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Defect tolerant lifing of airframe components and the influence of corrosion damage. / Christopher Morgans

Swansea University Author: Christopher Morgans

Abstract

The present thesis describes a programme of research into corrosion pitting in the airframe aluminium alloy AA 7010-T7651 and its subsequent influence on fatigue performance. The alloy is employed extensively in airframe structures, most commonly as wing spars and skins of the BAE SYSTEMS Hawk Mkl27...

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Published: 2007
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa42774
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Abstract: The present thesis describes a programme of research into corrosion pitting in the airframe aluminium alloy AA 7010-T7651 and its subsequent influence on fatigue performance. The alloy is employed extensively in airframe structures, most commonly as wing spars and skins of the BAE SYSTEMS Hawk Mkl27 lead-in fighter aircraft. The research programme followed from the major international project SICAS (Structural Integrity assessment of pitting Corrosion in Aircraft Structures), which was instigated as an attempt to minimise the costs associated with in-service corrosion damage. Existing corrosion management techniques are time consuming and expensive, typically involving grinding and mechanical blending of corrosion damaged areas. However, by adopting damage tolerant fatigue lifing procedures in partnership with corrosion detection, a reduction in the cost of corrosion management and safe extensions to aircraft operation lives may be achievable. Flat plate specimens were subjected to pitting damage via a laboratory based corrosion protocol. Secondly, a centre hole plate specimen was employed, in this case incorporating end grain corrosion within the root of central hole. Detailed characterisation of the pits demonstrated the critical role of microstructure on pit geometry. Both forms of pre-corroded specimen were subjected to a comprehensive matrix of constant amplitude load controlled fatigue testing under controlled humidity and room temperature. Multiple repeat tests were performed at specific stress levels to produce data sets corresponding to fatigue lives of approximately 1x104, 7x104 and 3x105 cycles. Post testing, LEFM based modelling was performed to describe test specimen performance. This proved successful for the relatively large scale corrosion pitting under consideration.
Keywords: Materials science.
College: College of Engineering