Stress Constrained Research On Multi-material Lightweight Of Pure Electric Bus Body Frame

At present,the sustainable development of the automobile industry is being plagued by increasingly severe energy shortages.Under this trend,passenger cars are developing in the direction of pure electric energy saving and environmental protec tion,but their commercialization is severely restricted by the cruising range problem.Under the real dilemma that battery technology cannot break through in the short term,it is a practical and effective way to promote its promotion and application to r educe the energy consumption of passenger cars and increase the cruising range of pure electric buses through lightweight structural design.In order to fully tap the potential of structural light-weighting,the application of various advanced materials,s uch as highstrength steel,aluminum,magnesium alloy,and carbon fiber,in the body structure has become the mainstream trend.However,there is currently no systematic design method for multi-material body structure,and the main method is still a simple replacement of traditional materials,which cannot give full play to the performance of materials.At the same time,the unlimited use of advanced materials will inevitably lead to a sharp increase in the cost of the car body.Although multi-material topology optimization can be applied to the design of multi-material structures,there is still a lack of practical application in the design of passenger car body structures.On the other hand,most of the existing multi-material topology optimization methods take stiffness as the main design goal,ignoring the requirements of structural strength,which may lead to structural damage such as fracture,fatigue,and plastic deformation.Therefore,it is necessary to conduct research on these issues.The main work of this paper is as follows:1.Based on the ordered SIMP method,a multi-material topology optimization model for the engineering problem of flexibility minimization under volume constraints is constructed,and the related sensitivity is derived.Combined with a numerical example,the effectiveness of the method is verified.2.On the basis of the ordered SIMP-like method,a processing method of establishing global stress constraints according to the material sequence is proposed,that is,using the P-norm stress correction strategy,the local stress constr aints are clustered into global stress constraints according to the m aterial,which greatly reduces up the scale of calculation.Then the multi-material topology optimization models for two engineering problems of minimizing volume under stress constraints and minimizing flexibility under stress and volume constraints are constructed,and the related sensitivities are deduced.Numerical examples verify the effectiveness of the proposed method.3.A complete three-dimensional geometric model of the body frame of a pure electric bus is established,which is reasonably simplified,and a plate-shell element finite element model of the body frame is constructed.A static test of the actual vehicle body frame of this type of bus was carried out.The accuracy of th e analysis model of the bus body frame was verified by comparing the test data and the simulation results,which provided a reliable basis for the subsequent application of stress-constrained multi-material topology optimization method to design the body structure model.4.Based on the actual characteristics of the bus body frame,in order to reduce the calculation cost,a finite element model of the pure electric bus body frame beam element is constructed,and its stress level is analyzed.Subsequently,b ased on the proposed multi-material topology optimization method considering stress constraints,a lightweight model of multi-material under the actual cost and stress constraints of the bus body frame was constructed and optimized.In the end,a clear and concise optimized structure was obtained,the quality of which was reduced by 11.4%,the goal of lightweight was achieved,and the structural strength also met the design requirements.In summary,this paper studies the multi-material topology optimization method under stress constraints.The proposed processing method of establishing global stress constraints according to the material sequence enables the allowable stress of each material to be satisfied at the same time and relieves the stress concentrat ion;it is applied to In the lightweight design of the pure electric bus body frame,a multi-material lightweight solution process considering stress has been developed to realize the lightweight design of the pure electric bus body frame under the constra ints of actual cost and allowable stress.