Mechanical APDL Structural Analysis Guide

11.3.1.2.2.1. Define the Crack-Tip Node Component and Crack-Plane Normal

For 2-D crack geometry, define a crack-tip node component (usually a node located at the crack tip).
You can also define a group of nodes around the crack tip, including the node at the crack tip. ANSYS
uses this group of nodes as the starting nodes to form the necessary information for the contour integ-
ra tion automatically.

For 3-D flat crack geometry, you must define a crack-tip node component that includes all of the nodes
along the crack front. At each node location, however, only one node can exist. All nodes in the crack-
tip node component must be connectable, and they must form a line based on the element connectivity
associated with it.This line is the crack front. ANSYS uses it to automatically determine the elements
for the contour integration. The procedure is similar to 2-D crack geometry, and is done through all the
nodes along the crack front.

The command syntax is:

CINT,CTNC,CMNAME

After the crack-tip node component is defined, use the CINT command's NORM option to define the
normal of the crack plane. The program automatically converts it into the crack-extension vector q,
based on the element information. The crack-extension vector is taken along the perpendicular direction
to the plane formed by the crack-plane normal and the tangent direction of the crack-tip node, and is
normalized to a unit vector.

The command syntax is:

CINT,NORM,par1,par2

where par1 is the coordinate system number and par2 is the axis of coordinate system par1.

Example 1

!local coordinate system

LOCAL,11,0,,,,

! select nodes located along the crack front and define it as crack front/tip node component

NSEL,S,LOC,X,Xctip

NSEL,R,LOC,Y,Yctip

CM,CRACK_TIP_NODE_CM

! Define a new J-Integral calculation

CINT,NEW,1

CINT,CTNC,CRACK_TIP_NODE_CM

CINT,NORM,11,2

Example 2

! select nodes located along the crack front and define it as crack front/tip node component

LSEL,,,,

NSLL

CM,CRACK_FRONT_NODE_CM,NODE

CINT,NEW,1

CINT,CTNC,CRACK_FRONT_NODE_CM,

11.3.1.2.2.2. Define the Crack-Extension Node Component and Crack-Extension Direction

Use this method when the crack plane is not flat, or when a set of nodes form the crack tip, as in the
case of a collapsed crack-tip mesh:

1. Define a node component consisting of one or more nodes forming the crack tip.The node com-
   ponent can have one or more nodes.

Example:CINT,CENC,CMNAME

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Fracture Mechanics