Internal friction has been known to be a cause of whirl instability in built-up rotors since the early 1900's. This internal damping tends to make the rotor whirl at shaft speeds greater than a critical speed, the whirl speed usually being equal to the critical speed. Over the years of research, though models have been developed to explain instabilities due to internal friction, its complex and unpredictable nature has made it extremely difficult to come up with a set of equations or rules that can be used to predict instabilities accurate enough for design. This thesis deals with suggesting improved methods for predicting the effects of shrink fits on threshold speeds of instability. A supporting objective is to quantify the internal friction in the system by measurements. Experimental methods of determining the internal damping with non-rotating tests are investigated, and the results are correlated with appropriate mathematical models for the system. Rotating experiments were carried out and suggest that subsynchronous vibration in rotating machinery can have numerous sources or causes. Also, subsynchronous whirl due to internal friction is not a highly repeatable phenomenon.

No description available.

Internal friction has been known to be a cause of whirl instability in built-up rotors since the early 1900's. This internal damping tends to make the rotor whirl at shaft speeds greater than a critical speed, the whirl speed usually being equal to the critical speed. Over the years of research, though models have been developed to explain instabilities due to internal friction, its complex and unpredictable nature has made it extremely difficult to come up with a set of equations or rules that can be used to predict instabilities accurate enough for design. This thesis deals with suggesting improved methods for predicting the effects of shrink fits on threshold speeds of instability. A supporting objective is to quantify the internal friction in the system by measurements. Experimental methods of determining the internal damping with non-rotating tests are investigated, and the results are correlated with appropriate mathematical models for the system. Rotating experiments were carried out and suggest that subsynchronous vibration in rotating machinery can have numerous sources or causes. Also, subsynchronous whirl due to internal friction is not a highly repeatable phenomenon.

No description available.

Thesis (Ph. D.)--Lehigh University, 2005. / Includes vita. Includes bibliographical references (leaves 221-224).

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Esta dissertação mostra a análise da interação de intersticiais pesados como oxigênio e nitrogênio em amostras policristalinas de nióbio e monocristalinas de nióbio e tânalo. Os dados experimentais foram obtidos através de medidas de atrito interno e freqüência de oscilação do pêndulo em função da temperatura, utilizando-se um pêndulo de torção invertido tipo Kê. Os resultados mostram estruturas de relaxação atribuídas à reorientação induzida por tensão de átomos intersticiais em torno de átomos da matriz metálica. Estas estruturas forma analisadas através de dois métodos: subtrações sucessivas e tempo de relaxação. A partir das medidas de atrito interno foram identificados os processos de relaxações Nb-O, Nb-N e Ta-O. Esses mesmos processos de relaxação foram confirmados por meio das medidas de freqüência de oscilação do pendulo usando um método proposto nesta dissertação, o qual relaciona o quadrado dessa freqüência medida e o inverso da temperatura. / This dissertation shows the analysis of heavy interstitials interaction, such as oxygen and nitrogen, in a policrystalline niobium sample and single crystal samples of niobium and tantalum. The experimental data were obtained by internal friction and oscillation frequency measurements as a function of temperature, using a Kê-type inverted torsion pendulum. The results show relaxation structures attributed to stress induced ordering of interstitial atoms around the mettalic matrix atoms. These structures were analysed by two methods: sucessive subtraction and relaxation time. From internal friction measurements, Nb-O, Nb-N and Ta-O relaxation processes were identified. These same relaxation processes were confirmed by oscillation frequency measurements, using a method proposed here, which relates squared frequency with inverse of temperature.

Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-06-22Bitstream added on 2014-06-13T18:41:33Z : No. of bitstreams: 1 souza_ac_dr_bauru.pdf: 4889412 bytes, checksum: b1b5556d4915022278e65a9a1b120315 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O desenvolvimento científico e tecnológico na área de novos materiais contribui para diversas aplicações do nióbio e suas ligas nas indústrias aeroespacial, aeronáutica, automobilística, naval, usinas nucleares, etc. O Brasil lidera o cenário mundial na oferta de nióbio, atingindo uma participação de 92,4% da produção mundial, justificando, assim, o interesse no estudo desse metal. Este trabalho tem dois objetivos: o primeiro é garantir a introdução do nitrogênio em solução sólida intersticial na matriz metálica Nb sob pressão parcial na ordem de 'X POT.-4' Torr e temperatura na ordem de 173 K, com diferentes tempos de dopagens; e, o segundo é caracterizar a liga Nb-1,0%pZr em termos de suas propriedades anelásticas, com diferentes concentrações de nitrogênio em solução sólida, tendo como referência padrão o metal nióbio. Pelo emprego do método de Espectroscopia Mecânica com base na técnia de atrito interno, que fornece informações sobre as interações Gás-Metal e outras técnicas auxiliares, como Difração de Raios X e Microscopia Eletrônica, foi possível mostrar a introdução de nitrogênio em solução em nióbio sob baixas condições de temperatura e pressão. Além disso, foi efetuada a caracterização anelástica da liga Nb-1,0%pZr em função do aumento da concentração de nitrogênio em solução sólida. / The scientific and technological development in the area of new materials has contributed to severa applications of niobium and its alloys to the aerospatial, aeronautical, automotive and naval industries, nuclear power stations, among others. Brazil is a worldwide leader in the supply of supply of niobium, reaching 92.4% share in the world production, thus justifying the interest in the study of that metal. In the present paper, there are two objectives: the first is to guarantee the introduction of nitrogen in an interstitial solid solution of niobium under partial pressure of 10-4 Torr and at a temperature of aound 1373 K, with different doping times. The second one is to characterize a Nb-1,0%Zr alloy according to its anelastic relaxation properties, with different nitrogen concentration in a solid solution, having niobium as a reference. By using Mechanical Spectroscopy, and bases on the internal friction technique - which provides information on Metal-Gas interactions and others auxiliary techniques, such as X-Ray Diffraction and Scanning Electron Microscopy - it was possible to show the introduction of nitrogen in a solid solution in niobium at a low temperature and pressure conditions. In addition, the anelastic characterization of the Nb-1,0%Zr alloy was performed in therms of the nitrogen concentration in a solid solution, showing complex anelastic relaxation structures, which were decomposed into their component relaxation processes due to stress-induced ordering of oxygen and nitrogen atoms around niobium and zirconium atoms.