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Afgrow use 2
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From the User's Guide & Technical Manual
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3.2.4.1.1 Spectrum Multiplication Factor (SMF)
The spectrum multiplication factor is multiplied by each maximum and minimum value in the user input stress spectrum. This allows a user to input spectra, which are normalized (maximum value = 1), and simply use one multiplication factor to predict the life for different stress levels. Of course, this can be done for non normalized spectra as well, but may be awkward since it requires the user to calculate the appropriate multiplication factor for the actual maximum value in the spectrum.
SMF is usable for a couple scenarios:
1) "what-if" evaluations, what happens to life if stress goes up by a certain %
2) poor man's transfer function, you know stress is nnn times something like Nz, and your spectrum file is in terms of Nz (disclaimer for the units weenies: check your units for consistency, this is merely one example).
3) stress spectra are commonly stored normalized to a 1 ksi maximum stress, SMF is then known maximum stress (divided by 1000).
Do study the User's Guide & Technical Manual; it is written well enough you can learn quite a bit from it. But do take a course in Fracture Mechanics at your next opportunity, it will be very enlightening.
(
3.2.4.1.1 Spectrum Multiplication Factor (SMF)
The spectrum multiplication factor is multiplied by each maximum and minimum value in the user input stress spectrum. This allows a user to input spectra, which are normalized (maximum value = 1), and simply use one multiplication factor to predict the life for different stress levels. Of course, this can be done for non normalized spectra as well, but may be awkward since it requires the user to calculate the appropriate multiplication factor for the actual maximum value in the spectrum.
SMF is usable for a couple scenarios:
1) "what-if" evaluations, what happens to life if stress goes up by a certain %
2) poor man's transfer function, you know stress is nnn times something like Nz, and your spectrum file is in terms of Nz (disclaimer for the units weenies: check your units for consistency, this is merely one example).
3) stress spectra are commonly stored normalized to a 1 ksi maximum stress, SMF is then known maximum stress (divided by 1000).
Do study the User's Guide & Technical Manual; it is written well enough you can learn quite a bit from it. But do take a course in Fracture Mechanics at your next opportunity, it will be very enlightening.
der8110 just did a great job explaining this aspect of AFGROW, but this isn't a subject matter to attempt to apply without someone that has a good deal of experience in either crack propogation and/or damage tolerance looking over your shoulder. Find someone that you can talk to about this before you actually apply it to an aircraft. This Forum is filled with great people, but there are limitations with what they can do through this media...
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