Fatigue behaviour of re-worked fastener holes in aluminum alloys

本计画旨在研究飞机铝合金试件再加工紧固件孔之疲劳裂纹与裂纹扩展行为。其目的是了解疲劳开裂的机理，并发展分析技术来模拟和设计老化飞机的修理方案。传统的铝合金飞机结构中的大多数疲劳裂纹来自紧固件孔，并在达到临界尺寸之前被检测到。这些孔被重新加工，通常是通过加大孔的尺寸来消除疲劳损伤;在飞机恢复使用之前安装新的紧固件。孔的再加工还可以包括以下中的一个或多个：冷膨胀以赋予有益的压缩残余应力，过盈配合紧固件以提高疲劳寿命，以及过盈配合衬套以提高刚度、恢复净截面并提高疲劳寿命。在这项研究中，一步一步的方法将被用来开发一个有限元模型的返工紧固件的细节，同时测量实验室标本上收集的实验疲劳数据的支持。将检查工艺变量，以确定哪些技术最有利于延长寿命，哪些技术不利于返工孔修复方案。处理变量将包括：边缘距离、冷膨胀量和过盈配合量。无论是军用还是民用航空航天工业，其效益都是巨大的。传统的铝合金机身继续大量生产;例如，波音737和747的产量仍然非常高。此外，加拿大部队继续使用和采购CC-130（大力神）和CH-148（支奴干）等新型飞机，并延长CF-188（大黄蜂）等平台的使用寿命。这种应用的寿命延长技术对于确保加拿大航空运输、搜索和救援以及防御系统在未来几十年的安全性和经济性至关重要。

This proposal is to study fatigue cracking and crack growth behaviour in re-worked fastener holes in aircraft aluminum specimens. The objective is to understand the fatigue cracking mechanisms involved and to develop analytical techniques to model and design repair schemes for aging aircraft.The majority of fatigue cracks in conventional aluminum airframe structures emanate from fastener holes and are detected before reaching critical size. These holes are re-worked, generally by over sizing the hole to remove the fatigue damage; new fasteners are installed before the aircraft is returned to service. Re-working of a hole may also include one or more of the following: cold expansion to impart beneficial compressive residual stresses, interference fit fasteners to improve fatigue life, and interference fit bushings to improve stiffness, restore net section and improve the fatigue life. In this research, a step by step approach will be used to develop a finite element model for reworked fastener details supported by simultaneously measured experimental fatigue data collected on laboratory specimens. Processing variables will be examined to determine which techniques are most beneficial to life extension and which techniques are detrimental to re-worked hole repair schemes. Processing variables will include: edge distance, amount of cold expansion, and amount of interference fit.The benefits to the aerospace industry, both military and civilian, are tremendous.Conventional aluminum airframes continue to be produced in great numbers; for example, Boeing's production of the 737 and 747 remains exceptionally high. Furthermore, the Canadian Forces continues to operate and acquire new versions of aircraft such as the CC-130 (Hercules) and CH-148 (Chinook), and have to extend the lifetime of platforms such as the CF-188 (Hornet). Life extension technologies for this application are vital to ensure the safety and economy of Canada's air transport, search and rescue, and defence systems for many decades to come.