Stress intensity factor of cracks in lugs

• Main Author: Li, Wen Hao
• Other Authors: Chai Gin Boay
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Aeronautical engineering::Materials of construction
• Online Access: http://hdl.handle.net/10356/64931
• Institution: Nanyang Technological University

This project explores the experimental determination of the stress intensity factor of straight aircraft attachment lugs made of aluminium alloy Al7075-T651. The specimen used for tests has two initial quarter corner elliptical part through cracks fabricated diametrically opposite each other at the sides of the lug hole. As such, the crack propagation can be estimated by applying a load. Three crack configurations were experimented on such that the results can be compared for various cases. The experimental process was design to follow the realistic loading conditions of an aircraft attachment lug closely. A tensile test was conducted on each crack configuration until it fails, giving the ultimate tensile strength of each configuration. After that, fatigue tests were conducted using specific percentages of the ultimate load, following a marker load history. This loading leaves striation marks on the fracture surface of the specimen as the crack propagates from the initial fabricated crack. These lines correspond to differing amplitudes of the periodic load sequence of the fatigue test. Pictures of the fracture surface were taken using a digital microscope camera, and its clarity enhanced using Photoshop. The lines were measured and analysed. The data obtain were processed through known equations and values to obtain the stress intensity factor of the various cracks.