An acoustic emission evaluation of environmentally assisted cracking of 7039-T6 aluminum

摘要

Environmentally assisted cracking (EAC) is a significant problem in modern structures. The combination of a susceptible material, an adverse environment and mechanical stress can lead to unexpected failure of a structure by catasticophic crack growth. The mid-air failure of the aluminum alloy bulkhead and the subsequent loss of life on a Aloha Airlines flight on April 28, 1988 as shown in fighure 1, illustrates this fact. Additionally, the operating environment of the US Army contributes to premature failure of structures such as aluminum alloy armor, high strength steel armor and high strength steel control components on Army helicopters [1]. These failures not only endanger life but they also seriously hamper the fighting readiness of U.S.forces because of equipment down time for inspection and repair of faulty components. Work has been performed to better characterie EAC resistance in high strength aluminum armor alloys [2]. These high strength alloys are particularly prone to failure in a chloride environment, an environment encountered in most of the world. If we plan to aviod such failures, we must better understand the EAC phenomena and more diligently detect growing cracks before they become critical in iength. One characterization technique that promises to serve well both as a laboratory tool for understanding EAC and as a field device for detecting EAC is acoustic emission evaluation.