Crashworthiness Optimization For Energy Absorbing Structures Of Car Body Based On Surrogate Models

As a developing country in vehicle domain, most of vehicle manufacturers are lack ofthe ability for independent research. However, with the gradual enhancement of the awarenessfor independent intellectual property rights, many vehicle companies pay attention to theindependent research and development. Hence, especially for the independent brands, thegovernment publishes series of programming, which improves the fast development ofnational vehicle industries. The innovation of construction principle, product innovation andindustrial innovation system were put forward in the national ‘12th Five Year Plan’.Consequently, structure lightweight, vehicle optimization and energy-saving for vehicleproducts have been focused on as a key development for vehicle industry. Moreover, not onlythe main technologies for reliability, safety and energy conservation, but also the developmentfor lightweight and materials application have been researched as major projects in thedomain of vehicle.For the reasons above, improving vehicle safety, especially the crashworthiness, is one ofthe urgent work, which will develop our own brand of automobile manufacturer and improveinternational competitiveness. The traditional procedure of carbody design requires long cycleand may not be effective guidance for preliminary design. Hence, it is necessary to take arelatively complete crash simulation analysis as a reference. However, vehicle collisionproblem, which is high nonlinear and contains huge degrees of freedom, will spend a lot offinancial resources and computation. In order to solve the problem, constructing surrogatemodels based on DOE method can effectively reduce the computation time, facilitate thecrashworthiness optimization design, and improve the efficiency of the carbody design, whichwill satisfy the security requirement of the vehicle. Moreover, computation of the simplified model equivalent to the detail FE model is less. The basic units of the simplified carbodycomponents are composed by beams, plates and joints. Especially, beams with differentsections take large proportions.Based on not only the analysis of geometrical properties and mechanical properties fordifferent types of thin-walled beams, but also the geometrical properties, mechanicalproperties and production process, this paper researches on the method of constructingparameterized structure for vehicle collision, and then establishes the FE models andcorresponding simplified models of the car body parts, which are the foundation forparametric modeling and optimization.This paper is supported by the National Natural Science Foundation of China, Scienceand Technology Development Plan of Jilin province in2009and2012, and the corporationwith body department of China Faw Group Corporation R&D Center. According to thespecial optimization platform for simplified vehicle frame structures which compliedindependently, fast parametric modeling and crashworthiness optimization for the mainenergy-absorbing components of vehicle based on surrogate models have been studied, whichare all considered for the concept design. During the process of optimization, both thelightweight and high energy conservation are taken as optimization objects. This may greatlyenhance the effectiveness of structure modification and optimization. The main work can beconcluded as follows.(1) Theories of crash safety simulation and crashworthiness optimization methods.Theories of vehicle crash safety simulation are introduced in detail, such as discussionsabout the application conditions for non-linear FE method, derivations of motion equations,conservation equations and boundary conditions. Also, the Gaussian integration method basedon a single point for unit calculation and the hourglass phenomenon are illustrated. Moreover,methods for crashworthiness optimization based on surrogate models are focused on. Afterillustrating several methods for DOE and the construction of surrogate models, this paperanalyzes their application ranges. Finally, both the basic principles and solving process of theparticle swarm optimization method are summarized. (2) Crashworthiness optimization of crash box structure based on its surrogatemodel during front collision.The crashworthiness optimization with low velocity impact, according to thin-walledtaper tube with square cross section, which often appears as an energy absorbing part of crashbox, has been researched. A multi-objective optimization problem based on a combination ofCFE and SEA, has been put forward. Grooves are induced in the original structure. Afteranalyzed the relationship between energy absorption and crash force of structure withinducing grooves, the feasible design area of inducing grooves is obtained. The number,non-uniform intervals and depth of inducing grooves are taken as optimal parameters. Afterchosen sampling points reasonably, surrogate models are constructed by cubic polynomialsresponse surface method and radial basis function method respectively. Then the optimalnumber and distribution of inducing grooves are obtained by PSO method. FE analysisvalidates the effectiveness of this method. Results prove that compared with the structurewithout inducing groove, crashworthiness of the structure added inducing groovesscientifically is improved efficiently, which can be useful during the design of crash box.(3) Crashworthiness optimization of car door structure based on its surrogatemodel during side collision.Simulation for FE model of a certain car door structure during side collision has beenresearched. The curves of energy, collision contact force, deformation displacement andacceleration has been employed for analyzing the crashworthiness safety. Then, based on theuniform design and polynomial response surface method, surrogate models of the energy,maximum collision force and total mass of the car door structure under a special condition areconstructed respectively, as well as the thickness of planes are taken as variables. PSO methodis used as a tool for optimization of the surrogate models. As well as the mass and maximumcollision force of the original structure are treated as constraint conditions, the optimal designfor the main parts thickness of car door structure has been determined finally. With the design,one can effectively increase the energy of car door structure and improve the crashworthinessof the whole car. (4) Analysis about the bending behavior of thin-walled beams with hexagonal andchannel sections and construction for simplified model of B pillar.According to the researches on bending behavior of thin-walled beams with hexagonaland channel sections and the law for conservation of energy, formulas for calculating thedissipated energy of thin-walled beams through each plastic hinge line. The curve ofrelationship between the moment and rotation (i.e. M(θ)-θ) has been obtained. So therelative properties of non-linear rotation springs can be defined quickly by LS-DYNA. Bysetting the non-linear rotation springs into the zone appearing plastic hinges which are causedby the bending of B pillar, one can construct the simplified model of B pillar by non-linearbeams and rotation springs. After comparing the deformation effect, displacement curve andenergy curve of simplified model with those of detailed model, the effectiveness of simplifiedmodel is verified. The work is benefit to the construction for simplified model of vehicle andimprovement of effectiveness for crashworthiness optimization.