【作者】 闫胜昝；

【导师】 童水光；

【作者基本信息】 浙江大学 ， 化工过程机械， 2008， 博士

【摘要】 车轮是汽车行驶系统中重要的安全部件,汽车前进的驱动力通过车轮传递,车轮的结构性能对整车的安全性和可靠性有着重要的影响。为满足强度及疲劳等的要求,ISO、JASO及GB等标准均规定,汽车铝合金车轮必须进行弯曲疲劳试验、径向滚动疲劳试验和冲击试验。传统的车轮设计多凭借经验展开,存在着设计盲目性大、设计制造周期长、成本高等弊端。面对日益激烈的市场竞争,企业迫切需要采用科学的手段改善设计方法。本文以浙江大学与浙江万丰奥威汽轮股份有限公司的合作项目“铝合金车轮轻量化设计与开发”为背景,研究车轮结构的有限元分析方法,在设计初期预测车轮试验的结果,提出轻量化和改进方案,解决传统车轮设计存在弊端的问题。为了达到研究目的,以固体力学(包括弹性力学、冲击动力学)数值模拟为理论依据,车轮结构实际性能试验和实验应力方法相结合,先后建立了汽车车轮弯曲疲劳试验和13°冲击试验的静态弹性有限元分析模型和动态有限元分析模型,并通过试验手段进行了验证。在建立车轮弯曲疲劳试验有限元分析模型时,通过建立瞬态载荷函数,模拟了旋转弯矩的作用,得出了车轮在旋转弯矩作用下的应力分布变化情况。在建立车轮冲击试验有限元分析模型时,首先进行了正则模态分析,以半正弦函数的冲击载荷谱进行了动态响应分析,初步实现了车轮结构的动态有限元分析。首先,针对车轮结构的三大性能试验进行了静态弹性有限元分析,分析中车轮结构的材料参数通过在实际车轮结构上取样,进行标准拉伸试验获得,在静态弹性分析中不考虑材料后期的塑性变形,只取弹性阶段的弹性模量E和泊松比μ作为材料参数,在最大应力不超过车轮材料屈服强度的条件下,通过静态弹性有限元分析可以得到车轮结构在相应试验条件下的应力分布,对于优化车轮结构的设计有一定的指导意义。对冲击试验的静态分析分别通过计算动荷系数和计算瞬时最大冲击载荷两种载荷计算方法,进行了分析,并对结果进行了比较,通过瞬时最大冲击载荷加载更合理。然而,车轮结构的弯曲疲劳试验和冲击试验均为动态试验,因此,有必要对其建立动态有限元分析模型,从而更准确地得到车轮结构在试验条件下的响应情况。首先,对车轮结构进行了弯曲疲劳试验和冲击试验条件下的模态分析,分析了车轮结构的模态振型和特点;然后,对车轮结构进行了旋转弯矩动态分析,发现在弯曲疲劳试验中车轮结构中的应力是非对称循环应力。针对两种弯曲疲劳试验装置工作原理的不同,对车轮结构进行了离心力分析,通过分析表明两种试验装置的试验结果是一致的。在对车轮结构进行了冲击试验条件下的模态分析后,参考相关文献,假定冲击载荷符合半正弦函数,对车轮结构在该冲击载荷作用下的动态响应进行了分析,由于I-DEAS软件碰撞分析是基于两个假设进行的,一是碰撞发生于事件的初始时刻,二是碰撞的持续时间极短以致可以忽略,因此,该动力学碰撞分析实际上进行的结构碰撞后的响应计算。分析得到了冲击试验后车轮结构中的应力、速度和加速度响应,车轮结构中的应力响应对于评判车轮结构的设计强度,指导车轮结构的设计优化起到了一定作用,但车轮结构的冲击试验涉及轮胎大变形、气固耦合、接触等问题,要做到完全准确地建立其有限元分析模型还有一定难度,这将是今后研究工作的重点。采用动态电阻应变仪及数据采集仪,利用实验应力分析电测法原理,对车轮结构在弯曲疲劳试验和冲击试验中的应力情况进行了实测,并采用先进的神经网络算法对试验数据进行了数据挖掘处理。对弯曲疲劳试验中车轮结构的应力测量结果表明,本文建立的车轮结构动态弯曲疲劳试验有限元模型是正确的,有限元计算结果能很好的反应车轮结构在实际弯曲疲劳试验中的应力情况;而对冲击试验中车轮结构中的应力测量结果表明,在冲击试验中,车轮结构中的应力波存在大约6个波峰,冲击作为一个瞬态的大位移和大变形过程,涉及几何、材料、接触状态等多重非线性,因此,试验数据的获得是很宝贵的,对于提高数值模拟精度有指导意义。以某型车轮为例进行了实验应力分析和极限疲劳寿命试验,拟建立一条有限元分析应力结果和实验应力分析结果与车轮结构实际极限疲劳寿命相对应的曲线,可以用做今后弯曲疲劳试验寿命预测的判定依据。以某型车轮结构为例,从初始设计,有限元分析后轻量化改进,到最终产品投产,通过试验,介绍了轻量化的多种方法,根据很多类似的经验,提出了各种尺寸规格车轮结构轻量化设计的目标重量。本文围绕车轮结构的性能试验,旨在提升车轮自主设计水平,进行了有限元分析方法的研究,并通过实验应力分析对本文建立的有限元分析模型进行了验证,指出了有限元分析的合理和不足之处,并通过极限疲劳寿命试验,建立了一条实用的车轮结构材料S-N曲线。提出基于等效损伤原则的冲击响应谱分析,对车轮结构冲击试验的实验应力分析结果进行了频谱分析,得出车轮结构冲击试验中的应力波及应力谱。更多还原

