【作者】 施欲亮；

【导师】 林忠钦； 朱平；

【作者基本信息】 上海交通大学 ， 车辆工程， 2008， 博士

【摘要】 减轻汽车质量以降低燃油消耗和减少排放污染是21世纪汽车发展的核心问题。由于拼焊板结构具有减轻重量、减少零件数量、提高材料利用率和提高结构性能等优点,在汽车车身的轻量化设计中,利用拼焊板结构替代传统结构已经成为主要方法之一。但是目前的零件拼焊板设计主要依赖于专家经验或以参照为主,缺乏相关方面的定性或者定量的设计方法研究,因此为拼焊板结构在车身零件上的应用,开展拼焊板车身零件轻量化设计方法研究具有重要的意义和应用价值。汽车零件的拼焊板轻量化设计绝不能以牺牲其关键力学性能为代价,尤其是关乎乘员安全的汽车耐撞性,而耐撞性数值仿真技术是汽车开发过程中不可缺少的重要工具。为了使得耐撞性数值仿真手段能够快速、精确地指导拼焊板设计,本文首先对耐撞性数值仿真的关键技术进行了研究,提供了精确、高效的分析模型基础,为耐撞性数值仿真正确指导零件拼焊板设计轻量化提供了保证。在此基础上分别以车身薄壁梁结构部件和板壳结构部件作为分析对象,进行了拼焊板轻量化设计方法研究,提出了综合考虑零件强度、弯曲刚度、扭转刚度、吸能能力和材料成本的薄壁梁零件拼焊板轻量化设计方法,以及综合考虑整车耐撞性能、零件强度、刚度和自然频率的板壳零件拼焊板轻量化设计方法,并将所形成的方法应用于车身具体零件的拼焊板轻量化设计。主要研究内容及结论如下:1.汽车耐撞性数值仿真的关键技术研究重点研究了基于汽车碰撞仿真的点焊连接关系模拟以及网格规模控制方法研究。针对已有方法的不足,引入弹-塑性梁接触模型来模拟点焊连接关系,对比分析了以刚性梁和弹-塑性梁接触模型来模拟点焊在冲击过程中对于失效判断的稳定性和可靠性,仿真解析结果表明弹-塑性梁接触模型更适合于模拟点焊冲击行为。从网格规模控制的角度,提出了徐变区域网格布置方法和CPU计算时间控制方程,并通过正碰仿真试验,验证了结合以上两种手段进行整车模型网格规模控制在提高计算效率的同时并不减少计算精度,证明了该方法的可行性。2.基于汽车碰撞仿真的拼焊板焊缝有限元模型建立针对目前没有合适的焊缝有限元模型来模拟拼焊板焊缝在汽车碰撞过程中的力学行为,提出了双层梁模型来模拟焊缝。采用不同建模技术,基于单轴拉伸仿真和碰撞仿真对拼焊板焊缝有限元模型进行研究,进行了与汽车碰撞有关的失效位置、变形和吸能等方面的精度影响分析。结果显示,不同的建模方式在有限元仿真中将对各种结果产生非常敏感的影响,从而证明了拼焊板焊缝模型研究的重要性。通过仿真与实验结果的比较与分析,验证了本文所提出的双层梁焊缝模型相对于现有的其它焊缝模型更合理。3.车身薄壁梁零件的拼焊板轻量化设计方法研究基于力学基本原理,推导了拼焊板薄壁梁的强度、弯曲刚度、扭转刚度和吸能能力轻量化控制方程。利用乘子罚函数方法进行拼焊板薄壁梁优化设计求解并提出了薄壁梁零件的拼焊板轻量化设计方法。在此基础上以汽车前纵梁作为范例进行拼焊板轻量化设计,首先进行零件的分块设计和材料的初选,然后根据所建立的轻量化方程对零件的厚度和材料进行约束控制,利用乘子罚函数方法获得优化结果并综合考虑质量和材料成本进行设计方案评价,最后对选取的轻量化方案进行了耐撞性数值仿真,验证了轻量化设计方法的可行性。4.车身板壳零件的拼焊板轻量化设计方法研究从泛化能力的角度,对比了响应面方法(RSM)和人工神经网络(ANN)两种近似模拟方法对于拼焊板设计中不同响应的拟和效果。分析结果表明,RSM更适合于拼焊板设计中简单响应(零件质量、刚度、自然频率)的模拟,而ANN则对于耐撞性响应有着更大的优势。对板壳典型零件车门内板进行实例设计,以零件质量和侧碰安全性能作为优化目标,以强度、刚度和自然频率作为优化约束,利用权重系数遗传算法进行了多目标优化计算,实现了车门内板的拼焊板轻量化设计,在此基础上提出集有限元数值模拟、近似模拟技术和遗传算法于一体的板壳拼焊板轻量化设计方法。本文对基于汽车碰撞的几个关键CAE技术进行了研究,目的在于提高CAE仿真精度和计算效率,为车身零件的拼焊板轻量化设计提供准确、快速的模型基础;根据薄壁梁和板壳零件不同的结构特点提出了两种不同类型的拼焊板轻量化设计方法,对拼焊板结构在车身上的应用具有很好的借鉴作用。更多还原

