轻量化设计的汽车零部件用高强度钢来抗凹外文文献翻译@中英文翻译@外文翻译

Lightweight design of automobile component using high strength steel based on dent resistance Abstract Lightweight and crashworthiness are two important aspects of auto-b-ody design. In this paper, based on the shallow shell theory,the express-ion of dent resistance stiffness of double curvatured shallow shell is obt-ained under the concentrated load condition. The critical loads resulting i-n the local trivial dent in the center of the shallow shell is regarded as the important index for the lightweight of the automobile parts. This rule is applied to the lightweight designof bumper system by using high stre-ngth steel instead of mild steel. The crashworthiness simulation of the li-ghtweight part proves the validity of the lightweighting process. Keywords: High strength steel; Lightweight; Dent resistance 1. Introduction In recent years, the retaining number of automobiles has been incre-asing steadily, which has impacted the society and human life greatly. S-uch situation leads to many severe problems such as fuel crisis, environ-ment pollution. The international association of aluminum stated that petr-ol consumption can decrease by 810% with 10% reduction of car weig-ht 2. Thus, automobile lightweight is a basic way to fuel saving. In order to reduce the automobile weight, there are two important methods 3: One, automobile parts are redesigned to optimize the struc-ture. By using thinning, hollowing, minitype, and compound parts, car we-ight can be reduced. The other, more and more lightweight materials, s-uch as aluminum alloy,high strength steel, composite material, are wide-ly used as lightweight materials to replace the traditional materials like mild steel 4. These materials could reduce the weight remarkably. Mat-erial replacement is generally more effective in automobile lightweighting than structure modification. With the introduction of automobile safety leg-islation, crashworthiness and safety should be considered as preconditio-ns in lightweighting design of auto-body. High strength steel is widely us-ed in automobile replacing the traditional material of mild steel.High strength steel sheet can be used in auto-body to improve com-ponents_ impact energy absorption capacity and resistance to plastic def-ormation. The automobile weight can be reduced by use of high strength steel sheet of a thinner thickness to replace the mild steel sheet of bo-dy parts 1,3. Comparing with aluminum, magnesium,and composite mat-erials, high strength steel has better economy in that its raw material an-d fabrication cost are cheaper. Besides, high strength steel can be direc-tly used in product line including forming, wielding, assembling, and painting. The operating cost can be saved since there is no need adjusting the whole line Outside of automobile body, there are several sheet metal Panels, most ofwhich are shallow panels. Dent resistance is the ability to retain- the shape against sunken deflection and local dent under the external force. Dent resistance of automobile panels becomes an important issue and quality criterion. Therefore, dent resistance stiffness of automobile p-anels should be tested and evaluated in the process of panel design an-d manufacture.Some reported methods of testing are listed below 68: 1. Test the displacement of sunken deflection fp underfixed external forc-e 2. Test the external force f to obtain fixed displacement of sunken defle-ction. 