In this work, the bending fatigue strengths of injection-molded symmetric and asymmetric nylon 66 gears were evaluated experimentally, and the results were substantiated using numerical studies. The symmetric (20°/20°) and asymmetric (34°/20° and 20°/34°) configurations were subjected to bending fatigue tests under a load controlled mode. The bending stresses of the symmetric and asymmetric gears were predicted by quasi-static simulations using a commercial finite element analysis software. The form factor ([Formula: see text]) and the stress correction factor ([Formula: see text]) were computed using an adapted ISO method. The 34°/20° configuration exhibited the lowest bending stress and highest bending fatigue life among the tested configurations. The form factor exerted a decisive influence on the magnitude of the bending stress compared to the stress correction factor. For the considered loading conditions, deflection-induced load sharing occurred in the 20°/20° and 20°/34° configurations but was absent in the 34°/20° configuration. Failure analysis indicated that a high stress concentration caused multiple cracks in the fillets of asymmetric gears.

Life of a metal on ultra‐high molecular weight polyethylene (UHMWPE) total hip replacement is often limited to 10–15 years, due to wear loss and aseptic loosening. Due to its high melt flow index, UHMWPE is typically processed by ram extrusion or compression molding technique, but yet to be processed to the full potential of its mechanical integrity in acetabular shape without any fusion defects or weak bonding. The main objective of the present study is to develop a novel technique to fabricate defect‐free acetabular cups with desired bearing characteristics and surface finish by sintering medical‐grade UHMWPE GUR 1050 powder after its cold isostatic compaction with optimum processing parameters. Sintering kinetics of UHMWPE is studied comprehensively using a thermomechanical analyzer. The influence of compaction pressure, sintering temperature, and sintering duration on sintering kinetics of UHMWPE is explored to realize their optimum. The optimally processed UHMWPE has the relative density of 97% and Vickers hardness of 5.4 with tensile yield strength and elastic modulus of 21.5 and 625 MPa, respectively. The newly developed acetabular cup exhibited inherent plateau‐finished bearing surface with an average surface roughness of <100 nm, having good bearing characteristics and desired dimension.

Polyamide, with its low friction coefficient, high heat resistance and good moldability, is a promising polymer to meet the rising demand for lightweight, durable gears. This paper considered injection-molded polyamide 66-polyamide 66 gear pair wear performance under unlubricated and wet lubricated condition. The experiment was conducted using in-house developed power absorption gear test rig. The torque of 1.8 Nm, rotational speed 800 rev/s and lubricant SAE 75W85 was considered during testing. During the test, gear tooth temperature under unlubricated condition and lubricant temperature under wet lubricant condition was measured and monitored. The net surface temperature on the gear surface and lubricant was observed as 370 K and 303.4 K, respectively. The transmission efficiency was increased by 5% compared to the unlubricated condition. Testing confirmed that the gear exhibited surface wear at both the face and flank region in unlubricated condition. While testing under wet lubricant condition, the wear was observed on the face of the gear. Simulation result confirmed that the deflection of test gear is significantly higher in double tooth contact region shared by the face side as compared to flank side of the driven (test) gear. That could be the possible reason for test tooth wear in the face region.

This study compares the bending fatigue performance of a selective laser sintered Nylon 12 spur gear with an injection moulded Nylon 66 gear. Test gears were subjected to load-controlled, single tooth bending fatigue tests in a custom-built test setup. Cyclic pulsating loads were applied on the test gear using a steel driver gear. The bending fatigue life of selective laser sintered gears was superior compared to the injection moulded gears. In the high cycle fatigue region, the difference between the fatigue life of selective laser sintered and injection moulded gears was higher, whereas it was lower in the low cycle fatigue region. The variation in the fatigue strength of the selective laser sintered gears was due to the different thermal behaviour at low cycle fatigue and high cycle fatigue regimes. The lower surface temperature caused the higher fatigue strength of the selective laser sintered gears in the high cycle fatigue regime. On the contrary, the selective laser sintered gears’ surface temperature was higher than injection moulded gear in the low cycle fatigue regime, which reduced fatigue strength. The crack path was tortuous in selective laser sintered gears and smoother in injection moulded gears. In selective laser sintered gears, the layered structure of the part aided in impeding the propagation of crack.

This study investigates the influence of tooth layer orientation on the bending fatigue behaviour of Nylon 12 spur gears manufactured by a selective laser sintering process in an ‘on-edge’ configuration. The test gears were submitted to single tooth bending fatigue tests, and the thermal response of gears was recorded using Infrared thermography. The surface morphology of failed teeth was examined using microscopy. The effect of tooth layer orientation on the fatigue strength of selective laser sintering gears was evaluated by testing each tooth configuration. The tooth configurations with the highest and lowest strength were 40° and 160°, respectively. The performance of selective laser sintering gears was compared with that of injection moulded Nylon 66 gears. The injection moulded, selective laser sintering 40°, and selective laser sintering 160° gear teeth were tested at multiple loads to investigate the high cycle fatigue and low cycle fatigue behaviour. The bending fatigue life was highest for the injection moulded gears in both low cycle fatigue and high cycle fatigue regimes. The surface temperature was higher in selective laser sintering gears, with 160° configuration exhibiting the highest temperature. The difference between the temperatures of selective laser sintering 40° configuration and injection moulded gear magnified as the applied load increased. Consequently, the strength of the selective laser sintering 40° configuration with respect to injection moulded gear deteriorated in the low cycle fatigue region. Fractography indicated that crack propagation in selective laser sintering 40° and selective laser sintering 160° configurations were cross-laminar and inter-laminar, respectively. In the cross-laminar mode of propagation, the crack propagation was impeded by the layer structure. However, the crack propagation was expedited in the inter-laminar mode, as the crack path was along the interlayer region, which presents a path of least resistance.