Study On Properties Of Z-pinned Composite T-joint

Compared with traditional materials,composite materials have many advantages.The high specific stiffness and the specific strength are theirs outstanding characteristics,which make them have a great prospect in the field of aerospace.Composite T-joints are commonly used in aircraft structures.The interlaminar properties of the composite laminates used in the T-joint is good,but their delamination toughness is weak.Therefore,it is necessary to use interlaminar reinforcement technology.Among the currently used reinforcement technologies,Z-pin reinforcement technology is easy to operate and the damage of Z-pinned structure is small,which is suitable for widespread promotion and application.In this context,the paper studies the properties of Z-pinned composite T-joints.Firstly,the advantages of Z-pin technology in composite reinforcement,the implantation technology of Z-pin,the production technology of Z-pin,the quality detection of Z-pin and the effect of Z-pin implantation on the properties of composite laminates are introduced.Then the basic principle of the interface element method is discussed,the calculation formula of the interface element method is derived,and the applicability of the interface element method in analyzing the interlaminar properties of composite laminates is studied.After that,the method and the principle of using the interface element method to simulate the onset and the progress of delamination of the composite laminates in the MSC.Marc software are introduced.Finally,the properties of Z-pinned composite T-joint are studied by experiment and numerical analysis.In the experiment,the influence of clamping span on the tensile property is analyzed by three groups of experiments with different clamping spans.The tensile experiments of Z-pinned,riveted and bonded composite T-joints with the same span are carried out,and the extent of the reinforcement effect between riveted and Z-pinned composite T-joints is compared.In the numerical simulation,the bilinear interface element of the software MSC.Marc is used to simulate the effect of Z-pin,the exponential interface element is used to simulate the adhesively bond,and the linear spring is used to simulate the effect of rivet.The properties of the Z-pinned T-joint and the riveted T-joint are compared,and the reasons of different reinforcement effects are analyzed.The results show that:(1)Z-pin has a good reinforcement on the composite T-joint,which greatly increases the tensile strength of T-joint: the maximum pullout force and the maximum pullout displacement of the Z-pinned T-joint are 2.08 times and 6.6 times that of the adhesively bonded T-joint respectively.(2)As the clamping span of the Z-pinned composite T-joint increases,the maximum pullout displacement increases,and the maximum pullout force decreases.This is mainly because of the reduce of the flexural stiffness and the bending strength.(3)The reinforcement of Z-pinned composite T-joint is better than that of the riveted composite T-joint,which is reflected in that: the stress concentration factor of the Z-pinned T-joint is smaller,and the maximum pullout force of the Z-pinned T-joint is 90.1% larger than that of the riveted T-joint,the maximum pullout displacement of the Z-pinned T-joint is 390.9%larger than that of the riveted T-joint,and the effect of Z-pinned T-joints to delay the decrease of the load is better than that of riveted T-joints.