Browsing by Subject "Strain"

Now showing 1 - 8 of 8
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    The Anhydride-HDDA Reaction and Further Expansion of Hexadehydro-Diels–Alder-based Reaction Methodologies
    (2024-06) Sneddon, Dorian
    Since its serendipitous rediscovery in 2012, the hexadehydro-Diels–Alder (HDDA) reaction has served as a means of generating benzyne in situ via cycloisomerization of poly-yne precursors under thermal or photochemical conditions. This allows for the formation of complex benzenoid products in a single reaction step upon trapping of the insipient aryne. Aside from more fundamental mechanistic studies, my contributions to this science have fallen into three broad areas: i) formation of N-heterocycles, ii) single-step synthesis of functional materials, and iii) generation of HDDA benzynes at ambient conditions. The first area has seen extensive exploration by our lab and others; however, the latter two categories, especially the third, are still revealing interesting contemporary novelties. In my initial work, I found that trapping of HDDA benzynes with C,N-diarylimines led to a reversal in reactivity with respect to the case of classical benzynes, furnishing acridine, as opposed to phenanthridine, products (Chapter 2). Next, I trapped HDDA benzynes with arylhydrazines to form azoarenes. I then recognized that simple azobenzenes could also trap HDDA benzynes in a binary fashion that could be toggled photochemically (Chapters 3 and 4). A fundamental investigation into trapping of HDDA benzynes with electron-deficient alkenes then led to the discovery of a novel mode of strain release of ortho-annulated benzene rings (Chapter 5). Reaction of HDDA benzynes with phosphine chalcogenides revealed a new mode of aryne-aryne ligand coupling from a P(V) center (Chapter 6). Finally, diynoic acid condensation was leveraged to form anhydrides that uniquely undergo HDDA cycloisomerization below room temperature (Chapter 7).
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    Calibration of New Concrete Shrinkage and Creep Model for ACI Committee 209
    (2022-04) Clement, Timothy
    A new semi-empirical concrete shrinkage and creep model is proposed and calibrated in which creep ages according to solidification theory. The impetus for this CRC-funded research is to propose new creep and shrinkage design guidelines for ACI Committee 209; previous guidelines were published in 1982 and are no longer up to date with modern understanding of time-dependent behavior. The new model proposes a coupling between autogenous and drying shrinkage using a volume-average pore relative humidity and treats drying creep as an additional stress-dependent shrinkage, linking together all these phenomena. The proposed expressions are designed to facilitate traditional integral-type analysis, but also uniquely support rate-type calculations that can be leveraged by analysis software. Model calibration uses the Northwestern University (NU) database of creep and shrinkage tests to determine new model parameters. Profile likelihood curves for each individual mix in the database are computed to quantify the sensitivity of the fitting parameters to the available data and to mix design inputs.
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    Complexity at cobaltite interfaces: the interplay between strain, stoichiometry, magnetism and transport
    (2014-12) Bose, Shameek
    Thin films and heterostructures of the perovskite cobaltites are of great interest, not only from the point of view of fundamental physics and materials science, but also for technological applications such as solid oxide fuel cells and gas membranes. Their properties are, however, severely deteriorated from the bulk, being dominated by the presence of interfacial "dead layers". Working with the prototypical SrTiO3 (001)/La1-xSrxCoO3 (LSCO) system, our group recently discovered that this degradation in the magnetism and electronic transport at the interface is caused by nanoscopic magneto-electronic phase separation. This was shown to occur primarily due to accumulation of oxygen vacancies near the interface, driven by the interplay between the strain state and the ordering of oxygen vacancies. In the present work we show how this understanding allows for engineering of the interfacial magnetic and electronic transport properties via manipulation of this oxygen vacancy superstructure. We first demonstrate a synthesis technique that utilizes a unique high pressure oxygen plasma to sputter LSCO thin films over a wide doping range 0.05  x  0.80. Then, using reciprocal space mapping and transmission electron microscopy, we demonstrate the ability to control, via the vacancy ordering, the critical strain relaxation thickness by changing the sign of the strain (from tensile on SrTiO3 to compressive on LaAlO3) and crystallographic orientation ((001) vs. (110)). We then provide cross sectional electron energy loss spectroscopy data to show that this strain and orientation control preserves both oxygen and hole carrier concentration at the LaAlO3(001)/LSCO and SrTiO3(110)/LSCO interfaces, strikingly different to the severely depleted SrTiO3(001)/LSCO interface. SQUID magnetometry, polarized neutron reflectometry (PNR) and magneto-transport confirm the concomitant mitigation of the interfacial degradation for LSCO films grown on LaAlO3(001) and SrTiO3(110), as compared to films grown on SrTiO3 (001). Finally, we use scanning tunneling microscopy to provide direct real space images of the magneto-electronic phase separation in ultrathin LSCO on SrTiO3(001). Our work thus demonstrates the ability to utilize oxygen vacancy ordering as a tunable control parameter to tailor interfacial electronic and magnetic properties, with profound implications for the myriad other systems that exhibit unique properties due to such ordering.
