轎車車身的碰撞有限元模型分析

1、附錄1 汽車的碰撞安全性越來越得到人們的重視,不論是對轎車、小客車或其它類型的車輛。由于進(jìn)行碰撞試驗(yàn)往往需要許多時(shí)間與金錢,計(jì)算機(jī)仿真就是一條較好的方法。而且,汽車被動(dòng)安全性研究的有限元方法的發(fā)展,非線性動(dòng)力顯式有限元方法的進(jìn)步,使得利用計(jì)算機(jī)仿真來進(jìn)行汽車安全性評價(jià)與改進(jìn)成為可能。目前,各大汽車公司與研究機(jī)構(gòu)已著手研究從仿真分析的結(jié)果中推演出進(jìn)一步的修改方案,達(dá)到在汽車重量與碰撞特性等方面最優(yōu)的研究。本文以提高汽車耐撞性為目標(biāo),以某型七座小客車的初步設(shè)計(jì)方案為基礎(chǔ),建立了用于正面碰撞仿真的前部碰撞有限元模型,并進(jìn)行了計(jì)算機(jī)碰撞模擬,提出了改進(jìn)方案,提高了汽車的被動(dòng)安全性設(shè)計(jì)水平,從而提高了新

2、車型滿足碰撞全法規(guī)的成功率。在對汽車進(jìn)行碰撞性能有限元分析時(shí),汽車整車的建模工作量巨大。本文中的整車有限元模型中的各個(gè)零件均由各零件的U G或CATIA 格式的幾何模型轉(zhuǎn)入HYPERME2SH 有限元建模軟件并進(jìn)行網(wǎng)格劃分,再進(jìn)行裝配而成。碰撞分析的有限元模型的節(jié)點(diǎn)數(shù)和單元數(shù)都超過了14 萬,規(guī)模較大。有限元分析軟件采用LS2DYNA ,它是當(dāng)前在汽車碰撞有限元仿真中應(yīng)用較多的一個(gè)非線性動(dòng)力顯式有限元軟件,它的主要算法采用Lagrangian 描述增量法,利用顯示中心差分法離散時(shí)間域,積分時(shí)間步長大小受Courant 穩(wěn)定性準(zhǔn)則制約。整車結(jié)構(gòu)由100 多個(gè)元件裝配而成。建模時(shí),連接的剛度和強(qiáng)度

3、根據(jù)實(shí)際情況確定。模型中的板殼單元以Be2lytschko - Tsay 四邊形殼單元為主。而節(jié)點(diǎn)也分為常規(guī)節(jié)點(diǎn)和模擬部分焊點(diǎn)情況的帶失效的固連。發(fā)動(dòng)機(jī)和變速器在整車碰撞中的變形不予以考慮,其材料定義為剛性材料。車門和車體的連接是通過鉸鏈和門鎖固定的,在數(shù)值仿真中,通過約束對應(yīng)節(jié)點(diǎn)的位移自由度建立球鉸模型來模擬。考慮到研究中仿真的碰撞方式是最為典型的正面碰撞,在正面碰撞過程中,A 柱前部的車身結(jié)構(gòu)是變形吸能的主要器件,其變形的模式極為復(fù)雜,而中柱之后在碰撞過程中幾乎不發(fā)生變形。為節(jié)省計(jì)算時(shí)間,將車身的前部單元?jiǎng)澐州^密,中柱之后則較稀。計(jì)算中采用彈性剛度沙漏控制。按照CMVDR294 碰撞法規(guī)的

4、要求,小客車以50km/ h的速度正面撞擊剛性墻。設(shè)置的初始邊界條件與實(shí)車實(shí)驗(yàn)的初始條件相同,模擬該車以50km/ h 的初速度正面撞擊剛體墻。在有限元計(jì)算后進(jìn)行后處理,并對模擬計(jì)算的結(jié)果進(jìn)行了分析。模擬結(jié)果顯示,變形主要集中在車輛前部,車輛后部基本沒有變形。 由于前縱梁的問題較大, 為了提高其碰撞性能, 解決方法是改變其局部結(jié)構(gòu)來得到更合理的變形模式和更好的能量吸收特性。兩處產(chǎn)生塑性鉸的局部區(qū)域,可以增加兩塊加強(qiáng)板來改善縱梁的總體的吸能情況。改進(jìn)設(shè)計(jì)后的小客車前圍部分零件。每年的道路交通事故數(shù)和死亡人數(shù)以及由此帶來的經(jīng)濟(jì)損失是驚人的。汽車被動(dòng)安全性的重要性在世界范圍內(nèi)得到認(rèn)同。人們認(rèn)識到碰撞

