Time-dependent reliability of spur gear system based on gradually wear process

Friction and wear are unavoidable for transmitting power in gear systems. Severe wear can cause mechanical component damage. The dynamic characteristic of gear system is affected not only by friction and wear but also by variation of geometrical shape and dimension parameter caused by mild wear, which lead to more serious wear. Therefore, the coupled relation between wear and dynamic load should be taken into consideration to study gear wear. Gear parameters might not be accurate after machining in practice, which is one of reasons why product failure still occurs. That is to say, parameters have uncertainty and randomness. Besides, wear depth accumulates over time gradually, so gear wear is a random process, which has random statistical regularity. As a result, more practical surface wear model and dynamic reliability model with gradually parameters can be established from the definition of reliability, the reliability of mechanical component can be observed all over its life cycle, and the tolerance of designed parameters can be determined to reduce failure probability. The wear model should be established based on failure mechanism to study gear wear. In recent 30 years, wear and failure mechanism of gears have been studied based on lots of laboratory tests, Zurowski[28] et al. employed TT-3 tester to research wear resistance of C45(norm)/145Cr6 and C45(600)/145Cr6 matchings and indicated that wear resistance of the two matchings had a significant dependence on friction area temperature and material hardness. However, research on establishing models and calculation methods for gear wear have little been touched on. In general, these models break down into three categories: The first model was established on undetermined coefficient or regression analysis method according to test data. The conclusion was convincing but only obtained laws for intermediate variables. For example, Põdra[15] studied wear had a linear correlation with normal load and had incomplete correlation with sliding velocity. The second was developed to discuss the influence of parameters from energy loss aspect. For example, Onishchenko[14] studied the effect of machine operation, corresponding tribological theories, the eccentricity of pitch circle and the instant temperature in the contact ZHU L, ZHANG Y, ZHANG R, ZHANG P. Time-dependent reliability of spur gear system based on gradually wear process. Eksploatacja i Niezawodnosc – Maintenance and Reliability 2018; 20 (2): 207–218, http://dx.doi.org/10.17531/ein.2018.2.05.