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    Effect of Gingival Margin Design on Clear Aligner Material Strain and Force Delivery
    (2021-06) Brown, Brooke
    Aim: To evaluate the effect of the gingival margin design on strain distribution and forces and moments delivered from Essix ACE and Zendura FLX to a maxillary central incisor during labial tipping about a simulated center of rotation.Methods: Clear aligners (CAs) were prepared from two materials, Essix ACE and Zendura FLX, in 0.030 mil (0.75 mm) thickness. For each material, three margin designs—scalloped, straight cut 0.75 mm above gingival zenith and straight cut 1.5 mm above gingival zenith—were fabricated with no tooth movement and 2.4 degrees of labial tipping about a simulated center of rotation, for a total of 12 designs. Three CAs were manufactured for each of the 12 designs, for a total of 36 aligners. Forces and moments were recorded with a force measuring device in all six degrees of freedom, from the center of the crown and the center of resistance (COR).
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    Effect of the Periodontal Ligament on Clear Aligner Material Surface Strain when Measured In-Vivo
    (2023-06) Nelson, Samantha
    Introduction: Clear aligner therapy has become increasingly popular as an alternative to traditional braces. Despite advances in technology, the efficacy and efficiency of clear aligner treatment remains challenged. Numerous in-vitro studies into the force systems of clear aligners have been developed. Currently, there are no guidelines for evaluating orthodontic force systems intraorally with clear aligners. The effect of the periodontal ligament and intraoral environment on orthodontic tooth movement with clear aligners remains unknown. Aim: To determine if surface strain can be measured in-vivo with digital image correlation (DIC). And to evaluate the effect of the periodontal ligament and intraoral environment on the surface strain delivered by a clear aligner to a maxillary central incisor during lingual tipping. Methods: Clear aligners were designed with 2.0 degrees of lingual crown tipping about an estimated center of rotation on a maxillary central incisor for 33 subjects. Clear aligners were fabricated using two materials, Essix ACE and Zendura A, in 0.030 mil (0.75 mm) thickness. A dual-camera, three-dimensional DIC system was used to record the transverse strain on the facial surfaces on the subject’s model, in the subject’s mouth, and on the subject’s model after submersion in artificial saliva. The relationships between transverse strain and the predictors, aligner material and environment, were examined using linear mixed effects models, with a random intercept for subject. A statistical model was also fit to test associations between transverse strains and predictors aligner material, gender, and presence of artificial saliva. Estimates are reported as a means with 95% confidence intervals. The passive and active models and aligners were assembled and scanned by micro-CT to measure the gap size between the aligner and model. Displacement at the incisal half of the target tooth was measured with GeoMagic software. Results: Initial forces delivered by clear aligners produced a strain threshold high enough to be detected and captured intraorally by DIC. The strain distribution and contour differed between in-vivo and in-vitro, as well as between material types, but followed the same pattern and peaks. Mean transverse strain increased as the point of focus narrowed to the incisal half of the target tooth. The effects of the environment were statistically significant at the incisal half of the target tooth, with increased transverse strain in-vitro compared to in-vivo. Zendura A expressed significantly less transverse strain than Essix ACE within both environments. The effect of the material was more pronounced in-vitro for the entire dentition, but not at the incisal half of the target tooth. No differences in transverse strain were noted with the presence or absence of artificial saliva, as well as between genders. Strong reproducibility existed between trials, with more similar strain profiles in-vitro compared to in-vivo. Micro-CT images demonstrated a lack of gap between the aligner and passive model on the labial surface of the target tooth, while gap sizes increased at the interproximal contact points and on adjacent teeth. Based on inciso-gingival crown length of tooth, there was no difference in incisor displacement between subjects. Conclusions: This is the first study in which the strain distribution on a clear aligner has been studied in-vivo with DIC. Initial force delivered by clear aligners can be detected and evaluated intraorally. The difference in surface deformation between environments is only significant at the point of greatest tooth displacement, with increased transverse strain in-vitro. Material type influences clear aligner strain, with a more pronounced effect in-vitro. Clear aligners distribute strain to multiple teeth despite efforts to isolate movement to a single target tooth. And the presence of artificial saliva and influence of gender do not affect strain level or surface deformation.