5、事故是不可避免的。被動(dòng)安全的研究從60年代開始不斷探入的開展越來越向著多樣化、專業(yè)化和高科技化的方向進(jìn)行。早期的汽車耐撞性研究主要采用實(shí)驗(yàn)手段進(jìn)行。汽車碰撞實(shí)驗(yàn)是破壞性實(shí)驗(yàn), 有著種種局限性。其實(shí)驗(yàn)成本很高, 實(shí)驗(yàn)周期長, 而且必須先制造出樣車。1970年以來, 計(jì)算機(jī)在汽車設(shè)計(jì)中的成功應(yīng)用,使汽車工業(yè)事實(shí)上進(jìn)入了一個(gè)新的發(fā)展階段。在汽車碰撞領(lǐng)域中首先應(yīng)用于計(jì)算機(jī)仿真的模型是提出的集中參數(shù)模型。隨后顯式有限元方法的發(fā)展和成熟, 使這一方法被迅速的應(yīng)用到汽車碰撞過程的仿真中來。1985年以德國大眾汽車公司出品的轎車為原型的第一個(gè)有限元模型成功地模擬了轎車的正面碰撞過程圖。有限元汽車碰撞數(shù)值仿真的

6、運(yùn)算代價(jià)較低, 設(shè)計(jì)周期短和可以實(shí)現(xiàn)無樣車的虛擬碰撞實(shí)驗(yàn)等顯著的優(yōu)點(diǎn)使各大汽車制造商在近15年來積極地開展這方面的工作。碰撞仿真已被運(yùn)用到貫穿概念可行性研究到整車設(shè)計(jì)和開發(fā)的全過程。同時(shí)由于80年代以來計(jì)算機(jī)運(yùn)算速度和存貯能力的飛速提高、顯式有限元方法的發(fā)展和成熟、對于薄壁鋼結(jié)構(gòu)在高速碰撞條件下如損傷、斷裂等新的本構(gòu)關(guān)系的認(rèn)識,以及各種連接方式的數(shù)值模型的建立, 使汽車碰撞的計(jì)算機(jī)仿真成為一門新興的學(xué)科。汽車碰撞過程是一個(gè)涉及大位移、大變形、大轉(zhuǎn)動(dòng)的復(fù)雜非線形的動(dòng)態(tài)接觸問題。為了解決計(jì)算效率的問題, 通常采用顯式算法。在碰撞仿真中, 準(zhǔn)確的模擬碰撞過程的關(guān)鍵是采用合理的接觸算法和能夠描述碰撞條

7、件下材料本質(zhì)的材料模型。本文以某型轎車為原型, 建立了白車身的碰撞有限元模型, 并針對計(jì)算效率和準(zhǔn)確性進(jìn)行了著重分析。本文進(jìn)行了對正面固定剛性墻的碰撞性能仿真。碰撞仿真的變形結(jié)果和整車實(shí)驗(yàn)結(jié)果較為吻合, 車身典型位置的加速度時(shí)間曲線和實(shí)驗(yàn)曲線的比較顯示本文所建立的白車身有限元數(shù)值仿模型是真實(shí)準(zhǔn)確的?，F(xiàn)代轎車的車身普遍采用承載式車身結(jié)構(gòu), 與早期的非承載式的車身結(jié)構(gòu)不同, 承載式車身沒有以前用來承重的貫穿車身全長的車架結(jié)構(gòu), 而是由沖壓成型的0.7-0.8mm的薄鋼板通過點(diǎn)焊、搭接而成的, 這樣既提高了整車的抗扭剛度又減輕了車重。承載式車身在發(fā)生高速正面碰撞時(shí), 整個(gè)前部車身發(fā)生潰縮, 碰撞能量

8、主要通過車身結(jié)構(gòu)的變形來吸收。因此對于碰撞仿真來說, 就必須建立一個(gè)能描述碰撞接觸區(qū)域內(nèi)車身結(jié)構(gòu)及其連接關(guān)系的精確的幾何模型。獲取這樣的幾何模型的最方便的途徑是內(nèi)部CAD數(shù)據(jù), 但是由于CAD和CAE本質(zhì)的不同使得描述了很多加工和裝配上工藝細(xì)節(jié)CAD的數(shù)據(jù)在CAE建模中反而成為工作的障礙。本文建立的轎車白車身幾何模型采用了曲面反演技術(shù), 即利用高精度三座標(biāo)測量儀CMM對覆蓋件的主模型或封裝模型進(jìn)行曲面掃描, 對得到的離散數(shù)據(jù)一般稱為云團(tuán)數(shù)據(jù)進(jìn)行擬合和光順處理,從而得到車身的三維模型。獲取了白車身的幾何模型之后進(jìn)行單元離散化就得到了碰撞有限元模型。汽車碰撞仿真中需對計(jì)算效率問題加以特別的關(guān)注。因

