|Title:||On propagation characteristics of three-dimensional elastic waves guided by thick-walled hollow cylinder and application to detection of damage in train axle|
|Subject:||Elastic wave propagation.|
Railroads -- Maintenance and repair.
Hong Kong Polytechnic University -- Dissertations
|Pages:||xiv, 195 pages : color illustrations|
|Abstract:||Development of reliable structural integrity assessment techniques requires a profound understanding of the physical phenomena existing in the structure under inspection. As an example, guided waves have been extensively studied to enhance their usability for Structural Health Monitoring in various fields of engineering. The knowledge on elastic wave propagation in various types of structures has enabled the development of effective damage detection methods with long range inspection capabilities. Despite the effort, there exists obvious lack of work on certain types of structures germane to industrial applications, an example of which is the high speed railway axle monitoring. Although guided wave-based approaches can potentially reduce the maintenance costs and allow for on-line monitoring, the lack of in-depth knowledge on thick-walled hollow cylindrical waveguides limits the current inspection techniques to non-destructive testing only. The main aim of this thesis is to provide a quantitative understanding on the elastic wave propagation in hollow cylindrical waveguides with significant thickness-to-wavelength ratio. The work consists of two major parts: 1). Investigation of the cylindrical guided wave theory and understanding of various types of propagating waves and their characteristics; and 2). Utilization of the acquired knowledge to develop an effective damage detection methodology for railway axle inspection. To this end, a semi-analytical analysis is first performed to investigate the characteristic features of cylindrical guided wave modes and to establish the relationship between a thick plate and a hollow cylindrical waveguide. The analysis reveals the pseudo-symmetry relations of displacement patterns, obtained using asymptotic approximations of Bessel functions. Hyperbolic behavior of the dispersion curves and mode-shape transitions due to the mode coupling phenomenon are also analysed. Theoretical solutions of the dispersion characteristics are compared with the numerical simulations with local interaction simulation approach, and validated through experiments using laser vibrometry. It is shown that, due to the high thickness-to-wavelength ratio, ultrasonic waves propagating in thick-walled cylindrical structures such as train axles exhibit complex multimodal dispersive behaviour, thus causing significant difficulties to the conventional guided wave-based damage detection techniques. Through numerical analyses, a strong damage-related feature in the 'quasi-surface' longitudinal guided wave signals is revealed and confirmed by experiments. Namely, a near-field wave enhancement effect due to the outer diameter change in the structure is found to be highly effective for damage identification. Based on this phenomenon, a novel inspection method is proposed and explored. Finally, a complete monitoring strategy for hollow railway axles is established and validated.|
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