3. Test the slope of forcedisplacement curve under external load. In this study, the second method will be used. The rest of this paper is organized as follows: In Section 2, the expression of dent resistance stiffness of double curvatured shallow shell is obtained under the concentrated load condition based on the shallow shell theory. The critical load resulting in the local trivial dent in the center of the shallow shell is regarded as the important evaluating index for the dent resistance of the automobile parts. This rule is applied in Section 2 to the lightweighting design of bumper system by using high strength steel instead o f mild steelwith crashworthiness simulation. 2. Dent resistance analysis of double curvatured shallow shell 2.1. Dent resistance stiffness analysis of shallow shell Shell with mid surface can be characterized into three features: thickness h, mid surface dimension L, curvature radius r, which satisfies h/r_ 1. When there exists h/L _ 1, the shell can be defined as thin shell. If L/ r _ 1 is added besides the above two conditions, the thin shell is regarded as shallow shell 10. As Fig. 1 shows, the plane xy is the projection of the mid surface of shallow shell along the z-axis. Supposing M is an arbitrary point on mid surface, two planes QMN & PMN are made paralleling to coordinate plane OYZ and OXZ, respectively. The two edges PM and QM can be regarded approximately as vertical because of mid surface_s flatness. At the same time, the line MN is normal to mid surface. Thus, MN, QM, PM can constitute a perpendicular reference frame MPQN, whose difference from orthogonal coordinate system OXYZ can be ignored. And PM and QM are denoted by a and b, the curvilineal coordinate of MPQN. Assuming the Z coordinate of the point M is z, the analytical equation of mid surface is expressed as follows: ( , )z F x y (1) The following equations can be obtained because of the flatness of the shell: 2 2 2( ) 1 , ) 1 , ) 1zzzx y x (2) The curvature and torsion of mid surface can be approximated to: 2 2 222,x y x yz z zk k kx y x y (3) The Lae coefficients of mid surface along a and b directions are deduced: 121 , 1d s d sd x d yABd d x d d y (4) Applying concentrated force P along Z-axis and ignoring the influence of the transverse shear resultant forces, the balance differential equations of shallow shell are: 120 , 0NNSSx y y x 1212( ) ( 0 , 0 ) 0 ,xy QQk N k N Pxy (5) 1 2 1 1 2 212 ,M M M MQQy x x y where d(0,0) is Dirac-d function. The compatibility equation of shallow shell is 2212( ) 0kN N E t w Where 2 2 2 2222 2 2 2 2 2, xykkx y x y (6) Expressing the moment resultants M1, M2 and M12 by the function of transverse displacement w, the basic equations of shallow shell under concentrated transverse forces are: 22 12D ( ) ( 0 , 0 ) ,xyw k N k N P 2212( ) 0kN N E t w (7) 2212NNxy where N1 is the membrane stress resultant in X-direction; N2, the membrane resultant in Y-direction; D, the Fig. 1. Double curvature shallow shell. bending stiffness of shallow shell. It is very difficult to solve above equation. According to practical situation, sunken deflection will only concentrate on a small area around external force P, so infinite large shallow shell 5 is assumed in this study. Because w, N1, N2 are symmetric about x-, y-axis, all orders of derivatives of w, N1, N2 become to zero at infinity. The following equations can be achieved by Fourier transformation to Eq. (7): 22 12 ( ) ( )xyD w k N k N P 2 2 2 212 ( ) ( ) ( ) 0yxN N E t k k w (8) 2212NN Where ( 0 , 0 ) i x i n yP e e d x d y P 00 4 c o s ( ) c o s ( )w w x y d x d y 1 00 4 c o s ( ) c o s ( )N w x y d x d y (9) 2 00 4 c o s ( ) c o s ( )N w x y d x d y From Eq.(8), w can be obtained. Reverse Fourier transformation to w and polar coordinates transformation to n, g, w under polar coordinate system can be gained /22 0 4 2 2 22c o s ( c o s ) c o s ( s i n )12 ( c o s s i n )pxyP x yw d dD kkt (10) Put x = 0 and y = 0 in Eq.