Thesis
Inspection at inaccessible locations using medium-range guided waves
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2024
- Thesis identifier
- T17047
- Person Identifier (Local)
- 202067055
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Medium-range guided wave testing is commonly employed for inspection of plate and plate-like structures. The method is attractive for crack imaging and wall loss quantification, especially in hidden locations where direct access is limited. Lamb wave excitation at high-frequency-thickness products offers a potential solution for high-resolution guided wave testing, especially sensitive to vertical cracks and sharps pits. The technique usually works in pulse echo mode and at high frequency-thickness products, around 20 MHz⋅mm, offering good sensitivity and resolution. Defect sizing is based on the reflection amplitude of the received mode(s). However, the scattering of guided waves is complex, and the amplitude of the reflected modes does not provide sufficient information for defect sizing. This work aims to overcome this limitation using a focusing technique based on Lamb waves. Specifically, multiple Lamb wave modes are excited individually and superimposed to form a new mode with a desired through-thickness energy distribution. This way, energy is focused on a single point in the structure. Using weighting functions, the location of the focal point is swept across the thickness of the sample. The technique allows for accurate sizing of flaws, such as cracks and wall loss. In contrast to abrupt thickness changes, corrosion scrabs can also appear as gradual wall thinning areas. The main objective is to determine the remaining wall thickness in the affected area in order to decide further actions. For this reason, wall loss quantification is performed utilising the cut-off frequency of mode SH1. The approach requires the excitation of SH1 across a range of frequencies. For this reason, a novel excitation technique using guided wave phased array steering is developed. Specifically, an array generating shear horizontal waves is employed. The influence of the array’s length, pitch, element width, and mode excitability on excitation is investigated. By appropriately phasing the elements of the array, mode SH1 is targeted and dynamically excited over a wide frequency-wavelength range. The directionality of SH1 is also studied, as in certain conditions, this can be critical for the success of the quantification. Simulation results show the technique can accurately quantify a 65% wall thinning defect, offering a 15% increase compared to established techniques. This is critical, as wall loss defects above 50% are considered severe. Additionally, using electronic steering, rapid quantification can be achieved. Experiments using an electromagnetic acoustic transducer and synthetic steering on an intact area and an artificially machined corrosion-like defect validate the technique.
- Advisor / supervisor
- Gachagan, Anthony
- Dobie, Gordon
- Resource Type
- DOI
Relazioni
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PDF of thesis T17047 | 2024-08-20 | Pubblico | Scaricare |