Finite Element Analysis and Shape Optimization of Aluminum Alloy Automobile Energy-absorbing Components.pdf

Finite Element Analysis and Shape Optimization of Aluminum Alloy Automobile Energy-absorbing Components Liu Yan-jie1 ,2,a, Ding Lin1,2,b , Li Qing-fen3, Wang Dan1 1 College of Civil Engineering, Heilongjiang University, Harbin 150086, China 2 Northeast Frost Civil Engineering Key Laboratory of Heilongjiang University, Harbin 150086, China 3College of Mechanical and Electrical Engineering, Harbin Engineering University, Harbin, China a lyj7171, bdinglin1 Keywords: Finite element analysis; aluminum alloy; shape optimization; energy-absorbing components Abstract. In the present work, the structure optimum design and simulation analysis of aluminum alloy automobile energy-absorbing components was carried out by using Finite Element (FE) method. The numerical simulations were carried out using the software LS-DYNA. Automobile energy-absorbing components usually was made a mental thin walled tube. In the paper, the tube was adopted aluminum alloy material. The FE model of the tube was validated by comparing the theoretical results and FE model results. The good correlation of results obtained show that the numerical analyses are reliable. Attention was focused upon finding an optimum cross- section shape of the tube in order to improve the crashworthiness. Several types of cross- section were studied and compared. Results show that the crashworthiness of the tube improved obviously when square cross section with the grooves was adopted. Introduction The safety of automobile has been an important problem in vehicle research field, since traffic accidents are one of the severest social problems around the world. As for in China, the death and injuries caused due to automobile high velocity impact, has been the focus of attention. However, low-speed collisions usual happened for the traffic jam in the city 1, 2. For no personnel injury, low speed crashed didnt get peoples attention. It is therefore necessary to study the technical problems involve in low velocity impact. Thin walled tube is one of the most important automotive parts for crash energy absorption, and it was equipped at the front end of a car. In low velocity impact accident, it is expected to be collapsed with absorbing crash energy prior to other body parts so that the damage of the main cabin frame is minimized and passengers may be saved 3, 4. It position in the bodywork was given in Fig. 1. In the present work, the automobile energy-absorbing component at low-velocity impact was studied by using Finite Element (FE) method and theoretical validated. And shape optimization for thin-walled tubes is proposed. Finite Element Modeling Main Crashworthiness Evaluation Parameters. In case of frontal low-speed collision, the tube absorbs impact energy and reduces the peak load of the impact mainly by the plastic deformation 3. The most important crashworthiness evaluation parameter of the tube is the total impact energy absorption via plastic deformation Es , the peak impact force Fp , the compressed displacement of the tube e , and the average impact load Fm . The average impact force Fm given by equation (2), where, Es is the total impact energy absorption, e is the compressed displacement. Applied Mechanics and MaterialsOnline:2012-12-13 ISSN: 1662-7482, Vols. 249-250, pp 954-957 doi:10.4028/ 2013 Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, . (#69714362, Pennsylvania State University, University Park, USA-13/09/16,05:27:40) e m E F = (1) Fm is arithmetic average value, with Fm increasing, the absorbing energy of the tube will increase. The greater Fm, the more energy absorb, the better the crew safety are protect. Therefore, in precondition of not more than the permission peak value, the bigger the average impact load is , the better the absorption performance is. Model Building. Thin walled tubes, particularly those of square cross-section mental tubes, are a common type of automobile crash-box since they are relatively cheap, versatile and efficient for absorbing energy. This has led to them being used in a wide variety of impact loading applications 5. In this paper, a finite element model was developed by using the software LS-DYNA. The axial low velocity impact of the square cross-section tube (70mm width, 160mm long and1.65mm thick) was studied firstly. The tube finite element mesh is illustrated in Fig. 2. A rigid plate of 1000kg, placed on the top of the tube as shown in fig. 2, axially impacted at the velocity of 4.44 m / h. The tube was modeled using 7075aluminum alloy, yield strength, y = 455MPa, Density, = 2.81 x 10-6kg / mm3, Poisson ratio, v= 0.33 and Youngs modulus, E = 71GPa. energy- absorbing components Fig. 1 Position of energy- absorbing components in the bodywork Fig. 2 Mesh model of the tube Simulation Analysis. The energy absorption character of the square cross-section tube on axial low velocity impact was simulated. The curve of impact load vs. displacement is shown in Fig. 3. The curve of energy vs. displacement is shown in Fig. 4.Where, the peak value of the impact load, one of the important parameter of energy absorption, is 237.427kN, much higher than the permissible value, 180kN. It is necessary to optimum the tube to improve the energy absorption characters, especially to reduce the peak value of the impact load. Fig. 3 Impact load vs. displacement curve of square tube Fig .4 Energy vs. displacement curves of square tube Displacement（mm） Impact Load（kN） Aluminum alloy Displacement（mm） Energy（J） Aluminum alloy Applied Mechanics and Materials Vols. 249-250955 Theory Validation .The FE model of the square cross-section aluminum alloy tube was validated by comparing both the theory and the FE model results. Due to space limitation, we only take the mean impact load Fm as an example. Some researchers have made experimental investigations to predict the critical stress more accurately for engineering applications. Among them, the experience formula of the mean impact load Fm for square cross-section thin-walled tube is given by 6. 3 1 2 0 06.13 = t b tFm (2) Where() u += 2 . 00 2 1 , and 02 is the yield strength, u is the limit strength. t is the wall thickness and b is the width of the square cross-section. For the material used in the present work: 62. 0 2 780. 0455. 0 2 02 0 = + = + = u GPa Therefore, the mean impact load calculated by Equation (3) is 88.76 65. 1 70 65. 162. 006.13 3 1 2 = m FkN (3) The theoretical calculation results of mean impact load Fm=76.88kN, compare with FE model result, Fm=77kN. Results show that on average the difference of theoretical calculation results and FE model results was 1.56%. The good correlation of results obtained place the confidence in the subsequent simulation analyses. Optimization Design Optimum Cross-section Shape. In order to improve the energy absorption character of the crash-box, it is necessary to optimum the structure of the tube. Attention was firstly focused upon finding an optimum cross- section shape of the tube. Five types of thin-walled tubes were studied and compared. The tube cross-section geometries are illustrated in Fig. 5, where, (a) square section, (b) circular section, (c) hexagon section, (d) octagon section, and (e) rectangle section. All the tubes are 120mm long , 1.65mm thick, circumference 280mm and same 7075aluminum alloy material was used. According to the same FE modeling method and boundary conditions, five aluminum alloy tube was simulated. Collapse of tubes under impact load after 20 ms was shown in Fig.6. Comparing the simulation results ( energy vs. displacement, and the impact load vs. displacement) as shown in Fig.7and Fig.8, we may conclude that the best cross-section is the shape (a), i.e. the square section. The peak value of the impact load for different shape tube is (a) 237.433kN, (b) 273.66kN, (c) 272.81kN, (d) 276.27kN, and (e) 238.68kN respectively. All are much higher than the permissible value, 180KN. Among them, the least one is shape (a). We therefore take the thin-walled tube of square cross section for further optimization design. (a) (b) (c) (a) (b) (c) (d) (e) (d) (e) Fig. 5 Sectional dimensions of five models Fig .6 70s deformation diagram of five FEM models 956Applied Mechanics and Mechanical Engineering III Optimum Groove. Due to the thin walled tube subjected to impact, the tube has occurred internal and external iterative shrinkage deformation, shown in Figure 4. According to deformation trend set groove, impact load will be reduced. Fig. 7 Energy vs. displacement curve Fig. 8 Impact load vs. displacement curve In this paper, grooves on the square cross section tubes were adopted as shown in Fig. 9(a). FE simulation results( tube with groove square aluminum alloy model deformation, and the impact load vs. displacement) as shown in Fig.9(b). (a) （b） Fig. 9 Model and deformation of square with groove Fig.10 Impact load vs. time curve Comparison for tubes without groove and with grooves is given in Fig. 10. Results show that the energy absorption characters of thin-walled tube of square cross section obviously when grooves adopted. Where the peak value of impact load is 70 kN, decreased about 70.5% compare with the one without gro