Lightweight Design Of Aluminum Vehicle Frame Based On The Section Optimization And Load Path Analysis

The progress of lightweight vehicle bod y is much affected by the popularity of electric vehicles.Aluminum alloy usage in automobiles has increased over time with the low density,high strength and excellent energy absorption properties.Nowadays,aluminum alloy frame becomes the most representative lightweight body structure.So,this thesis takes aluminum alloy frame as the research object and the space frame consists of thin-walled closed extrusions which are connected by welding and bolting.For this structure,section design and load transfer evaluation are two key technologies during the design stage.Therefore,the method of beam section optimization is investigated and A optimization method based on section control points is proposed.Another method for load transfer path analysis based on generalized structural stiffness is also proposed.Stiffness experiments were conducted while an accurate 3D-FE model for simulating the bending and twisting based on MSC.Nastran was established.The error between the experiment and simulation is less than 10%,which shows highly simulation precision and proves the validity of simulation method.Then the modal frequencies of frame are obtained by simulation.Taking the rocker as an example,a multi-objective optimization method for size optimization is established.The prediction accuracy of four kinds of approximately models including quadratic polynomial(RSM),radial basis function(RBF),Kriging and Chebyshev polynomials for five different performance indexes are comparatively studied.The quadratic polynomial is suitable for the mass,bending stiffness and torsional stiffness,while the RBF is more reasonable for the first order model of bending and twisting.Taking the minimum mass,the maximum torsional stiffness and the maximum frequency of first order twisting frequency as the objective functions,and the minimum bending stiffness and the first order bending frequency as the restraints,and the key points and thickness of rocker section as the variables,the multi-objective mathematical model is built and solved through NSGA-? algorithm.Then,the Pareto optimality is achieved and 0.54 kg weight is reduced,2.16% of torsional stiffness and 4.97% of twisting frequency are improved.The results verify the effectiveness and practicability of the optimization method.For the correct evaluation of load transfer performance,general structure stiffness principle is introduced.Firstly,A cyclic calculation method based on the thought of experimental design to solve gen eralized structural stiffness is put forward.Secondly,in order to verify the correctness of the load path identification method,a simple plate FE model is established and solved.Then,the load path analysis method is applied to the finite element model of the automobile frame and defects of the structure at the joint are detected,and optimization is carried out.Finally,29.45% of bending stiffness,10.45% of torsional stiffness,12.73% of first order bending frequency and 3.41% of torsional frequency are improved per unit mass.The results verify the validity and feasibility of the load path identification method.