Mechanical APDL Structural Analysis Guide

σaijuxεijaux iaux

are the stress, strain and displacement of the auxiliary field,

and qi is the crack-extension vector.

The interaction integral is associated with the stress-intensity factors as

= 
+ 
 


∗(^1122 )+μ^33

where:

 (i = 1,2,3) = mode I, II, and III stress-intensity factors





(i = 1,2,3) = auxiliary mode I, II and III stress-intensity factors

E* = E for plane stress and E* = E / (1 - ν^2 ) for plane strain

E = Young’s modulus

ν = Poisson’s ratio

μ = shear modulus

11.3.3.1.2. Calculating the Stress-Intensity Factors

Mechanical APDL calculates the stress-intensity factors via interaction integral evaluation at the solution
phase of the analysis, and then stores the values to the results file.

The CINT command's SIFS option initiates the stress-intensity factors calculations. Similar to the J-integral
calculation,CINT is also used to specify the parameters necessary for the calculation. For element type
and material behavior support for CINT, see Element Selection and Material Behavior (p. 352).

Following is the general process for calculating the stress-intensity factors:

11.3.3.1.2.1. Step 1: Initiate a New Stress-Intensity Factors Calculation

11.3.3.1.2.2. Step 2: Define Crack Information

11.3.3.1.2.3. Step 3: Specify the Number of Contours

11.3.3.1.2.4. Step 4: Define a Crack Symmetry Condition

11.3.3.1.2.5. Step 5: Specify Output Controls

11.3.3.1.2.1. Step 1: Initiate a New Stress-Intensity Factors Calculation

To start a stress-intensity factors calculation, issue the CINT command twice, as follows:

CINT,NEW,n

CINT,TYPE,SIFS

where n is the number identifying this stress-intensity factors calculation.

For example:

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

CINT,TYPE,SIFS! specify stress-intensity factor calculations

11.3.3.1.2.2. Step 2: Define Crack Information

Similar to the J-integral calculation, the crack-tip node component and the crack-extension direction
are both necessary for the stress-intensity factors calculation. Two methods, both involving the CINT
command, are available for specifying the values:

Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information

Fracture Mechanics