Load Distributions in Bolted Single Lap Joints Under Non-Central Tensile Shear Loading

Load Distributions in Bolted Single Lap Joints under non-Central Tensile Shear Loading

Chaiwat Sinthusiri, Sayed A. Nassar

Fastening and Joining Research Institute (FAJRI)

Department of Mechanical Engineering

Oakland University, Rochester, Michigan 48309   USA

Abstract

 The bolted joints are widely used in mechanical systems because they are relatively reliable to transfer higher loads and ease to assemble and disassemble for a maintenance. To ensure the reliability, the safety and the durability of the bolted joint, the bolt load distribution determination has been widely studied because it plays a significant role in any joint failure analysis. This study provides a theoretical and numerical investigation of the load distributions in a bolted single lap joint under non-central tensile shear loading. Using a spring based method, the bolts and plates flexibility which include the bending flexibility of the bolt shank, the shearing flexibility of the bolt shank, and the bearing flexibility of the bolt shank and the joint plates to determine the load distribution for each bolt. With the increase of the joint plate thickness ratio, the contact force is non-uniformly distributed along the bolts shanks, therefore, the correlation factors obtained using the three dimensional (3D) finite element (FE) model of a single lab and single bolted joint is used to adjust the theoretical formula. When the bolts are tighten with preloads, the friction forces between the two plates and nut are analyzed into three stages, the initial stage is when the external load is low, then secondly once the static friction force is overcome, then the two plates begin to slip relative to each other. Finally, the external load is increasingly higher, then the bolt head and nut are fully slipped. The bolt underhead pressure distribution is unevenly distributed at the bolt underhead due to the transverse bending moment of the bolt, is analyzed and included into the theoretical formula of the load distribution determination. In the practical application, the applied tensile shear load does not necessary pass through the center line of the multi- bolted joint line, then the load is eccentric and a moment is considered in the analysis. The load is not equally distributed between all the bolts. The effect of each distributed load is considered separately, the total bolt load distribution is then summed vectorially. Finally, the effects of various joint parameters (plate thickness, plate width, plate length, plate material and bolt size), the bolt tightening torque and the location of non-central tensile shear loading in a single lap, multi-bolted joint are investigated and discussed. The results from the mathematical model are compared with the results of a three dimensional (3D) finite element (FE) model. These data will be very useful in enhancing the reliability and safety of bolted joints.

Keywords: bolt load distribution, bolted single lap joint, non-central tensile shear loading