+publisher:"Vanderbilt University" +contributor:("Douglas E Adams")

Vanderbilt University

1. Hu, Ruize. Multiscale Computational Methods for Wave Propagation in 2D Phononic Crystals and Acoustic Metamaterials.

Degree: PhD, Civil Engineering, 2019, Vanderbilt University

► Periodic composites with tailored microstructures and material properties such as phononic crystals and acoustic metamaterials exhibit extraordinary capabilities in controlling elastic waves by manipulating band… (more)

▼ Periodic composites with tailored microstructures and material properties such as phononic crystals and acoustic metamaterials exhibit extraordinary capabilities in controlling elastic waves by manipulating band gaps that forbid waves to propagate within targeted frequency ranges. Modeling these phenomena using direct numerical simulations by resolving all relevant scales is computationally prohibitive for structural design and analysis. This dissertation presents multiscale models for wave propagation in periodic elastic and viscoelastic composites, towards more efficient modeling of their dynamic behaviors. Multiscale models for heterogeneous materials are broadly classified in two categories: (1) scale-separation assumption dependent and (2) scale-separation assumption independent. The scale-separation assumption assumes that the deformation wavelength is much larger than the size of microstructures. In this dissertation, both scale-separable and scale-inseparable multiscale models are formulated for wave propagation in periodic elastic and viscoelastic composites in order to capture short-wavelength phenomena and band gaps. A spatial-temporal nonlocal homogenization model has been developed for transient wave propagation in periodic elastic and viscoelastic composites. The homogenization model is derived by employing high order asymptotic expansions, extending the applicability of asymptotic homogenization to the short-wavelength regime. A gradient-type spatial-temporal nonlocal macroscopic governing equation is consistently derived from the momentum balance equations of successive asymptotic orders. This homogenization model is valid in the frequency regime that scale-separation assumption is weakly satisfied. A spectral variational multiscale model is proposed for the scale-inseparable problems. This model is based on the variational multiscale enrichment method. The proposed approach employs a two-scale additive split of the displacement field, and does not make assumptions on the relative size of microstructures and the macroscopic wavelength. The two important ingredients of the proposed spectral variational multiscale approach in achieving both accuracy and numerical efficiency are: (1) higher-order spectral representation of the coarse-scale solution, and (2) material-phase-based modal basis reduction to the fine-scale solution. Advisors/Committee Members: Douglas E. Adams (committee member), Prodyot K. Basu (committee member), Ravindra Duddu (committee member), Jason G. Valentine (committee member), Caglar Oskay (Committee Chair).

Subjects/Keywords: computational mechanics; wave propagation; multiscale method; composites; viscoelasticity

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APA (6^th Edition):

Hu, R. (2019). Multiscale Computational Methods for Wave Propagation in 2D Phononic Crystals and Acoustic Metamaterials. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/10604

Chicago Manual of Style (16^th Edition):

Hu, Ruize. “Multiscale Computational Methods for Wave Propagation in 2D Phononic Crystals and Acoustic Metamaterials.” 2019. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021. http://hdl.handle.net/1803/10604.

MLA Handbook (7^th Edition):

Hu, Ruize. “Multiscale Computational Methods for Wave Propagation in 2D Phononic Crystals and Acoustic Metamaterials.” 2019. Web. 15 Apr 2021.

Vancouver:

Hu R. Multiscale Computational Methods for Wave Propagation in 2D Phononic Crystals and Acoustic Metamaterials. [Internet] [Doctoral dissertation]. Vanderbilt University; 2019. [cited 2021 Apr 15]. Available from: http://hdl.handle.net/1803/10604.

