Sinésio Domingues Franco

Effect of coarse hard particles on high-temperature sliding abrasion of new metal matrix composites

Abstract Iron-base and nickel-base powders as well as several powders of different hard particles were tested by microscratching and microindentation up to 900°C. Those most suited were mixed and hot compacted to give new metal matrix composites(MMC). Up to 50v/o of coarse WC W 2 C particles were dispersed in a high speed steel matrix or in a NiCr20AlSi matrix. The wear rate in three-body sliding abrasion by flint under an argon atmosphere decreases with temperature to about 700 °C due to the formation of a self-protecting flint layer and a change in the hardness ratio of the microstructural constituents and the abrasive. MMC with 30 v/o of hard particles in the steel matrix are suitable for service up to 650 °C and those with a nickel matrix up to 750°C.

Measurement of Elastic Modulus and Vickers Hardness of Surround Bone Implant Using Dynamic Microindentation - Parameters Definition

The clinical performance of dental implants is strongly defined by biomechanical principles. The aim of this study was to quantify the Vickers hardness (VHN) and elastic modulus (E) surround bone to dental implant in different regions, and to discuss the parameters of dynamic microindantion test. Ten cylindrical implants with morse taper interface (Titamax CM, Neodent; 3.5 mm diameter and 7 mm a height) were inserted in rabbit tibia. The mechanical properties were analyzed using microhardness dynamic indenter with 200 mN load and 15 s penetration time. Seven continuous indentations were made distancing 0.08 mm between each other perpendicularly to the implant-bone interface towards the external surface, at the limit of low (Lp) and high implant profile (Hp). Data were analyzed by Students t-test (a=0.05) to compare the E and VHN values obtained on both regions. Mean and standard deviation of E (GPa) were: Lp. 16.6 ± 1.7, Hp. 17.0 ± 2.5 and VHN (N/mm2): Lp. 12.6 ± 40.8, Hp. 120.1 ± 43.7. No statistical difference was found between bone mechanical properties of high and low profile of the surround bone to implant, demonstrating that the bone characterization homogeneously is pertinent. Dynamic microindantion method proved to be highly useful in the characterization of the individual peri-implant bone tissue.

Rotation Control Performance of a Friction Welding Repair System Using a Neural Network

This paper presents the rotation control performance of a friction welding repair system. The control parameters are adjusted by a neural network (NN). This control is capable of supporting the wide variations in torque that occur in this type of repair process. The rotation system consists of a hydraulic motor whose speed is controlled by a proportional directional valve. For this, a NN was developed with various structures composed of one, three, four and six neurons having activation functions of the following type: linear, quadratic, sigmoid and step. A theoretical plant was developed that simulates the behavior of the rotation system of a friction drive unity. This plant was used in the adjustment of the weights of the NNs by means of a genetic algorithm (GA). This plant was also used to evaluate the performance of NNs in the rotation control after their adjustment. The choice of the most suitable NN was made taking into consideration not only their control performance, but also the number of parameters to be adjusted, because the higher the number of these parameters, the greater the difficulty faced by the GA in the adjustment. Having selected the NN, its performance was compared to that of a PID controller. It was observed that the NN that reached the best performance was of one neuron with a linear activation function and its performance was higher than that of the PID controller.

Evaluation of Abrasive Wear of Polymeric Materials Using Single-Pass Pendulum Scratching

Scratching abrasion due to rubbing against the sediment layer is an important degradation mechanism of flexible cable in deep water oil and natural gas exploitation. The present study was initiated to gain relevant data on the wear behaviour of some commercial materials used to externally protect these cables. So, Comparison tests were carried out using the single-point scratching technique, which consists of a sharp point mounted at the extremity of a pendulum. The energy dissipated during the scratching is used to evaluate the relative scratch resistance. The results showed, that the contact geometry strongly affects the specific scratching energy. Using SEM imaging, it was found, that these changes were related to the operating wear mechanisms. The observed wear mechanisms are also compared with those observed on some cables in deep water operations.© 2002 ASME

Caracterização in Situ de Propriedades Mecânicas de Materiais Resistentes ao Desgaste Abrasivo Usando o Método da Indentação

O desempenho de materiais polifasicos em sistemas tribologicos envolvendo desgaste abrasivo e funcao de uma serie de fatores, a saber: condicoes de operacao, caracteristicas de projeto e das propriedades do abrasivo e dos microconstituintes do material utilizado. Neste trabalho sao apresentados resultados de ensaios de indentacao em diferentes microconstituintes e particulas duras, atraves dos quais as propriedades mais importantes para o fenomeno abrasivo sao determinadas in situ. Dentre essas destacam-se a dureza H, a tenacidade a fratura KIC, o modulo de elasticidade E, a relacao trabalho plastico / trabalho elastico Wp / We e a relacao de durezas entre o microconstituinte e o agente abrasivo. Em muitas situacoes praticas esses sistemas encontram-se em temperaturas elevadas. Assim, neste trabalho, e tambem apresentada a influencia da temperatura sobre algumas dessas propriedades. Os resultados obtidos mostram a grande potencialidade dessa tecnica no processo de selecao e desenvolvimento de materiais resistentes ao desgaste.