Numerical Analysis Of Mechanical Properties And Failure Mode Of CFRP Straight-Through T-Joints

Composite materials are widely used in the aerospace field due to their high specific strength,high specific stiffness,good fatigue resistance and excellent designability.As a common connection form in the aerospace field,the bonded T-joint is also often used in wind turbine blades.It has attracted more and more attention and research because of its uniform force transmission and small structural damage.However,there are many studies on the T-joint of the wing plate,and there are few studies on the direct T-joint.The potential engineering application value of the direct T-joint is large,so this study is necessary.In this paper,the mechanical properties and failure modes of CFRP laminates bonded T-joints under tensile and bending conditions will be studied by numerical methods.The main contents are :1)The experimental results of the wing T joint in the literature are compared with the model simulation results,and the two are in good agreement,which shows the scientific rationality of the model.At the same time,the mesh number of the model is changed to verify the mesh independence,and the optimal mesh size used in the subsequent calculation model is obtained.2)The cohesive zone model was used to simulate the mechanical properties of bonding and laminates.The 3D Hashin criterion and Camanho criterion were used to simulate the damage initiation and stiffness degradation of laminates.The effects of joint parameters on mechanical properties were studied,including the ply order of the bottom plate,the thickness of the bottom plate and the number of tenons.The results show that the joint stiffness increases with the increase of the thickness of the bottom plate.Whether it is tensile or bending loading,the interlayer strength is the primary factor restricting the joint performance.The failure mode of different types of joints is mainly interlayer failure,and some joints have laminate element damage.3)The laminated plate variable thickness technology and z pin reinforcement technology were applied to the joint to study its effect on the performance of the joint.The results show that the variable thickness technology has no obvious enhancement effect on the joint performance due to the limitation of interlayer strength.The z pin reinforcement technology can significantly enhance the performance of the joint under both tensile loading and bending loading conditions,with an increase of more than 20 %,and the failure mode changes from the original single interlayer failure to the simultaneous pull-out of interlayer and z pin.The influence of z pin spacing on the reinforcement effect was studied.The joint with z pin spacing of 3 has a worse bearing capacity than the joint with z pin spacing of 4 due to the high density of the nail,the large occupied area and the difficulty in transferring the peel stress.The research on T-joint in this paper can provide effective guidance for engineering practice.