Advanced Magnetic Barkhausen Noise for Residual Stress Measurement in Aircraft Landing Gear

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Residual stress can lead to catastrophic failure of aircraft landing gear components. Currently, there is no reliable non-destructive inspection technology for residual stress measurement on in-service components without paint removal. X-Ray diffraction (XRD) requires both paint and metal plating removal, followed by etching of the base metal. Current Magnetic Barkhausen noise (MBN) technology only requires paint removal. However, while MBN has been employed to detect areas of high residual stress in aircraft landing gear using only a single measurement parameter, it has been found to be unreliable in its current form. Recent advances in control of the magnetic flux generated by the excitation field used to generate Barkhausen noise havedemonstrated a potential for improving measurement repeatability, as well as providing additional characterization of relative magnetic properties. Furthermore, development of mutually orthogonal field excitation has prospects to provide rapid evaluation of a component's anisotropic magnetic properties, which may be correlated with its stress state. Signal analysis techniques have also been advanced, including evaluation of MBN energy, Barkhausen noise envelope and pulse height distribution. Further development of MBN technology is required to identify and compensate for significant parameters that may affect measurement outcomes. Examples include effects of paint thickness variation, variability in compressive surface stress state induced by shot peening and the effects of plastic deformation in steel. Probe designoptimization is also required, in order to accommodate unique geometries, such as tight curvature radii. Advancement in the understanding and compensation for parameters that affect MBN signal generation is part of the proposed work. In addition, advanced MBN signal analysis methodology for residual stress measurement will be developed. Finite element modelling will be used for probe design and prediction of magnitude and direction of residual strain fields in plastically deformed aircraft landing gear. The proposed work is in collaboration with Safran Landing Systems Inc., located in Ajax Ontario that manufactures aircraft landing gear.