Analysis On Macro-Micro Modeling And Mechanical Properties Of 2D Triaxial Braided Composites

Basalt fiber is a kind of inorganic fiber with high temperature resistance,high strength modulus,natural pollution-free and renewable utilization.At the same time,it is also one of the four major fibers in China.Basalt fiber products have been widely used in aerospace,military industry,automobile,electronics and civil engineering.Compared with unidirectional fiber composite,braided composite has more uniform mechanical properties,better integrity and designability.It is a high-tech lightweight structural material with great potential in automotive applications.In this paper,2D triaxial basalt fiber braided composite specimens are prepared and the basic mechanical properties are tested to obtain the overall performance parameters of the material.According to the geometric configuration of braided composites,the micro representative volume element finite element analysis model is established to explore the influence of different braiding angles on the elastic properties of materials,and the braiding angle with better performance parameters is selected for subsequent research and analysis;The distribution of stress and strain under different loads is analyzed.It is found that the axial fiber bundle bears larger stress.The representative volume unit is equivalent to four homogeneous proton units by homogenization method,and the array is extended to a macro model.The elastic properties and strength parameters of the sub elements in the macro equivalent model are determined by volume average method and top-down decomposition method.The three-point bending and low velocity impact test results and simulation results under different volume fractions are compared and analyzed.The validity of the macro model is verified.At the same time,the effects of impact position and impact angle on the low velocity impact response of the composites are analyzed.Finally,the material is applied to the outer panel of automobile hood to explore its application effect.The specific research contents are as follows:(1)Preparation of test samples and related experimental research.Firstly,six layers of2 D triaxial basalt fiber braided composites were prepared.According to the relevant test requirements,tensile,compression,in-plane shear,three-point bending and drop weight impact tests were carried out to obtain the performance parameters of the composites.(2)The micro model of composite materials was established and the correlation analysis was carried out.The structural dimension parameters of 2D triaxial braided composites are analyzed and the meso finite unit analysis model is established.Periodic boundary conditions are applied to the model to make it meet the continuity of stress and displacement.The influence of different braiding angles on the elastic parameters of composites is explored and the stress-strain distribution under different loads is studied.The results show that the elastic properties of the composites are the most stable when the braiding angle is 60 degrees.When the material is subjected to axial tensile load,the axial fiber bundle bears most of the load.When the material is subjected to transverse tensile load,the axial and oblique fiber bundles bear the load together.Under the shear condition,the stress value in the axial fiber bundle region is larger than that in the oblique fiber bundle region.(3)The macroscopic equivalent model is established.According to the structural characteristics and the distribution of stress and strain of 2D triaxial braided composites,the representative volume unit model is equivalent to four uniform proton units and extended to a macro model to improve the efficiency of simulation.According to the volume average method,the equivalent elastic performance parameters of the sub elements are obtained.The top-down decomposition method is used to pseudo design the strength parameters of the element based on the stress-strain continuity.Based on the continuous damage model and bilinear cohesion model,the macroscopic equivalent finite unit models of three-point bending and low velocity impact with different fiber units fraction are established respectively.The simulation results are compared with the experimental results to verify the effectiveness of the macroscopic equivalent model.The effects of impact position and impact angle on the low velocity impact performance of the composite are analyzed.The results show that the peak impact force near the confinement area is higher,where the composite is easier to be penetrated.With the increase of impact angle,the component of impact energy perpendicular to the material direction increases and the peak impact force of the composite increases.At the same time,the more energy the material absorbs.The damage types of composites under low velocity impact are analyzed.It is found that the damage types on the front and back of the impact are fiber compression damage and fiber tensile damage respectively.After the material is impacted,the damage extends along the braiding direction.(4)2D triaxial basalt fiber braided composite was applied to the outer panel of engine hood.The static simulation of the hood shows that the stiffness of each working condition is improved compared with the original steel hood.At the same time,the hard points of important components are selected for pedestrian head impact simulation analysis.The results show that the performance of pedestrian head protection can meet the requirements of the regulations and the performance of the material is improved after replacing the engine hood outer panel with 2D triaxial basalt fiber braided composite.