Study On The Design Method Of Automotive Parts With Tailor-Welded Blanks Based On Crashworthiness Simulation

Reduction of automotive weight is the core problem in the 21 century for its potential to decreasing the fuel consumption and emission pollution. The tailor-welded blank (TWB) has the advantages of weight reduction, parts count decreasement, material utilization efficiency enhancement and structure performance improvement. Therefore, the utilization of TWB structure to replace the traditional structure has become the main approach among the automotive lightweight design methods. However, the current TWB design mainly relies on the expert experience and reference,lacking the related qualitative or quantitive study. Therefore, designing a lightweight method for the TWB components is of great significance and value for the application of TWB in automotive industry.The automotive lightweight design using TWB structure can not be conducted at the cost of the key mechnical performances, especially the automotive crashworthiness relating to the passenger safety. Furthermore, the impact simulation technique is an important tool in the development of automobiles. In order to make the crashworthiness numerical serve the TWB design quickly and precisely, this paper firstly performs a study on the key techniques in the crashworthiness numerical simulation, which provides precise and efficient analytical modals for the lightweight. Then, the methodology study is performed by using the TWB structure to reduce the automotive weight, with the thin-walled beam components and shell-shaped compnents as the design target. A lightweight design method for thin-walled beam components is presented in which the strength, bending stiffness, torsion stiffness, energy absorption capability and material cost are comprehensively considered. In the mean time, we put forward a design framework for lightening the shell-shaped components using TWB structure, in which the crashworthiness performance, part strength, stiffness and natural frequency are taken into account. Finally, the established method is applied to the lightweight design for the detailed automotive parts using TWB. The works and results in this paper are mainly as follows:1. Study on the key technologies based on vehicle impact simulationA study is performed to model the spot weld and control the mesh dimension based on the vehicle impact simulation. An elastic-plastic beam contact model is put forward to represent the spot weld, aiming at compensating the shortage of the current methods. Comparison between the rigid beam and the elastic-plastic beam is performed to analysize the stability and reliability in predicting the failure time of the spot-weld under impact loading. The analytical results of simulations show that the elastic-plastic beam contact model is more suitable for modeling the spot welds under impact loading compared with the rigid beam model. Method of meshing a vehicle using gradually changing areas and CPU time governing equation are presented from the point of view of mesh dimension control. The full-width frontal impact simulation of the whole car shows that combining the above two methods to control the mesh dimension of the car model can enhance the simulation efficiency with no sacrifice of simulation accuracy, which proves the validity of the methods.2. Impact modeling of the weld line of tailor-welded blankSince currently there are no proper models to represent the weld line of TWB under impact loading, a novel welding model is put forward, which uses twofold beams to simulate the behavior of the weld line. Simulations of uniaxial tensile tests and impact tests are conducted to study the influences of different weld modeling methods on mechanical behaviors of tailor-welded blanks involved in vehicle impact such as failure position, deformation, and energy absorption. The results indicate that there are a number of relatively subtle effects associated with the manner in which the weld line is modeled. The simulation and test analysises prove that the two-fold beam model presented in this paper is more reasonable than other existing models.3. Method study on the TWB lightweight design method for the automotive thin-walled beam componentsBased on the basic mechanical principle, the lightweight governing equations of strength, bending stiffness, torsion stiffness and energy absorption capability are derived. Method of multiplier penalty function is used to optimize the TWB thin-walled structure and the design approach is presented for lightening the TWB thin-walled components. Then, the automotive front side rail is taken as the example to do the TWB lightweight design. Firstly, the partition and initial material selection for the TWB component is performed. Secondly, constraints are applied to the thicknesses and materials according to the established lightweight governing equations. Whereafter, the method of multiplier penalty function is utilized to obtain the optimal results and design schemes are evaluated based on the mass and material cost. Finally, crashworthiness numerical simulation is performed to assess the selected lightweight scheme and prove the feasibility of the lightweight approach.4. Method study on the TWB lightweight design method for the automotive shell-shaped componentsFrom the point of view of generalization capability, the approximate efficiency of two meta-model technologies response surface method (RSM) and artificial neural network (ANN) are compared in the different TWB design. The analytical results show that the RSM is more suitable for the simple response approximation (part weight, stiffness and natural frequency), while the ANN has more advantages in impact reponses. When taking the automotive inner panel as the design example, the weight-sum genetic algorithm (GA) is used to optimize the multi-objective problem, with the part weight and side impact crashworthiness as the optimization objectives and the strength, stiffness and natural frequency as the optimization constraints. Thereby, the lightweight design of the automotive inner door panel is realized by using the TWB structure. In this way, an integrated approach is defined using FEA, ANN and GA for the optimization design of shell-shaped components with a TWB structure.This paper studies sevel key CAE technologies existing in the crash simulation, in an attempt to enhance the preciseness and calculation efficiency thus supplying a correct and fast-running model for the further TWB lightweight design of the automotive components. Then according to the different structural characteristics of thin-walled beam and shell-shaped components with TWB concept, two different design framework are properly defined, which makes a good reference for the application of TWB structures in auto body.