Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Michaels, Jennifer; Committee Member: Habetler, Thomas; Committee Member: Jacobs, Laurence; Committee Member: Michaels, Thomas; Committee Member: Vachtsevanos, George.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering, Johannesburg, 1998 / This research examines fatigue in WC-Co, both under compressive and tensile loading conditions. A new macro-mechanism for compression fatigue crack propagation is put forward, which contradicts existing data on compression fatigue cracks as being self-limiting. Evidence of this macro-mechanism is presented in the form of final crack length versus number of cycles data, and micrographs of the compression fatigue cracks. A finite element study of the stress distribution in the WC-Co microstructure during compression fatigue loading has been developed. This model verifies possible methods of compression fatigue crack initiation. Examination of tensile fatigue and fast: fracture surfaces is used to show that fatigue is a separate mechanism to fast fracture in WC-Co. Characteristic features of the fatigue fracture surface are presented. A possible fatigue crack propagation mechanism is also presented. Finally, fatigue crack growth rate data in the form of the Paris equation is presented for WC-Co grades T6 and G6. / MT2017

In spite of many multiaxial fatigue life prediction methods proposed over decades of research, no universally accepted approach yet exists. A multiaxial fatigue damage model developed for approximately proportional random amplitude loading is proposed in this study. A normal strain based analysis incorporating the multiaxial state of stress is conducted along a critical orientation assuming a constant strain ratio. The dominant deformation direction is chosen to be the critical orientation which is selected with the help of a principal strain histogram generated from the given multiaxial loading history. The uniaxial cyclic stress-strain curve is modified for the biaxial state of stress present along the critical orientation for the plane stress conditions. Modified versions of Morrow's and of Smith, Watson, and Topper's (SWT) mean-stress models are used to incorporate mean stresses. A maximum shear strain based analysis is, in addition, conducted to check for the shear dominant fatigue crack growth possibility along the critical direction. The most damaging maximum shear strain is chosen after analyzing the in-plane and the two out-of-plane shear strains. The minimum of the two life values obtained from SWT model and the shear strain model is compared with the life estimated by the proposed model with the modified Morrow's mean stress model. The former is essentially the life predicted by Socie. The results of the proposed model, as reduced to the uniaxial case, are also compared with the experimental data obtained by conducting one-channel random amplitude loading history experiments. / Master of Science

The development of structural monitoring systems is a critical research area because of the age and sustainment costs associated with many aircraft in use today. Specifically, integrated structural health monitoring (SHM) systems are advantageous because they allow for automated, near real-time assessment of the state of the structure, where the automation improves both the accuracy of the measurements and allows for more frequent system interrogation than possible with traditional nondestructive evaluation methods. Ultrasonic techniques are particularly well-suited for SHM systems because of their potential to detect and track damage well before structural failure using in situ sensors. The research problem considered in this thesis is detection and tracking of fatigue cracks emanating from fastener holes in metallic structural components. The sensing method utilizes attached ultrasonic transducers, and tracking of damage is achieved by employing a state estimation framework that incorporates a well-known empirical model for crack growth and a measurement model relating the ultrasonic response to crack size. The state estimation process is preceded by an automated crack detection algorithm, and can be followed by a prediction of remaining life assuming future usage. The state estimation framework provides a better estimate of crack size than either the ultrasonic measurement model or crack growth model alone. Although the example application is monitoring of fastener holes, the general approach is applicable to a variety of SHM problems.

Devido à resistência dos fabricantes de automóveis quanto à utilização de engrenagens de FNA estudos tem sido feitos para averiguar o desempenho deste material em engrenagens. Dentro deste contexto esta dissertação tem como objetivos principais o desenvolvimento e construção de uma máquina de ensaios de fadiga de contato em engrenagens e a comparação quanto à resistência ao desgaste de engrenagens cilíndricas de dentes retos fabricadas em aço liga 8620 (cementado e temperado) e em ferro fundido nodular austêmperado (FNA). Estas engrenagens foram fornecidas em dois estados de acabamento superficial (shaving ou por fresamento). O equipamento desenvolvido funciona com o princípio de recirculação de potência e é comumente chamado de FZG. Os experimentos de desgaste têm sido feitos com dois estágios de torque: 135 N.m (running-in) e 302 N.m (steady-state) e as engrenagens são de perfil modificado. Após a realização dos ensaios, foi possível verificar que: (1) a área danificada dos flancos, devido ao fenômeno de pitting, das engrenagens de FNA foi maior do que das de aço AISI 8620; (2) a comparação entre os parâmetros de rugosidade nos estágio de fornecimento e após cada estágio do experimento mostra que as engrenagens com acabamento por shaving apresentam uma melhor distribuição da carga e um menor desgaste, (3) o regime de lubrificação na região do diâmetro primitivo durante os ensaios foi o limite (ou limítrofe) para ambos os processos de fabricação, porém o parâmetro de espessura de filme (λ) é maior para engrenagens fabricadas por shaving, fazendo com que a espessura do filme lubrificante seja maior, (4) o efeito da redução da área resistente aos esforços de contato, devido à presença dos nódulos de grafita, na resistência a fadiga foi evidenciado, porém o acabamento superficial mostrou-se mais relevante do que a distribuição e tamanho dos nódulos. / Due to the resistance of automotive manufactures on apply ADI gear studies have been made to verify the performance of this material. Inside this context this work has a main objective the construction of contact fatigue test machine in gears and the comparison, related to the wear resistance, between spur-gears made of carburized and quenched AISI 8620 low steel and austempered ductile iron (ADI). These gears were supplied in two states of finish surface (by shaving or by machining). The developed equipment functions with the principle of the power recirculation and commonly called FZG. The wear experiments were performed in two stages of torque: 135 N.m (running-in) and 302 N.m (steady-state) and the gears have modified profile. After the accomplishment of the experiments, was possible verify that: (1) The damaged area of flanks, due to the phenomenon of pitting, at ADI gears was bigger than AISI 8620 low-alloy steel gears. (2) The comparisons between the roughness parameter in the supply state and after each period of the experiment shows that gears with surface finish by shaving have better load distribution and minor wear. (3) Lubricant regime at pitch diameter was the boundary for both manufacture process, but the film thickness parameter λ is higher for shaved gears, making the lubricant film thickness has major value, (4) The reduction effect the resistive area of contact due the presence of the graphite nodules in the contact fatigue resistance was evidenced, however surface finishing was more relevant than the distribution and size nodules.