Council of Science Editors:

Hu R. Multiscale Computational Methods for Wave Propagation in 2D Phononic Crystals and Acoustic Metamaterials. [Doctoral Dissertation]. Vanderbilt University; 2019. Available from: http://hdl.handle.net/1803/10604

Vanderbilt University

2. Njoroge, Ian Gitata. Poly(Ionic Liquid) Thin Films via Surface-Initiated Ring-Opening Metathesis Polymerization.

Degree: PhD, Chemical Engineering, 2017, Vanderbilt University

URL: http://hdl.handle.net/1803/14000

► Ionic liquids (ILs) are organic salts that are liquid at or near room temperature (i.e. below 100 ^◦C). They possess unique materials and solvent properties… (more)

▼ Ionic liquids (ILs) are organic salts that are liquid at or near room temperature (i.e. below 100 ^◦C). They possess unique materials and solvent properties that have led to their use in multiple applications. Poly(ionic liquids) (PILs) refer to a special type of polyelectrolyte that carries an IL species in each of the polymer repeating units. PILs offer advantages over ILs in enhanced mechanical stability, and improved processability, durability and spatial control over the IL moieties. The ability to generate surface-tethered polymer films with IL functionality as side chains can enable coatings with versatile and tailorable properties. This dissertation describes the preparation and characterization of surface-polymerized ILs. Surface-tethered poly(ionic liquid) (PIL) films were prepared via surface-initiated ring-opening metathesis polymerization (SI-ROMP) of ionic liquid-tethered monomers on gold, silicon, and glass substrates and were shown to be adaptive to their anionic environment. A simple anion exchange of PIL films with aqueous solutions containing a binary mixture anions led to the formation of random copolymer PIL films, that offered a continuous tuning of film properties between the extremes of the two homopolymers incorporating the anions present in the copolymer films. For surface-tethered PIL films on gold substrates, anion exchange with certain anions such as triflate, led to the desorption of the PIL films from the surface due to entropic effects and an increase in the glass transition temperature of the films. Part of the dissertation examines polydicyclopentadiene (pDCPD), which is a rigid, cross-linked polymer with excellent impact strength, high modulus, and high chemical resistance. Commercially used for automotive panels and sporting goods, pDCPD has been experimentally explored for a broad range of applications including ballistic protection. While bulk pDCPD has broad commercial impact, the ability to prepare surface-immobilized polymer films of pDCPD, especially with minimal environmental impact, could lead to tough, impact- resistant surfaces with numerous applications. Surface-tethered pDCPD films were prepared on gold and silicon substrates via a novel SI-ROMP with monomer in the vapor space. The choice of ROMP catalyst was an important factor when SI-ROMP was conducted on different substrates.<p/> Advisors/Committee Members: Paul E. Laibinis, Ph.D. (committee member), Clare M. M (committee member), Douglas E. Adams (committee member), G. Kane Jennings, Ph.D. (Committee Chair).

Subjects/Keywords: Thin Films; Ionic Liquids; Polymeric Ionic Liquids; PILs; Surface-Tethered; Dicyclopentadiene; Polydicyclopentadiene; pDCPD; Ring-Opening; Metathesis; Polymerization; ROMP; SI-ROMP; Grubb's Catalyst

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Njoroge, I. G. (2017). Poly(Ionic Liquid) Thin Films via Surface-Initiated Ring-Opening Metathesis Polymerization. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/14000

Chicago Manual of Style (16^th Edition):

Njoroge, Ian Gitata. “Poly(Ionic Liquid) Thin Films via Surface-Initiated Ring-Opening Metathesis Polymerization.” 2017. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021. http://hdl.handle.net/1803/14000.

MLA Handbook (7^th Edition):

Njoroge, Ian Gitata. “Poly(Ionic Liquid) Thin Films via Surface-Initiated Ring-Opening Metathesis Polymerization.” 2017. Web. 15 Apr 2021.

Vancouver:

Njoroge IG. Poly(Ionic Liquid) Thin Films via Surface-Initiated Ring-Opening Metathesis Polymerization. [Internet] [Doctoral dissertation]. Vanderbilt University; 2017. [cited 2021 Apr 15]. Available from: http://hdl.handle.net/1803/14000.

