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Tamber, JS, 2025. Numerical modelling for detecting delamination in layered waveguides. PhD, Nottingham Trent University.
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Abstract
The investigation into nonlinear bulk strain wave propagation within layered elastic waveguides offers numerous practical applications, notably in the domain of non-destructive testing. In situations where even a minor flaw in the bonding between waveguide layers can trigger a catastrophic structural failure, the utilisation of strain solitons in a waveguide of large domain holds significant promise in detecting a lack of bonding and structural fault. Experimental findings reveal that strain solitons propagate over considerably greater distances in comparison to the waves employed in existing methodologies, such as linear wave methods. In this thesis, we investigate the impact of delamination, the lack of bonding between structural layers, aiming to detect its presence and identify its location.
We consider three scattering problems. First, we study the scattering of a nonlinear bulk strain wave in a two-layered waveguide with a delaminated region ‘sandwiched’ between soft bonded regions, where soft bonding refers to weak adhesive contact. The lower layer is assumed to be much denser than the upper layer. The longitudinal displacement of the waves within this structure are modelled by a system of Boussinesq equations with continuity conditions at the interface. Given the complexity of the equations, we develop both direct numerical and semi-analytical methods, detailed in the appendices.
We vary the delamination length and analyse the phase shift of the wave packet in the second soft bonded region, comparing to the case of no delamination. Generally, across various small wave parameters, ε, as the delamination length increases so does the phase shift. We also use theoretical predictions, such as the linear dispersion relation, to validate the numerical simulation findings.
Next, we consider the same two-layered structure, but with layers made of different materials, but without a significant contrast in densities, resulting in distinct characteristic wave speeds in each layer. We model this by a system of coupled Boussinesq equations. We vary the delamination length and analyse the leading wave packet in the second soft bonded region, which is easier to locate. Examining various soft bonded region lengths, we find that increasing the delamination length generally causes a phase shift to increase/decrease in correlation. These results allow us to determine the delamination length solely based on the observed phase shift, even without prior knowledge of the structure configuration.
The final structures that we considered were an n-layered waveguide with delamination between perfectly bonded regions, and a two-layered waveguide with delamination between soft bonded regions. As with the other structures, we vary the delamination length but focus on the change in amplitude of the leading wave peak. For the perfectly bonded case, we introduced a measure comparing the wave peak to the theoretical prediction of the Inverse Scattering Transform. In the soft bonded region, a similar measure was used, but only with the leading wave packet from the first and second soft bonded region. We observe that increasing the delamination length results in a decrease in wave amplitude.
| Item Type: | Thesis |
|---|---|
| Creators: | Tamber, J.S. |
| Contributors: | Name Role NTU ID ORCID |
| Date: | July 2025 |
| Rights: | The copyright in this work is held by the author. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required, should be directed to the author. |
| Divisions: | Schools > School of Science and Technology |
| Record created by: | Jeremy Silvester |
| Date Added: | 15 Aug 2025 09:11 |
| Last Modified: | 15 Aug 2025 09:11 |
| URI: | https://irep.ntu.ac.uk/id/eprint/54214 |
https://orcid.org/0000-0002-6019-8819Actions (login required)
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