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Finite Element Analysis of a Car’s Front Sub-frame

Author: ZhangHaiYan
Tutor: YaoWeiMin
School: Jilin University
Course: Vehicle Engineering
Keywords: Sub-frame Finite Element Static Analysis Modal Analysis Fatigue Life Analysis Structure Optimization
CLC: U463.32
Type: Master's thesis
Year: 2011
Downloads: 166
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Abstract

With the development of science and technology, people put forward higher requirements to the performance of the cars. In order to improve the performance of comfort and handling, a structure of sub-frame comes (?)to people’s life. The structure has been widely used in compact and small cars. Firstly, in order to fully enhance the car’s performance, most sub-frame’s material is aluminum alloy. Aluminum sub-frame has lighter weight and good performance but its cost is high. In order to (?)hieve a balance between vehicle’s performance and economy, peopledually began to use steel instead of aluminum. This article bases on this background, we choose the material of a steel to check the various properties of steel sub-frame weather meet the requirements or not.This article takes a car’s front sub-frame to study. Firstly, ensure its structure’s mechanical features, Then make some necessary simplification to the structure. We use HyperMesh’s shell element to create the sub-frame’s finite element model. In order to improve the accuracy, we create the connected components such as the control arm, steering and stabilizer bar. Through establishing the connections we can get the assembly of the sub-frame. We can calculate its strength and stiffness by Optistruct. The result showed that the sub-frame’s maximum stress is less than the material’s yield limit, so that it could meet the requirements. In the modal analysis we use Block Lanczos to calculate the sub-frame’s former 12 modes, the result shows that the steel sub-frame is impossible to cause dynamic interference with road and engine. It means the steel sub-frame’s mode distribution are reasonable, generally speaking the resonance does not occur. We make a comparison with the likely sub-frame’s modal initial validation experiment data, it shows that the finite element model is reasonable. Thanks to the sub-frame undertakes the alternating loads, its damage is mainly fatigue damage. Therefore, we need to analyze the fatigue quality of the steel sub-frame. We use the stress-life analysis methods because the sub-frame is typical high-cycle fatigue. In the use of Nastran, we can get the structural response under cyclic loadings. By Palmgren-Miner damage accumulation theory, bring the SN curve of the left-arm vibration acquisition and right-arm vibration and engine mount vibration analysis module that is got by rain-flow cycle counting method into MSC. Fatigue Whole Life.At the last of the paper, it described the basic concept and the three elements of topology optimization. Established a system of shell element optimization model of the subframe, take the place where exert the load’s nodal displacement as constraint conditions, minimize the total volume of the subframe as the optimization target, take the thickness of the shell element as the design variables, make the size optimization design of the subframe system, and make static linear analysis of the subframe system after the round size under the limit loads.Based on the static analysis, modal analysis and fatigue life analysis of the steel sub-frame, not only to verify the steel sub-frame can basically meet the requirements but also to provide more intuitive basis which can improve the design of the sub-frame, which has a positive meaning to improve the sub-frame.

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