Council of Science Editors:

Njoroge IG. Poly(Ionic Liquid) Thin Films via Surface-Initiated Ring-Opening Metathesis Polymerization. [Doctoral Dissertation]. Vanderbilt University; 2017. Available from: http://hdl.handle.net/1803/14000

Vanderbilt University

3. Nannapaneni, Saideep. Uncertainty Aggregation in System Performance Assessment.

Degree: PhD, Civil Engineering, 2017, Vanderbilt University

URL: http://hdl.handle.net/1803/14095

► Probabilistic performance assessment evaluates a system’s capability to accomplish the required functions under uncertainty. The results of probabilistic performance assessment can be used to support… (more)

Subjects/Keywords: Uncertainty; Performance; Bayesian; Cyber-Physical; Multi-Physics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Nannapaneni, S. (2017). Uncertainty Aggregation in System Performance Assessment. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/14095

Chicago Manual of Style (16^th Edition):

Nannapaneni, Saideep. “Uncertainty Aggregation in System Performance Assessment.” 2017. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021. http://hdl.handle.net/1803/14095.

MLA Handbook (7^th Edition):

Nannapaneni, Saideep. “Uncertainty Aggregation in System Performance Assessment.” 2017. Web. 15 Apr 2021.

Vancouver:

Nannapaneni S. Uncertainty Aggregation in System Performance Assessment. [Internet] [Doctoral dissertation]. Vanderbilt University; 2017. [cited 2021 Apr 15]. Available from: http://hdl.handle.net/1803/14095.

Council of Science Editors:

Nannapaneni S. Uncertainty Aggregation in System Performance Assessment. [Doctoral Dissertation]. Vanderbilt University; 2017. Available from: http://hdl.handle.net/1803/14095

Vanderbilt University

4. Cummins, Joshua Joseph. Characterization of a Pneumatic Strain Energy Accumulator: Efficiency and First Principles Models with Uncertainty Analysis.

Degree: PhD, Mechanical Engineering, 2016, Vanderbilt University

URL: http://hdl.handle.net/1803/11159

► Several technical needs were identified and addressed for advancing the Strain Energy Accumulator (SEA), which is an energy storage device consisting of an expandable rubber… (more)

▼ Several technical needs were identified and addressed for advancing the Strain Energy Accumulator (SEA), which is an energy storage device consisting of an expandable rubber bladder inside of a rigid shroud that stores energy in the form of pressure and strain. First, multiscale modeling methods were investigated to estimate the homogenized elastic modulus of carbon nanotube (CNT) rubber. The result is homogenized modulus estimates ranging from a few times to almost 80 times the elastic modulus of rubber, indicating the need for validation of existing models or development of new models to estimate the modulus for matrix and inclusion materials having drastically dissimilar moduli. Second, an analytical methodology was developed for simultaneously characterizing the energy storage in pneumatic and strain energy systems including component efficiency. By incorporating uncertainty analysis, the efficiencies of the strain energy accumulator are measured in over 2500 cycles of testing to be consistently over 93 %. Third, system state efficiency models were developed and expanded. Through experimentation, the model was determined to be favorably conservative with system efficiency projections ranging from 31 % to over 60 % depending on the system configuration. In addition, materials challenges in high pressure applications led to the conceptual investigation of CNT elastomers offering improved material strength properties and the potential for self-sensing. In previous research, carbon nanotube sensor thread was tested as a distributed sensor on carbon fiber reinforced composites and was able to monitor strain and detect damage in composite panels. The use of nanomaterials for self-sensing was extended in the current work with proof of concept tests performed on electrically conductive elastomers that exhibited the ability to monitor load and detect damage in specific directions. Each of these contributions in the areas of materials modeling, uncertainty analysis, and component and system efficiency quantification techniques has helped to advance the Strain Energy Accumulator technology. Advisors/Committee Members: Eric J Barth (committee member), Sankaran Mahadevan (committee member), Thomas J Withrow (committee member), Florence Sanchez (committee member), Douglas E Adams (Committee Chair).

Subjects/Keywords: Efficiency; Modeling; Strain Energy; Pneumatics; Conductive Elastomers; Load and Damage Monitoring

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Cummins, J. J. (2016). Characterization of a Pneumatic Strain Energy Accumulator: Efficiency and First Principles Models with Uncertainty Analysis. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/11159

Chicago Manual of Style (16^th Edition):

Cummins, Joshua Joseph. “Characterization of a Pneumatic Strain Energy Accumulator: Efficiency and First Principles Models with Uncertainty Analysis.” 2016. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021. http://hdl.handle.net/1803/11159.

