Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Mechanical Engineering | en_US |
| dc.contributor.advisor | Cheng, Li (ME) | en_US |
| dc.creator | Liu, Ze | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/13383 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Topologically customized metamaterial devices for enhancing nonlinear-guided-wave-based structural health monitoring | en_US |
| dcterms.abstract | Structural Health Monitoring (SHM) offers areal-time and online method for the detection of damage/defects inside structures/materials. In particular, the nonlinear-guided-wave-based SHM exhibits a high sensitivity to incipient damage, or even their precursor, owing to the inherent wave-damage-interaction mechanism. However, the detection accuracy is significantly threatened by the presence of non-damage-related sources within the SHM system, and is also limited by the weak intensity of probing waves in terms of wave excitation and propagation. To address these issues, this thesis explores the feasibility of using metamaterials in nonlinear-guided-wave-based SHM through improving its detection capability. In light of the SHM-specific requirements, a topology-optimization-based inverse design strategy is developed to customize metamaterial devices with specific functions including wave filtering, steering, and mode conversion of guided waves. | en_US |
| dcterms.abstract | As background work, a unified inverse-design framework based on topology optimization is first established as a tool to facilitate the design of metamaterials for guided wave manipulation. Genetic algorithm is adopted as the searching method to update design variables. Constraints in both geometry and physics are investigated to examine their influences on optimization results. Both numerical and experimental results are systematically conducted to verify the efficacy of the designed metamaterial devices in terms of expected guided wave manipulation functions. The proposed inverse-design strategy lays out the foundation for the customization of the subsequent SHM-specific meta-device designs. | en_US |
| dcterms.abstract | The first task is to purify the nonlinear responses by eliminating the non-damage-related nonlinear components (such as those originating from the actuation area)that exist in an SHM system. To this end, a wave filtering device, referred to as a meta-filter, is developed, which is constructed through mounting periodic stubs on the surface of the structure under inspection. Through topological optimization, the meta-filter enables ultra-wide stop bands to eliminate the second harmonic Lamb waves of the probing waves while preserving their strong fundamental wave components. Upon tactically introducing deceptive nonlinear sources such as the nonlinear adhesive bonding layers, the performance of the meta-filter is examined from the SHM perspective, which is finally validated experimentally using a metal specimen containing local plasticized incipient damage. | en_US |
| dcterms.abstract | Second, the cumulative second harmonic (2nd) lowest-order symmetric-mode (S0) Lamb waves are tactically enhanced using a meta-structure, which can convert the A0 (lowest-order antisymmetric) mode components into S0 mode waves. Topology optimization is conducted to design the meta-structure to achieve high-efficiency A0-to-S0 wave mode conversion. Numerical simulations demonstrate that the strain amplitudes of the fundamental S0 mode waves can be increased by 60% with the deployment of the meta-structure, alongside an enhancement of the 2nd S0 mode waves. Finally, the designed meta-structure is fabricated via the 3D metal printing technique and tested experimentally on an aluminum plate subjected to thermal aging treatment for monitoring the heating-induced microstructural changes inside the structure. | en_US |
| dcterms.abstract | Third, the 2nd A0 waves, generated by the mixing of fundamental S0 and A0 waves, are significantly affected by the wave beam divergence, which compromises the inspection area. A metasurface is thus designed to steer the energy distribution of Lamb waves through manipulating their phases and amplitudes simultaneously. Theoretical analyses are first carried out to reveal the features of the 2nd A0 wave generation in a weakly nonlinear plate. The inverse-design strategy based on topology optimization is again employed to tailor-make the phase gradient and ensure the high transmission of the primary waves, thus transforming cylindrical waves into plane waves. Results confirm that the transmitted S and A mode waves can propagate in a nearly planar waveform after passing the meta surface. When the material microstructural properties of a local region inside the host plate change, the amplitude variation of the 2nd A0 waves in the metasurface-assisted system exhibits a higher sensitivity to this material degradation. | en_US |
| dcterms.abstract | Finally, to cope with the difficulty in generating Shear Horizontal (SH) waves for SHM applications, meta-structures are topologically designed to convert Lamb waves into SH waves. Specifically, typical scenarios of incident waves including pure S mode, pure A mode, and combinational S and A modes are considered. The amplitude ratio between the converted and incident waves reaches 47% in terms of the time-domain response. Band analyses for the unit cell attribute the occurrence of broadband mode conversion to multiple scattering. Finally, the meta-structure samples are printed with mode conversion efficacy validated in experiments. | en_US |
| dcterms.abstract | In conclusion, the work presented in this thesis offers a complete set of tools and assessment methods for tactically designing SHM-specific wave manipulation meta-devices to facilitate the detection of incipient damage inside engineering materials/structures using nonlinear guided waves. | en_US |
| dcterms.extent | xxiv, 218 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2024 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.LCSH | Structural health monitoring | en_US |
| dcterms.LCSH | Nonlinear acoustics | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | open access | en_US |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/13383