Bending Fatigue Behavior of Carburized Gear Steels: Planetary Gear Test Development and Evaluation

Investigation of bending fatigue strength limit of alloy steel gear teeth

“…The estimated median endurance limit of 430 MPa corresponded to the life 10 6 cycles (50 per cent reliability and confidence level). The majority of researchers such as Phelan et al [1], Zhao et al [2], Lyu et al [3], Lassen and Recho [5], Bathias et al [8], Eyercioglu et al [9], and Yang [10] employed the bilinear representation of their respective S-N data like line ACD in Fig. 1 in evaluating their fatigue performance.…”

“…The endurance limit obtained in conjunction with the UDTM at three maximum stress levels at a limit cycle number of 3 Â 10 6 for a reliability of 0.99 was about 530 MPa at a knee cycle of 3 Â 10 6 . In all the aforementioned works [1][2][3][4][5][8][9][10], none of the researchers took the confidence level into account in their fatigue data analysis, though a few [2,3,10] considered the reliability of their fatigue data.…”

“…This is particularly the case for the metal gears of materials lacking a distinct declining trend, which would allow determination of fatigue strength or endurance limit. In the past two decades, the development of analytical predictive techniques such as the extension method (EM) [1] and up-down test method (UDTM) [2,3] have attracted considerable attention for estimating either fatigue life cycle or endurance limit for a given limited amount of experimental data in the form of S-N curves.…”

“…Second, the initial data trend line AB is extended to a limit cycle N b (line ABE in Fig. 1) to determine an endurance limit [1,2,5]. In the gear industry at present, this limit cycle N b is generally set to a number of 3 Â 10 6 cycles [6,7] such that the fatigue tests could be terminated in order to minimize the experimental cost if the fatigue test specimens do not fail by then.…”

“…For the induction-hardened forged gears, the median endurance limit of 797 MPa was estimated using the UDTM with the maximum stress levels ranging from 780 to 800 MPa up to the (knee) limit cycle N k of 10 7 . In the study carried out by Phelan et al [1], the bending fatigue tests of SAE 8620 and 4615 steel gears were conducted with the maximum stress levels ranging from 600 to 900 MPa and all the specimens failed before 10 6 cycles. Their fatigue life cycles were analysed according to two-parameter Weibull distribution and their S-N curves were fitted in terms of 90 per cent reliability without a confidence level.…”