MLA Handbook (7^th Edition):

Cummins, Joshua Joseph. “Characterization of a Pneumatic Strain Energy Accumulator: Efficiency and First Principles Models with Uncertainty Analysis.” 2016. Web. 15 Apr 2021.

Vancouver:

Cummins JJ. Characterization of a Pneumatic Strain Energy Accumulator: Efficiency and First Principles Models with Uncertainty Analysis. [Internet] [Doctoral dissertation]. Vanderbilt University; 2016. [cited 2021 Apr 15]. Available from: http://hdl.handle.net/1803/11159.

Council of Science Editors:

Cummins JJ. Characterization of a Pneumatic Strain Energy Accumulator: Efficiency and First Principles Models with Uncertainty Analysis. [Doctoral Dissertation]. Vanderbilt University; 2016. Available from: http://hdl.handle.net/1803/11159

Vanderbilt University

5. Brown, Lesa Renee. Effect of Carbon Nanofiber Clustering on the Chemo-mechanical Behavior of Cement Pastes.

Degree: PhD, Civil Engineering, 2016, Vanderbilt University

URL: http://hdl.handle.net/1803/13817

► The degradation of cementitious materials typically begins on the nanoscale and progressively worsens to the macroscale, therefore, carbon nanofibers (CNFs) are excellent candidates for reinforcement… (more)

▼ The degradation of cementitious materials typically begins on the nanoscale and progressively worsens to the macroscale, therefore, carbon nanofibers (CNFs) are excellent candidates for reinforcement of cementitious materials at the nanoscale due to their distinctive properties (high aspect ratio, high strength, low density, and corrosion resistance). The goal of this research was to develop a fundamental understanding of the relationships between the CNF dispersion state, microstructure, and chemo-mechanical behavior of cement pastes from the micro- to the macroscale during exposure to aggressive environments (i.e., decalcifying environment and sulfate attack). Destabilization of the CNF dispersion in the hydrating cement environment resulted in nano- and microscale CNF clustering in cement pastes. The CNF clusters influenced the chemo-mechanical behavior of the cement pastes with a chemical dissolution-filling effect seen in the clusters during decalcification that slowed the loss of flexural strength and the development of a reinforcement network that delayed cracking and spalling while allowing expansive pressures to grow during sulfate attack. Correlation between grid nanoindentation data and chemical phase composition revealed that the CNF clusters promoted the formation of high density C-S-H and an increase in the number of indents associated with high calcium phases. A decrease in indentation modulus and hardness that was independent of the silicon to calcium ratio was seen for the cement pastes with and without CNFs during decalcification. A micro-macro homogenization approach based on the Mori-Tanaka scheme and an area-averaging method was developed to upscale the local micromechanical properties derived from grid nanoindentation to the overall macroscale elastic modulus of the decalcified material. Overall, the micro-macroscale homogenization approach was able to capture the microscale mechanical changes due to decalcification as well as the influence of the CNF clusters, and a good correlation was achieved between the homogenized modulus and macroscopic experimental measurements. Advisors/Committee Members: David S. Kosson (committee member), Prodyot K. Basu (committee member), Douglas E. Adams (committee member), Paul G. Allison (committee member), Robert D. Moser (committee member), Florence Sanchez (Committee Chair).

Subjects/Keywords: cementitious materials; carbon nanofiber dispersion; degradation; grid nanoindentation; micromechanical properties; micro-macro homogenization model

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Brown, L. R. (2016). Effect of Carbon Nanofiber Clustering on the Chemo-mechanical Behavior of Cement Pastes. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/13817

Chicago Manual of Style (16^th Edition):

Brown, Lesa Renee. “Effect of Carbon Nanofiber Clustering on the Chemo-mechanical Behavior of Cement Pastes.” 2016. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021. http://hdl.handle.net/1803/13817.

MLA Handbook (7^th Edition):

Brown, Lesa Renee. “Effect of Carbon Nanofiber Clustering on the Chemo-mechanical Behavior of Cement Pastes.” 2016. Web. 15 Apr 2021.

