Alpha-alumina is known to exhibit photo-luminescent (PL) properties, mainly characteristic R-lines that shift according to applied stress. In addition to showing excellent PL properties, polymers with embedded alumina nanoparticles have been shown to improve the overall composite mechanical properties. While the use of the PL properties to develop stress-sensing materials using an alumina-epoxy material has been success- fully shown in compression, the properties have not been developed for tension. In this study, the PL response of variable volume fraction alumina-epoxy composites will be determined under tensile conditions. It is expected that increasing the volume fraction of alumina nanoparticles will increase the sensitivity of the particles PL emission shift to applied stress. Three tensile alumina-epoxy specimens of 21.0%, 31.2%, and 34.5% volume fractions were manufactured and tested under tensile static loads. The results of this experiment will determine the piezospectroscopic (PS) coeffi cient and calibration of bulk alumina nanocomposites in tension. A linear region was identified in the PS response of the nanocomposite to the applied tensile load. The PS coeffi cient of this linear region increased as the volume fraction of the nanocomposite increased. To demonstrate the application of structural composites with stress sensing capabilities, alumina nanoparticles were integrated in the manufacturing of a carbon fiber composite specimen. The results of the stress-sensing composite mechanical experiment showed that alumina nanoparticles were able to detect changes in stress. The results for both the bulk nanocomposite calibrations and the application of stress-sensing alumina nanoparticles in a carbon-fiber composite will advance the development of this novel stress-sensing method.

Entomopathogenic fungi, including Beauveria bassiana are being developed as an alternative to chemical insecticides. Their effectiveness can be enhanced through understanding of the mechanisms of response to environmental stresses and conditions. An aspect of repair of ultraviolet radiation induced DNA damage and response to high temperature were studied here. A region of the photolyase gene (phr-1), encoding cyclobutane pyrimidine dimer photolyase (CPD-PHR), an enzyme pivotal to DNA repair, was cloned, sequenced and identified for species of the genera Beauveria, Isaria, Lecanicillium, Metarhizium and Tolypocladium. The DNA and deduced amino acid sequences were analysed using several in silico methods and annotated for functionality. The data suggested that the DNA encoded a protein with conserved residues known in CPD-PHR function, which had structural homology with other CPD-PHRs and molecular phylogeny that was generally consistent amongst this group of fungi. These results are the first for a phr-1 from the genera Isaria, Lecanicillium and Tolypocladium. In bacteria and yeasts, tolerance to environmental stress was shown to be aided through an inducible phenomenon that involves extracellular sensory component (ESC) proteins in Escherichia coli, which have yet to be purified or sequenced. The presence of an ESC-like factor (ELF) was examined in cell-free filtrate (CFF) from B. bassiana cultures. It was revealed that the tolerance of conidiospores and blastospores (BS) to ultraviolet radiation or heat could be increased by preheated CFF, respectively, but not after pretreating the CFF with trypsin. Several novel polyacrylamide-based in situ and binding bioassays were developed to screen for and characterize ELF candidate (EC) proteins. Two were detected (EC1 and EC2) and EC1 was found to interact with BS, while bioassays with purified ECs showed that EC1 could increase heat tolerance in BS. De novo peptide sequencing revealed that the ECs were the same protein, but differed by EC1 being glycosylated. An expressed sequence tag from B. bassiana, encoding six peptides that were also found in the ECs, was identified in the public data base. This sequence information was exploited to amplify the remaining coding regions of the suspected ELF gene (elf) using polymerase chain reactions. Through this a 741 nucleotide open reading frame was cloned and sequenced. Structure-function analyses of the amino acid sequence encoded by the open reading frame revealed features that were consistent with the ECs, such as eight shared peptides, its nascent derived size (26 kDa), potential glycosylation sites and secretion signal peptide. In addition, other features such as the high proportion of cysteine residues and internal amino acid repeats will be discussed. The elf gene was inserted into an expression vector and introduced into the methylotrophic yeast Pichia pastoris for its controlled over-expression. Heterologously expressed ELF conferred elevated tolerance to heat in BS to similar levels produced by ELF synthesized by B. bassiana. Several functional and molecular features of the ELF system have certain commonalities with many agonist-receptor systems involved in signal transduction, but remain to be detailed. This is the first report of the cloning and functional analyses of elf and ELF, respectively, from any organism.

Coatings utilizing the piezospectroscopic (PS) effect of alpha alumina could enable on the fly stress sensing for structural health monitoring applications. While the PS effect has been historically utilized in several applications, here by distributing the photo-luminescent material in nanoparticle form within a matrix, a stress sensing coating is created. Parallel to developing PS coatings for stress sensing, the multi-scale mechanics associated with the observed PS response of nanocomposites and their coatings has been applied to give material property measurements, providing an understanding of particle reinforced composite behavior. Understanding the nanoparticle-coating-substrate mechanics is essential to interpreting the spectral shifts for stress sensing of structures. In the past, methods to experimentally measure the mechanics of these embedded nano inclusions have been limited, and much of the design of these composites depend on computational modeling and bulk response from mechanical testing. The PS properties of Chromium doped alumina allow for embedded inclusion mechanics to be revisited with unique experimental setups that probe the particles state of stress under applied load to the composite. These experimental investigations of particle mechanics will be compared to the Eshelby theory and its derivative theories in addition to the nanocomposite coating mechanics. This work discovers that simple nanoparticle load transfer theories are adequate for predicting PS properties in an intermediate volume fraction range. With fundamentals of PS nanocomposites established, the approach was applied to selected experiments to prove its validity. In general it was observed that the elastic modulus values calculated from the PS response were similar to that observed from macroscale strain measurements such as a strain gage. When simple damage models were applied to monitor the elastic modulus, it was observed that the rate of decay for the elastic modulus was much higher for the PS measurements than for the strain gage. A novel experiment including high resolution PS maps with secondary strain maps from digital image correlation is reviewed on an open hole tension, composite coupon. The two complementary measurements allow for a unique PS response for every location around the hole with a spatial resolution of 400 microns. Progression of intermediate damage mechanisms was observed before digital image correlation indicated them. Using the PS nanocomposite model, elastic modulus values were calculated. Introducing an elastic degradation model with some plastic deformation allows for estimation of material properties during the progression of failure. This work is part of a continuing effort to understand the mechanics of a stress sensing PS coating. The mechanics were then applied to various experimental data that provided elastic property calculations with high resolution. The significance is in the experimental capture of stress transfer in particulate composites. These findings pave the way for the development of high resolution stress-sensing coatings.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24896号 / 工博第5176号 / 新制||工||1988(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)准教授 PIPATPONGSA Thirapong, 教授 肥後 陽介, 教授 岸田 潔, 教授 安原 英明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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