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Abstract
Three Ti-6Al-4V bolts from mid-life jet aircraft failed during service operation. Each of the failed bolts were installed on a landing gear component. Metallurgical failure analysis indicated that the fracture mechanism is low temperature creep, possibly resulting from a sustained tension load over a long time. Visual inspection revealed ductile fracture morphology with no macroscopic deformation or corrosion. For all bolts fracture occurred close to the root at the first pitches of the thread. Scanning Electron Microscope (SEM) analysis revealed dimple morphologies with micro-void coalescence. Energy Dispersive X-Ray (EDX) analysis did not reveal any material deficiency that would have precipitated failure.
Highlights
Titanium alloys are widely used in aerospace applications since they combine high tensile strengths and low density, resulting in significant weight savings in relation to other high strength alloys e.g. in replacement of high strength low alloy (HSLA) steels used in upper links, struts and truck beams of landing gears [1]
Titanium is an ideal material for applications in aircraft manufacturing with its high strength, low modulus, low density, and excellent corrosion resistance
Ti–6Al–4V alloy is a two phase titanium alloy, and usually exhibits a variety of microstructure morphology depending on the chemical composition, processing history and thermal treatment procedures
Summary
Titanium alloys are widely used in aerospace applications since they combine high tensile strengths and low density, resulting in significant weight savings in relation to other high strength alloys e.g. in replacement of high strength low alloy (HSLA) steels used in upper links, struts and truck beams of landing gears [1]. Ti-6Al-4V alloy is the most important and widely used titanium alloy in the aerospace industry because of its high strength to weight ratio, good corrosion resistance and attractive mechanical properties. Ti–6Al–4V alloy is a two phase titanium alloy, and usually exhibits a variety of microstructure morphology depending on the chemical composition, processing history and thermal treatment procedures. Its microstructure depends on chemical composition, processing history and thermal treatment procedures and plays an important role in the mechanical properties of alloys, such as strength, ductility, fracture toughness and crack propagation resistance [4,5]. The dependence of elastic properties on temperature, thermal expansion along with the time dependent creep behaviour of components play a crucial role in relaxation of gasket stresses with time [12]. The paper focuses on the metallurgical analysis of the failed bolts and the fractographic findings to identify the failure cause
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