Mechanical APDL Structural Analysis Guide

Example 11.1: Initiating a New Material Force Calculation

CINT,NEW,1! initiate a new material force calculation as #1

CINT,TYPE,MFOR! set calculation type to material force

11.3.5.2.2. Step 2: Define Crack Information

The crack-tip node component and the local crack direction are both necessary for a material force
calculation. Two methods using the CINT command are available for specifying the values:

• Define the crack-tip node component and crack-plane normal.

This approach applies to both 2-D crack geometry and 3-D flat crack surfaces. It offers a simple way

to define a 3-D material force calculation, as you need only define the crack-tip (front) node component

and the normal of the crack plane.

Use this method when the crack plane is flat.

• Define the crack-extension node component and crack-extension direction.

This approach applies to 3-D curve crack planes, where a unique normal may not exist. However, you

must define the crack-extension node component and the crack-extension direction at each crack-

tip node location. 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.

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.

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

For 2-D crack geometry, you can 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. The program uses this group of nodes as the starting nodes to form the necessary information for
the contour integration 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. The program uses it to automatically determine the elements
for the contour integration. The procedure is similar to 2-D crack geometry, and is performed through
all nodes along the crack front.

The command syntax is:

CINT,CTNC,CompName

where CompName is the crack-tip node component name.

After defining the crack-tip node component, define the normal of the crack plane:

CINT,NORM,Par1,Par2

where Par1 is the coordinate system number and Par2 is the axis of that coordinate system.

The program automatically converts the crack plane normal into the local crack coordinate system,
based on the element information. The local coordinate system is evaluated along the perpendicular

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Numerical Evaluation of Fracture Mechanics Parameters