A Study Of Gear Bending Fatigue Strength Under Random Load In Compliance With Weibull Distribution

Gear transmission is one of the most important forms of mechanical transmissions. It has a series of advantages, such as large transmission ratio range, high transmission efficiency, broad power ratio and compacted structure. With the economic and technological development, the transmission speed has been required for constant increase. For instance, in the fileds of high speed EMUs and aerospace, gear drive has drawn people’s concern as an extremely important form of mechanical drive.Fatigue failure is a main failure mode of gear parts when they work under random load. When the load spectrum collected and statistics analyzed, the random load is generally found to obey the continuous probability distributions, like Exponential Distribution, Normal Distribution, Extreme Value Distribution and Three-parameter Weibull Distribution. Among these distributions, Three-parameter Weibull Distribution is the most widespread form to cover the others as a special form of its distribution. In this thesis, a study of gear bending strength is carried out under random load in compliance with Three-parameter Weibull Distribution by means of theoritical analysis and experimental studies.The present study is sponsored by national science and technology project funding (the serial number is 2006036004099). In this theis, first of all, formula for calculating the equivalent load was derived according to accumulated fatigue damage equivalent to the principle of random loads. And then, the impact of three parameters on equivalent load and load proportion coefficient was analyzed as well as load fluctuation on load spectrum. As followed, comparison between Normal Distribution and Weibull Distribution was done when they were in the cases of the same variance factor and the same material factor under equivalent load. It is found that the gear bending fatigue strength complying with Weibull Distribution is lower than that subjected to Normal Distribution. At last, the theoretical formula for calculating the gear bending fatigue strength under random load was derived, appropriate parameters were selected, the random load spectrum for experiment was prepared, and the theoretical value of the gear bending fatigue strength subjected to Three-Parameter Weibull Distribution was derived.The gear bending fatigue experiment was carried out on MTS machine and then statistical analysis of the test results was done, which proved the validity and feasibility of the approaches in theory and application. Detailed comparative analysis on the test results of gear bending fatigue strength was carried out under constant load, the Normal Distribution as well as Three-parameter Weibull Distribution. In this thesis, the impact of the distribution of gear fatigue load on the life of gear was summarized by comprehensive study. It is hoped that the results will be in favor of the design and optimization of the gear design under random load.