Rainflow - Goodman Eq. Stress

[mdelsol]

Hi,

To calculate Goodman Eq. Stress is necessary to find the number of cycles corresponding to a specific mean and amplitude stress of a signal.

I tried using the rainflow function, but without success. The matrixes don’t give to me any relation of the Amplitude that is given for a specific Class means.

Selecting single parameter results I obtain the correct number of cycles (frequency) of a class mean and also Amplitude, but I don’t find the way to determine for a specific class mean how many cycles have Amplitud “A” and how many have Amplitude “B”.

Please some one can help me? Maybe I need to use another function?

Thanks in advance.

Marc.

[Christian_S]

Hi Marc,

I think you want to do a two parametrical range mean couning.

The result of the rainflow analysis in DIAdem is a matrix containing the minimum and maximum values of the counted hysteresis. That means, DIAdem is storing the results in a FROM-TO matrix. The X axis contains the FROM counting and the Y axis the TO counting. The information content is the same as in a RANGE-MEAN matrix.

But it's easy to convert a FROM-To matrix into a RANGE-MEAN matrix. I've attached a small VBS to convert the matrices.

I hope this helps,

Christian

[mdelsol]

Hi Christian,

I tried your VBS with a known signal that I generated and it works perfectly, you were right my desired output was a RANGE-MEAN matrix. I had no time to see how the conversion is performed, but I will do it to understand everything better. Do you know where can I find more information related to FROM-TO and RANGE-MEAN matrix?

Could you explain me exactly the difference between the Rainflow and Transition matrix? or tell me where can I find this information?

Thanks a lot for your help, especially for the VBS to convert matrices. Without your help I couldn’t continue my calculations.

Thx again,

Marc.

[Christian_S]

Hi Marc,

here you can find more information:

Metal Fatigue in Engineering
Ralph I. Stephens; Henry O. Fuchs
Wiley 2001
ISBN 0471510599
Chapter 9

or

Merkblatt FVA 0/14 "Zählverfahren zur Bildung von Kollektiven aus Zeitfunktionen - Vergleich der verschiedenen Verfahren und Beispiele" der Forschungsvereinigung Antriebstechnik (www.fva-net.de)

Christian

[AMBRO]

Can you please tell me a step by step guide to pass from a one channel time history to mean-range-cycle rainflow?

Thanks

ambro

[Christian_S]

Hello ambro,

I have attached a new example which at first calculates a transition matrix (not needed here) and a rainflow matrix from an example load-time function with the build-in DIAdem function ChnRainCalc. This piece of code is the same you get when running the rainflow calculation interactively with teach-in mode enabled.

Pay attention that there is the new parameter RainInclFirstLastVal introduced with DIAdem 2010. However the example is running with DIAdem 11.1.

In a second step the range-mean matrix is calculated from the rainflow matrix with a small script function.

The load-time function and all results are shown on several pages of a report layout.

Regards,

Christian