Research On Open Hole Connection Performance Of Multi-layer Multi-directional Woven Composite

The connection structure is the most common structural form in the design of composite materials,Mechanical connection is one of the most widely used connection methods in connection structures.With the increasing application of three-dimensional woven composite materials in the aerospace field,the application of three-dimensional woven composite joints in components such as wings and landing gear is also increasing.Therefore,how to improve the open-hole connection performance of threedimensional woven composites and accurately reveal its failure mechanism is very important for composite structure design.The orientation and distribution of fibers in the composite material have an important influence on the pinned-joint performance of the composite material.,however,traditional three-dimensional woven composite materials only contain yarns of 0° and 90°.It has poor pinned-joint performance Therefore,multilayer multiaxial structures are proposed,which can introduce ±45° yarn in the plane,improve the stress concentration at the edge of the hole and improve the performance of composite material joint with pin.First,the experiment was investigated to study the influence of the interwoven structure parameters and the joint geometry parameters of the multilayer multiaxial woven composite on the pinned-joint performance of the material.4 kinds of multilayer multiaxial woven structures and 5 kinds of joint geometry.The composite material specimen was prepared by the RTM composite process,The single pin tensile properties of the composite material test piece with a hole was obtained,the digital image correlation system(DIC)was used to obtain the strain response of the composite material.The results showed that,introducing ±45° yarns or increasing the ratio of 0°warp yarns would improve the load-bearing strength;The strength variation caused by different W/D ratio was related to the content of 0° yarns in the structure.The reduction of E/D ratio caused debonding damage to the yarn at the end.Secondly,a macro-meso coupling analysis model was established.The tensile failure mechanism of single pin of multilayer multiaxial woven composite was analyzed.Based on the meso-structure of composites.A three-dimensional woven composite unit cell model was established,and engineering constants of composite materials was obtained.Based on the meso-structure of unit cell model,a macro-meso coupling and full-scale analysis model for the three-dimensional woven composite was proposed.The progressive damage process of the joint structure of the 3D woven composite was analyzed.The failure process of the joint structure was revealed.The validity of the model was verified by comparison with the experimental results.Finally,CT scanning technology was used to extract the meso-structure damage state of the composite material.Combined with the results of numerical simulation,the influence of fabric structure and joint geometry on the failure mode and damage mechanism of the pinned-joint multilayer multiaxial woven composites was analyzed.The failure mechanism of the composite material with different structural parameters and different joint geometry parameters was revealed.Research showed that the introduction of ±45° yarns into the three-dimensional woven structure improved the stress concentration at the edge of the hole.And when 0°,±45° and 90° simultaneously existed,Increasing the content of 0° yarn had little obvious effect on the failure mechanism.When there were only ±45° and 0° yarns in the structure,the damage spreaded significantly along the transverse direction.When E/D or W/D radio was small,the damage spreaded to the end-to-diameter or width-diameter direction,respectively.