【Abstract】 Reduction of automotive weight is the core problem in the 21 century for its potential to decreasing the fuel consumption and emission pollution. The tailor-welded blank (TWB) has the advantages of weight reduction, parts count decreasement, material utilization efficiency enhancement and structure performance improvement. Therefore, the utilization of TWB structure to replace the traditional structure has become the main approach among the automotive lightweight design methods. However, the current TWB design mainly relies on the expert experience and reference,lacking the related qualitative or quantitive study. Therefore, designing a lightweight method for the TWB components is of great significance and value for the application of TWB in automotive industry.The automotive lightweight design using TWB structure can not be conducted at the cost of the key mechnical performances, especially the automotive crashworthiness relating to the passenger safety. Furthermore, the impact simulation technique is an important tool in the development of automobiles. In order to make the crashworthiness numerical serve the TWB design quickly and precisely, this paper firstly performs a study on the key techniques in the crashworthiness numerical simulation, which provides precise and efficient analytical modals for the lightweight. Then, the methodology study is performed by using the TWB structure to reduce the automotive weight, with the thin-walled beam components and shell-shaped compnents as the design target. A lightweight design method for thin-walled beam components is presented in which the strength, bending stiffness, torsion stiffness, energy absorption capability and material cost are comprehensively considered. In the mean time, we put forward a design framework for lightening the shell-shaped components using TWB structure, in which the crashworthiness performance, part strength, stiffness and natural frequency are taken into account. Finally, the established method is applied to the lightweight design for the detailed automotive parts using TWB. The works and results in this paper are mainly as follows:1. Study on the key technologies based on vehicle impact simulationA study is performed to model the spot weld and control the mesh dimension based on the vehicle impact simulation. An elastic-plastic beam contact model is put forward to represent the spot weld, aiming at compensating the shortage of the current methods. Comparison between the rigid beam and the elastic-plastic beam is performed to analysize the stability and reliability in predicting the failure time of the spot-weld under impact loading. The analytical results of simulations show that the elastic-plastic beam contact model is more suitable for modeling the spot welds under impact loading compared with the rigid beam model. Method of meshing a vehicle using gradually changing areas and CPU time governing equation are presented from the point of view of mesh dimension control. The full-width frontal impact simulation of the whole car shows that combining the above two methods to control the mesh dimension of the car model can enhance the simulation efficiency with no sacrifice of simulation accuracy, which proves the validity of the methods.2. Impact modeling of the weld line of tailor-welded blankSince currently there are no proper models to represent the weld line of TWB under impact loading, a novel welding model is put forward, which uses twofold beams to simulate the behavior of the weld line. Simulations of uniaxial tensile tests and impact tests are conducted to study the influences of different weld modeling methods on mechanical behaviors of tailor-welded blanks involved in vehicle impact such as failure position, deformation, and energy absorption. The results indicate that there are a number of relatively subtle effects associated with the manner in which the weld line is modeled. The simulation and test analysises prove that the two-fold beam model presented in this paper is more reasonable than other existing models.3. Method study on the TWB lightweight design method for the automotive thin-walled beam componentsBased on the basic mechanical principle, the lightweight governing equations of strength, bending stiffness, torsion stiffness and energy absorption capability are derived. Method of multiplier penalty function is used to optimize the TWB thin-walled structure and the design approach is presented for lightening the TWB thin-walled components. Then, the automotive front side rail is taken as the example to do the TWB lightweight design. Firstly, the partition and initial material selection for the TWB component is performed. Secondly, constraints are applied to the thicknesses and materials according to the established lightweight governing equations. Whereafter, the method of multiplier penalty function is utilized to obtain the optimal results and design schemes are evaluated based on the mass and material cost. Finally, crashworthiness numerical simulation is performed to assess the selected lightweight scheme and prove the feasibility of the lightweight approach.4. Method study on the TWB lightweight design method for the automotive shell-shaped componentsFrom the point of view of generalization capability, the approximate efficiency of two meta-model technologies response surface method (RSM) and artificial neural network (ANN) are compared in the different TWB design. The analytical results show that the RSM is more suitable for the simple response approximation (part weight, stiffness and natural frequency), while the ANN has more advantages in impact reponses. When taking the automotive inner panel as the design example, the weight-sum genetic algorithm (GA) is used to optimize the multi-objective problem, with the part weight and side impact crashworthiness as the optimization objectives and the strength, stiffness and natural frequency as the optimization constraints. Thereby, the lightweight design of the automotive inner door panel is realized by using the TWB structure. In this way, an integrated approach is defined using FEA, ANN and GA for the optimization design of shell-shaped components with a TWB structure.This paper studies sevel key CAE technologies existing in the crash simulation, in an attempt to enhance the preciseness and calculation efficiency thus supplying a correct and fast-running model for the further TWB lightweight design of the automotive components. Then according to the different structural characteristics of thin-walled beam and shell-shaped components with TWB concept, two different design framework are properly defined, which makes a good reference for the application of TWB structures in auto body.更多还原