Vancouver:

Brown LR. Effect of Carbon Nanofiber Clustering on the Chemo-mechanical Behavior of Cement Pastes. [Internet] [Doctoral dissertation]. Vanderbilt University; 2016. [cited 2021 Apr 15]. Available from: http://hdl.handle.net/1803/13817.

Council of Science Editors:

Brown LR. Effect of Carbon Nanofiber Clustering on the Chemo-mechanical Behavior of Cement Pastes. [Doctoral Dissertation]. Vanderbilt University; 2016. Available from: http://hdl.handle.net/1803/13817

Vanderbilt University

6. VanWie, Talitha Marie. The Effects of Quantum Dot Surface Chemistry on Fluorescence and Additive Manufacturing Applications.

Degree: PhD, Chemistry, 2019, Vanderbilt University

URL: http://hdl.handle.net/1803/15125

► Quantum dots (QDs), have been extensively studied for their unique optical properties, such as their lasting photostability, size-tunable band gaps, and narrow photoluminescence. Additionally, by… (more)

▼ Quantum dots (QDs), have been extensively studied for their unique optical properties, such as their lasting photostability, size-tunable band gaps, and narrow photoluminescence. Additionally, by controlling the surface chemistry of QDs, the optical properties can be modified. With these exceptional optical properties, QDs are an ideal materiel to be used in lighting technologies and as sensors. With the discovery of ultrasmall CdSe QDs, a single-component white-light emitter, the exhibits a broad emission that spans from 420 to 710 nm was realized. For the ultrasmall CdSe to be viable for commercial lighting technologies, the quantum yield must be increased from the average 6%. This was accomplished with a post-synthesis ligand treatment with both formic acid and citric acid. The citric acid treated CdSe QDs have the highest reported quantum yield for a single-component white light emitter, with 61%, and a cool white emission. These QDs were also found to have a higher stability in solution than those of the formic acid treated QDs. With the broad white emission being determined by the surface of the CdSe QDs, these are an optimal material to be used as an in-situ material state monitor for structural health monitoring. As the surface ligands are removed from the QDs during external compressive or tensile loading the emission is observed to decrease in intensity. The unique optical properties of QDs can be utilized with the development of functional materials compatible with 3D printing applications. CdSSe QDs were embedded in a polylactic acid (PLA) host matrix to obtain nanofunctionalized, fluorescent filament compatible with stock 3D printing systems. Absorbance, photoluminescence, thermal analysis, and mechanical testing are studied to quantify how filament functionalization modulates the optical and material properties of the embedded quantum dots and PLA host matrix following printing. Advisors/Committee Members: Dr. Lauren E. Buchanan (committee member), Dr. Timothy P. Hanusa (committee member), Dr. Douglas E. Adams (committee member), Dr. Sandra J. Rosenthal (Committee Chair).

Subjects/Keywords: 3D printing; ultrasmall; surface chemistry; quantum dots

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

VanWie, T. M. (2019). The Effects of Quantum Dot Surface Chemistry on Fluorescence and Additive Manufacturing Applications. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/15125

Chicago Manual of Style (16^th Edition):

VanWie, Talitha Marie. “The Effects of Quantum Dot Surface Chemistry on Fluorescence and Additive Manufacturing Applications.” 2019. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021. http://hdl.handle.net/1803/15125.

MLA Handbook (7^th Edition):

VanWie, Talitha Marie. “The Effects of Quantum Dot Surface Chemistry on Fluorescence and Additive Manufacturing Applications.” 2019. Web. 15 Apr 2021.

Vancouver:

VanWie TM. The Effects of Quantum Dot Surface Chemistry on Fluorescence and Additive Manufacturing Applications. [Internet] [Doctoral dissertation]. Vanderbilt University; 2019. [cited 2021 Apr 15]. Available from: http://hdl.handle.net/1803/15125.

Council of Science Editors:

VanWie TM. The Effects of Quantum Dot Surface Chemistry on Fluorescence and Additive Manufacturing Applications. [Doctoral Dissertation]. Vanderbilt University; 2019. Available from: http://hdl.handle.net/1803/15125

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