PSI - Issue 71

Ninad Vasant Pawar et al. / Procedia Structural Integrity 71 (2025) 134–141

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Fig. 7 Schematic details of abutment of cone face on pinion gear face with relative projections of cone features

Fig. 8 Vickers hardness observations of cone groove and flange surface

compared to the core. In the presence of fluctuating stress spikes, the less tough groove surface can crack due to insufficient toughness in the given application condition. The microcrack can grow circumferentially as well as into the flange section towards the large cone. The possibility of microcrack spreading on the groove is greater because at the surface the tensile stress amplitude is greater as compared to the inner section. Once the circumferential spread of crack was complete, the crack could have propagated further into the flange section. As the crack grew, the flange surface shifted axially with respect to the cone track under the action of a continuous axial load. This might have damaged the outer edges of the pinion gear (refer to Fig. 1(a)) tooth as the flange would have contacted it with the shifting flange section. Complete separation took place once the fracturing section was not able to take the incoming load from pinion gear operation. 3.6. Evaluation and experimentation for improvement The unsupported groove area of the flange in tooth space, combined with the lower toughness of the surface-treated and quench-tempered cone made of 52100, makes it unsuitable to withstand the current application conditions of pinion gear application. As per values reported by the K IC value of case carburized SAE 8620 is better than that of through hardened SAE 52100 grade (Lee and Ho, 1989)( Diesburg and Eldis, 1978)( Beswick, 1989)( Nakazawa and Krauss, 1978). Considering this advantage, along with a tougher, softer core, cones were made with similar geometry as the current cone. These cones were case-carburized, hardened, and tempered. To compare the static cross-sectional strength at the flange area, cones made from 52100 and 8620 (the new proposal) were tested for breaking load on a universal testing machine. The values are shown in fig.9(a) in the form graph. Charpy impact test values of 6 specimens each of surface treated SAE52100 and case-carburized 8620 are given in fig. 9(b). The impact energy as well as flange breaking load is observed higher for case carburized variant indicating the cone of 8620 can withstand higher loads as well as it has higher toughness than surface treated 52100. The Charpy impact test uses equation 1 to calculate the impact energies. However, the test machine uses angles of pendulum to measure the height of hammer before and after impact. = ( 1 − 2 ) (1) Where E = Impact energy (J) m = mass of pendulum (kg)

H 1 = Height of pendulum before impact (m) H 2 = Height of pendulum after impact (m)