【Abstract】 Wheel is an important safety component of vehicle driving system. Since all driving force of running vehicle is transferred through wheels, the performance of wheel structure is very important to the safety and reliability of the vehicle. In order to meet the requirements on strength and fatigue, ISO, JASO and GB all prescribe that aluminum alloy car wheels must do bending fatigue test, radial load fatigue test and impact test. In the past, the design of wheel mostly depends on experience. So there are a lot of shortages, such as blindly design, long design and manufacturing period, high cost, and so on. In face of the increasingly stinging competitions, enterprises cry for new scientific design method. The background of this research is the cooperative project "Aluminum wheel weight optimization design and development" between Zhejiang University and Zhejiang Wanfeng Auto Wheel Company. This dissertation focuses on the finite element method using in wheel structure design. The proposal of weight optimization and structure modification can be aroused through the finite element analysis (FEA) result which solved the shortage of traditional wheel design method.In order to achieve the objective of this research, according to the theory of numerical simulation of solid mechanics (including elastic mechanics and impact dynamics), by a way of combining real test on wheel and experimental stress analysis method, the FEM of bending fatigue test and 13°impact test were established, and verified through experiments. When establishing the FEM of bending fatigue test a transient load function was used to simulate the rotatory bending moment, the stress distribution in the wheel under this load was obtained. When establishing the FEM of impact test a half-sine function was used to define the impact load, after normal mode analysis the dynamic response analysis on impact test was elementarily realized.First of all, static elastic FEA was done on three performance test of aluminum alloy wheel. The material property of wheel used in FEA was measured on specimens taken from the real wheel. When doing static elastic analysis, only the modulus of elasticity E and the Poisson’s ratioμwere set as the material parameters. When the maximum stress in the structure is lower than the yield strength of the material, static elastic analysis is usable to calculate the stress distribution in the structure under test condition. And the result can be used to guide the structure optimization of wheel. For impact test static analysis two load calculation methods were considered, one is using dynamic load coefficient and another is calculating the transient maximum impact load. The results of two ways were compared and the way by calculating the maximum impact load is more reasonable.But bending fatigue test and impact test of wheel are both dynamic tests. So it isnecessary to establish a dynamic FEM. First, mode analysis of wheel under bendingfatigue test and impact test condition was separately done. The mode vibration modality ofwheel structure was analyzed. Then the dynamic analysis of wheel under rotatory bendingmoment was done, and the stress in the wheel during bending fatigue test is not asymmetrical one. To compare the different working principle of two kinds of bendingfatigue test machines, stress distribution of wheel under centrifugal force was analyzed.And the result shows that the test result with these two different machines should be same.After doing mode analysis to wheel structure under impact test condition, referring torelated literature, dynamic response analysis on wheel’s impact test was done with anassumption that the impact load meet half-sine function. Since the I-DEAS software has twoassumptions (1. impact occurred at the beginning of event; 2. the persistence timing is tooshort, so can be neglected.), when doing initial impact analysis, this dynamic responseanalysis was a response analysis after the impact. The displacement, stress, velocity andacceleration response of wheel structure after impact were analyzed. These results are usefulto judge the strength of wheel design and to optimize the wheel design. But to build acompletely accurate FEM is still difficult because there are tyre big deformation, gas-solidcoupling and contact issues in wheel’s impact test. To solve this difficult problem is thekeystone of future study.Using dynamic resistance strain gauge and the data collection instrument, based on the theory of electricity measurement method, the real stress of wheel structure under bending fatigue test and impact test were separately measured. Data mining was done on the stress data using artifical neural networks method. The stress measuring result of wheel in bending fatigue test shows that the FEM on bending fatigue test established in this dissertation was correct. The stress in wheel structure under bending fatigue test can be correctively reflected by the FEA result. The measuring stress result of wheel structure under impact test shows that during impact test there were 6 obvious wave crests on the stress wave of the wheel structure. As a transient process with big displacement and big distortion, there are many unlinear issues, such as geometry, material and contact. So the measuring results are very precious and have directive meaning to increase the digital simulation precision.Experimental stress analysis and limited fatigue life test were done using one kind of wheel as an example. A stress and fatigue life curve based on the FEA result and experimental test result was planned to set up which can be used as a judgment basis when predict the fatigue life of wheel based on FEA result in the future. Using a wheel structure designing process as an example, from the original design, FEA, weight optimization ways to final design, several typical way to optimize the weight were described. A target weight of weight optimization on different size wheels was brought forward.Focus on the performance tests of wheel structure the research on FEA method was carried through in order to improve the self-determination design level. Then experiments were used to verify the FEA model. The shortage of the FEA was found. Through limited fatigue life test an applied S-N curve was going to be established based on the real material of wheel through common casting techniques. Analysis of shock response spectrum based on equivalent damnification principle was brought forward. The stress wave and stress spectrum in wheel structure during impact test were gained through frequency spectrum analysis to the test result.更多还原