XFEM Modelling in Multi-bolted Joints Using a Unified Bolt Preload

Abstract Multi-bolted joints are adopted and designed to provide efficient load transfer within assembled engineering parts. Bearing failure is favorable during design phase due to more progressive failure mode, however, ability of by-pass stress to be transferred to adjacent bolts in multi-bolted joints prone to catastrophic net-tension failure. Former approach known as equivalent spring stiffness (ESS) was proposed but it requires experimental sliding load value. This has led to semi-empirical approach to require experimental set-up than incorporating a generic bolt preload value. This paper aims to provide a unified bolt preload (UBP) value to be implemented in each bolt independent upon plate properties and bolts arrangements. Strength prediction were taken place by 3-D Extended Finite Element Method (XFEM) framework of various staggered and non-staggered arrangements to include various lay-ups types and plate thickness. The failure loads predictions in each testing series were investigated and then validated against experimental datasets and also compared with previous technique (ESS approach). Crack patterns and failure modes from this approach were consistent with experimental observations, where net-tension failures were observed within all testing series. Less good prediction compared to from ESS technique, partly due to semi-empirical nature in former approach. Nevertheless, reasonable agreement in UBP technique with experimental datasets were obtained (average discrepancy of approximately 20%).

摘要 多螺栓连接副被广泛应用于装配工程构件中，以实现高效的载荷传递。设计阶段中，承压失效因具备渐进式破坏的特征更具优势，但多螺栓连接副内的旁路应力可传递至相邻螺栓，这一特性易引发灾难性的净拉伸失效。此前提出的等效弹簧刚度（ESS）方法需依赖实验测得的滑移载荷值，正因如此，半经验方法往往需要搭建实验装置，而非直接采用通用的螺栓预紧力参数。本文旨在提出一种通用螺栓预紧力（UBP）值，可独立于板材属性与螺栓排布应用于每一颗螺栓。本研究采用三维扩展有限元法（XFEM）框架，针对不同交错排布与非交错排布的多螺栓连接副开展强度预测，涵盖多种铺层类型与板材厚度工况。对各测试序列中的失效载荷预测结果展开分析，并与实验数据集进行验证，同时与此前的ESS方法进行对比。该方法得到的裂纹形貌与失效模式与实验观测结果一致，所有测试序列均观测到净拉伸失效现象。与ESS技术相比，本方法的预测效果稍逊，这在一定程度上源于此前方法的半经验特性。尽管如此，UBP方法与实验数据集仍取得了合理的吻合度，平均偏差约为20%。