Renato Chaves Souza

Aluminium alloys have been one of the leading materials used in aircraft structural components due to their mechanical performance, low density, and different manufacturing and inspection techniques. The mechanical, chemical, and electrical properties of metallic alloys relate to the microstructural arrangement, which depends on the alloying elements and manufacturing parameters. Therefore, this study aims to experimentally develop an Al-2wt.%Ni-0.5wt.%Co alloy as an alternative for aerospace applications, evaluating the main metallurgical aspects influencing mechanical strength. The samples were solidified in brass moulds with four different diameters, allowing four different cooling rates. A statistical analysis of the correlation between microstructural parameters and mechanical properties is proposed to optimise the conditions for obtaining the best mechanical strength. A microstructure with an essentially cellular matrix of the α-Al phase was observed. The tensile strength limit values (σ_U) of 117 MPa, specific elongation (δ) of 13.8%, and average microhardness of 33 HV were obtained. The Al-2wt.%Ni-0.5wt.%Co alloy exhibits impressive high cycle fatigue performance, with an endurance limit of 91 MPa at 10⁷ cycles, driven by the synergistic effects of Al₃Ni for strength and Al₉Co₂ for enhanced ductility and toughness.

The resonant-mass gravitational wave detector SCHENBERG is a spherical detector that will operate with a central frequency around 3200 Hz with a bandwidth of 100 to 200 Hz. It has a spherical mass that works as an antenna that weighs 1150 kg and is connected to the outer environment by a suspension system designed to attenuate local noise due to seismic as well as other sources of vibration. The sphere is suspended by its center of mass. When a gravitational wave passes by the detector, the antenna is expected to vibrate; this motion is monitored by six parametric microwave transducers whose output signals are digitally analyzed. In order to determine the detector performance better, it is necessary to obtain the vibration frequencies of the sphere with a better precision. To achieve such a goal the sphere with the holes to mount the transducers and the central hole from which the sphere is suspended is simulated in a finite element method program when the gravity is applied to the sphere and the deformation is kept. After that the vibration normal modes of the sphere are calculated and they are compared to the experimental results. After that the gravity is misaligned with the suspension of the sphere to simulate the effects of it, then the simulation is done again and no differences were found.

Interferometric gravitational wave detectors (IGWD) are very complex detectors, the need for locking the detector in a dark fringe condition besides the vibrations that affect the mirrors is very difficult challenge, creating the need for active suspension systems. These active systems make the system reach the desired sensitivity but make the calibration of such detectors much more difficult. To solve this problem a calibrator is proposed, a resonant mass gravitational wave detector could be used to detect the same signal in a narrower band and use the measured amplitude to calibrate the IGWD, as resonant mass gravitational wave detectors are easily calibrated. The main challenge in this design is the operational frequency of the calibrator, these massive detectors usually were built in frequencies close to 1 kHz but the frequency of the Gravitational Waves detected is around 100 Hz, then the design should adapt to this. This work aims to design and simulate a suspension of the mechanical antenna of such a calibrator. The suspension is modelled in finite elements method and a design of such a suspension is presented as its normal vibration modes.

This work shows the optimization process of a quadrupole mass at high-speed rotation using the finite element modeling (FEM). Such a mass should compose a gravitational signal generator device, which is intended to use in an experiment to measure the speed of gravity. The device must produce a tidal gravitational signal with a frequency of 3200 Hz. The gravitational wave detector Mario Schenberg is the first option as the detector of the signal. The previous steps of the project are briefly discussed, and the FEM simulations for the quadrupole mass are shown. An analysis of the mechanical stresses produced at high-speed rotation is presented. The most successful FEM simulation yields a favorable geometry for the inclusion of the magnetic suspension of the quadrupole mass. The results indicate the feasibility for the continuation of the project and subsequent construction of the real device.

ANVISA made changes to its regulations, setting new values for the fatigue tests, increasing the number of cycles that prostheses must endure without presenting failures. The standard used is ABNT NBR 7206-6:2013, in which all prostheses being commercialized must be tested in the new parameters. In this article, studies were conducted based on the requirement to revalidate the Co-26Cr-6Mo metallic alloy (ASTM F75). Microstructural characterizations (Optical and Scanning Electron Microscopies), and fatigue tests were carried out, with the aim of obtaining the mechanical behavior and features of the materials used in hip prostheses and comparing them with the standard. The grain size and inclusion contents were found to be controlled. Likewise, the prosthesis has withstand 10,000,000 cycles, and has not shown cracks, nor plastic deformations, enabling the biomedical use of this alloy according to the new regulations. Tensile test and liquid penetrant inspection were also carried out to take the parameters of the related physical properties. In the analysis with strain gauges, it was possible to detect the purely elastic deformation that occurred with the application of the load during fatigue tests, resulting in a slight variation of stress in the data acquisition system.

Cerâmicas apresentam excelente durabilidade química, resistência ao desgaste, biocompatibilidade, respeito ao meio ambiente e estética. Uma das propriedades mais importantes a ser considerada em implantes dentários totalmente cerâmicos é a fadiga cíclica, devido às solicitações mecânicas cíclicas as quais os implantes estão subjugados durante processos de mastigação, que pode induzir milhares de ciclos de tensão por dia em uma restauração, com isso exibir significativo crescimento subcrítico de trinca e assim poder diminuir a resistência de componentes cerâmicos, ao longo do tempo. Nesse trabalho, a previsão de vida em fadiga cíclica do compósito ZrO2-Al2O3 foi investigada. Mistura de pós contendo 80% de ZrO2 e 20% de Al2O3 foi compactada e sinterizada a 1600 °C. As amostras sinterizadas foram caracterizadas por difração de raios X e microscopia eletrônica de varredura. Dureza, tenacidade e resistência à fratura por flexão foram determinadas, e os resultados utilizados na determinação dos parâmetros de fadiga. Os testes de fadiga foram realizados em dispositivo de flexão em 4 pontos, sob freqüência de 25 Hz e razão de tensão de 0,1. Um aumento do nível de tensão levou à redução do tempo de vida sob fadiga. Baseado nos parâmetros determinados pelos ensaios mecânicos e de fadiga, e utilizando-se a estatística de Weibull, associada a modelos de determinação de crescimento subcrítico de falha, a velocidade de propagação de trincas nesse compósito é determinada e relacionada com os mecanismos de transformação martensítica e tensão residual entre as fases. Os componentes submetidos ao carregamento cíclico exibiram propagação subcrítica de trinca, em níveis de tensão significativamente menores do que o KIC. Apesar desta susceptibilidade ao crescimento subcrítico de trinca, cálculos com base nos parâmetros de fadiga e nas tensões aplicadas indicam que os componentes com estruturas do compósito ZrO2-Al2O3 podem exibir vidas maiores que 20 anos, se o diâmetro do componente estrutural é adequadamente projetado.