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dc.contributor.author
Krödel, Sebastian
dc.contributor.supervisor
Daraio, Chiara
dc.contributor.supervisor
Constantinescu, Andrei
dc.date.accessioned
2017-11-27T07:10:44Z
dc.date.available
2017-11-26T10:53:42Z
dc.date.available
2017-11-27T07:06:42Z
dc.date.available
2017-11-27T07:10:44Z
dc.date.issued
2017
dc.identifier.uri
http://hdl.handle.net/20.500.11850/213856
dc.identifier.doi
10.3929/ethz-b-000213856
dc.description.abstract
The mechanical properties of a material are governed by its atomic- and microstructure: The arrangement of atoms in a perfect crystal defines the macroscopic stiffness and the grain size in a metal determines the fracture resistance. Rapid developments in microfabrication allow to fabricate artificial microstructures at unprecedented sub-micrometer resolution. A key technology to architect fully 3D microstructures is direct laser writing using two-photon polymerisation. This breakthrough in fabrication led to the emergence of microlattice materials, which are composed of periodically arranged microscale truss elements. By adjusting the geometry and topology of the unit cell, it is possible to realise microlattices with effective mechanical properties that exceed the performance of any available engineering material. These properties include extreme strength and stiffness, lightweight or negative Poisson’s ratio. Until now, most of the work on microlattices was focused on understanding the mechanical response of single material microlattices at quasi-static timescales. However, many of the suggested applications for microlattices, such as energy absorption or wave control, require knowledge of their dynamic response. Moreover, the ability to create microlattices from nanocomposites is a promising approach: Mechanically reinforced polymers would allow to overcome current fabrication and application limitations that stem from failure of the weak base polymer. In addition, nanocomposites microlattices can be designed to express additional functionality such as electrical conductivity based on the filler properties. This work extends the current knowledge on microlattices to the mechanical behavior of composite microlattices and dynamic timescales. The first part of this thesis describes how the mechanical properties of microlattices are impacted by reinforcing the base polymer with carbon nanotubes. In the studied composite microlattices, the confinement of carbon nanotubes along the truss axis, which is driven by physical mechanisms during fabrication, yields a tremendous increase in mechanical stability and static mechanical properties. We observe a size effect for decreasing truss thickness when the carbon nanotubes size scales become comparable to the truss size. To answer fundamental questions about the time-dependent properties we study the mechanics of single material microlattices at low frequencies. We characterise the dynamic stress relaxation in polymeric microlattices with varying density and topology. Stress relaxation is the footprint of viscoelasticity and therefore crucial for potential applications that rely on viscous absorption and dissipation of mechanical vibration energy. In our study, we show that the damping loss factor of microlattices can be controlled over a wide range and independently from the static properties. Furthermore, the microlattices are shown to outperform the dissipation of a bulk polymer. Then we turn to high frequencies and describe the interaction of megahertz ultrasonic waves with fluid saturated polymeric microlattices. It is shown that in the long-wavelength limit, wave propagation in microlattices can be described by Biot’s theory of porous media. However, at short wavelengths microlattices constitute a strongly scattering media with frequency dependent group velocity and high signal attenuation. Finally, we show that truss resonances can be exploited to filter ultrasonic waves in frequency ranges that are central to high resolution biomedical imaging applications. The frequency position of the obtained filtering properties can be deliberately controlled by tailoring the truss geometry. The designed microlattices show a high transmission of ultrasound over a large frequency range, while still effectively attenuating the signal when resonance occurs.
en_US
dc.language.iso
en
en_US
dc.publisher
ETH Zurich
en_US
dc.subject
Mechanics; wave propagation; metamaterials
en_US
dc.title
Mechanics Of Architected Microlattices Across Time And Length Scales
en_US
dc.type
Doctoral Thesis
dc.date.published
2017-11-27
ethz.size
212 p.
en_US
ethz.identifier.diss
24538
en_US
ethz.publication.place
Zurich
en_US
ethz.publication.status
unpublished
en_US
ethz.leitzahl
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02130 - Dep. Maschinenbau und Verfahrenstechnik / Dep. of Mechanical and Process Eng.::02618 - Institut für Mechanische Systeme / Institute of Mechanical Systems::03985 - Daraio, Chiara (ehemalig)
en_US
ethz.date.deposited
2017-11-26T10:53:43Z
ethz.source
FORM
ethz.eth
yes
en_US
ethz.availability
Embargoed
en_US
ethz.date.embargoend
2019-05-30
ethz.rosetta.installDate
2017-11-27T07:07:23Z
ethz.rosetta.lastUpdated
2017-11-27T07:11:22Z
ethz.rosetta.exportRequired
true
ethz.rosetta.versionExported
true
ethz.COinS
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