Structural health monitoring on a mooring chain using acoustic emission technique

Abstract

The aim of this research project is to evaluate the feasibility of Acoustic Emission Technique for the crack growth monitoring on a mooring link. Moreover, this research work focus to do waves decomposition in a bar, bend bar and link to know how the bends in a link have an effect of wave conversion. Therefore, wave modes decomposition in frequency and time domain are done to know how the bends in a link could impact the wave propagation. In addition, AE technique is implemented in a test rig to monitor crack growth generated by Tension-Tension in a studless chain link of large diameter. In first part, a chain tensile test is carried out in artificial seawater using a single grade R5 link of diameter 160 mm, where different tensile loads were applied during almost a period of four months. The AE features are analysed to monitor crack growth, where selected peak amplitude filters are applied to plot the trends of the AE features. In second part, Pochhammer-Chree theory is used to know the dispersive curve and the wave modes in a straight rod. Then, the novel wave mode decomposition method was implemented to identify the wave with higher amplitude in a specific frequency range. Moreover, a study of wave modes decomposition was carried out in time domain in a cylindrical steel bar of small diameter (45 mm diameter). The work was carried out on simulation data and validated with experimental measurements. In last part, the wave decomposition is carried out in time domain for a bar, bend bar and link of large diameter (160 mm diameter). Comparison of wave mode decomposition between bar, bend bar and chain are obtained to know how the bends generate wave mode conversion. The wave decomposition is more complex for bar of large diameter because the number of excited waves increases. Therefore, a Hilbert transformation is applied to the axial component to get that the three components (radial, circumferential and axial) could be in phase to be able to obtain the wave decomposition. The simulations were validated against experimental work in straight bar and link, where good agreements of wave decomposition are obtained.

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