m is the fatigue strength exponent from the material S-N curve F is the frequency (Hz) is the one-sided, wideband stress power spectral density (stress^2/Hz) j is the th moment of the one-sided spectral density j M S is the stress cycle range (peak-to-valley) N(S) is the histogram function for stress cycles is the exposure time (sec) S is the response stress overall RMS level is the narrowband correction factor is the gamma function The fatigue strength coefficient for the purpose of this paper is taken as the stress level on the S-N A curve where N=1/2 cycles, assuming no reduction in slope due to strain hardening in the low-cycle range. An alternate method is to calculate the value using fracture mechanics for the case of a preexisting A crack. Note that (1) The index may be a non-integer. j The rate of zero up-crossings can be estimated as (2) The rate of peaks is (3) The irregularity factor is (4) A special case is (5) The spectral width is
m is the fatigue strength exponent from the material S-N curve F is the frequency (Hz) is the one-sided, wideband stress power spectral density (stress^2/Hz) M j is the j th moment of the one-sided spectral density S is the stress cycle range (peak-to-valley) N(S) is the histogram function for stress cycles is the exposure time (sec) S is the response stress overall RMS level is the narrowband correction factor is the gamma function The fatigue strength coefficient A for the purpose of this paper is taken as the stress level on the S-N curve where N=1/2 cycles, assuming no reduction in slope due to strain hardening in the low-cycle range. An alternate method is to calculate the A value using fracture mechanics for the case of a preexisting crack. Note that (1) The index j may be a non-integer. The rate of zero up-crossings can be estimated as (2) The rate of peaks is (3) The irregularity factor is (4) A special case is (5) The spectral width is