QC 351 A7 no. 48 / New materials of low thermal expansion are finding wide application. The expansion coefficient (a) is a function of temperature, and this function must be known for each material before its applicability can be assessed. A novel method for determining a, which is at once precise and easily implemented, has been devised. It is based on the dependence of mode frequencies in a Fabry-Perot interferometer on the mirror separation. The expansion sample is formed into an interferometer spacer with ends polished flat and parallel. Spherical mirrors are optically contacted to the ends, forming a confocal interferometer. The assembly is maintained at controlled temperatures in an environmental chamber. The two lowest -order transverse modes are probed by variable -frequency sidebands derived from a 633 -nm He- Ne laser by amplitude modulation. A change in sample temperature AT causes a change in interferometer length AL, which shifts the resonance frequencies by Av. Then a = (1 /AT) (AL /L) _ - (1 /AT)(iv /v). Thus, a can be measured with precision limited ultimately by the stability of the source laser, in practice 1:109 with presently available commercial lasers. For a sample of Owens -Illinois Cer -Vit, a has been measured at 10 temperatures in the range 3.0 to 32.4 °C, with a mean error of 2 x10-9 and a maximum error of 3 x10 -9. For a sample of Corning ULE silica, a has been measured at six temperatures in the same range, with a mean error of <1 x10 -9 and a maximum error of <1.3 x10 -9.

Detta examensarbete har genomförts på ABB Power Products/Instrument Transformers i Ludvika. Syftet med arbetet har varit att undersöka temperaturexpansionen för en isolerande olja som använd i produkten Capacitor Voltage Transformer (CVT). Oljans egen temperatur­expansionskoefficient                          var redan känd, men arbetets syfte var att bestämma en Brutto­temperaturexpansionskoefficient, med andra ord undersöka hur mycket de ingående komponenterna i en CVT påverkar den totala volymexpansionen inuti enheten. För att bestämma bruttotemperaturexpansionskoefficienten har ett prov i klimatkammare utförts. Provet bestod av två aluminiumkärl vardera med ett monterat mätrör. Det ena kärlet fylldes med olja och det andra kärlet med olja och kondensatorinnehåll motsvarande inne­hållet i en CVT. Provobjekten utsattes sedan för en bestämd tid i temperaturer från -60°C till 65°C med intervall om 10°C. Under denna tid utfördes ett antal mätningar av oljevolymen i de båda provobjekten. Dessa mätningar användes sedan tillsammans med ett några korrektions­faktorer för att beräkna temperaturexpansionskoefficienten för både oljan (enbart för kontroll­erande syfte) och kondensatorinnehållet. Tillsammans ger dessa bruttotemperaturexpansions­koefficienten för alla möjliga volymkombinationer. Resultatet från provet har sedan analyserats och visualiserats i form av tabeller och diagram. Efter det beräknades temperaturexpansionskoefficient för oljan samt  för kondensator­innehållet vid olika temperaturer. Utifrån dessa värden beräknades de genomsnittliga temperatur­­expansionskoefficienterna för temperaturintervallet och slutligen angavs en formel för att bestämma bruttotemperaturexpansionskoefficienten för olika procentuella fördelningar mellan olja och kondensatorinnehåll. Till sist drogs slutsatser utifrånfrån resultatet. / This bachelor thesis was carried out at ABB Power Products/Instrument Transformers in Ludvika. The purpose of the work has been to examine the thermal expansion for an isolating oil that is used in the product Capacitor Voltage Transformer (CVT). The oil’s own expansion coefficient                          was already known, but the purpose of the work was to determine a gross thermal expansion coefficient, with other words to examine the amount of influense the other componets had on the volume expansion inside the unit. To decide the gross thermal expansion coefficient a test has been carried out in a climat chamer. To performe the test two aluminum tanks, each with a measurement tube mounted on the top were used. One of the tanks was filled with oil and the other one was filled with oil and capacitor contents corresponding tio the contents in a CVT. The two test objects were then exposed to temperatures reaching from -60°C to 65°C in steps of 10°C. During this time a number of volume measurements were performed on the two test objects. These measure­ments together with a few correction parameters were used to decide the thermal expansion coefficient for both the oil (only for control purpose) and the capacitor contents. Together these two gives the gross thermal expansion coefficient for all posible volume combinations. The results from the tests has been analised and visualised in the form of tables an diagrams. After that the thermal expansion coefficient for the oil and the capacitorcontents, for different temperatures was calculated. Bult on those calculations the avarege thermal expansion coeff­icient for the temperatureintervals was calculated, and finaly an modle for calculating the gross thermal expansion coefficient was created. At the end conclusions were drawn from the results.

