Behaviour of threaded steel fasteners at elevated deformation rates: An experimental and numerical study

Abstract

The main objective of this work is to investigate the ultimate load, behaviour characteristics and failure modes of threaded steel fasteners subjected to various combinations of tension and shear loads at elevated deformation rates. Threaded steel fasteners are often used to assemble members and components in engineering structures, and the behaviour characteristics of each individual fastener can have a significant influence on the performance of the total structure. Hence, before the response of a structure can be determined based on a given load scenario the behaviour of each of the involved components and joints must be known as well as the material behaviour at the deformation rates representative for the load situation. The work carried out in this thesis is presented in a synopsis, providing the background, the objectives, the strategy and a summary of the project. Then three individual papers/parts follow where two have been published in peer reviewed journals and the third has been submitted for potential journal publication.

The first two papers are dealing with the tensile behaviour of threaded steel fasteners at elevated rates of strain. The objective was to investigate the ultimate tensile load, behaviour characteristics and failure modes. In the first paper, results and observation from the experimental study were presented, and the Alexander model was modified to consider the ultimate load and mode of failure at high loading rates. In the second paper, results from a numerical study were presented. The numerical study was based on the experimental results obtained from the first part. An axisymmetric finite element model was used to predict the tension behaviour characteristics and the failure modes of the threaded steel fasteners. Comparison of results between simulations and experiments showed that the axisymmetric finite element model captured the ultimate load and the overall behaviour characteristics with good accuracy. It was observed that the failure modes were influenced by the thread engagement length, the grip length and the strain-rate.

The third paper explores the ultimate load and behaviour characteristics of threaded steel fasteners exposed to combined tension and shear load at elevated deformation rates. An experimental and a numerical study were conducted. In the experimental study, the loading angle was 0°, 45° and 90°, where 0° corresponded to loading along the axis of the threaded steel fasteners. The numerical study was carried out using a three-dimensional finite element model. Simulations were performed at the same deformation rates as in the experiments, while the load was applied at different angles varying between 0º and 90º with 15º intervals. Interaction curves were established based on both the experimental and the numerical results. The numerical model was found to capture the ultimate load and the overall behaviour characteristics with reasonable accuracy.