Research On The Equalization Of Load Distribution Of Carbon Fibre Composite Bolt Joints

There exists a lot of mechanical joints in aerial composite structures. Mechanical joints are cruial to the efficiency and safety of aircraft. However, the lack of plastic zone of composite material will result in severe unevenness in load distribution of muti-bolt composite joint and affect joint strength and efficiency. Analyzing the influence factor and finding out a way to equalize the load distribution of composite bolt joints can improve the whole strength and joint efficiency of composite mechanical joint.This article combines experiment study and 3D finite numerical simulation method to study the equalization of load distribution in composite bolt joint. Firstly, the geometrical parameters of the composite bolt joint has been designed with reference and 3D models of composit mutibolt joint for finite simulation have been established in ABAQUS software. Then the unevenness of load distribution in muti-bolt composite bolt joint is proven through single and muti bolt models. After that, the article carrid on an experiment study on load distribution of composite muti-bolt joint with surface strain test based method and compared the experiment data with simulation results from ABAQUS so as to validate the way the article choose to model the muti-bolt composite joints. Then the parametric research on the load distribution of composite bolt joint was performed in the 3D finite models, and influence factors such as geometric parameters, bolt preload, clearence, interference and friction were studied in this process. The results show that clearence and interference can severely affect the load distribution of muti-bolt joint while geometric parameters and bolt preload have little influence on it. The way clearance and interference impact on the load distribution is to change the initial load distribution proportion ?Moreover, the load proportion has negative linear correlation to the clearance scale, and it also has negative correlation to the interference scale when the interference is below 0.75% of the hole diameter. Once the interference is above 0.75% of the hole diameter, it will not affect the load distribution any more.In the sequent muti-factor reseach, the article found out that the presence of both clearance and interference can effectively equalize the unevenness in load distribution of muti-bolt joints with less amount of the clearance and interference. The wise and practical way to equalize the load distribution is to use proper clearence fit(0.5% of the hole diameter) at bolts transmitting larger load and proper interference fit(0.5%-0.75% of the hole diameter) at bolts transmitting smaller load.