# Fatigue tool for the last step of a multiple-step analysis

Member

Hi everyone,

I am performing an analysis with multiple steps and I want to calculate the fatigue life of the model when only the load of the last step is applied as cyclic loading.

I have been told that I can do that by using tabular data. However I was not able to find where do I define the tabular data.

Can anyone help me with that?

• Member

In addition, will the program calculate the fatigue life of the model due to cyclic loading implemented on the last step by default?

• Forum Coordinator

For Constant Amplitude, Proportional loading (r-ratio) or Non-Constant Amplitude Proportional loading (e.g., history data), the Mechanical Fatigue Tool will use whatever result set that you specify (in Details Window). By default, the last result set is specified.

• Member

• Member

At the "Display Time" tabs in "Definition" I understand that I can set the ending time of the cyclic loading, but always the starting time is at 0 sec. How can I define the starting time to be at the 4th sec, since my cyclic loading is implemented at the 4th till the 5th sec.

• Forum Coordinator

The Fatigue Tool (FT) just uses the FE results from the specified result set. In a static analysis, time does not have any physical meaning. It is just a counter. When you set the Display Time to be equal to 2 seconds, you are just telling the FT to use the FE results that are associated with a solution time of 2 seconds.

If you want to examine the fatigue damage caused by cycling between result set 4 and result set 5, you need to do a Constant Amplitude, Proportional Loading analysis. You need to set up a Solution Combination that contains result set 4 and result set 5; and then place a FT under that Solution Combination. The FT will use the alternating stress between result set 4 and result 5 to determine the fatigue damage.

• Member

Thank you for the answer once again!

Does this has to be on a discrete analysis?

Do I have to export the remaining stresses from the previous steps and import them in a new analysis in order to perform the last step and calculate the fatigue damage?

• Forum Coordinator

I am not sure what you mean by a "discrete" analysis. You need to result sets from the same model. They can be 2 results from the same multi-step solution or they can be 2 result sets from separate solutions that share the same mesh.

• Forum Coordinator

I meant to say "two" results sets from the same model.

• Member

I understood what you mean and I appreciate your interest!

I am afraid that I do not know how to extract the 2 result sets that I am interested in, from the multi-step solution and how to prepare the simulation that will consider cycling loading between these two results sets.

• Forum Coordinator

You need to use a Solution Combination. The image shown below uses 2 results sets from the same analysis. You could also use 2 results sets from different analysis.