Study On Influence Factors Of Tensile Performance For Composite Multi-bolt Joints

As a new type of strategic material in the 21 st century,carbon fiber composite materials have been more and more widely used in various fields and have been gradually applied to the bearing structure in the automotive structural design.Due to the anisotropy of composite materials,there may be mechanical errors for the connecting hole during the drilling processs,which include perpendicularity errors and other geometrical errors.The drilling may cause the breakage of the fibers,make it easier to form stress concentration around the hole,and reduce the strength,stiffness and fatigue endurance of the overall structure.Therefore,it is necessary to investigate the mechanical errors during the drilling processs,such as the effects of the perpendicularity error and the fitting mode on the tensile performance of the composite joints,which may provide a reference for the machining of carbon fiber composite materials.The paper focuses on the effects of the perpendicularity error and fitting mode on carbon fiber composite multi-bolt single-shear joints,and major works and results are as follows:(1)First of all,the mechanical connection forms and progressive damage method for composite materials were introduced.The improved Hashin failure criteria and the stiffness degradation scheme were used to establish the finite element model.UMAT subroutine was added to the ABAQUS to analyze the damage initiation,propagation and final failure modes of the composite material.And the validity of the progressive damage method was verified.At the same time,several parameters influencing the tensile performance of the composite bolted joints were analyzed.(2)Tensile experiments for single-shear multi-bolt composite joints were conducted,and the change of the load-displacement curve and the failure morphology under tensile load were studied.The effects of both non-perpendicularity error case and perpendicularity error case on the tensile performance were considered indicidually in the tensile experiments.The experimental results were compared with the corresponding simulation results to validate the effectivity of the finite element model.Then the effect of the other perpendicularity error modes on the bearing performance of the single-lap multi-bolt composite joints was analysed using the finite element model.(3)A finite element model for single-lap multi-bolt composite joints was established using ABAQUS,and the effects of perpendicularity error,fitting mode and bolt pre-load on the tensile performance of the single-lap multi-bolt composite connection stucture were analyzed,and the influencing mechanism was discussed in terms of the stress distribution around holes and the load distribution of the bolts.