Tooth root bending fatigue strength of small-module sinter-hardened spur gears

Abstract

The present paper is aimed at investigating the effect of the sinter-hardening treatment in improving the tooth root fatigue resistance of gears obtained by Powder Metallurgy. The gears were produced using two types of low-alloyed partially diffused steel powders, Distaloy DC and Distaloy DH (Höganäs AB, Sweden), that were conventionally sintered as well as sinter-hardened. A different microstructure was obtained after the two sintering processes that led to different fatigue response. As expected, the martensitic microstructure is responsible for good fatigue performances, slightly less than those of gears made with wrought low-alloyed quenched and tempered steels.

The role of pores and microstructural heterogeneity on the tooth root fatigue strength of sintered spur gears

“…The cracks not involved in this process of coalescence stop growing as that shown in figure 14. This observation agrees with the crack propagation behaviour reported in the technical literature [5,8,12,13].…”

“…In the figures 8-10 the results of the bending fatigue tests and the P 10 , P 50 and P 90 fatigue curves are plotted. The obtained results are compared with results published in [3][4][5] for similar microstructures with different porosity contents. In general, the literature data show a progressive but not particularly marked decrease in the fatigue strength with density for relative densities higher than 90%, whereas a very marked worsening occurs at lower densities.…”

“…The microstructural heterogeneity can play a very important role in the damage localization and in the definition of a preferential crack path [5,8]. Particularly critical are the soft phases that usually envelop the critical pores and represent the microstructure of first propagation of the fatigue crack.…”

“…The gears represent one of these applications, where maximum advantages in terms of competitiveness and quality can be achieved by using a near net shape technique such as P/M [1][2][3][4][5].…”

Tooth Root Bending Fatigue Strength of High-Density Sintered Small-Module Spur Gears: The Effect of Porosity and Microstructure

“…This test configuration fails to apply the fatigue load along the line tangent to the base circle and passing to the tooth tip as prescribed by ISO6336. For this reason, rather than the formula available in this standard and used for instance in [28], the stress state in the critical location of the tooth root was evaluated through a finite element (FE) analysis able to reproduce the actual testing configuration. The FE model employs quadratic 20-node brick elements.…”