Refinement Modeling And Stiffness Prediction Of Z-pin Composites

Z-pin reinforced technology is a kind of interlaminar reinforcement technology by inserting z-pins in through-thickness direction,which can effectively improve the weak interlaminar performance of composite materials.Z-pin reinforced composites are simple to mold and highly configurable,and are the only 3D reinforcement technology that can be used directly in prepregs.However,the implantation of z-pins changes the original fiber morphology of the fabric,making the micro-structure of z-pin composite very complex,which brings great difficulties to the highfidelity modeling of such materials.The purpose of this paper is to study the influence of z-pin implantation process on fabric layer,establish the relationship between process parameters and structural parameters,and realize the high-fidelity 3D virtual reconstruction of z-pin reinforced structure.The virtual fiber embedded technology is proposed,and the unit cell model of z-pin composite is established to obtain the accurate stress and strain fields of fiber and matrix under arbitrary load conditions.It can be used to predict the effective stiffness performance of z-pin composite and provide theoretical support for z-pin process design.In this paper,the researching development of z-pin reinforced composites at home and abroad is reviewed and analyzed in detail,including the development history,micro-structure modeling methods and experimental researches.The geometric characteristics of z-pin structure were analyzed by ?-CT technique.The tensile and shear properties of quartz fiber / phenolic resin z-pin composite were tested.According to the order of virtual fiber,virtual yarn and virtual fabric,the geometric model of preform layer was established.The 3D virtual reconstruction of z-pin reinforced structure was realized by simulating the process of z-pin implantation.The influence of z-pin diameter,implant position and tilt angle on the fiber structure was studied by numerical method.In this paper,a virtual fiber embedded element technology is proposed.The micro analysis model of z-pin composite is obtained by restraining the virtual fiber reinforced structure and the matrix through the "embedded element".The mechanical response of z-pin under tensile and shear loads is studied.Compared with the traditional micro analysis model,the model in this paper can calculate the stress and strain fields of the fiber in the yarn and the matrix,which is higher accuracy.Based on the volume average method,a fiber reinforced voxel element is constructed to predict the stiffness of z-pin composite.The numerical results are in good agreement with the experimental data,which can provide theoretical basis for the actual process design.In this paper,the high-fidelity model of z-pin reinforced structure is obtained by virtual fiber reconstruction.The virtual fiber structure is combined with matrix voxel grid by embedded element technology.The z-pin process parameters,preform structure parameters and the mechanical properties of composite materials are linked to form a complete analysis route of mechanical properties of z-pin composite materials,which provides theoretical guidance for the process design and engineering application of z-pin composite materials.