Devido à resistência dos fabricantes de automóveis quanto à utilização de engrenagens de FNA estudos tem sido feitos para averiguar o desempenho deste material em engrenagens. Dentro deste contexto esta dissertação tem como objetivos principais o desenvolvimento e construção de uma máquina de ensaios de fadiga de contato em engrenagens e a comparação quanto à resistência ao desgaste de engrenagens cilíndricas de dentes retos fabricadas em aço liga 8620 (cementado e temperado) e em ferro fundido nodular austêmperado (FNA). Estas engrenagens foram fornecidas em dois estados de acabamento superficial (shaving ou por fresamento). O equipamento desenvolvido funciona com o princípio de recirculação de potência e é comumente chamado de FZG. Os experimentos de desgaste têm sido feitos com dois estágios de torque: 135 N.m (running-in) e 302 N.m (steady-state) e as engrenagens são de perfil modificado. Após a realização dos ensaios, foi possível verificar que: (1) a área danificada dos flancos, devido ao fenômeno de pitting, das engrenagens de FNA foi maior do que das de aço AISI 8620; (2) a comparação entre os parâmetros de rugosidade nos estágio de fornecimento e após cada estágio do experimento mostra que as engrenagens com acabamento por shaving apresentam uma melhor distribuição da carga e um menor desgaste, (3) o regime de lubrificação na região do diâmetro primitivo durante os ensaios foi o limite (ou limítrofe) para ambos os processos de fabricação, porém o parâmetro de espessura de filme (λ) é maior para engrenagens fabricadas por shaving, fazendo com que a espessura do filme lubrificante seja maior, (4) o efeito da redução da área resistente aos esforços de contato, devido à presença dos nódulos de grafita, na resistência a fadiga foi evidenciado, porém o acabamento superficial mostrou-se mais relevante do que a distribuição e tamanho dos nódulos. / Due to the resistance of automotive manufactures on apply ADI gear studies have been made to verify the performance of this material. Inside this context this work has a main objective the construction of contact fatigue test machine in gears and the comparison, related to the wear resistance, between spur-gears made of carburized and quenched AISI 8620 low steel and austempered ductile iron (ADI). These gears were supplied in two states of finish surface (by shaving or by machining). The developed equipment functions with the principle of the power recirculation and commonly called FZG. The wear experiments were performed in two stages of torque: 135 N.m (running-in) and 302 N.m (steady-state) and the gears have modified profile. After the accomplishment of the experiments, was possible verify that: (1) The damaged area of flanks, due to the phenomenon of pitting, at ADI gears was bigger than AISI 8620 low-alloy steel gears. (2) The comparisons between the roughness parameter in the supply state and after each period of the experiment shows that gears with surface finish by shaving have better load distribution and minor wear. (3) Lubricant regime at pitch diameter was the boundary for both manufacture process, but the film thickness parameter λ is higher for shaved gears, making the lubricant film thickness has major value, (4) The reduction effect the resistive area of contact due the presence of the graphite nodules in the contact fatigue resistance was evidenced, however surface finishing was more relevant than the distribution and size nodules.

Indiana University-Purdue University Indianapolis (IUPUI) / Belt-drives are used in many applications such as industrial machines, washing ‎machines, and accessory drives for automobiles and other vehicles. Multibody dynamics/finite ‎element numerical models have become an effective way to predict the dynamic response of ‎belt-drives. In this thesis, a high fidelity numerical model was built using a multibody ‎dynamics/finite element code to simulate a belt-drive. The belt-drive transmits power from a ‎turbine of a Rankin cycle (that uses the exhaust waste heat of the internal combustion engine as ‎heat source) to the crank shaft of the engine. The code uses a time-accurate explicit numerical ‎integration technique to solve the multibody dynamics differential equations. The belt was ‎modeled using three-node beam elements to account for the belt axial and bending ‎stiffness/damping, while the pulleys, shafts and tensioner body were modeled as rigid bodies. ‎The penalty technique was used to model normal contact between the belt and the pulleys. An ‎asperity-based friction model was used to approximate Coulomb friction between the belt and ‎the pulleys. The dynamic response predicted using the model was validated by comparing it to ‎experimental results supplied by Cummins Inc. A parameter sensitivity study was performed to ‎evaluate the change in response due to change in various belt-drive parameters. A fatigue ‎model was developed to predict the belt fatigue life using output from the explicit finite ‎element code including normal and tangential forces between the belt and the pulleys and belt ‎tension. The belt fatigue life was evaluated for alternative belt-drive configurations in order to ‎find the configuration with the longest life.‎