Finite Element Analysis Of The Flexural Properties And Damage Evolution Of Three-dimensional Five-directional Carbon/aramid Hybrid Braided Composites

Three-dimensional braided composites are widely used in various engineering fields due to their near-net-shape and excellent overall mechanical properties.At present,this kind of composite material is mainly prepared by using a single fiber as a reinforcement.Although the performance is stable,it has a single function and cannot take into account performance and cost,brittleness and toughness,damage and life.Therefore,the introduction of an additional high-performance fiber can make this kind of material achieve a new balance between various properties,increasing its designability and application range.In this paper,three-dimensional five-direction braided structures are used.Two high-performance materials,aramid fiber and carbon fiber,are used as reinforcement materials to prepare braided composite materials with different hybrid structures.Hybrid effects,damage evolution and structural characteristics further provide a reliable basis for the design of hybrid three-dimensional braided composite materials and the application of related structural parts.In this paper,the three-point bending and low-speed impact mechanical response of three-dimensional five-direction hybrid braided composite materials are first studied experimentally.The three-point bending strength,bending modulus,load-displacement curve,and energy of three-dimensional five-direction hybrid braided composite materials are tested.The displacement curve analyzes the load-displacement and energy absorption of a three-dimensional five-direction hybrid braided composite under lowspeed impact.At the same time,the load-time curve is used as the original signal to obtain the shock stress wave in the frequency domain and time by fast Fourier transform and wavelet transform.Features within the domain.The results show that mixing can cause changes in the stiffness,strength and damage evolution of the material.The introduction of aramid fibers can further improve the fracture toughness of the braided composite material,and transform it from the brittle fracture to the tough fracture behavior of the pure carbon braided composite material.Then,a finite element analysis of the quasi-static three-point bending behavior of the three-dimensional five-direction hybrid braided composite is performed.The material constitutive structure is obtained by the average field homogenization method,and the elastic-plastic constitutive structure is introduced during the calculation process to obtain the elastic-plastic equivalent performance of the hybrid braided composite.Load calculations are performed on this basis.The results show that the finite element results can well predict the bending mechanical properties of three-dimensional five-direction hybrid braided composites.A comparative analysis of the stress cloud diagrams of different hybrid structural materials reveals that two different synergistic effects occur between the knitted yarn and the axial yarn during the three-point bending loading process,and the hybrid can further reduce the overall damage of the composite material.Among them,the material selected for the axial yarn has a greater impact on the overall performance of the three-dimensional and five-directional braided composite material.When carbon fiber is used as the axial yarn,its internal stress distribution is dispersed,which is prone to stress concentration and damage;and aramid fiber is used as the shaft.When the yarn is oriented,the stress distribution in the loading area is relatively continuous,which can promote the load diffusion and make the overall composite material bear the load together,thereby reducing the damage caused by excessive local stress concentration.Finally,a finite element analysis is performed on the three-dimensional five-direction hybrid braided composite under low-speed impact conditions.In order to obtain the overall damage evolution process of the hybrid braided composite at different speeds,a three-cell finite element model representing the full structure is selected for calculation in this study.The model divides the three-dimensional five-direction braided structure into regions,and establishes three representative cyclic units that can represent different regional structures.Each representative unit uses the bridge model and the incremental method in linearization theory to establish the elastic-plastic model Structure and introduce damage factors.The stiffness assembly is performed according to the proportion of three representative units in the material,and finally the overall equivalent performance of the three-dimensional five-direction braided composite material is obtained.The results show that the representative unit can well predict the mechanical properties of three-dimensional five-direction hybrid braided composites under low-speed impact.Through stress cloud diagram and stress wave analysis,it is found that there are obvious differences in the direction of stress diffusion and the law of change of stress under different impacts.In terms of damage evolution,under the impact speed of 6m / s,the number of failure units of the two hybrid braided composite materials is 589 and 984,respectively,which is less than 1250 of the pure carbon fiber braided composite material,further indicating that the hybrid material has better impact resistance.performance.At the same time,by extracting the stress value at the internal nodes of the material,the relationship between the stress value and time and the distance from the loading center is analyzed.The results show that after the maximum stress is reached,the internal stress of the hybrid composite material with aramid fiber as the axial yarn varies with There is no obvious attenuation trend in time and distance,while the internal stress of other structural braided composite materials decays rapidly with time,showing a decreasing gradient in distance.