| The ship unloader in the department of transportation undertakes the important task of transporting the production of raw materials into the plant. The stability and reliability of its operation determines wether the raw materials can be unload and sent to plant in time.Gears are the main parts of shipunloader gearbox. Once damaged, the user often unprepared. It seriously affects the production efficiency, resulting in great economic losses, and even leads to disastrous consequences. It is necessary to estimate the life for those gears, and to ensure they are in safe condition.After a certain period of time, pitting,tooth scuffing,tooth bending,tooth fracture will occur in gears, causing the system could not work properly, or even cause incidents. The anti-pitting and anti-scuffing capacity of low speed hard surface gear is good. Therefore, tooth is usually broken during the process of transmission. Under such background, this article studies the tooth bending fatigue life of low speed hard surface gear.This article taking the final reduction gears as the object of study, obtained the gear's tooth bending fatigue life based on GB/T3480-1997, and realized in MATLAB.Based on nominal stress method, this article propose a method to forecast gear's life which include the PRO/E 3-D modelling, the HYPERMESH grid division, the ANSYS finite element analysis and the nSoft fatigue analysis unifies.By the computers'popularization and application, utilizing 3-D software to build the model and utilizing the modern finite element method to analyze how the gears stress distribute, makes it more precise. Based on this, unifies the specialized fatigue analysis software to be able to obtain the relatively accurate tooth bending fatigue life forecasting result.At present, lots of softwares simultaneously have certain modelling and the finite element analysis function, but each kind of software's prominent superiority is various. For better make use of each software's predominance, and utilize the good data I/O between various softwares, this article has used different software to do different job to obtain gear's fatigue life.The precise helical gear 3-D model is important to the gear's finite element analysis. The software of PRO/E and ANSYS both have the ability to build the model and analyze the finite element, but they have different advantages, PRO/E is good at building the model, however, ANSYS is good at finite element analysis. FE-fatigue module of the nSoft is special software to forecast component's fatigue life. Unionning these softwares to forecast gear's fatigue life is an effective way, also provide a kind of reference for other component's life forecast.This article is divided into five chapters altogether. The research content is as follows:1,ExordiumThe first chapter is exordium, which describes the meaning of subject and points out the situation of gear fatigue life predictions. The main content and method of subject are also introduced.2,The gear's theory bending fatigue lifeAccording to GB/T3480-1997, this article carries on the gear's bending strength computation, and estimates gear's working life.This article use MATLAB program to get the relevant data. Introduced the fatigue theory briefly, provide theoretical support for further sdudy how to predict the tooth bending fatigue life of the main reduction gears of shipunloader.3,Gear bending stress analysisBased on the finite element analysis steps, using PRO/E establish the 3D model of the main reduction gears of shipunloader and assembly; Grid mesh is generated by HYPERMESH. To control the number of mesh, generate the two-generated finite element model. This article generated the gear teeth end surface grid first, and then use solid map to produce the high quality gear simplified model body grid. This article using the approach of local mesh refinement meshes the tooth root and the contact surface. Established tooth contact pairs, definite the key options and real constant; this article has analysised the helical gear by using ANSYS (finite element analysis software). Regard the influence of the restraint, the load and the engaging position to the result of finite element analysis. Through the ANSYS solution operation, obtained the helical gear tooth von miss stress distribution result of 7 engaging positions and determine the maximum stress of the most danger point.4,Gear bending fatigue life predictionBased on the gear tooth stress analysis, this article predicted the gears' bending fatigue life. First of all, based on the analysis of the actual status, this article worked out the load spectrum. In accordance with the material constants of carburized steel, this article generated the bending fatigue S-N curve. Based on the linear cumulative damage theory, this article use nSoft estimated the gears' bending fatigue life, and the conclusion shows that the main reduction gears' life is unlimited. nSoft can also shows the risk regional of the tooth root. Come to the conclusion: in this paper, the bending fatigue life of gears is satisfied with the need in practical work. Compared to the standard calculating method, each link of the finite element analysis of the fatigue life is closer to the actual situation. The results of the fatigue life better meet the actual situation, Which have a higher credibility, can be applied with engineering design and analysis.5,ConclusionIt gives the conclusion of full text, analysis the shortcomings of this article, and proposed the key point of further research.
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