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

Abstract

The present paper is aimed at investigating the effect of porosity and microstructure on tooth root bending fatigue of small-module spur gears produced by powder metallurgy (P/M). Specifically, three steel variants differing in powder composition and alloying route were subjected either to case-hardening or sinter-hardening. The obtained results were interpreted in light of microstructural and fractographic inspections. On the basis of the Murakami a r e a method, it was found that fatigue strength is mainly dictated by the largest near-surface defect and by the hardness of the softest microstructural constituent. Owing to the very complicated shape of the critical pore, it was found that its maximum Feret diameter is the geometrical parameter that best captures the detrimental effect on fatigue.

Early Crack Propagation in Single Tooth Bending Fatigue: Combination of Finite Element Analysis and Critical-Planes Fatigue Criteria

“…Exploiting the Wildhaber property [1], these forces are applied perpendicularly to two tooth flanks, resulting in tangent to the base circle [23]. STBF tests are interrupted if a tooth fails or if it withstands the run-out condition (10 6 -10 8 ) cycles [24][25][26][27][28]. The statistical elaboration of failures and run-outs (the load levels are defined with the staircase approach [29,30]) leads to the determination of the load-carrying capacity [20].…”

Numerical Study of the Impact of Shot Peening on the Tooth Root Fatigue Performances of Gears Using Critical Plane Fatigue Criteria

“…STBF tests are widely exploited in the technical and scientific literature thanks to their simplicity and low cost. Many references can be found in the literature dealing with STBF tests [8,11,18,19,25,[43][44][45][46][47][48][49][50][51][52][53][54][55]. The results of STBF tests should be used in combination with standards (e.g., [13]) for the design of new gears.…”

Fatigue Design and Defects in Metals and Alloys

“…Twelve research articles have been published in this Special Issue of Metals. The subjects are multidisciplinary, including (i) the effect of microstructural defects on the high and very high cycle fatigue strength of metallic materials [1][2][3][4][5], (ii) probabilistic fatigue prognosis incorporating the size of defects and control volume [2,4,6], (iii) the effects of plasticity, high temperature, and aggressive environment on the fatigue response [7][8][9], (iv) thermo-chemo-mechanical treatments to mitigate the detrimental effect of defects on the fatigue strength [10,11], and (v) non-destructive techniques to detect fatigue critical defects [12].…”

“…The critical inclusions were significantly larger in Gaussian specimens than those in hourglass specimens. Fontanari et al [4] investigated the tooth root bending fatigue strength of small-module gears fabricated via powder metallurgy. They found that the fatigue strength is the result of a complex interplay between porosity and microstructure, as the former factor essentially depends on the size and shape of the critical pore leading to crack initiation, the latter is related to the microhardness of the softest microstructural constituent surrounding the critical defect.…”

“…They were able to rationalize the fatigue data collected on plain and notched samples made of Ti-6Al-4V alloy. Tridello [4] analyzed the fatigue data using marginal (not conditioned to the inclusion size) P-S-N curves. Deng et al [2] used the generalized extreme values (GEV) distribution to estimate the maximum defect size.…”