Running a progresive fatigue analysis

[jensglud]

I want to run a progressive fatigue analysis using Simulation Composite Analysis 2014 and Ansys.

In order to check whether I have implemented the SN-data correctly and are running the analysis with the right settings I have made an FE-model of a standard coupon test specimen. I want to see whether I can get the same SN-curves out of my analysis as I have applied as material data.

I have encountered some difficulties in running the analysis, which I believe is mainly due to the fact that I am not entirely sure what should be solved when and how.

I have saved a .hin file in the same folder as running the job in and with the same name as the jobname. The .hin file contains:

*FATIGUE,STEP=2
*BLOCK,REPEATS,5000
0.1,0.0
1,0.125
0.1,0.25

which simulates a loadratio of R=0.1 at a loading frequency of 4Hz (the same as one of my input SN-curves)

In my ANSYS .inp I have 2 load steps where each load is the maximum load applied to the specimen at a given number of cycles to failure.

The load and the number of repeats correspond to each other such that fatigue failure should occur at 5000 cycles.

However when I plot fx. SDV2 (cycles to failure as stated in .mct file) I get 2.19E9 which makes no sense. The damage variables SDV1, SDV3 & SDV4 seems to be unaffected by the number of repeats specified in the .hin file.

Can anyone see what I might be doing wrong or instead maybe upload an example (.inp & .hin file) of a fatigue analysis that should run properly? 

[milligd]

Modify your .hin file definition to look like:

*FATIGUE,STEP=2
*BLOCK,REPEATS,1
0.1,0.0
1,0.125
0.1,0.25

The *BLOCK, REPEATS=nrepeats is used for block loading.  If you have 1 block of a certain frequency/amplitude followed by 1 or more of a different frequency/amplitude, this would be more than 1.  If your load history is only comprised of 1 amplitude & frequency (like a sine wave), then it should be 1.

An online tutorial for running a progressive fatigue solution using ANSYS + Simulation Composite Analysis can be found here:

http://help.autodesk.com/view/ACMPAN/2015/ENU/?guid=GUID-EE9B2B3D-4560-4BF1-99D4-B6FF3A9A5F18