考虑钉头传载的阶梯搭接钉载分配特性

确定钉载分配比例是机械连接强度分析的基础和关键，也是研究孔周应力分布的前提。以某型飞机铝合金阶梯形搭接板螺栓群连接结构为研究对象，利用应变电测法初步测量了各排螺栓的钉载分配比例。随后通过ABAQUS有限元三维实体建模，考虑钉头传载及接触摩擦、螺栓预紧、材料非线性、防弯夹具等因素，对螺栓群的钉载分配行为进行了模拟。计算发现：阶梯形搭接板多钉连接的钉载分配比例呈两端大中间小的规律，且台阶高度是影响钉载分配比例的重要因素。在此基础上，进一步研究了台阶高度对钉载分配均匀性的影响。分析结果表明：阶梯形搭接板多钉连接处于弹性范围以内时，随着台阶高度的增加，钉载分配趋于均匀；结构产生塑性变形后，随着台阶高度的增加，钉载分配先趋于均匀后随之变差。最后，基于钉载分配与孔边最大应力，对阶梯搭接多钉连接的几何构型进行了优化。优化后阶梯搭接的钉载分配比例极差不超过1.1%，最危险部位的孔边最大应力及螺栓最大剪切应力分别减小了约4.4%与10.2%。

Characteristics of bolt load distribution of stepped lap joints considering load transferred by bolt-head

Determination of bolt load distribution ratio of multi-bolted joints is essential for structural strength analysis, and is also the precondition for investigation of stress distribution in critical bolts and neighboring regions of plates. In this paper, the multi-bolted aluminum stepped lap joints from a certain type of aircraft are studied in terms of the bolt load distribution ratio, which is preliminarily estimated by means of the strain gauge electric testing technique. Then, a three-dimensional finite element model, taking into account of the load transferred by the bolt-head, contact friction, bolt clamp-up,material nonlinearity and anti-bending fixture, is constructed with ABAQUS software to simulate the load distribution between bolts for the joints. The calculation results reveal that edge rows carry more amount of load than the inner ones, and the step height is an important influence factor for bolt load distribution ratio of stepped lap joints. The effect of step height on uniformity of bolt load distribution is further analyzed. The analysis shows that during the elastic range, with the increase of step height, the bolt load distribution becomes more even; during the plastic range, with the increase of step height, the bolt load distribution grows even initially and then deteriorates. The configuration of stepped lap joints is optimized based on bolt load distribution and the maximum stress around the bolt-holes. It is shown that for the optimized stepped lap joints, the extreme difference of bolt load distribution ratio is less than 1.1%, and the maximum stress around the serious bolt-holes and the maximum shear stress of bolts decreases by 4.4% and 10.2% of those of the original ones, respectively.