Study On The Mesostructure And Mechanical Properties Of Multi-layer Multi-directional Woven Composites

Three-dimensional(3D)woven composites are widely used in aerospace,national defense and other important fields due to their advantages of good overall structure performance,excellent interlayer performance and low preparation cost.However,the traditional 3D woven composites only have yarns in the direction of 0° and 90°,which leads to relatively weak in-plane shear performance.Therefore,they cannot be used in composite structures with high shear performance requirements,such as joint webs and torsion rudder shafts.The shear and torsion properties of 3D woven composites can be greatly improved by inserting bias yarn into the fabric.This paper focuses on the preparation,microstructure,mechanical behavior and elastic properties prediction of multilayer multiaxial interlock woven composites.Firstly,by analyzing the motion rule of the spindle of the multilayer multiaxial 3D loom,6 kinds of multilayer multiaxial interlock structure and 1 kind of interlock structure with stuffer yarn were designed by changing the arrangement of main yarn and the way of bias yarn movement.The weaving work of 7 kinds of three-dimensional woven fabrics with different structures was completed,and Resin Transfer Molding(RTM)composite Molding process was used to compound various structural fabrics to prepare multilayer multiaxial interlock structure and interlock structure with stuffer yarn woven composites.Second,micro-CT was used to observe the internal structure of the composites,and its microstructure was analyzed based on the observation results.It was assumed that: The cross section of the weft yarn is like a double convex lens,the cross section of warp yarn and stuffer yarn are like a rectangle,and the shape of the cross section of binder yarn will change with the change of the yarn layer.The geometric relationship between the yarns was determined,and the geometric cell model was established,which was accurate and effective.Using this model,the calculated material thickness and fiber volume content were in good agreement with the actual values.In addition,Digital Image Correlation system(DIC)and Dynamic resistance strain gauge were employed to study the tensile,compression and in-plane shear properties of 7 kinds of composites with different structures in warp and weft loading directions.The stress-strain curve and fracture morphology were analyzed,the failure mechanism was discussed,and the effects of bias yarns and the changes of position,content and angle of bias yarns on the mechanical properties of the composites were compared and analyzed,the results show that: The stress-strain curves of 7 kinds of composites at warp and weft loading directions show nonlinear characteristics,and the fracture morphologies at warp and weft loading directions are quite different.In addition,the inserting of bias yarn will reduce the tensile and compression properties of composites,and the properties will gradually decrease with the increase of bias yarn Angle(in the loading direction)and volume content.The change of bias yarn position will affect the distribution of load-bearing fiber,When the distribution of load-bearing fibers is relatively concentrated,the mechanical properties are favorable.At the same time,bias yarn can enhance the in-plane shear performance of composites.In this study,SY04 showed the best in-plane shear performance,with the shear strength up to 180 MPa and shear modulus up to 17 GPa.Finally,based on the established single cell model,the elastic properties of the model are predicted by ANSYS software.The predicted results are in good agreement with the experimental results,and the validity of the analytical model is verified.