Fatigue behaviour of re-worked fastener holes in aluminum alloys

该提案旨在研究飞机铝制样本返工紧固件孔中的疲劳裂纹和裂纹扩展行为。目的是了解所涉及的疲劳裂纹机制，并开发分析技术来建模和设计老化飞机的维修方案。传统铝机身结构中的大多数疲劳裂纹源自紧固件孔，并在达到临界尺寸之前被检测到。这些孔需要重新加工，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一项或多项：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，将采用逐步方法为返工的紧固件细节开发有限元模型，并由实验室样本上收集的同时测量的实验疲劳数据支持。将检查加工变量，以确定哪些技术最有利于延长寿命，哪些技术不利于重新加工的孔修复方案。加工变量包括：边缘距离、冷膨胀量和过盈配合量。这对军用和民用航空航天工业的好处是巨大的。传统的铝制机身继续大量生产；例如，波音 737 和 747 的产量仍然异常高。此外，加拿大军队继续运营和采购新版本的飞机，例如 CC-130（大力神）和 CH-148（支奴干），并且必须延长 CF-188（大黄蜂）等平台的使用寿命。此应用的寿命延长技术对于确保未来几十年加拿大航空运输、搜索救援和国防系统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.