Abstract
An innovative approach to the design of the gear-tooth root-profile, and its effects on the service life is reported in this paper. In comparison with the widely used trochoidal and the recently proposed circular-filleted root profiles, the optimum profile proposed here is a $$G^2$$ -continuous curve that blends smoothly with both the involute of the tooth profile and the dedendum circle. Following the AGMA and ISO standards for fatigue loading, the von Mises stress at the critical section and stress distribution along the gear tooth root are studied. The process leading to gear-tooth failure is composed of the crack initiation phase, in number of cycles $$N_i$$ , and the crack propagation phase, in $$N_p$$ cycles. The strain-life ( $$\epsilon$$ -N) method is employed to determine $$N_i$$ , where the crack is assumed to initiate at the critical section. Based on the ANSYS crack-analysis module, the effects of $$G^2$$ -continuous blending on the stress intensity factor (SIF) are investigated for different crack sizes. Paris’ law, within the framework of Linear Elastic Fracture Mechanics, is used to correlate the SIF with crack size and, further, to determine $$N_p$$ . The optimum profile provides a significant reduction in SIF and improvement in both $$N_i$$ and $$N_p$$ . Spur gears are made of high-strength steel alloy 42CrMo4, the effects of its properties and surface treatment on service life improvement not being included in this study.
Highlights
With the increasing demands on gear transmissions in the automotive and the aerospace industry, spur gears have become the focus of intensive research during the last two decades
The increase of gear-tooth strength serves as an important factor for the improvement of service life due to fatigue; on the other hand, the critical area for short service life always falls into the stress concentration area, which could contribute to a decrease in the tooth strength
This paper focuses on the gear-tooth breakage problem, the authors proposing a novel methodology to optimize the tooth-root profile, for the improvement of gear service life
Summary
With the increasing demands on gear transmissions in the automotive and the aerospace industry, spur gears have become the focus of intensive research during the last two decades. An optimum gear design with reduced bending stress plays significant roles in improving the fatigue service life. Two approaches are commonly adopted to reduce bending stress for a given tooth size: a) to alter the generating cutter-tooth tip; and b) to modify the geartooth root-fillet profile [3]. The prediction of crack initiation is based on the strain-life method, correlating the number of cycles Ni to initiate a fatigue crack with deformation , and stress σ. The most popular standards for tooth-root profile design are AGMA and ISO Following both standards, the critical section is defined, where the potential crack is initiated under fatigue loading. Conclusions regarding the effects of gear tooth-root profile optimization on the improvement of fatigue service life are drawn.
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