Strength Analysis And Progressive Damage Research For The Bonded-bolted Hybrid Composite Joints

Carbon fiber reinforced composites?CFRP?have been widely used in the design of connecting structures in aerospace and other fields due to their excellent properties.Reasonable composite?bonded-bolted?hybrid joints can take into account the advantages of bonding and bolt connection,which not only postpones the appearance of damage in the adhesive layer,but also greatly alleviates the adverse effects of stress concentration at the hole edge.It is one of the research hotspots of composite joint structure at present.In this study,a numerical modeling strategy is proposed to predict the failure strength of Titanium alloy-CFRP?boned-bolted?hybrid joint,and it is validated based on the comparison between experimental and numerical results.The effect of the principle design parameters within the hybrid joint structure,such as stacking-sequence,on the final failure strength and damage behaviors of composite hybrid joints is investigated numerically.Furthermore,the optimal design parameters of the hybrid joints are obtained accordingly.Numerical failure tests have been performed on the optimal design to capture the progressive damage process.This provides a theoretical reference for the engineering application of composite?bonded-bolted?hybrid joints structure.The main contents of this paper are as follows:Firstly,the improved Tserpes failure criterion and material performance degradation criterion are used to judge the failure phenomena of composite materials,and Von Mises yield criterion is used to judge the failure phenomena of adhesive layer.The above criterion is combined with APDL parametric language in finite element ANSYS software.Moreover,a numerical modeling strategy is proposed to predict the failure strength of composite?boned-bolted?hybrid joint,and it is validated based on the comparison between experimental and numerical results.Secondly,the effect of the principle design parameters within the hybrid joint structure,such as stacking-sequence,end-to-diameter ratio,width-to-diameter ratio and adhesive thickness,on the final failure strength and damage behaviors of composite hybrid joints is investigated numerically.Furthermore,the optimal design parameters of the hybrid joints are obtained accordingly.From the simulation,it is found that,the optimum stacking-sequence of composite for the joint structure is[45/0/-45/90]_3S.And the failure strength of composite hybrid joints is significantly improved by increasing the end-to-diameter and width-to-diameter ratios within a certain range.Moreover,the rise of adhesive thickness mainly postpones the appearance of initial damage.However,it contributes limitedly to the final strength of the hybrid joint.Finally,numerical failure tests have been performed on the optimal design to capture the progressive damage process based on the material degradation criterion.The progressive damage analysis of the optimal design indicates that,the matrix cracking initially occurs near the compressive side of bolt hole as loading increasing.Then,in the 45°,-45°,90°layer,a mixed damage mode in which the matrix cracking still dominates,appears and extends to laminate width edge at the corresponding layup angle.The damage of the 0°layer extends along the 135°direction of the nail hole in the failure mode of fiber breakage to the edge of the plate width,resulting in the final failure of the composite bonded-bolted hybrid joint structure.