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The work presented in this thesis detail the measurement of the thermal expansion coefficient of three magnetic spin materials. Thermal expansion coefficient values were measured by capacitive dilatometry in several key low (T < 250 K) temperature regions specific to each material. This thesis is separated into several key parts. The first part establishes the theory behind observing phase transitions through the thermal expansion coefficient. Beginning with the classical definitions of the specific heat, compressibility and thermal expansion coefficient, the three properties are related using a property known as the Grüneisen parameter. To first order, the parameter allows phase transitions to be observed by the thermal expansion coefficient. The second part introduces capacitive dilatometry; a technique used to measure the thermal expansion coefficient. Three capacitive dilatometer devices are presented in this section. The silver compact dilatometer, the fused quartz dilatometer and the copper dilatometer. Each device discusses merits and weaknesses to their designs. Particular focus is made on the fused quartz dilatometer which was built during the duration of this thesis. The third part presents research on three magnetic spin materials; LiHoF4, Tb2Ti2O7 and Ba3NbFe3Si2O14. These materials are studied individually focusing on specific aspects. LiHoF4, a candidate material for the transverse field Ising model, provides insight to quantum phase transitions. Thermal expansion coefficient and magnetostriction along the c-axis for T ≈ 1.3-1.8 K and transverse field Ht ≈ 0-4 T were measured extracting critical points for a Ht-T phase diagram. Existing thermal expansion coefficient measurements had evidence of possible re-entrant behaviour. With a high density of low transverse field critical points it was established that LiHoF4 showed no evidence of re-entrant behaviour. The highly debated material Tb2Ti2O7 has a rich, controversial low temperature behaviour. Originally believed to be a spin liquid, specific heat results propose a scenario involving a sample composition dependent ordered state. Still under considerably attention, thermal expansion coefficient measurements were performed for T < 1 K. The results are interpreted to either fit into the proposed scenario or provide evidence for an alternate scenario. The material Ba3NbFe3Si2O14 exhibits a magnetoelectric multiferroic phase below TN ≈ 27 K; a phase where magnetic and electric order simultaneously exist. The formation of this phase is believed to have a similar structural shift observed in hexagonal perovskite multiferroic materials. The ferroelectric ordering in those materials are brought about through a centrosymmetric to non-centrosymmetric structural shift. The thermal expansion and thermal expansion coefficient coefficient along the a and c axis are measured for T > TN searching for a displacive structural phase transition.

In this work , impurity free vacancy diffusion (IFVD) quantum well intermixing(QWI) technology by high thermal-expansion-induced stress is used to perform bandgap engineering. In this paper, 1530nm InGaAsP multiple QWs sandwiched by p-InP (2£gm thickeneess, top) and n-InP (bottom) material is used as testing material structure also laser fabrication material, where contact materials (InGaAs and InP) on p-InP are used for comparison. By the difference between thermal expansion coefficients of SiO2 on the different material (InGaAs, InP), large different behaviors of QWI are observed, while low different dependence on defects created by ion-implantation is found. Above 70nm photo luminance (PL) wavelength shift of InGaAsP MQW below 2£gm thick InP is realized in this method. Further more, CW in-plane laser structures are also successfully fabricated and demonstrated by such QWI, giving the same shift as PL. It shows that good qualify of material can be obtained in such QWI method. Using local deposition of SiO2 causes different bandgap materials, re-growth free processing for monolithic integration can be expected, offering a powerful scheme of QWI for bandgap engineering.

Turbine components operate under severe loading conditions and at high and varying temperatures that result in thermal stresses in the presence of temperature gradients created by hot gases and cooling air. Moreover, static and cyclic loads as well as the motion of rotating components create mechanical stresses. The combined effect of complex thermo-mechanical stresses promote nucleation and propagation of cracks that give rise to fatigue and creep failure of the turbine components. Therefore, the relationship between thermo-mechanical stresses, chemical composition, heat treatment, resulting microstructure, operating temperature, material damage, and potential failure modes, i.e. fatigue and/or creep, needs to be well understood and studied. Artificial neural networks are promising candidate tools for such studies. They are fast, flexible, efficient, and accurate tools to model highly non-linear multi-dimensional relationships and reduce the need for experimental work and time-consuming regression analysis. Therefore, separate neural network models for γ’ precipitate strengthened Ni based superalloys have been developed for predicting the γ’ precipitate size, thermal expansion coefficient, fatigue life, and hysteresis energy. The accumulated fatigue damage is then estimated as the product of hysteresis energy and fatigue life. The models for γ’ precipitate size, thermal expansion coefficient, and hysteresis energy converge very well and match experimental data accurately. The fatigue life proved to be the most challenging aspect to predict, and fracture mechanics proved to potentially be a necessary supplement to neural networks. The model for fatigue life converges well, but relatively large errors are observed partly due to the generally large statistical variations inherent to fatigue life. The deformation mechanism map for 1.23Cr-1.2Mo-0.26V rotor steel has been constructed using dislocation glide, grain boundary sliding, and power law creep rate equations. The constructed map is verified with experimental data points and neural network results. Although the existing set of experimental data points for neural network modeling is limited, there is an excellent match with boundaries constructed using rate equations which validates the deformation mechanism map.

