Published Online: 1 July 2012
Page Count: 8
Dabiru, Venkata Rambabu
Mechanical Engineering, Indian Institute of Science, Bangalore,
Mechanical Engineering, Indian Institute of Technology, Kharagpur,
(Received 12 October 2011; accepted 27 February 2012)
We reconsider standard uniaxial fatigue test data obtained from handbooks. Many S-N curve fits to such data represent the median life and exclude load-dependent variance in life. Presently available approaches for incorporating probabilistic aspects explicitly within the S-N curves have some shortcomings, which we discuss. We propose a new linear S-N fit with a prespecified failure probability, load-dependent variance, and reasonable behavior at extreme loads. We fit our parameters using maximum likelihood, show the reasonableness of the fit using Q-Q plots, and obtain standard error estimates via Monte Carlo simulations. The proposed fitting method may be used for obtaining S-N curves from the same data as already available, with the same mathematical form, but in cases in which the failure probability is smaller, say, 10 % instead of 50 %, and in which the fitted line is not parallel to the 50 % (median) line.
Paper ID: JTE104419