以特定工况下某骨架式车身为例,进行结构力流试验分析研究。测量车身骨架关键位置的应力应变,分析车身骨架的力学性能;提出以具有相同量纲的应力成分描述力流分布、以内力矩描述力流传递的力流评价方法;引入并改进承载因子和承载均匀性系数作为车身结构承载能力的评价指标;基于力流分析给出车身骨架结构的优化方案。研究结果表明,弯矩应力成分可以作为力流分布的主要评价依据,翘曲应力成分可以作为观测力流走向的辅助手段;扭转工况下车身骨架纵梁主要起传递力流的作用,横梁和立柱组成抗扭环,主要起分担力流的作用,车身的前部、中部和后部都应存在抗扭环,若缺失必将影响车身结构的承载能力;力流优化使骨架式车身结构的承载能力提升18.71%,载荷分布均匀性提高14.89%。力流分析对车身结构设计及优化有重要参考价值。
An experimental method to investigate the load path in a vehicle body frame under certain condition is presented. The mechanical characteristic of vehicle frame is analyzed through strain gauge measurements of stress state at every corner of the key measuring sections. Stress composition is adopted to describe load distribution and internal moment is employed to represent load transfer. Load-carrying factor(LCF) and Christiansen uniformity coefficient(CUC) are used to evaluate the load-carrying capacity of the vehicle body frame. Based on the concept of load path, a modification plan for the vehicle body frame is proposed. The results show that bending stress can be treated as the principle evaluation index of load distribution, and warping stress can be a supplementary tool to observe the direction of load path. In the torsional condition, longitudinal members carry major portions of loads, transverse members and pillar members constitute the anti-torsional rings to share and discharge loads. The anti-torsional rings should exist in the frontal cabin, passenger cabin and rear cabin of vehicle body. If any anti-torsional ring is missing, the load-carrying capacity of the vehicle frame body would be sharply weaken. In the modified version, the load-carrying capacity and the load-distribution uniformity increase of 18.71% and 14.89% respectively. Load path analysis has an essential practical value for vehicle body structure design.
[1] 兰凤崇,赖番结,陈吉清,等. 考虑动态特性的多工况车身结构拓扑优化研究[J]. 机械工程学报,2014,50(10)：122-128.
LAN Fengchong,LAI Fanjie,CHEN Jiqing,et al. Multi-case topology optimization of body structure considering dynamic characteristic[J]. Journal of Mechanical Engineering,2014,50(10)：122-128.
[2] MARHADI K,VENKATARAMAN S. Comparison of quantitative and qualitative information provided by different structural load path definitions[J]. International Journal for Simulation and Multidisciplinary Design Optimization,2009,3(3)：384-400.
[3] BURR A H,CHEATHAM J B. Mechanical analysis and design [M]. NJ：Prentice Hall,1995.
[4] JUVINALL R C,MARSHEK K M. Fundamentals of machine component design[M]. New York：J. Wiley,1991.
[5] 陈贻伍. 力流法及其在机械设计中的应用[J]. 中国有色金属学报,1994,94(2)：94-96.
CHEN Yiwu. Load path and its application to the mechanical design[J]. Transactions of Nonferrous Metals Society of China,1994,94(2)：94-96.
[6] THAMM F. The role of the stress trajectories as an aid in the choice of the suitable shape of load-bearing structural elements of engines and structure[J]. Mechanical Engineering,2000,44(1)：171-183.
[7] KELLY D,ELSLEY M. A procedure for determining load paths in elastic continua[J]. Engineering Computations,1995,12(5)：415-424.
[8] KELLY D,HSU P,ASUDULLAH M. Load paths and load flow in finite element analysis[J]. Engineering Computations,2001,18(1-2)：304-313.
[9] KELLY D,TOSH M. Interpreting load paths and stress trajectories in elasticity[J]. Engineering Computations,2000,17(2)：117-135.
[10] KELLY D W,REIDSEMA C A,LEE M C. An algorithm for defining load paths and a load bearing topology in finite element analysis[J]. Engineering Computations,2011,28(2)：196-214.
[11] HARASAKI H,ARORA J. A new class of evolutionary methods based on the concept of transferred force for structural design[J]. Structural and Multidisciplinary Optimization,2001,22(1)：35-56.
[12] HARASAKI H,ARORA J S. New concepts of transferred and potential transferred forces in structures[J]. Computer Methods in Applied Mechanics and Engineering,2001,191(3)：385-406.
[13] HARASAKI H,ARORA J. Topology design based on transferred and potential transferred forces[J]. Structural and Multidisciplinary Optimization,2002,23(5)：372-381.
[14] HOSHINO H,SAKURAI T,TAKAHASHI K. Vibration reduction in the cabins of heavy-duty trucks using the theory of load transfer paths[J]. JSAE Review,2003,24(2)：165-171.
[15] OKANO Y,MATSUNAGA T,MARUYAMA S,et al. Load path analysis of vehicle body structures under eigenmode deformation of bending vibration[R]. SAE,2009-01-0770,2009.
[16] 高云凯,李翠,崔玲,等. 力流分析法在大型客车车身结构分析上的应用[J]. 汽车技术,2009(12)：8-11.
GAO Yunkai,LI Cui,CUI Ling,et al. The application of load path analysis in the large sized bus body structure analysis[J]. Automobile Technology,2009(12)：8-11.
[17] KOMAROV V A,WEISSHAAR T A. New approach to improving the aircraft structural design process[J]. Journal of Aircraft,2002,39(2)：227-233.
[18] CHRISTIANSEN J. The uniformity of application of water by sprinkler systems[J]. Agricultural Engineering,1941,22(3)：89-92.
[19] MARHADI K S,VENKATARAMAN S,WONG S A. Load redistribution mechanism in damage tolerant and redundant truss structure[J]. Structural and Multidisciplinary Optimization,2011,44(2)：213-233.
