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01-29-2018 05:25 AM

Hi!

I have problems in LMS Test.Lab Mission Synthesis MRS/FDS computing.

How is the Stress/Displacement K factor defined? The software does not accept larger values than 1E10.

We have defined in FEM the K factor so, that we have given a displacement at the same point and direction where vibration measurements are carried out and FEM computes the corresponding stress (MPa) in specified point.

Are the other parameters Woehler exponent b and Woehler constant A somehow connected together, because the software also sometimes asks to change these values.

In my computing i have used values A = 1.574E9 and b = 13.

Regards, Juha Miettinen

Tampere university of technology

Tampere, Finland

juha.s.miettinen@tut.fi

1 REPLY

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02-01-2018 08:50 AM

The “GUI part” of Mission Synthesis seems to impose that the values have to be below 1E10. This is not just for the K, also for the other values.

A workaround for this is that in fact only the ratio K/A is important when calculating damage. So for a K value > 1E10, instead adjust the A value so that the ratio K/A gets the proper value.

In formulas:

*K*is the proportionality constant between stress and displacement:

*A*is related to the intercept of the Wohler (S/N) curve, which we define as:

- In FDS damage calculations you will always see a factor (K/A)^B, e.g.

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