Deterministic Analysis of Crack Growth Rates in Carburized Steels

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

“…Three and four point or cantilever design plane bending tests are mainly carried out under load ratio close to zero R ≈ 0, being relevant to the teeth of a drive gear. Tests presented in refs [5,6,[9][10][11] were carried out on cantilever specimens with rounded corners to avoid edge effects during the carburization process, according to an improved geometry of the original specimen introduced by Brugger [12]. In fact, at specimen's corners the amount of adsorbed carbon during carburization is higher than at flat surfaces, resulting in different microstructure after quenching and tempering, eventually leading to a lower endurance limit [13].…”

“…The specimens analysed in refs. [5,6,[9][10][11] were characterized by a net-section stress concentration factor equal to K t =1.3 and by surfaces chemically polished before the case-hardening treatment, consisting of gas-carburization, quenching and then tempering. The influence of different temperatures and holding times on fatigue properties was also investigated.…”

“…The range of notch tip radii was from 0.5 to 7.62 mm. The experimental data concerning all plane bending tests taken from the literature [5,6,[9][10][11][14][15][16] are reported in Figure 1, where the net-section nominal bending stress amplitude (σ an , half the difference between maximum and minimum applied stresses) has been used to present the results (N f is the number of cycles to failure). Figure 1 reports also three test series investigated in the present work, namely A1, C1 and X1, which will be considered later on in the paper.…”

“…It should be noted that specimens taken from [16] were affected by tensile rather than compressive residual stresses and present the lowest values of the notch tip radius. In some cases [5,6,10,11] the scatter of fatigue test results is significantly higher, so that failures are spread almost over a whole decade for the same applied stress amplitude.…”

Bending fatigue design of case-hardened gears based on test specimens

“…Moreover, specimens' testing may be faster, easier and less expensive than using gears. Several authors systematically tested specimens made of case-hardened gear steels using plain bending, [3][4][5][6][7][8][9][10][11] rotating bending, [12][13][14][15][16][17] or axial test configurations. 18,19 However, the aim of such experimental campaigns was mainly to evaluate comparatively different materials and/or manufacturing processes and to investigate the damage mechanisms, rather than obtaining fatigue curves to assess the bending fatigue strength.…”