Repeat this method for all node locations along the crack front. Although the program automatically
calculates the local coordinate system at the crack tip to determine stress-intensity factors, it is usually
best to use the NORM option to help align the calculated normals of the crack-tip nodes.
Example 1
! local coordinate systems
local,11,0,,,,
local,12,0,,,,
...
local,n,0,,,,
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,SIFS
CINT,CENC,CRACK_FRONT_NODE_CM1,,11,2
CINT,CENC,CRACK_FRONT_NODE_CM2,,11,2
...
CINT,CENC, CRACK_FRONT_NODE_CM2,,n,2Example 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_CMnCINT,NEW,1
CINT,TYPE,SIFS
CINT,CENC,CRACK_FRONT_NODE_CM1,,,,Vx1,Vy1,Vz1
CINT,CENC,CRACK_FRONT_NODE_CM2,,,,Vx2,Vy2,Vz2
...
CINT,CENCOMP,CRACK_FRONT_NODE_CM2,,,,Vxn,Vyn,VznLocal Crack-Tip Coordinate System
The auxiliary crack-tip field is based on the local crack-tip coordinate systems. To ensure the accuracy
of the stress-intensity factors calculation, it is crucial to have a correct 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.
The local coordinate systems must be consistent across all nodes along the crack front. A set of incon-
sistent coordinate systems results in no path dependency of the calculated stress-intensity factors and
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationNumerical Evaluation of Fracture Mechanics Parameters