Abstract
After a quick-release fitting of an ejection seat broke, an investigation was performed to determine the manner and cause of crack propagation. Most fractography-based investigations aim to characterize only qualitative characteristics, such as the fracture orientation and origin position, topology, and details of interactions with microstructural features. The aim of this investigation was to use quantitative fractography as a tool to extract information, including striation spacing and size of the stretched zone, in order to make a direct correlation with fracture mechanic concepts.
As the crack propagated, striations were created on the fracture surface as a result of service-induced load changes. The size of the striations were measured to estimate crack propagation rate. Remaining lifetime estimates were also made. The dimensions of plastically stretched zones found at the tips of the cracks were evaluated using electron micrograph stereo image pairs to characterize local fracture toughness.
To complete the failure analysis, nondestructive evaluation, metallographic examination, and chemical investigations were carried out. No secondary cracks could be found. Most of the broken parts showed that the microstructure, the hardness, and the chemical composition of the Al-alloy were within the specification, but some of the cracked parts were manufactured using a different material than that specified.
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References
J.E. Forsyth and D.A. Ryder: “Some Results Derived from the Microsoft Examination of Crack Surfaces,”Aircr. Eng., 1960, pp. 96–9.
P.G.T. Howell and A. Boyde: “Comparison of Various Methods for Reducing Measurements from Stereo-Pair Scanning Electron Micrographs to ‘Real 3-D Data’,” Scanning Electron Microscopy Symposium, Chicago, 1972.
J.D. Landes, J.A. Begley, and G.A. Clarke: “Elastic-Plastic Fracture,” ASTM Symposium, Atlanta, GA, ASTM, 1977.
O. Kolednik and P. Stüwe: “Abschätzung der Rißzähigkeit eines duktilen Werkstoffs aus der Gestalt der Bruchfläche,”Metallkunde, Bd. 73, 1982 (in German).
DVM-002, Ermittlung von Rißinitiierungswerten und Rißwiderstandskurven bei Anwendung des J-Integrals, 1987 (in German).
O. Kolednik: “Stereogrammetrische Untersuchungen des Rißwachstums bei duktilen Materialien,”Gefüge und Bruch 9, 1989 (in German).
K.-H. Schwalbe, A. Cornec, K. Baustian, and M. Homayan: “Intercomparison of Fracture Toughness Measurements of Ductile Materials,” Synthesis Report, Geesthacht, July 1990.
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Wolf, K. Ejection seat quick-release fitting: Quantitative fractography and estimation of local toughness using the topography of the fracture surface. Practical Failure Analysis 2, 51–56 (2002). https://doi.org/10.1007/BF02719190
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DOI: https://doi.org/10.1007/BF02719190