Research On The Design And Strength Performance Of A New Z-pin Structur

Z-pin reinforced technology can effectively improve the interlaminar performance of composites materials by inserting fiber rods or metal rods in thickness direction of fabrics or prepregs.The insertion of z-pin is easy and flexible so that z-pin reinforced technology is widely used in improving the interlaminar performance of various composite structures now.In order to further improve the interlaminar performance of composite laminates,the spiral z-pin was designed and fabricated,and the pull-out loads of the spiral z-pin were increased because the interface areas between the z-pin and composite laminates were enlarged.In addition,the micro-structures of composites at the insertion site of z-pin are usually very complex,which bring difficulties to the modeling of the z-pinned structure.Therefore,this paper established a high-precision model of the z-pinned structure through numerical simulation.Firstly,a kind of pultrusion die to process the spiral structure on the z-pin was designed,and four groups of z-pins with different helicities(including a group of z-pins without spiral structure)were prepared.The axial tension property and bridging forces of the spiral z-pins were evaluated by tension tests and pullout tests respectively.It was found that although the spiral structure would make a certain adverse effect in the axial tension performance of the z-pin,the pullout forces of the z-pin were increased significantly.Then Micro-CT observations and analysis were carried on the three stages of the prepregs in z-pinning process.Based on the concept of virtual fiber,virtual fiber plain weave fabric layers were established.The high-precision model of z-pinned structure was obtained in the quasi-fiber scale by simulating the z-pinning process and the influences of z-pinning on the fabrics were analyzed.It was found that two results had a high similarity between the virtual fiber structures and CT scan morphologies.Finally,based on the “embedded element” technology,the virtual bundle was embedded into the meshed matrix model to establish the finite element model of z-pin.The mechanical responses of four kinds of z-pins under tension loads were simulated numerically,and the accuracy of simulation was verified by the comparisons to z-pin tension tests.This paper mainly focuses on the design of the spiral z-pin and the high-precision modeling of z-pinned structure.The finite element model of spiral z-pin and z-pinned structure were established using virtual fibers.And the mechanical properties of spiral z-pin were explored by experimental and numerical methods,which provided experimental and theoretical basis for the explorations of new z-pin and mechanical properties of z-pinned composites.