Learning Forum

[mart]

Hi,

Could You please give me instruction how to perform fatigue analysis with the sinusoidal load 1200N,  frequency 5Hz. Min load in the load cycle is 200N.

I need to check if the speciment survives 5000000 cycles, determine von mises stresses and principal stresses.

Thanks!

 

[peteroznewman]

First, you need a material in Engineering Data with S-N curve data that goes out to 5 million cycles.  Did you type that correctly? Most S-N curve data stops at 1 million cycles, for example, the Structural Steel that is included in the installation.

1) Build a Static Structural analysis with a static load of 1200 N.

2) Right click on Solution and insert a Fatigue Tool.

3) Edit the Fatigue Tool and set the Loading Type to Ratio

4) Set the Ratio to 200/1200 = 0.166666, Scale Factor =  1.

5) This will cause the analysis to cycle between a maximum load of 1200 (factor 1) and a minimum load of 200 (factor 0.16666).

6)  Insert Life into the Fatigue Tool and evaluate.

The cycles to failure in the S-N curve is when 50% of the samples failed.

If the Minimum Life = 5e6 cycles then you predict a 50% probability of survival.

 

[mart]

Thanks a lot for Your help!

I have one more question. I need to do analysis based on ISO standard, which assumes the use of a frequency between range 1Hz and 30Hz for a cyclic load. How does it affect for the result if I choose for example 5Hz or 25Hz? Where can i change this setting in the simulation?

[peteroznewman]

Under normal conditions, fatigue failure is independent of frequency.

[mart]

peteroznewman thank you for Your help.

Last thing, Is the situation analogous with the increasing torque (20Ncm-40Ncm) in analysis?  I need to calculate the ratio and perform the same step or there is another solution?

[peteroznewman]

Same process. If the torque is always positive, then the ratio is positive 20/40 = 0.5 and the load in the model must be 40 Ncm.

[mart]

peteroznewman thanks a lot for Your help!