Experimental Study of Sable Crack Growth in Thin Aluminium Sheet



Recent failure information from research teams in NASA Langley and others has shown that CTOA based fracture models calibrated on large C(T) and M(T) specimens can be transferred successfully to cracked aircraft fuselage structures for the assessment of their residual strength. A major difficulty that could limit the more extensive use of this failure parameter is its experimental measurement either in the real structure or in a laboratory scale test. This paper describes the use of a DCB-like specimen for direct measurement of critical CTOA data for thin sheet 2024-T3 aluminium alloy used in aeronautical applications. It outlines the features of ductile crack growth in thin walled structures, the specimen design geometry for reproducing these features in a laboratory scale experiment, the experimental set up and loading configuration for tear test specimens, and the CTOA measurement scheme. Using the test technique developed, the CTOA resistance curves for test samples of 2.3mm ligament thickness were generated for fractures propagating in the rolling and transverse direction of the original rolled plate. The results of this research showed that the technique was capable of producing large amounts of highly consistent CTOA data even from one single specimen. This is promising as it provides a precise and relatively easy experimental method for direct evaluation of CTOA toughness levels of test materials using small-scale laboratory specimens. A comparison of the test results from the current work with similar data from the literature concludes the paper.