The work presented in this thesis detail the measurement of the thermal expansion coefficient of three magnetic spin materials. Thermal expansion coefficient values were measured by capacitive dilatometry in several key low (T < 250 K) temperature regions specific to each material. This thesis is separated into several key parts. The first part establishes the theory behind observing phase transitions through the thermal expansion coefficient. Beginning with the classical definitions of the specific heat, compressibility and thermal expansion coefficient, the three properties are related using a property known as the Grüneisen parameter. To first order, the parameter allows phase transitions to be observed by the thermal expansion coefficient. The second part introduces capacitive dilatometry; a technique used to measure the thermal expansion coefficient. Three capacitive dilatometer devices are presented in this section. The silver compact dilatometer, the fused quartz dilatometer and the copper dilatometer. Each device discusses merits and weaknesses to their designs. Particular focus is made on the fused quartz dilatometer which was built during the duration of this thesis. The third part presents research on three magnetic spin materials; LiHoF4, Tb2Ti2O7 and Ba3NbFe3Si2O14. These materials are studied individually focusing on specific aspects. LiHoF4, a candidate material for the transverse field Ising model, provides insight to quantum phase transitions. Thermal expansion coefficient and magnetostriction along the c-axis for T ≈ 1.3-1.8 K and transverse field Ht ≈ 0-4 T were measured extracting critical points for a Ht-T phase diagram. Existing thermal expansion coefficient measurements had evidence of possible re-entrant behaviour. With a high density of low transverse field critical points it was established that LiHoF4 showed no evidence of re-entrant behaviour. The highly debated material Tb2Ti2O7 has a rich, controversial low temperature behaviour. Originally believed to be a spin liquid, specific heat results propose a scenario involving a sample composition dependent ordered state. Still under considerably attention, thermal expansion coefficient measurements were performed for T < 1 K. The results are interpreted to either fit into the proposed scenario or provide evidence for an alternate scenario. The material Ba3NbFe3Si2O14 exhibits a magnetoelectric multiferroic phase below TN ≈ 27 K; a phase where magnetic and electric order simultaneously exist. The formation of this phase is believed to have a similar structural shift observed in hexagonal perovskite multiferroic materials. The ferroelectric ordering in those materials are brought about through a centrosymmetric to non-centrosymmetric structural shift. The thermal expansion and thermal expansion coefficient coefficient along the a and c axis are measured for T > TN searching for a displacive structural phase transition.

Turbine components operate under severe loading conditions and at high and varying temperatures that result in thermal stresses in the presence of temperature gradients created by hot gases and cooling air. Moreover, static and cyclic loads as well as the motion of rotating components create mechanical stresses. The combined effect of complex thermo-mechanical stresses promote nucleation and propagation of cracks that give rise to fatigue and creep failure of the turbine components. Therefore, the relationship between thermo-mechanical stresses, chemical composition, heat treatment, resulting microstructure, operating temperature, material damage, and potential failure modes, i.e. fatigue and/or creep, needs to be well understood and studied. Artificial neural networks are promising candidate tools for such studies. They are fast, flexible, efficient, and accurate tools to model highly non-linear multi-dimensional relationships and reduce the need for experimental work and time-consuming regression analysis. Therefore, separate neural network models for γ’ precipitate strengthened Ni based superalloys have been developed for predicting the γ’ precipitate size, thermal expansion coefficient, fatigue life, and hysteresis energy. The accumulated fatigue damage is then estimated as the product of hysteresis energy and fatigue life. The models for γ’ precipitate size, thermal expansion coefficient, and hysteresis energy converge very well and match experimental data accurately. The fatigue life proved to be the most challenging aspect to predict, and fracture mechanics proved to potentially be a necessary supplement to neural networks. The model for fatigue life converges well, but relatively large errors are observed partly due to the generally large statistical variations inherent to fatigue life. The deformation mechanism map for 1.23Cr-1.2Mo-0.26V rotor steel has been constructed using dislocation glide, grain boundary sliding, and power law creep rate equations. The constructed map is verified with experimental data points and neural network results. Although the existing set of experimental data points for neural network modeling is limited, there is an excellent match with boundaries constructed using rate equations which validates the deformation mechanism map.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22673号 / エネ博第405号 / 新制||エネ||77(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 平藤 哲司, 教授 馬渕 守, 教授 土井 俊哉 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

The properties of composite materials in which spherical inclusions are embedded in a matrix of some kind, have been studied for many decades and many analytical models have been developed which measure these properties. There has been a steady progression in the complexity of models over the years, providing greater insight into the nature of these materials and improving the accuracy in the measurement of their properties. Some of the properties with which this thesis is concerned are, the elastic, thermal and electrical properties of such composites. The size of the spherical inclusion which acts as the reinforcing phase, has a major effect on the overall properties of composite materials. Once an inclusion is embedded into a matrix, a third region of different properties between the inclusion and matrix is known to develop which is called the interphase. It is well known in the composite community that the smaller the inclusion is, the larger the interphase region which develops around it. Therefore, with the introduction of nanoparticles as the preferred reinforcing phase for some composites, the interphase has a major effect on its properties. It is the aim of this thesis to consider the role of the interphase on the properties of composites by modeling it as an inhomogeneous region. There is much scientific evidence to support the fact that the interphase has an inhomogeneous nature and many papers throughout the thesis are cited which highlight this. By modeling the inhomogeneous properties by arbitrary mathematical functions, results are obtained for the various properties in terms of these general functions. Some specific profiles for the inhomogeneous region are considered for each property in order to demonstrate and test the models against some established results.