Study On Car Body's Lightweight Based On Advanced Theories And Improving Vehicle's Safety Performance

In recent years, national automobile industry is meeting rapid growth and autos'holding amount is gradually increasing, which makes the problem of energy consumption and environmental protection much more critical and this will obviously obstruct sustainable development of our national automobile industry. As an effective way to reduce energy consumption and emission, automobile lightweight has already become critical research issue. In the near future, it will be one of the core competitiveness among domestic and international auto companies. Car body's lightweight is one of the effective way of automobile lightweight, which has been widely used for the past few years. It has been deeply studied by many national and international researchers and many achievements have been made, for example, optimal design of car body's structure, replacing some traditional steel parts by lower density materials such as aluminum and magnesium alloy, composite materials etc., using of new technics and so on. Based on predecessor's achievements, this paper does systemic and in-depth study on some homemade independent-brand car by use of optimal design of car body's structure. By ensuring car's comprehensive performance such as static and dynamic stiffness and safety, the objective of reducing weight and consumption has been achieved.Centering on the issue of lightweight, main researches are showed as follows:1. As far as some homemade car is concerned, development flow of complete vehicle and simulation contents have been introduced in this paper. And it also illustrates finite element modelling method of complete vehicle in detail. In concept phase of developing a car, it is indispensable to have one finite element model of complete vehicle which can not only simulate vehicle's mechanical performance accurately but also its computational time is acceptable. It can provide some supports for predicting vehicle's structure performances and conducting optimal design. Concerned on body-in-white(BIW) and powretrain and transmission system, this paper systematically discusses modelling method of sheet metal, spotwelds, glue connection, MAG welding, bolt connection and so on. Then the complete vehicle's crash finite element model is created.2. Conducting modal test of BIW of this homemade car. From the test frequencies and modes of vibration and dynamic performance have been extracted. The concept of Trimmed Body has been introduced in this paper, then its the modelling method is discoursed in detail and its finite element model is created. After that it calculates the mode and frequency response function(FRF) of Trimmed Body and then its modal test is conducted in order to get the FRF curve of Trimmed Body which is related to vehicle's vibration and harshness. It also makes Modal Assurance Criterion(MAC) analysis between simulation and test and the result validates accurateness of Trimmed Body's model. This way of making simulation and test of Trimmed Body has been applied to some homemade car's development.3. Calculation on sensitivity and optimization of homemade car's BIW. Through sensitivity analysis Those parts have bigger sensitivity on stiffness and weight are identified through sensitivity analysis. In process of optimization static and dynamic stiffness have been taken into account and algorithm of stiffness has been illustrated specially. After optimization, the objective has been achieved, that is, the first mode of BIW has 1.2 percent increase and mass of BIW has 5.4 percent decrease.4. The complete vehicle's crash finite element model is validated by crash time history and strutures deformation in 100% frontal impact test. Based on this, it is the first time that this paper parallelly applies simulation of frontal and side impact to study the crashworthiness of the whole car before and after car body's lightweight. The whole car's safety performance has been guaranteed through comparison between frontal impact test and simulation of B-pillar and tunnel's acceleration curve, intrusion displacement of front and rear door and B-pillar and intrusion velocity of B-pillar of side impact before and after optimization. At the same time, this paper introduces some limit velocity curves in side impact simulation and this provides some experience for the other same class cars'development. It also introduces two different structures of B-pillar and threshold. One of this struture can decrease intrusion displacement of B-pillar in side impact.5. A lightweight method has been proposed which takes stiffness and pedestrian head protection of engine hood into account. By considering those factors, this paper takes struture and thickness of inner part of engine hood as design variables. It uses Taguchi design to do DOE and builds approximate mathematical finite element model for stiffness and head protection of engine hood by use of Kriging method. Based on Kriging model, it does optimization. The optimized results shows that stiffness and head protection performance has been improved. Mass of engine hood has 6.7 percent decrease from 13.5 kg to 12.6 kg and HIC value has 15.8 percent decrease from 1373 to 1156.