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Made available in DSpace on 2014-10-09T12:35:29Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:35Z (GMT). No. of bitstreams: 0 / Muitas especificações de engenharia, procedimentos de fabricação, inspeção e controle de qualidade já começam a exigir que a análise da tensão residual de determinado componente seja avaliada. Isto está se tornando tão corriqueiro quanto às exigências referentes às propriedades mecânicas. No país existem poucos laboratórios de pesquisa qualificados para execução destes ensaios e também é constatada uma preocupante falta de mão de obra qualificada. A relevância do estudo e pesquisas em tensões residuais, ressalta para o desenvolvimento científico, tecnológico e inovação nos processos de fabricação de componentes para a indústria. Novos ferramentais e instrumentações para a investigação de microestrutura dos materiais, disponíveis em laboratórios de pesquisas tanto em instituições governamentais como em instalações privativas necessitam de pesquisadores habilitados o que está associado à formação de pessoal especializado dedicado a medidas de tensões residuais, ao desenvolvimento de procedimentos experimentais e técnicas de preparação de amostras que envolvam extensometria. A tensão residual, em componentes metálicos e ligas, tem origem em decorrência de processos de fabricação (fundição, tratamento térmico, usinagem, conformação mecânica) pelo qual se obtém a conformação estrutural do componente desejado. Estudar a formação e arranjo dos campos de tensões residuais podem permitir, entre outros ganhos, a elaboração de simulações por modelagem matemática mais refinada. Assim pode-se inferir, com maior detalhamento o comportamento destes componentes somando ganhos na resiliência à fadiga, sobrevida, segurança e redução de custo operacional de equipamentos e máquinas. O uso de extensometria na investigação de tensões residuais em rodas na industria automotiva contribuirá para a formação de uma maior base de dados que permitirá obter softwares de simulação FEM, com melhor índice da relação com modelagem matemática com o componente físico real. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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D. Phil. / Conventional internal wind tunnel balances are designed and constructed to accommodate foil strain gauges which measure the deformation (strain) of the material. Foil strain gauge balances are known to be affected by electromagnetic interference and temperature. These balances are expensive and their manufacture is time consuming. With an increasing demand for higher accuracy, stiffness, increased resolution and temperature compensation, current balance designs are becoming inadequate. To overcome identified balance deficiencies a research programme in the application of optical Bragg gratings to wind tunnel balances was initiated. In this programme a new concept of using optical fibre Bragg grating sensors, with the advantage of using mechanical amplification to increase sensitivity, and the implementation of temperature compensation techniques was demonstrated on a simulated two component balance.

This study investigates the use of vibration and strain measurements on machine tools in order to identify the propagating wear of the selected tools. Two case studies are considered, one of which was conducted in the plant of a South African piston manufacturer. The purpose of the ftrst case study was to investigate the feasibility of vibration monitoring to identify tool wear, before attempting to implement a monitoring system in the manufacturing plant. During this case study, data from a turning process was recorded using two accelerometers coupled to a PL202 real time FFT analyser. Features indicative of tool wear were extracted from the sensor signals, and then used as inputs to a Self-Organising Map (SOM). The SOM is a type of neural network based on unsupervised learning, and can be used to classify the input data into regions corresponding to new and worn tools. It was also shown that the SOM can also be used very efficiently with discrete variables. One of the main contributions of the second case study was the fact that a unique type of tool was investigated, namely a synthetic diamond tool specifically used for the manufacturing of aluminium pistons. Data from the manufacturing of pistons was recorded with two piezoelectric strain sensors and a single accelerometer, all coupled to a DSPT Siglab analyser. A large number of features indicative of tool wear were automatically extracted from different parts of the original signals. These included features from time and frequency domain data, time series model coefficients as features and features extracted from wavelet packet analysis. A correlation coefficient approach was used to auto-lJUltically select the best features indicative of the progressive wear of the diamond tools. The SOM was once again used to identify the tool state. Some of the advantages of using different map sizes on the SOM were also demonstrated. A near 100% correct classification of the tool wear data was obtained by training the SOM with two independent data sets, and testing it with a third independent data set. It was also shown that the monitoring strategy proposed in the second case study can be fully automated and can be implemented on-line if the manufacturer wishes to. Some of the contributions of this study are the use of the SOM for tool wear classification, and conclusions regarding the wear modes of the synthetic diamond tools. / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

Composites are now being incorporated into aircraft designs because of their high strength to weight ratio compared to traditional metal materials. Due to the complexity of the material, composite parts are presently being over designed to satisfy static and fatigue requirements. A greater understanding of composite fatigue behavior will allow for even greater weight savings leading to increased fuel economy. A critical part of an aircraft that is subjected to fatigue bending loads are its wings. The forces acting on the wings include its lift distribution, powerplant, and fuel which can be carried in the wing body. When in flight these forces repeatedly cause cyclic displacements which could ultimately lead to failure. It is important to design the wing spars which carry the bending loads, to be fatigue resistant so that damage or expensive inspections could be avoided. Wing models were be made from composite materials with a NACA 0016 airfoil shape, chord length of 9.25”, and a span of 15.25”. The C – channel spars were located at 22% and 72% of the chord. Strain gages on the wing model were used to measure strain at different locations. Static test were conducted on the specimens in order to validate a finite element analysis(FEA) model to be used for simulations. Overall, the strain measurements on the leading edge from two of the wings matched the model within 9% of the simulation results. Additional spar designs were then analyzed to determine the optimal one for static and fatigue bending loads. The wings were fatigue tested under displacement control at a test frequency. A model 8801 servo-hydraulic Instron machine and Wave Matrix software was used to fatigue the wings. After 100,000 cycles the test would be deemed a success and concluded.

Two high temperature fiber optic based strain sensors have been developed for use in a coal combustor environment. An intensity based sensor uses losses created by longitudinal misalignment as a sensing mechanism and has a maximum operating temperature of 700°C. An interferometric based sensor makes use of a Fabry-Perot cavity created by aligning two fibers in a splice tube with a small gap in between. The Fabry-Perot based sensors' maximum operating temperature is 950°C. Attachment methods and sensor design are discussed as well as the presentation of results from <i>in situ</i> testing. / Master of Science

Although bond-normal stresses have been shown to be responsible for the failure of most laboratory adhesive joint geometries, the measurement of these stresses has been accomplished only through the use of very sophisticated optical techniques. In order to develop a more versatile measurement technique, poly(vinylidene fluoride) film was used to develop piezoelectric stress sensors. The sensitivities of the film to normal stresses in the three principal material directions of the orthotropic film were accurately measured using a charge amplifier and a storage oscilloscope. These measured sensitivities comprised the calibration constants of the film. In order to reduce the detrimental effect on bond strength caused by embedding the low surface energy film into adhesive bondlines, surface treatment methods were investigated using contact angle studies, XPS analysis and 1800 peel and tapered double cantilever beam adhesion specimens. An acid etch using a mixture of acetic, phosphoric and nitric acids was found to greatly improve the bond strengths to an epoxy adhesive without reducing the piezoelectric activity of the film. The bond-normal stresses in both the elastomeric butt joint and the single lap shear joint were measured using the developed stress sensors. Comparison of the measured stresses with calculated values obtained from closed-form analytical solutions and finite element analysis for the stresses was excellent. The piezoelectric sensors do have several important limitations. The piezoelectric activity of the film is lost at temperatures above 100°C (210°F). Also, the sensors are only sensitive to dynamic loads. Nonetheless, the sensors provide an accurate means of measuring peel stresses in many adhesive joints of practical interest. / Ph. D.