Structural wood design standards recognize lateral torsional buckling as an important failure mode, which tends to govern the capacity of long span laterally unsupported beams. A survey of the literature indicates that only a few experimental programs have been conducted on the lateral torsional buckling of wooden beams. Within this context, the present study reports an experimental and computational study on the elastic lateral torsional buckling resistance of wooden beams. The experimental program consists of conducting material tests to determine the longitudinal modulus of elasticity and rigidity modulus followed by a series of 18 full-scale tests. The buckling loads and mode shapes are documented. The numerical component of the study captures the orthotropic constitutive properties of wood and involves a sensitivity analysis on various orthotropic material constants, models for simulating the full-scale tests conducted, a comparison with experimental results, and a parametric study to expand the experimental database. Based on the comparison between the experimental program, classical solution and FEA models, it can be concluded that the classical solution is able to predict the critical moment of wood beams. By performing the parametric analysis using the FEA models, it was observed that loads applied on the top and bottom face of a beam decrease and increase its critical moment,respectively. The critical moment is not greatly influenced by moving the supports from mid-span to the bottom of the end cross-section.

Benzothiazole dibenzoic acid derivative (BTDB) is well-known organic linkers utilized for the syntheses of various metal organic frameworks, and demonstrates interesting photophysical properties upon concentration variations in solution. The presence of two carboxylic acid functional groups at each side of the rod-like molecule, facilitates dimerization and oligomerization equilibria. Interestingly, dimers and oligomers have completely different emission behaviors from the monomer of the same species. At a low range of concentration, 0.1 – 64 μM, dimerization process is dominant, and that the equilibrium constant of dimer formation found to be 18,000 M-1. On the other hand, in the 64 – 1000 μM concentration range, oligomerization takes over, and that it results in the formation of a small linear chain of 8 molecules, or 4 dimers, with a high equilibrium constant of 1.2 × 1013 M-3. Various experimental measurements and theoretical calculations have suggested hydrogen-bond formation is the main driving force for the dimerization and oligomerization in the nano- and micro- molar regime, and that structure rigidity of a species is a key factor in controlling its photophysical properties, such as emission quantum yield and excited state lifetime.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21462号 / 工博第4537号 / 新制||工||1707(附属図書館) / 京都大学大学院工学研究科マイクロエンジニアリング専攻 / (主査)教授 田畑 修, 教授 鈴木 基史, 准教授 土屋 智由, 教授 平方 寛之 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

No description available.

In February of 2017 after a period of heavy rainfall, a slope destabilized behind Fremont Hall on the campus of Cal Poly San Luis Obispo. The geology of this slope stability failure is the Franciscan Complex. The Franciscan Complex, when weathered in place, results in clay soil that makes up the typical soil mantle on the hills throughout the region. Peak strength is the typical parameter tested to assess the strength of the soil. For the Franciscan-derived clay, the residual strength is the focus of this study to understand slope failure since the clay is the weakest portion of the matrix in the Franciscan Complex. Both intact and remolded specimens were processed from the samples obtained from the slide for laboratory testing. The tested material is considered representative of the soil found in the Franciscan Complex along the California coast and other similar regions worldwide where the presence of this mélange results in slope instabilities. Three different shearing tests were performed to study the residual strength: direct shear reversal, ring shear, and large-scale direct shear reversal. Sampling soil from the slide took place twice: once in 2017 and once in 2019. A block of soil sampled in 2017 was taken after the toe of the slope was cut for reconstruction which resulted in an exposed slide plane. In 2019, additional samples were retrieved near the toe of the slope after subsequent failure of the slope. Although the material was assumed to be from the slide plane, there is a possibility it may have originated from the surrounding matrix. Intact and remolded specimens were tested in direct shear reversal tests, and remolded specimens were tested in ring shear tests. The 2019 source was tested in the large-scale direct shear reversal tests because the material obtained during 2017 was not enough to replicate the large specimen. Remolded specimens were prepared by passing through sieve No. 40. A secondary set of tests were performed on specimens prepared by passing through sieve No. 200. When comparing remolded against intact specimens, the clasts within the intact material exhibited an influence on the residual strength by an approximate difference of 20%. The results also indicated the liquid limit (LL) had an impact on the residual strength; higher value LL exhibited lower residual strength, and lower value LL exhibited higher residual strength. When comparing the laboratory results against in situ CPT tests, the values from the CPT fell within the range of the laboratory residual strength corresponding to the slide’s depth of movement. The results from testing these specimens showed the soil obtained directly from the slide failure exhibited a residual strength represented as friction angle of 14° ± 2° for intact soil specimens, 11° ± 3° for remolded specimens of the 2017 failure plane passing through No. 40 sieve, and 22° ± 2° for remolded specimens of the 2019 sample location passing though No. 40 sieve. The remolded specimens passing through sieve No. 200 produced even lower results. However, since all clasts were removed by the No. 200 sieve, those results are not considered representative of field conditions. Based on the test results, and the infinite slope limit equilibrium slope stability analysis, a median range of residual strength for this slide is approximately 12.5 to 14.0°.

Finite element is used to predict the torsional stiffness and natural frequency response of a FSAE vehicle hybrid chassis, utilizing a carbon fiber reinforced polymer sandwich structure monocoque and a tubular steel spaceframe. To accurately model the stiffness response of the sandwich structure, a series of material tests for different fiber types has been performed and the material properties have been validated by modeling a simple three-point-bend test panel and comparing the results with a physical test. The torsional stiffness model of the chassis was validated with a physical test, too. The stiffness prediction matches the test results within 6%. The model was then used to model the natural frequency response by adding and adjusting the materials’ densities in order to match physical mass properties. A hypothesis is made to explain the failure of the engine mounts under the dynamic response of the frame.

No description available.

No description available.

No description available.

A novel rotary series elastic actuator (RSEA) with a two-mode, or bimodal, elastic element was designed and tested. This device was developed to eliminate the compromise between human safety and robot performance. Rigid actuators can be dangerous to humans within a robot's workspace due to impacts or pinning scenarios. To increase safety, elastic elements can soften impacts and allow for escape should pinning occur. However, adding elasticity increases the complexity of the system, lowers the bandwidth, and can make control of the actuator more difficult. To get the best of both types of actuators, a bimodal clutch was designed to switch between rigid actuation for performance and elastic actuation for human safety. The actuator consisted of two main parts, a rigid rotary actuator using a harmonic gearhead and a drum brake designed to act as a clutch. The 200 W rotary actuator provides 54.7 Nm of torque with a maximum speed of 41.4 rpm. The measured efficiency was 0.797 due to a timing belt speed reduction that was then speed reduced with a harmonic gearhead. The clutch was a drum brake actuated with a pantograph linkage and ACME lead screw. This configuration produced 11 Nm of holding torque experimentally but was theoretically shown to produce up to 51.4 Nm with larger motors. The elastic element was designed using finite element analysis (FEA) and tested experimentally to find a measured stiffness of 290 Nm/rad. / Master of Science