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Dissertação para a obtenção de Grau de Doutor, em Engenharia Mecânica, Universidade de Coimbra, 2006
Dissertação de Mestrado em Engenharia Mecânica apresentada ao Instituto Superior Técnico da Universidade Técnica de Lisboa.
Tese de Doutoramento em Engenharia Mecânica –Especialidade de Construções Mecânicas apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
Abstract. Fatigue strength of welded joints is significantly influenced by the presence of residual stresses due to welding, of flaws and notch sharpness at the weld toe. Compressive residual stresses enhance the fatigue behavior of the structure, while tensile ones impair it. TIG dressing at the weld toe is frequently used to remove flaws to lessen the notch sharpness at the weld toe and to introduce compressive residual stresses. This paper presents a 2D finite element model to predict the residual stresses generated in a TIG dressing at the weld toe of a T joint. The welded T joints are made in St 52-3 steel and are obtained by covered electrode process. The analysis was developed with the Marc finite element code. The modeled stress field is compared with some measurements of residual stresses obtained using X-ray diffraction and the strain gauges technique.
Resumo. As técnicas de refusão do pé do cordão de soldadura por TIG e plasma são frequentemente usadas para aumentar a resistência e a fiabilidade de peças solicitadas à fadiga. Neste trabalho apresentam-se resultados de um estudo de investigação sobre a utilização destas técnicas na recuperação da resistência à fadiga de juntas soldadas em T solicitadas por flexão em três pontos. As juntas são fabricadas em aço St 52 – 3 e obtidas por soldadura com eléctrodo revestido. São estudadas quatro situações: juntas não tratadas, juntas tratadas por refusão TIG, juntas pré-fissuradas e posteriormente tratadas por refusão TIG e juntas pré-fissuradas e posteriormente tratadas por refusão plasma. A eficiência dos tratamentos de refusão TIG e plasma na reabilitação da resistência à fadiga é analisada e discutida com base nos resultados de fadiga e em elementos complementares determinados durante a investigação, tais como: o perfil do pé dos cordões, a microestrutura e os perfis de dureza nas regiões soldada e afectada térmicamente e dos defeitos detectados no cordão. A eficiência obtida pelo processo de refusão por plasma é bastante satisfatória e muito superior à da refusão por TIG.
This paper presents an approach for automatic anomaly detection through vibration analysis based on machine learning algorithms.The study focuses on induction motors in a predictive maintenance context, but can be applied to other domains. Vibration analysis is an important diagnostic tool in industrial data analysis to predict anomaliescaused by equipment defects or in its use, allowing to increase its lifetime.It is not a new technique and is widely used in the industry, however withthe Industry 4.0 paradigm and the need to digitize any process, it gainsrelevance to automatic fault detection. The Isolation Forest algorithm isimplemented to detect anomalies in vibration datasets measured in anexperimental apparatus composed of an induction motor and a coupling
system with shaft alignment/misalignment capabilities. The results showthat it is possible to detect anomalies automatically with a high level ofprecision and accuracy.
Este estudo tem como objetivo dar resposta ao desafio que nos foi lançado por uma empresa industrial de produção de pasta de papel – os dentes do descascador do parque de madeiras da sua unidade de industrial apresentavam um desgaste excessivo, face ao expectável, obrigando à sua substituição mensal, implicando custos excessivos, associados ao equipamento, material, recursos humanos e à perca de produção.
O material utilizado, Hardox 500, tem caraterísticas consideradas adequadas para a utilização requerida, no entanto, concluiu-se neste estudo, que o processo de fabrico das lâminas degradava as suas propriedades mecânicas, conduzindo ao seu rápido desgaste quando colocadas em serviço. A solução proposta, consiste na alteração da tecnologia de corte dos dentes e encontra-se em fase de implementação.
In this paper is presented a 2D finite element model to predict the residual stresses generated by Tungsten Inert Gas (TIG) dressing at the weld toe of a T-joint. The welded T-joints, made of S355AR steel, are obtained by covered electrode process and improved with TIG dressing. The analysis was developed with the MSC.Marc finite element code. The estimated stress field is validated with experimental stress results obtained using X-ray diffraction.
Over the estimated residual stress field is simulated the growth of fatigue cracks. The simulation is performed with the virtual crack closure technique, implemented in the MSC.Marc software. The obtained results are compared with the integration solutions of the Paris-Erdogan law, without influence of residual stresses, where the stress intensity factor is obtained using the Mk factor proposed by Bowness and Lee, included in BS 7910 standard. The numerical predictions are also compared with experimental results.
Current research uses a finite element analysis to characterize the effect of the materials mechanical and tribological properties on the interaction between the biological tissues of a transfemoral amputation and the combined prosthesis. Considering that both friction and mechanical properties influence the stress distribution between different interfaces, these were analyzed on the contacts of the prosthesis and the liner, the liner and the soft tissues and, finally, the soft tissues and the cortical bone. This is of significant importance, as it has been acknowledged that the shear stress distribution at these interfaces significantly impacts the patients’ comfort. These shear stresses have also been reported as one of the leading causes of pressure ulcers in osteotomized patients. Finally, this research discusses the influence of the soft tissues and the liner constitutive law in the stress field generated at the biological tissues. In particular, for the liner, the results using a linear elastic model are compared with those using the Mooney-Rivlin hyperelastic model. The results using a linear elastic model are compared with the Neo-Hookean and Ogden models’ results for the soft tissues.
his experimental study focuses on the comparison between two different sensors for vibration signals: a magnetoresistive sensor and an accelerometer as a calibrated reference. The vibrations are collected from a variable speed inductor motor setup, coupled to a ball bearing load with adjustable misalignments. To evaluate the performance of the magnetoresistive sensor against the accelerometer, several vibration measurements are performed in three different axes: axial, horizontal and vertical. Vibration velocity measurements from both sensors were collected and analyzed based on spectral decomposition of the signals. The high cross-correlation coefficient between spectrum vibration signatures in all experimental measurements shows good agreement between the proposed magnetoresistive sensor and the reference accelerometer performances. The results demonstrate the potential of this type of innovative and non-contact approach to vibration data collection and a prospective use of magnetoresistive sensors for predictive maintenance models for inductive motors in Industry 4.0 applications.
Within a pulp industry production process, a drop in the performance of a wood log rotary debarker
was identified. Such loss of performance was due to the occurrence of excessive wear of the device’s
cutting blades, requiring their regular and premature replacement. The material used to manufacture
the cutting blades, Hardox 500, has characteristics considered adequate for the required use. However,
it was concluded that the blade manufacturing process degraded its mechanical properties, leading
to its premature wear when placed in service. The present study intends to propose, characterize, and
validate an alternative cutting process to manufacture the debarker’s cutting blades. Abrasive waterjet
cutting technology was proposed to produce the cutting blades. The suitability of this manufacturing
process is discussed considering the specified geometry and the material characteristics of the resulting
cutting blades.
