Study On Failure Of Composite Bolted Joints

Advanced composite materials have become the primary materials of aerospace and other equipment structures because of their excellent performance,such as high strength-to-weight ratio,high stiffness-to-weight ratio,performance designability and integration of materials and components.Due to the extensive application of complex composite structures in engineering,composite joints are inevitable in composite structural design.Bolted joints of composite structures are widely used because of their high load transfer capability,reliable connection and easy disassembly and repairment.However,many factors play an important role in affecting the ultimate bearing capacity and failure modes of bolted joint composite structures,such as width-to-hole diameter ratio(W/D),edge distance-to-hole diameter ratio(E/D),friction coefficient,pre-tightening force,stacking sequence,proportion of plies with the same fiber orientation,etc.Therefore,it is necessary to study the influence of these factors on the ultimate bearing capacity and failure mode of bolted joints.In this dissertation,a finite element method is proposed to predict the failure strength and failure modes of bolted joints of composite structures.The finite element model of bolted joint is built in the finite element procedure ABAQUS v6.14.The mechanical response of composite laminates is simulated by using the built-in fiber reinforced composite elastic-damage model in ABAQUS v6.14.Also,the modeling method of pre-tightening force and contact in the bolted joint structures is introduced.The proposed finite element modeling method is verified by comparing the finite element simulation results with the experimental results.Furthermore,the ultimate bearing capacity and failure modes of single-pin single-shear bolted joint structure under different width-hole diameter ratio,edge distance-to-hole diameter,friction coefficient,pre-tightening force,stacking sequence and proportion of plies with the same fiber orientation are studied.The numerical results show that,in a certain range,the ultimate load-carrying capacity of the bolted joint structure increases firstly and then decreases with the increase of pre-tightening force,increases with the increase of friction coefficient,decreases first and then increases with the increase of width-to-hole diameter ratio,and increases first and then decreases with the increase of edge distance-to-hole diameter ratio;When the outermost layer is 90°ply,the ultimate bearing capacity of the structure is significantly improved.Increasing the proportion of 0° and 45° plies and decreasing the proportion of 90° plies caneffectively improve the ultimate bearing capacity of the single-pin single-shear bolted joint composite structure.The failure mode also changes with the change of different working conditions.