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# LMS Test.Lab Mission Synthesis MRS and FDS computing

Experimenter

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

# Re: LMS Test.Lab Mission Synthesis MRS and FDS computing

Siemens Legend

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.