Material-structure Integration Design For The Axial Energy Absorption Characteristics Of A Two-dimensional Triaxial Hybrid Braided Composite Energy-absorbing Beam

With the increasing seriousness of global carbon emission problem,the electric vehicle industry has gradually emerged in recent years.However,range has always been a pain point for the development of the electric vehicle industry.On the premise of ensuring the safety of the vehicle,reducing the quality of the vehicle will greatly improve the battery life and the durability of the battery.Therefore,the lightweight design of electric vehicles has become a research hotspot in recent years.Composite materials have the characteristics of low density,high strength and designability,etc.,while composite materials with two-dimensional triaxial braided structure have better integrity and stronger shear strength and impact damage resistance than traditional unidirectional lay-up composites,which have broad application prospects in automotive,aerospace and defense fields.This paper takes the two-dimensional and three-axis hybrid braided composite energy-absorbing beam as the research object.Carbon fiber yarns are introduced in the axial direction to enhance its axial mechanical properties,while glass fiber hybrid braiding is used to improve its toughness and impact performance on the one hand,and reduce the cost on the other.Starting from the microscopic braided structure of the material,the influence law of the design parameters of the material microstructure on the macroscopic crush energy absorption performance is studied,and the design method of material-structure integration is established to optimize the design of the crush energy absorption characteristics of the two-dimensional triaxial hybrid braided composite energy-absorbing beam.The details are as follows:First of all,a series of mechanical performance tests including axial tension and compression,transverse tension and compression,and shear tests were carried out to obtain the elastic and strength material parameters of the two-dimensional triaxial hybrid braided composite material.Based on LS-Dyna software,suitable material model,strength criterion and performance degradation model were selected to establish the finite element model for the performance analysis of the 2D triaxial hybrid woven composites,and the calculated elastic and strength performance parameters were compared with the experimental results to verify the applicability of the model.Secondly,by introducing the representative volume units,combining the concentric cylinder model(CCM)elastic parameter prediction model and the extended laminate strength theory,the elasticity and strength parameters of the two-dimensional triaxial hybrid braided composite material from the microscopic parameters to the macroscopic properties are established.The prediction model is verified by experiments.The effect of braiding angle on the elastic and strength properties of the material was investigated.It is found that as the braiding angle increases,the axial Young's modulus E_xx decreases,and the transverse Young's modulus E_yy continues to increase;while the shear modulus G_xy and shear strength both reach their peaks at about 45 degrees,showing a quadratic curve change;The change trend of Poisson's ratio is similar to that of shear modulus,reaching its peak at about 0.3,and then keeps decreasing.As the braid angle increases,the axial tensile and axial compressive strengths keep decreasing before about 45 degrees,and then keep increasing;the transverse tensile and compressive strengths keep increasing in general.Finally,the stable and unstable failure modes of the energy-absorbing beam made by the two-dimensional triaxial hybrid braided composite material under crushing load are analyzed,and a finite element model of the energy-absorbing beam crushing is established and a parametric proxy model of this finite element model is developed combined with the Kriging proxy model and the Latin hypercube experimental design method.The leave-one-out method(Loo)was used to verify the model error,and the relationship between fiber volume fraction and macroscopic crushing performance was analyzed.It is found that the peak load of energy-absorbing beam crush gradually increased with the increase of the total fiber volume fraction,and the specific energy absorption(SEA)showed a triangular function fluctuation.As the volume fraction of carbon fiber in the total fiber increases,the specific energy absorption and peak load continue to decrease;on the contrary,as the braiding angle increases,both the specific energy absorption and peak load keep increasing.Then based on the proxy model,two types of multi-objective optimization models are established.The first type optimizes the maximum crashworthiness of the designed energy-absorbing beam with the maximum specific energy absorption and the minimum peak load as the objective functions,respectively.The second class is designed for lightweighting from the perspective of engineering applications,with the cost and density of the material minimized as the objective function while safeguarding the crashworthiness.Pareto fronts are plotted and Knee Point is selected for analysis and validation,and the final performance is improved by about 20%in both cases.