Experimental analysis of bending fatigue strength of plain and notched case-hardened gear steels

Fatigue tests were performed on two commercial case-hardened steels using plain and notched speci- 27 mens and results were compared with data available in the literature for similar steels. The purpose of 28 the paper was to compare performances of different materials under the same testing conditions. 29 Moreover, the results obtained may form the basis to apply ISO Standard methods mentioned in the 30 Annex, which estimate the fatigue life of gears starting from experimental data generated from speci- 31 mens. Even though ISO Standard suggests primarily the use of experimental results generated from test- 32 ing gears, specimens’ testing is faster and cheaper to evaluate different materials during the design 33 process. From this point of view, specimens’ based approaches seem promising. Plane bending as well 34 as axial fatigue tests were carried out, along with static tensile tests. Fatigue design coefficients relevant 35 to the notch support effect, surface finish, mean stress effect in bending and load type (axial or bending) 36 were derived from the experimental test results and, whenever possible, were compared with ISO 37 Standard recommendations. Microstructures, hardness profiles, residual stresses and fracture surfaces 38 were analyzed as well. To evaluate the accuracy of specimens-based approaches mentioned in the 39 Annex of ISO Standard, additional work is needed in order to compare theoretical estimations with exper- 40 imental results obtained from gears.