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    Effects of Implements of Husbandry (Farm Equipment) on Pavement Performance
    (Minnesota Department of Transportation Research Services Section, 2012-04) Lim, Jason; Azary, Andrea; Khazanovich, Lev; Wang, Shiyun; Kim, Sunghwan; Ceylan, Halil; Gopalakrishnan, Kasthurirangan
    The effects of farm equipment on the structural behavior of flexible and rigid pavements were investigated in this study. The project quantified the difference in pavement behavior caused by heavy farm equipment as compared to a typical 5-axle, 80 kip semi-truck. This research was conducted on full scale pavement test sections designed and constructed at the Minnesota Road Research facility (MnROAD). The testing was conducted in the spring and fall seasons to capture responses when the pavement is at its weakest state and when agricultural vehicles operate at a higher frequency, respectively. The flexible pavement sections were heavily instrumented with strain gauges and earth pressure cells to measure essential pavement responses under heavy agricultural vehicles, whereas the rigid pavement sections were instrumented with strain gauges and linear variable differential transducers (LVDTs). The full scale testing data collected in this study were used to validate and calibrate analytical models used to predict relative damage to pavements. The developed procedure uses various inputs (including axle weight, tire footprint, pavement structure, material characteristics, and climatic information) to determine the critical pavement responses (strains and deflections). An analysis was performed to determine the damage caused by various types of vehicles to the roadway when there is a need to move large amounts agricultural product.
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    Strain effect on the ground-state crystal structure of Sr2SnO4 Ruddlesden-Popper oxides
    (2022-09-08) Yun, Hwanhui; Gautreau, Dominique; Mkhoyan, K. Andre; Birol, Turan; yunxx133@umn.edu; Yun, Hwanhui; Theoretical Materials Physics Group
    Simulation data for a manuscript 'Strain effect on the ground-state structure of Sr2SnO4 Ruddlesden-Popper oxides'. Key data including structures and input files for structural relaxation and phonon calculation of various phases in Sr2SnO4 are included.
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    Transverse shear microscopy: a novel microstructural probe for organic semiconductor thin films.
    (2010-08) Kalihari, Vivek
    The microstructure of ultrathin organic semiconductor films (1-2nm) on gate dielectrics plays a pivotal role in the electrical transport performance of these films in organic field effect transistors. Similarly, organic/organic interfaces play a crucial role in organic solar cells and organic light emitting diodes. Therefore, it is important to study these critical organic interfaces in order to correlate thin film microstructure and electrical performance. Conventional characterization techniques such as SEM and TEM cannot be used to probe these interfaces because of the requirement of conducting substrates and the issue of beam damage. Here, we introduce a novel contact mode variant of atomic force microscopy, termed transverse shear microscopy (TSM), which can be used to probe organic interfaces. TSM produces striking, high contrast images of grain size, shape, and orientation in ultrathin films of polycrystalline organic materials, which are hard to visualize by any other method. It can probe epitaxial relationships between organic semiconductor thin film layers, and can be used in conjunction with other techniques to investigate the dependence of thin film properties on film microstructure. In order to explain the TSM signal, we used the theory of linear elasticity and developed a model that agrees well with the experimental findings and can predict the signal based on the components of the in-plane elastic tensor of the sample. TSM, with its ability to image elastic anisotropy at high resolution, can be very useful for microstructural characterization of soft materials, and for understanding bonding anisotropy that impacts a variety of physical properties in molecular systems.