Research On Lightweight Optimization Design Method Of Multi-material Cab Structure For Commercial Vehicle

Automotive lightweight is an important technical way to achieve energy saving and emission reduction of vehicles.As an important part of commercial vehicle,the cab’s structural weight reduction plays an important role in lightweight of the vehicle.At present,the commercial vehicle cabs are made of single materials and low material strength,which leads to a low level of lightweight design compared with similar international cabs.And the new regulation of GB26512-2021 "The Protection of the Occupants of the Cab of Commercial Vehicles" puts forward higher requirements for cab safety,which makes the research on the forward lightweight design method of multi-material cab structures more urgent.However,the development and application of multi-material cab is a complex system engineering involving performance analysis and evaluation,structural material selection,structural design,connection design,electrochemical corrosion and process optimization.However,the systematic design process has not yet been established,and there are still many key common technologies problems to be solved,including the rapid lightweight material selection design for complex parts of the body,the influence of dissimilar material connection parameters on body performance,and the integrated optimization design method structure-connection-performance for body.Based on the design concept of "appropriate materials are used in the right place" and the original steel cab as the research object,a multi material selection method that comprehensively considers the material index,bearing capacity,stress,deformation and energy absorption of the key parts of the cab is proposed.And steel/aluminum multi-material cab structure is designed considering the manufacturing process.Then,an integrated rapid optimization design method and simplified model of different steel/aluminum self-piercing riveted connection forming-joint mechanical properties are established.The multi-objective lightweight optimization design of multi-material cab structure-connection-performance integration is realized.The main contents are summarized as follows:A fully parametric model of the cab body-in-white is established.Taking the original cab as the research object,a fully parameterized cab body-in-white model is built by the implicit parameterization technology.Furthermore,the simulation accuracy of the implicit fully parameterized cab body-in-white model is verified via comparing with the cab’s inherent modal characteristics and passive safety test data.Based on the parameterized model,the simulation analysis conditions of bending stiffness,torsional stiffness and structural strength of the cab are established.It lays the foundation for the material selection and optimization design of the cab structure in the following.A lightweight material selection method for cab parts is proposed.On the basis that the thinwalled beam is subjected to small deformations of tension and bending,and that the thin-walled beam is subjected to large deformations of axial crushing and bending,the material indexes of the structural stiffness,strength and dynamic crashworthiness of the thin-walled beam are deduced.The relationship between the part-level parameters and the overall bending stiffness,torsional stiffness and strength of the cab is established.A part decoupling method combining dynamic structural crashworthiness and equivalent static load is proposed,and the corresponding relationship between the material and size of different parts considering the manufacturing process is determined.Subsequently,an evaluation method of value function that comprehensively considers the mass and material costs of selected parts is established.The accuracy of the material selection method is verified by axial crushing and three-point bending impact test of thin-walled beams.It provides theoretical guidance for the material selection of cab skeleton structure.The material selection scheme and section structure of the cab skeleton structure are determined.The load-bearing deformation,stress distribution and impact energy absorption of the key parts of the cab are considered,and the performance requirements of the key parts and the influence of the parameter changes of key parts on the overall performance of cab are analyzed.The classification and material selection scheme of key parts is determined.The relationship between the structural stiffness and strength performance of the cab and the partlevel material selection index is established.Considering the aluminum alloy extrusion process requirements,a multi-working condition joint topology optimization method combining variable density and compromise programming is proposed,and the topology optimization design of aluminum alloy material selection parts is carried out to determine the cross-sectional structure and size.Then,different material selection schemes for each part are determined according to the established material selection method.Finally,the material selection scheme and initial structural parameters of the multi-material cab are determined via the evaluation method of value function.The structure-process-performance integrated optimization design method of the cab steel/aluminum self-piercing riveted connection and the simplified model of the joint are constructed.A integrated simulation model of self-piercing riveting forming-joint and drawing/shearing/peeling mechanical performance is established,and the forming quality and mechanical performance indexes of the self-piercing riveting joint are analyzed.The accuracy of the simulation model is verified by experiments.A combined sequence optimization method is proposed.Based on this,a structure-process-performance integrated optimization design method for self-piercing riveting connection of steel/aluminum dissimilar materials is established,and the optimal riveting process parameters are determined.The results show that the connection performances are effectively improved.Subsequently,the optimized simplified model of the steel/aluminum self-piercing riveted joint is determined.And the influence law of rivet position distribution on mechanical properties of steel/aluminum parts is analyzed.It lays the foundation for the optimization design of the cab structure in the following.The structure-connection-performance integrated multi-objective lightweight adaptive RBFNN optimization design of cab is established.Combined with the implicit parameterized cab body-in-white model after material selection,the cab structure and connection process parameters are considered as variables,and an improved grey relational analysis-TOPSIS decision method is proposed to screen the variables and determine the design variables of multiobjective optimization.Extrusion process requirements and material costs are introduced as constraints.Considering the bending and torsional stiffness,structural strength,inherent modal characteristics and passive safety performance of the cab,an adaptive RBFNN optimization method is proposed to carry out the structure-connection-performance integrated lightweight optimization design of the cab.And the Pareto frontier solution is obtained.The scheme with the best comprehensive performance is determined using the improved grey relational analysisTOPSIS method.Compared with the initial model,the cab mass is reduced by 9.58% after the lightweight design.The maximum relative error between the predicted optimal solution and the simulated optimal solution for each performance of the cab is within 5%,which verifies that the proposed adaptive RBFNN optimization method is feasible and effective for the lightweight optimization design of the cab structure.