This presentation was made at the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

Bolt self-loosening is a phenomenon that can occur in various types of fastened joints. Joint compliance, bolt geometry, and external loading can all contribute to conditions where self-loosening can be observed. Understanding the mechanisms that contribute to self-loosening will lead to higher product confidence and reduced development costs for new product introductions.



Standardized methods of replicating the loosening of a bolted joint subjected to a repeated transverse load include tests such as DIN 25201 and its predecessor DIN 65151 (also known as a Junker test). Many joint configurations have been evaluated using similar tests. Previous studies have simulated the effects of transverse loading on bolt loosening using FEA. Various aspects, such as thread shape, pretension, and transverse load magnitude have been analytically explored.



The current study further explores the effects of transverse loading on bolted joints by accounting for more details in thread geometry, investigation of boundary conditions, and increasing contact definition fidelity. Physical testing and corresponding finite element analyses were performed in order to further evaluate these features and to measure the degree of correlation of the analytical simulations.



Two types of variables were evaluated in detail with respect to their effects on joint loosening. One of these is the friction below the bolt head and between threads. The relationship between these two friction values was found to be especially significant in the self-loosening characteristics of a joint. The other variable evaluated is class fit, and sensitivities to self-loosening with various joint properties were explored as functions of thread geometry.