Preparation And Mechanical Performance Of 2.5D Woven Composites

Two-dimensional laminated structural composites are made by stacking and curing unidirectional fibers in different directions with pressure.The strength between the layers is bounded only by the resin,and when subjected to impact or in-plane loading,the twodimensional laminated composites will suffer severe delamination damage,resulting in underutilization of the overall properties of the material.2.5D woven composite materials(2.5DWC)are widely used as main load-bearing members in aerospace,automotive industry,and military defense fields by introducing weft fibers when two adjacent layers of warp fibers exchange positions with each other to form a monolithic structure,which significantly improves the overall strength and damage tolerance of the materials.During the production and use of 2.5DWC,the fiber state in different directions greatly influences the materials’ mechanical properties,and the materials often exhibit different damage patterns when loaded in different directions.Meanwhile,the temperature significantly affects the mechanical properties of resin matrix composites,and the materials exhibit different mechanical properties and damage patterns at different temperatures.Therefore,it is essential to study the mechanical behavior of 2.5DWC in different directions and temperatures to reveal the effects of temperature on the mechanical properties of composites as well as the ways in which material microstructure and ambient temperature affect the mechanical properties of sample parts,which forms the basis of and the key to realizing the safe application of composites.In this paper,2.5D carbon fiber woven fabric preforms were woven,and the preparation of 2.5DWC was completed by vacuum-assisted resin infusion molding process(VARIM).The bending properties and damage mechanism of the material were studied by three-point bending experiments,and the compression behavior of the material under different loading directions was investigated;The internal damage of the material was characterized by X-ray computed tomography(X-CT)in the compression experiments,and the difference in the compression response and damage pattern exhibited by the material in different directions was analyzed based on the experimental results.In addition,the compression behavior of the material under different temperature fields is investigated in this paper,and the microscopic damage morphology of the material is characterized by scanning electron microscopy(SEM)to explore the rules of how temperature effects the compressive properties and damage mode of the material.Finally,the damage characteristics of 2.5DWC in meridional compression are represented with the aid of finite element simulation to reveal the damage process and failure mode of the material.The main contents and conclusions are presented as follows:(1)The three-point bending test of 2.5DWC samples was carried out to obtain the bending properties and load-displacement curves of the material,and the microscopic damage morphology of the material was characterized by SEM.The results show that2.5DWC has excellent bending properties,and matrix cracking,fiber fracture,and partial delamination due to fiber/matrix interface damage are the main failure mechanisms of the material under bending load.(2)Quasi-static compression tests were conducted on 2.5DWC in the warp,weft,and thickness directions and,with the aid of computed tomography,the difference in mechanical behavior and damage patterns of the material in different directions were explored.The results show that the damage patterns of materials in the warp,weft and thickness directions are quite different,and the compression performance in the thickness direction is better than that in the latitudinal and longitudinal directions.(3)Temperature effects were evaluated by quasi-static compression tests on the compression performance of 2.5DWC specimens in high temperature environments.The research show that temperature exerted a significant effect on the compressive properties of 2.5DWC,the plasticity of the material increase with the increase of temperature,and the compressive properties decrease with the increase of temperature;under the same high temperature environment,the peak stress and energy absorption of the material in the warp and weft directions are lower than those in the thickness direction;with the increase of temperature,the material exhibits different damage characteristics.(4)A finite element model of 2.5DWC with cohesive layer cells was established to analyze the warp compression process of the specimen under quasi-static compression load,the damage area of the material was characterized by the simulation results and compared with the experimental results,further verifying the damage and failure mechanism of the material.