9、為象整車碰撞仿真這樣的大規(guī)模數(shù)值計(jì)算動(dòng)輒進(jìn)行上百小時(shí), 占用了大量的機(jī)時(shí), 進(jìn)行重復(fù)計(jì)算是很困難的。汽車碰撞是一個(gè)動(dòng)態(tài)的大位移和大變形過程,系統(tǒng)具有幾何、材料和邊界等多重非線性特征。因此,汽車碰撞的數(shù)值計(jì)算分析一般采用非線性動(dòng)態(tài)顯示有限元分析。有資料顯示,汽車發(fā)生碰撞事故時(shí),發(fā)生正面碰撞(包括斜碰)的概率在40%以上,居于各種碰撞類型之首。因此,研究正面碰撞特性,對降低乘員的傷害非常重要。本文采用ANSA和LS - DYNA對國產(chǎn)某轎車的保險(xiǎn)杠橫梁正面撞擊剛性墻過程進(jìn)行了數(shù)值仿真,并對保險(xiǎn)杠橫梁的結(jié)構(gòu)進(jìn)行優(yōu)化設(shè)計(jì),說明結(jié)構(gòu)優(yōu)化后的橫梁碰撞安全性優(yōu)于原始結(jié)構(gòu)。大變形碰撞問題通常需要耗費(fèi)大量的計(jì)算

10、時(shí)間,如何提高求解速度是求解的主要問題。與常規(guī)有限元計(jì)算不同的是,為了避免大型聯(lián)立方程組求解,提高計(jì)算速度,碰撞分析軟件一般采用顯示算法。附錄2 The safety car collision has been more and more peoples attention, whether for cars, small buses or other types of vehicles. As a result of a collision test often requires a lot of time and money, computer simulation is a bette

11、r way. Moreover, the passive vehicle safety study of the development of the finite element method, nonlinear dynamic explicit finite element method of progress, making use of computer simulation for vehicle safety evaluation and improvement is possible. At present, the major car companies and resear

12、ch institutions has embarked on research from the analysis of the simulation results show a further push to amend the proposal to reached in a collision with the vehicle weight, and other characteristics of the best aspects of the study. In this paper, in order to improve the crashworthiness car as

13、the goal, to a seven-passenger preliminary design for the foundation, set up positive for the simulation of the collision before the collision the Department of finite element model, and a computer simulation of the collision, a program to improve To improve the cars passive safety design standards

14、so as to enhance the all-new models to meet the collision regulations of the success rate. In the car collision on the performance of the finite element analysis, the vehicles enormous workload modeling. In this paper, the finite element model of vehicle in all the parts are parts of the CATIA or UG

15、 format of the geometric model into HYPERME2SH finite element modeling software and mesh, and then carried out by the assembly. Collision Analysis of the finite element model of nodes and units are more than 140,000, and larger. Finite element analysis software used LS2DYNA, it is in the car crash i

16、n the application of finite element simulation of a more dynamic non-linear explicit finite element software, its main method used to describe Lagrangian incremental method, showed that the use of discrete-time center-difference Domain, the time step size of the points by the Courant stability crite

17、ria constraints. Structure of the vehicle by more than 100 components from the assembly. Modeling, to connect the stiffness and strength to determine the actual situation. The shell model unit to Be2lytschko - Tsay quadrilateral shell element-based. The nodes are divided into conventional analog nod

18、es and part of the solder joints of the solid even with failure. Engine and transmission in vehicle collision in the deformation not be taken into account, the material is defined as rigid materials. The doors and body are connected through the hinges and locks fixed, in numerical simulation, bound

19、by the corresponding node through the displacement of the establishment of degrees of freedom model to simulate the ball joints. Taking into account the study of the collision simulation is the most typical collision positive, positive in the course of the collision, A column of the front body struc

20、ture is a deformation of the main energy absorption device, the deformation of complex patterns, and in column after a collision in the process of Almost no distortion. In order to save calculation time, the body of the front unit more closely, in the column after more rare. Elastic stiffness in the

