Composite Multi-nail Connection Uniform Load Distribution Method

Multi-bolt mechanical composite joints are widely used in the main load structures of the aviation field. However, because of its brittleness and lack of extending, the load distribution is much more unequal in each bolt than metal bolt joints, the hole that bear more load will failure first, which will seriously influence the statistic strength and fatigue life. Therefore, how to proportion the load distribution is taken attention by many experts.This article has, through the method of classic elasticity and model of spring, deduced the linear equations, used in the bolt load distribution as well as the side-road load of the symmetrical structures; also it has, with the method of 3D FEA, through use clearance fit in the higher load hole and interference fit in the lower load hole to proportion load distribution. The calculation shows that the maximal stress in the dangerous area is much lower and the minimal stress is greater in the same condition; for judge the macroscopically failure and failure model, we use the 3D Tsai-Wu and Hashin failure criterion, the result shows that the failure area is decreases by use this method. Also by introducing the characteristic curve hypothesis method and the Yamada-Sun failure criterion, the strength, which use suitable clearance and interference in each hole, can improve obviously.Finally, in order to figure out the optimized fit parameter in the composite multi-bolt mechanical joints, the article has, by introducing the artificial neural network, the target function is proportion the load distribution and the strength ratio in each hole, the result shows when the target function is the proportion the strength ratio, the holes are failure at the same time, which can make the strength of the multi-bolt structure improve 20% more or less. So the method that use suitable clearance and interference fit in each is doable.