(8), the relationship between deflection fp and concentrated force P of rectangle shallow shell can be achieved as follows: 224(1 ) 3xypE t k kPf (11) Finally, dent resistance stiffness of shallow shell K is obtained 224(1 ) 3xypE t k kPKf (12) This equation explains synthetically the relationship between the dent resistance stiffness of double curvature shallow shell and all influencing factors including material properties, geometry parameters, which can be used to guide design, material select and manufacture. 2.2. Analysis of critical load causing local trivial dent For quantitative evaluation of critical load against local dent resistance of panels, several experience formulas have been brought forward by researchers. Based on large numbers of experiments, Dicellello 9 stated a formula that expresses minimum energy W causing visible trivial dent trace by thickness t, yield stress rs and basic dent resistance stiffness K 24s tWCK(13) where C is proportional constant. From Eqs. (12) and (13), the critical load Pcr resulting in the local trivial dent in the center of the shallow shell can be achieved, which is defined as the evaluating index 2er sP C t (14) From Eq. (14), there is a closely correlation between critical loads Pcr and thickness t, yield stress rs. The critical load can be a rule to carry out lightweight design of automobile parts by using high strength steel instead of mild steel. 3. Example and crashworthiness analysis 3.1. FE model of full car and its crash simulation A detailed finite element model has been established based on a passenger car refitted from a saloon car, which is showed in Fig. 2. To ensure the correctness and effectiveness of FE model, the following methods are adopted: 1. Since the goal is to simulate the frontal impact of the car, the meshing of front car body is denser than that of the rear car body. 2. Reduced integration method with hourglass control is taken for 4 noded shell element and 8 noded brick solid element to improve the efficiency of simulation. 3. By using of the meshing and mass scaling technology, the characteristic length of the minimal element is ensured to improve the simulation efficiency. 4. Materials constitutive with CowperSymonds strain rate item is used for steel parts. 5. Automatic single surface contact algorithm is adopted in the simulation aiming at complexity of car impact simulation. 6. Spot weld element with failure rule that considering the couple of normal force and shear force is used to simulate the spot weld connection between auto parts. Explicit dynamic FEM software LS-DYNA Version 950 is used to simulate the frontal impact of the car against a rigid wall at the speed of 50 km/s according to the National Crash Legislation CMVDR294. A real car crash experiment is done at Car Crash Lab settled in Tsing Hua University. By comparing the time history of acceleration of certain position on the A pillar within 0.1 s, the simulation gives a reasonable fit to the experiment results, which guarantees the correctness of FE model and gives a nicer base for the next lightweighting optimized design. 