PSI - Issue 22

Carlos D.S. Souto et al. / Procedia Structural Integrity 22 (2019) 376–385 Author name / Structural Integrity Procedia 00 (2018) 000–000

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5

A flowchart of the algorithm based on the mentioned ASTM standard is shown in Fig. 3. Note that the range of X and Y are defined as the absolute value of the di ff erence between the amplitude of their points. Note that in a code the word “reversal” can be interchanged by the word “index”, since, programmatically, a reversal is an index of the data array that contains the known stress history.

Start

Set Z to the first reversal in the history

Read the next reversal

Out of data?

Count each remaining range as 1/2 cycle

YES

NO

End

< 3 reversals?

YES

NO

Form X and Y using the 3 latest nondiscarded reversals: Y = (P i , P j ), X = (P j , P k )

range(X) < range(Y) ?

YES

NO

1. Count range(Y) as 1/2 cycle 2. Discard the first reversal of Y 3. Set Z to the second reversal of Y

YES

Y includes Z ?

NO

1. Count range(Y) as 1 cycle 2. Discard both reversals of Y

Fig. 3: A flowchart of the rainflow counting algorithm based on the ASTM E1049-85 standard.

4. Fatigue Damage Tool (FDT) software overview

When FDT is launched, the user can see that the interface is comprised mainly out of 3 tabs. The first tab is dedicated to all the inputs the user must submit in order for the program to run. The second tab is dedicated to the rainflow counting algorithm and its results. The third tab is dedicated to the fatigue damage calculation and its results. By going to File > Report , the user can also generate a PDF report that shows all the inputs submitted as well as all the results generated by the program. As mentioned earlier, to execute the rainflow counting algorithm, the stress-time history must be comprised only by peaks and valleys, however, if the user’s stress spectrum is not entirely made out of peaks and valleys, it can be converted by going to Tools > Convert to Peaks and Valleys. This will sequentially remove

all bad points of the data (points that are neither a peak nor a valley). Fig. 4 shows FDT’s user interface and Fig. 5 shows FDT’s basic usage.