Mechanical APDL Structural Analysis Guide

! Define the elastic-plastic material parameters:

FP,61,1.7,.3! M and N

3. Define stress locations and stress concentration factors.

The following option allows you to explicitly define a nodal location of interest to your fatigue

evaluation, define stress concentration factors (SCFs) for that location, and assign a short (20

character) title to that location.

Command(s):FL

GUI: Main Menu> General Postproc> Fatigue> Stress Locations

Note

Not all fatigue analyses will require the FL command. Locations are automatically defined

for nodes when FS,FSNODE, or FSSECT are issued (see below). If your model contains suffi-

cient grid detail, your stresses could be accurat e enough that you would not need to apply

calculated SCFs. (Supplemental SCFs for surface, size, or corrosion effects might still be re-

quired, however.) Where only one location is being examined, you could omit a title. If explicit

definition of locations, SCFs, or titles are not required, you could forgo the FL command

entirely.

Here is an example of some FL commands for a cylinder with a global Y axis, having two wall thicknesses
of interest, where SCFs are to be applied (to the axial linearized stresses) at the outside wall.

FL,1,281,,,,Line 1 at inside

FL,2,285,,1.85,,Line 1 at outside

FL,3,311,,,,Line 2 at inside

FL,4,315,,2.11,,Line 2 at outside

Figure 14.1: Cylinder Wall with Stress Concentration Factors (SCFs)

311

281

315

285

SCF=1.8 5

SCF= 2. 11

X

Y

14.3.3. Store Stresses and Assign Event Repetitions and Scale Factors

14.3.3.1. Storing Stresses

In order to perform a fatigue evaluation, the program must know the stresses at different events and
loadings for each location, as well as the number of repetitions of each event. You can store stresses
for each combination of location, event, and loading, using the following options:

• Manually stored stresses

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Fatigue