3.2. Lightweighting design and crashworthiness analysis The use of high strength steel is one of the effective ways to reduce car weight. However, the performance (such as crashworthiness, stiffness, and dent resistance) of part made of new material should be assured. For example, the front parts of a car are major energy absorption parts in the process of car crash, so energy absorption performance without affecting the safety of passengers should be assured in the design of front parts of a car. In this research, the bumper of the passenger car is studied under different materials but remaining its dent resistance. The mechanical properties of mild steel and high strength steel are listed below (see Table 1). The evaluation index of dent resistance for bumper using mild steel is 21 1 1 1cr sP C t When high strength steel is used to replace the mild steel remaining its primary shape and dent resistance performance, the new thickness t2 of high strength steel can be achieved 112122ssCttCFrom (16), the thickness of bumper that uses high strength steel is gained and updated in the full car FE model. The deformation history of bumper using new material is achieved after the car crash is re-simulated with updated part thickness (see Fig. 3). By simulation, the deformations of bumper made of two different kinds of material are similar in that plastic hinge and tensional plastic deformation appear in the middle part of bumper. And the energy absorption history is shown in the following for beam of the bumper. From Fig. 4 the difference of the energy absorption between twomaterials is small, about 4.1%for beamof the bumper,from which a conclusion can be drawn that it is feasible to reduce the thickness of the bumper panel based on the dent resistance evaluation index studied in this research. 4. Conclusion Dent resistance performance of small curvature shallow shell parts in automobile is studied in this paper, which enables the follows: 1. Dent resistance stiffness under concentrated force is given for such parts. 2. The critical load resulting in the local trivial dent in the center of the shallow shell has been deduced, which in turn becomes the index to evaluate the dent resistance of automobile parts. 3. The validity of evaluating index is proven by applying the developed rule to the lightweight design of bumper system using high strength steel instead of mild steel through crashworthiness simulation. 轻量化设计的汽车零部件用高强度钢来抗凹 摘要 ：轻巧耐撞性是汽车车身设计的两个重要因素。在这篇文章中，基于浅壳理论，表达抗凹刚度的双曲率扁壳是在集中载荷条件下取得的。该临界负荷导致当地琐碎的凹痕在该中心的浅壳被视为轻量级对汽车零部件的 重要影响指数。本规则适用于轻量化设计的保险杠系统用高强度钢代替温和钢。耐撞模拟轻量级的一部分，证明了轻量化进程的有效性。 关键词 : 高强度钢 轻量 抗凹 1、介绍 近年来，由于汽车保有量的急剧增长，大大影响了社会和人们的生活，这种情况带来了很多严峻的问题比如能源危机，环境污染。国际铝组织协会声明石油的消耗可降低 8-10与减少约 10的汽车重量。因此，汽车轻量化是节约燃料的一个基本方式。 为了减少汽车的重量，这又两个较好的方法。一种方法是重新设计汽车零部件优化其结构，通过使用细薄的、空心的、小型的和 混合材料的零部件，来减轻汽车的重量。另一种是使用新的轻型材料，如今这种材料越来越多，如铝合金，高强度钢，复合材料都被广泛作为轻质材料以取代传统材料如低碳钢。这些材料可以显着的减轻汽车的重量。使汽车轻量化材料替换比优化结构更有效。根据引进的汽车安全法规，轻量化设计的车身中耐撞性和安全性被视为先决条件。高强度钢被广泛的应用于汽车上以代替传统的低碳钢。 高强度钢板可用于汽车车身来提高部件碰撞能量吸收能力和耐塑性变形能力。汽车体重可减少通过使其零部件用一个更薄厚度的高强度钢板取代低碳钢板来制造。与铝相比，镁，复合材 料和高强度钢具有更好的经济性因为这些材料的原料和制作费用比较便宜。此外，高强度钢可直接应用到生产线上，包括成型，焊接，装配和油漆。经营成本节省了，因为没有必要对整个线路进行调整。 在车身外，有几个薄的金属板，其中大部分是浅水面板。凹痕阻力是有能力保持形状对沉没挠度和地方凹痕在外力的作用下。凹性汽车板成为汽车的一个重要方面和质量标准。因此，抗凹刚度的汽车板应在面板设计和制造过程中被测试和评估。一些报道的测试方法列举如下 : 1）、在外力不变的情况下，测量位移沉没挠度的 fp 2）、测试外力 F 到获得固定位移沉没偏转 量 3）、在外力载荷作用下测试得边坡力位移曲线 在这篇文章中，第二种方法将被采用，该表达抗凹刚度双曲率浅壳是通过浅壳理论和集中负载的条件下得到的。该临界负荷导 致该中心浅壳琐碎的凹痕被视为凹性汽车零部件的重要评价指数。本规则适用于在第 2 条中，轻量化设计连年系统用高强度钢代替低碳钢与耐撞性仿真。 2、双曲率浅壳的抗凹性分析 2.1 浅壳的抗凹刚度分析 壳牌与中表面特点可以分为三特征：厚度 h，中面尺寸 L，曲率半径 r ，并满足的 h / r1。当 h/L1 时，定义外壳为薄壳，如果在上述两条件满足的同时又满足 L r1，这个薄壳被认为是浅壳。 如图 1 所示，平面 x-y 是浅壳中表面沿着 z轴的投影。假设 M 是中表面上的任意一点，两平面 QMN&PMN 分别去平行 OYZ 和 OXZ。边 PM 和 QM可近似认为是垂直的因为中表面和平坦。同时， MN 正交于中面。因此， MN,PM,QM 可构成垂直参考系 MPQN。其差额由正交坐标系统 OXYZ 可以忽略不计，同时 PM 和 QM 通过 和 来表示，该曲面坐标 MPQN。 假设 M是 Z 轴上的一点，对中表面的详细分析方程如下： z=F(x,y) （ 1） 由于是平坦的外壳，就有如下方程： （ 2） 中面的曲率和挠度可近似至： （ 3） 该中面的下载系数可沿和方向导出： （ 4） 运用集中力 P沿 Z轴和忽略横向剪切力造成的影响，得到浅壳的平衡微分方程： （ 5） 其中 （ 0， 0）是狄拉克 - 函数。 浅壳的兼容性方程是： （ 6） 其中 通过横向位移 w 来表达瞬时结果 M1, M2 和 M12，浅壳在横向集中力下的基本方程： （ 7） 其中 N1 是膜应力在 X方向， N2 是膜应力在 Y 方向， D 表示浅壳的抗弯刚度。 这是很难解决上述方程。据要立足现实，沉没的偏转将只集中就在小范围内左右对外力 P ，所以无限大型浅水壳牌是假定在这项研究中。因为 w， N1,N2 关于 X,Y 轴对称，所有顺序衍生的 w,N1,N2 都无限接近于零，以下方程可通过傅立叶进行变换。 （ 8） 其中：