the accuracy of

the energy-release rat e calculation, it is crucial to have a local crack-tip coordinate system in which

the local x-axis is pointed to the crack extension, the local y-axis is pointed to the normal of the

crack surfaces or edges, and the local z-axis pointed to the tangential direction of the crack front.

Local coordinate systems must be consistent across all nodes along the crack front. A set of incon-

sistent coordinate systems results in irregular behavior of the energy-release rat e distribution along

crack front.

The program automatically calculates the local coordinate systems based on the input crack front

nodes and the normal of the crack surface or ext ension directions. Because there may be not enough

information to determine a set of consistent coordinate systems, however, ANSYS, Inc. recommends:

• Using the CINT command's CTNC option to define a crack-face node to help identify the coordinate
  systems,or


• Using the CINT command's NORM option, followed by the CENC option, to define the coordinate systems.

11.3.2.2.3. Step 3: Define a Crack Symmetry Condition

If the crack is located along a symmetry plane, and only a half model is created, define a symmetric
condition so that the program can account for it.To do so, issue the following command:

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Fracture Mechanics