Rotating Bending Fatigue Test of Large Press-Fitted Shaft under Two-Step Pulsating Load

Abstract

In order to study rotating bending fatigue strengths and fatigue lives of press-fitted shafts under fluctuating load, fatigue tests were carried out under a two step pulsating load by using 29 specimens of 140 mm diameter. The test conditions are specified by the following notations : n₀ : Reversal numbers in one loading cycle. n_l : Reversal numbers under lower stress amplitude σ_l in one loading cycle. n_h : Reversal numbers under higher stress amplitude σ_h in one loading cycle. n_t : Transitional reversal numbers under the amplitude between σ_l and σ_h in one loading cycle. Six kinds of tests were made by varying the above factors, as n₀, n_h/n₀, n_t/n₀ and σ_l. The fatigue lives were converted into cumulative values of n_h by using the linear damage law. Through a logical analysis of these test results, it has been found that the fatigue lives decrease most remarkably comparing with those tested under constant stress amplitude if n₀ becomes smaller and n_t/n₀ larger, and remarkably decrease when σ_l exceeds the crack initiating limit. On the contrary, it has been also presumed that the fatigue lives increase if n₀ becomes larger, n_t is negligible and σ_l does not exceed the crack initiating limit. Irrespective of the changing of the fatigue lives, the fatigue strengths at 10 million reversals under the higher stress amplitude were scarcely affected by the test conditions.