Master thesis and internship[BR]- Master's thesis : Influence of pretension on aeronautic bolted assemblies working in shearing[BR]- Internship

Abstract

Pretension, the intentional application of preload to bolted joints before they are subjected to external loads, is vital for the functionality and reliability of bolts in aeronautical assemblies. This preload is achieved by tightening the bolt to a specified torque or stretching it to a predetermined length, ensuring the joint remains secure and stable under operational loads. Pretension creates a compressive load within the joint, eliminating gaps and enhancing load transfer, reducing the likelihood of fretting or fatigue failure. It also prevents bolt self-loosening during flight-induced vibrations and dynamic loads, maintaining bolt clamp load and resisting relaxation. In the aerospace industry, the significance of pretension on bolts is often overlooked, leading to designs without preload, which is considered conservative. This thesis investigates the influence of prestressing in bolted assemblies under shear conditions. It compares cases with and without preload, examining loosely assembled configurations and those with only enough torque to bring parts into contact. The study evaluates the physical behavior of a slat track assembly under different preload levels, focusing on the axial load in the bolt, as well as the shear load and bending moment. The research involves evaluating an analytical method developed by Sonaca, which analyzes the behavior of bolted joints under shear forces without considering prestressing, providing a foundational understanding of bolted joint principles. To incorporate prestressing effects, a finite element model (FEM) is developed and compared with the analytical method to validate or challenge initial hypotheses. Additionally, the study explores the influence of various materials and geometric configurations on bolted joint performance through a parametric study, aiming to identify key factors that affect behavior and performance. Finally, the results are discussed in detail, highlighting their implications, limitations, and future research directions, offering valuable insights into the significance of prestressing in bolted assemblies. Overall, pretension optimizes the performance and reliability of bolts within aeronautical assemblies, ensuring secure fastening, resistance to self-loosening, and enhanced load-bearing capacity, crucial for maintaining aircraft safety and the longevity of critical components.