Learning Forum

[Stat]

Hi everyone,nI 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.nI 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.nCan anyone help me with that? n

[Stat]

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

[danielshaw]

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.n

[Stat]

I appreciate the answer!n

[Stat]

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.nn

[danielshaw]

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. nIf 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.n

[Stat]

Thank you for the answer once again!nDoes this has to be on a discrete analysis?n 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?n

[danielshaw]

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.n

[danielshaw]

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

[Stat]

I understood what you mean and I appreciate your interest!nI 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.nn

[danielshaw]

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.nnn