21、 calculation used to control the hourglass. CMVDR294 collision regulations in accordance with the requirements of small passenger cars to 50km / h speed frontal impact in the rigid wall. The initial set of boundary conditions and the experimental car is the same as the initial conditions, the simula

22、tion of the car to 50km / h speed frontal impact in the beginning of the rigid wall. In the finite element method after the post-processing, and the simulation results are analyzed. The results show that the deformation concentrated in the front of the vehicle, no deformation at the rear of the vehi

23、cle. As the beam before the larger issues, in order to improve the performance of its collision, the solution is to change its regional structure to a more rational pattern of distortion and better energy absorption characteristics. Produced two plastic hinge of the local area, will increase two to

24、strengthen the board to improve the overall beam of energy absorption situation. To improve the design of passenger cars before some of the parts Wai. The annual number of road traffic accidents and death toll, as well as the resulting economic losses are staggering. Automotive passive safety of the

25、 importance of the world it was accepted. It is recognized that collisions are inevitable. Passive safety research from the age of 60 began to explore the means to carry out more and more toward diversification, professional and high-tech direction. Early automobile crashworthiness research using ex

26、perimental means. Automobile collision experiment is destructive experiment with various limitations. The high cost of the experiment, the experimental long, but must first create kind of car. Since 1970, computers in the design of the success of the automotive applications, so that in fact the auto

27、 industry has entered a new stage of development. In the first car collision in the field of applied computer simulation of the model proposed by the focus is parameter model. Followed by explicit finite element method and the development of mature, so that this method has been applied to the fast-c

28、ar collision simulation in the course of the past. In 1985 by Germanys Volkswagen production cars for the first prototype of the finite element model successfully simulated the cars front collision course map. Finite element simulation of vehicle collisions lower the cost of computing, and short des

29、ign cycle can be achieved without the kind of virtual car collision experiments, such as significant advantages so that all the major car manufacturers in the past 15 years to carry out active work in this area. Collision simulation has been applied to study the feasibility of the concept through th

30、e vehicle design and development of the whole process. At the same time, since the age of 80 due to the computing speed and storage capacity of the rapid increase in explicit finite element methods for the development and maturity, the thin-walled steel in conditions such as high-speed collision dam

31、age or crack the new constitutive relation of understanding, As well as a variety of ways to connect the numerical model, so that the vehicle collision computer simulation has become an emerging disciplines. Automobile collision involving a large displacement, large deformation and large rotation of

32、 the complex non-linear dynamics of the contact problem. In order to solve the problem of computing efficiency, usually explicit algorithm. In the simulation of collision, the accurate simulation of collision course, the key is to adopt a reasonable method of contact and be able to describe the coll

33、ision of the nature of the material conditions of model material. Based on a prototype for the car, a white body finite element model of the collision, and for calculating the efficiency and accuracy of the analysis focused. This article was positive for the fixed rigid walls of the collision simula

34、tion performance. The simulation results of the collision and deformation of the vehicle is more in line results, the typical location of the bodys curves and acceleration of time compared with the experimental curve in this paper shows that the establishment of the body in white like finite element

35、 model is true and accurate. Modern cars commonly used by body-bearing body structure, with the early non-bearing structure of the body, carrying the body-weight people do not have to run through the length of the body frame structure, but by stamping forming the 0.7-0.8mm The thin plate through the

36、 spot, by lap, so that not only improved the vehicles torsional rigidity and reduced weight. Body-bearer in the event of a positive high-speed collision, the front of the entire body shrink collapse occurred, the collision energy, primarily by the deformation of the structure of the body to absorb.

37、For the simulation of collision, it is necessary to establish a description of the collision to contact the region connection body structure and the relationship between the geometric precision of the model. Access to such a geometric model of the most convenient way to internal CAD data, but becaus

38、e of the nature of CAD and CAEs description of the different makes a lot of processing and assembly processes on the details of the CAD data in the CAE modeling instead become an obstacle to the work. In this paper, the car body in white geometric model of the surface using inversion, that is, the u

39、se of high-precision coordinate measuring instrument panel on the CMM model for the main package or model surface scan, to be known as the discrete data cloud data Fit smoothness and to carry out processing, in order to get three-dimensional model of the body. Access to a white car after the geometric model of discrete units have been on a collision finite element model. Automobile collision simulation to be calculated on the efficiency of special concern. As the vehicle collision because such a large-scale numerical simulation calculation at eve