Mechanical APDL Structural Analysis Guide

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.

Example 11.2: Defining the Crack-Tip Node Component and Crack-Plane Normal

! 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 material force calculation

CINT,NEW,1

CINT,CTNC,CRACK_TIP_NODE_CM

CINT,NORM,11,2

Example 11.3: Defining the Crack-Tip Node Component and Crack-Plane Normal

! 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,

11.3.5.2.2.2. 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,CompName

2. Identify the crack-tip node separately if the node component has more than one node. If a crack-
   tip node is not identified, then the first node of the node component is taken to be the first node.

Example: Example:CINT,CENC,CompName,NODE1

3. Define the crack-extension direction.

Identify the local coordinate system associated with the crack under consideration, and the local

axis for that coordinate system along which the crack is supposed to extend.

Example:CINT,CENC,CompName,NODE1,11,2

Alternatively, define the crack-extension direction by directly specifying the global X,Y, and Z

components of the crack-extension vector.

Example:CINT,CENC,CompName,NODE1,,,CompX,CompY,CompZ

Repeat this method for all node locations along the crack front.

Example 11.4: Defining the Crack-Extension Node Component and Crack-Extension Direction

! Local coordinate systems

local,11,0,,,,

local,12,0,,,,

...

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Fracture Mechanics