Stress Analysis And Fatigue Life Prediction Of Shafts And Hubs In Reducer Of Ship Unloader

The speed reducer is the key component for speed reduction and power transmission of the opening and closing machanism. The working process of the ship unloader is full of lifting, running, brake and other movements. The lifting and descending of the bucket is running along with the car's transportation. During the hoisting and unloading process, the changes of the hoisting weight and lifting speed will cause complexed impact to components of the speed reducer, which will have an important influence on the expected life of the structure of the gearbox.As the key parts of the opening and closing machanism, the shafts' strength, performance, life expectancy and reliability has a crucial influence on the entire ship unloader's work performance and security. The life prediction and analysis of the shafts of the opening and closing reducer box under different conditions and loads can help to make maintenance plans to prevent serious accidents due to fatigue fracture caused by the shafts failure.In the states of the combinations of bending and torsion, the most damage of the shafts is caused by the alternating load form . The stress analysis results of the components must be given before fatigue life assessment of the main transmission shafts. During the 21st century, the finite element method based on computer-aided engineering (CAE) has been widely used around the world gradually. In this paper, the load and stress theoretical calculation of the dangerous parts of the shafts has been done based on elastic solid mechanics, material mechanics, fatigue cumulative damage theory and the theory of fracture mechanics. At the same time, simulation of the shafts is completed by the way of the non-linear contact finite element analysis and calculation according to the actual working conditions of the gearbox.The results of stress analysis of finite element method make a more accurate reflection of the shaft stress concentration of the most dangerous parts of the stress distribution than the traditional method of elasticity theory.Considering the state of high-speed rotating, being subject to heavy load and poor working conditions, the load spectrum of the input shaft with the load changes in the process of actual work condition has been generated, and the prepocessing and cyc modules have been used to exclude singular value, detect the peak and valley value, compress the equivalent points during the data processing and finally acquire the rain-flow counting statistics of the load spectrum ; This paper brings up the life estimation model of the shafts and obtains the corresponding material S-N curve with the use of empirical formula. The methods of the combination of equivalent stress and Miner linear cumulative damage law performed the fatigue analysis and life prediction of the key parts of the shafts in the simulation software named nSoft under variable amplitude loading, which has been relatively reliable life prediction and saved a lot of testing costs, leading to the realization of the product maintenance and periodic replacement of ship unloader in order to ensure the security and prevention of major accidents.The full text is divided into six chapters, research results and conclusions are as follows:1. First chapter includes the source of the topic, the purpose and significance of the thesis. Fatigue research and development at home and abroad has been presented to point out the cutting-edge study and development direction. Finally, the content of the paper is described briefly.2. Systemic introduction of the theory of fatigue fracture and fatigue life theory has been described in detail to highlight the merits of nominal stress analysis in industrial application. Then this paper summed up the commonly used cumulative fatigue damage model and their basic principles and application in engineering. Then, the actual impact of fatigue life by a variety of factors was taken into consideration. Finally, the steps of finite element fatigue analysis was introduced.3. The loads in different conditions were calculated, and the dangerous parts of the shafts with stress concentration such as the keyway and interference was calculated according to elasticity theory in the full-loaded cases. Then, the inversion of the load time history and and its data processing of the actual load spectrum of the input shaft is done due to rain-flow counting method.4. The three-dimensional solid models were imported into pre-processing software named Hypermesh, the details of the structure is refined in the finite element model to increase the calculating speed and ensure the accuracy of solving the problem and the simultaneous control of the mesh quality quantity. Then, a typical operating boundary condition is applied in solving the contact stress analysis in finite element software. The results of finite element results was more veritable than the theoretical calculation and prepared for further fatigue analysis.5. Finite element analysis shows that: the keyway part is subjected to greater stress and serious stress concentration and thus is the main damage source of the shaft in gearbox which affect the reliability of opening and closing machanism. Local refinement method can be extended to the general structure analysis and large-scale structure with local area of concern for analysis.6. First of all, introduced the S-N curve in form of the commonly used power function formula, and its further derivation created the S-N curves of materials in the absence of precise experimental data using the known material constants. Based on linear cumulative damage theory, the paper finally completed the shafts' fatigue life predictionin under the reliability of 95%, providing a viable method for fatigue life prediction of high-cycle fatigue life prediction of metal structure.7. The final chapter is the concluding part of this thesis, presenting a summary of the inadequacies need to be improved in this thesis.