Abstract
The article is devoted to the refinement of the flexural strength assessment of surface-strengthened gears with Novikov’s engagement. For standard involute wheels the results that were calculated in accordance with existing regulations and experiments could differ by an order of magnitude, or even more, then for Novikov’s transmissions, only partial recommendations based on experiments are relatively reliable. The influence of several factors, such as the possible initiation of flexural fractures under the action of contact stresses on the tooth’s leg, as well as the peculiarities of cyclic loading of gear teeth with two lines of engagement, have not been studied in practice. The purpose of this article is to assess the influence of tensile stresses on the boundary of the instantaneous contact spot in the conditions of reducing the plastic properties of the material due to thermal (chemical-thermal) treatment. The presence of a dangerous cross-section on the border of the active and transitional sections of the tooth profile is presented, which may not coincide with the area of action of the maximum tensile stresses, in which two essentially different types of stress-strain state will alternate, which considerably complicates the assessment of accumulation of fatigue damages.
Highlights
For gears with hardness H ≥ (57 ... 58) HRC, the tooth strength is often limited by the bending stresses
Even for standard involute wheels with more than a century and a half experience and a design model in a modification adopted in most calculation regulations, the results of calculations differ from the experimental data by an order of magnitude, and even more [1]
The purpose of this work is to investigate the features of the stress-strain state of the teeth of Novikov gears subjected to heat treatment or chemical heat treatment: the evaluation of the influence of tensile stresses on the boundary of the instantaneous contact spot in conditions of a decrease in the plastic properties of the material, justifying the need to consider the boundary of the instantaneous contact patch on the gear tooth two lines of engagement as potentially dangerous along the fracture
Summary
For gears with hardness H ≥ (57 ... 58) HRC, the tooth strength is often limited by the bending stresses. 58) HRC, the tooth strength is often limited by the bending stresses. Even more significant difficulties related to the evaluation of the loading capacity of Novikov's gears, the insufficient bending strength of which in some cases did not allow them to realize their high contact resistance. The problem was solved by the development of the design of the teeth with a mutual displacement of the head and the tooth, which significantly increased the base of the tooth. By this principle, several contours were developed [2], included RGU-5 (Figure 1b)
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