Research On Stability Of Integrally Stiffened Planes Of 3D Braided Composites

Three-dimensional braided composites have good structural integrity and can effectively overcome the weaknesses such as low interlayer strength and easy stratification of the traditional laminated composite materials,so that the application prospect of the three-dimensional braided composites is becoming more and more extensive.As a new type of lightweight and efficient structure,study the three-dimensional braided compositestructure stability of the reinforced wall,explore the structural buckling and post-buckling behavior,ultimate bearing capacity evaluation structure,is to ensure that the structure safety should be one of the important problems to be solved.However,due to the complexity of the meso-structure of the three-dimensional braided composites,it is difficult to increase the design and analysis of the integral stiffened panels.Therefore,how to study the mechanical model of structural stability analysis based on the macroscopic structural characteristics of the three-dimensional braided composites,and systematically study the influence of material parameters and structural parameters on the structural stability,and have important research value and Engineering significance.Based on the macroscopic structural characteristics of the three-dimensional braided composite structure,the structural stability of the three-dimensional four-direction braided composite wall and the whole stiffened plate under typical load conditions is studied by using the idea of cross-scale mechanical modeling.Firstly,in terms of mesoscale,the spatial motion law and distribution configuration of yarns in different regions were studied according to the four-step weaving process.The parametric solid unit inner and double-layer surface cells was established,Four-dimensional braided composites,a finite element model of elastic properties of materials based on inner and double-layer surface cells was established.The validity of the elastic modulus prediction model was validated and discussed in detail The influence of weaving angle and fiber volume on the elastic properties of the material.Secondly,on the macroscopic scale,a three-dimensional four-direction braided composite "laminated cell mechanical structure model" is proposed,and the finite element analysis model of the stability of the wall and the reinforced slab is established.The buckling characteristics under the load conditions,the effects of weaving angle,fiber volume content,wall size and so on on the buckling characteristics of the structure are discussed.Finally,the structure of the three-dimensional four-direction braided composite is designed,and the post-buckling behavior under axial load is studied by nonlinear finite element method.The equilibrium path and buckling mode And the influence of the parameters such as fiber volume content,braided angle and the number of ribs on the post-buckling behavior of the structure are discussed in detail.