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Analysis of Structure Strength and Welding Fatigue for Automotive Exhaust System

Author: LiJinLong
Tutor: HouXianJun；LiuZhiEn
School: Wuhan University of Technology
Course: Power Machinery and Engineering
Keywords: automotive exhaust system finite element method modal analysis weld fatigue life
CLC: U464.134.4
Type: Master's thesis
Year: 2011
Downloads: 311
Quote: 4
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Abstract

Exhaust system is an important part of vehicle with internal combustion engine propulsion system for discharging exhaust gas from engine. Though performances of acoustics, exhaust purification and pressure loss of the exhaust system have been widely investigated, its structural strength and weld fatigue durability haven’t been attracted enough research attention, and have gradually become the focus of attention. In view of the less study of exhaust system in this respect less domestic, and the great gap between the level of research over the same Period abroad, so it’s necessary to strengthen research in the field to make up deficiencies in short term, research results obtained in the analysis will add a certain extent to this field, and it can be the important references of the research and design of the exhaust system.In this paper, based on a multi-DOF features of elastic hangers and rigid connectors of the exhaust system, combined with the structural design of the exhaust system, according to the characteristics of the various parts of the exhaust system, and simplify it, completed the finite element meshing and modeling of a vehicle exhaust system in HyperMesh. Meanwhile, the loading of the exhaust system in a variety of conditions have been applied to complete the car exhaust system static analysis.In this paper to analyze the modal of the system in both free and restricted status, and get the natural frequency and the amplitude of every modal. Then, learn the natural frequency and corresponding amplitudes of the system by experimental modal analysis in those status, and compare them with the theoretical calculated and experimental results, show that the corresponding natural frequencies and mode shapes are consistent, and indicate that the distribution on hanger locations of the exhaust system to a more reasonable position, but also reflect the system’s finite element model of the high degree of confidence. To further verify the reasonableness, the analysis of dynamic analysis of exhaust system is carried out and the transfer force of the hangers are very reasonable, showing the structure of higher strength and better overall design.Because the most prone to Welding fatigue failure location of exhaust system is at the muffler, the fatigue life of welded muffler exhaust system have a significant impact on the life of the system. Finally, based on the high accuracy model, the stress analysis have been carried out in Nastran, and obtained the stress analysis results from stress analysis after applied load on the exhaust system model. Then the results were imported into MSC. Fatigue, and completed the fatigue life analysis of the muffler using cumulative damage theory after set material S-N curve and post-load characteristics. According to the results of stress and fatigue analysis shows that large stress is corresponding to the low life, and Occurred in the welds, the results obtained by analyzing the fatigue durability of the exhaust system is very reliable,and meeting the design requirements.

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