Luciana Sgarbi Rossino

Detailed design of fretting fatigue apparatus and tests on 7050-T7451 Al alloy

Abstract The aim of this work was to design a fretting apparatus and to carry out a series of tests to evaluate the effect of a mean bulk load on the fretting fatigue life of an aeronautical Al 7050-T7451 alloy. The device was mounted on a servohydralic test system. The configuration chosen to carry out the experimental program was of cylindrical pads pressed against flat tensile specimens. A model was proposed to compute the apparatus equivalent stiffness, which controls the magnitude of the fretting load. The tests were designed so that all relevant parameters, apart from the mean bulk load (always applied before the contact loads), were kept constant. This essentially means that the equivalent shear stress amplitude computed at a material point, as defined in many multiaxial stress based high cycle fatigue models, was identical from test to test although the registered fretting lives varied greatly. These results pose a great challenge to a number of fretting lifing methodologies available in the literature.

Desenvolvimento de dispositivo e estudo do comportamento ao microdesgaste abrasivo do aço AISI 420 temperado e revenido

O ensaio de micro desgaste abrasivo tem sido objeto de uma quantidade significativa de pesquisas nos ultimos anos, quando o seu potencial para avaliar o comportamento de recobrimentos finos se tornou relevante. O objetivo deste trabalho e a construcao de um dispositivo para a realizacao de ensaios de micro desgaste abrasivo por esfera fixa. O contato abrasivo e realizado por uma esfera de aco AISI 52100, a qual e presa num eixo que gira com grande precisao, com ajuda de um motor, em relacao a uma amostra plana que se mantera estacionaria. A carga normal de ensaio e aplicada atraves de ajustes de peso no suporte pivotado do corpo de prova, a qual pode ser variada a cada ensaio realizado. Este dispositivo foi utilizado para a determinacao da resistencia ao desgaste abrasivo e da eficacia de tratamentos de superficie utilizados em pecas que sofrem este tipo de solicitacao em servico, alem de utiliza-lo para estudar novos produtos desenvolvidos para o aumento de resistencia ao desgaste de superficies. Foi avaliada a resistencia ao microdesgaste abrasivo de aco AISI 420 temperado e revenido. Observou-se que o aumento da dureza do material tratado aumentou a resistencia ao desgaste abrasivo quando comparado com o material sem tratamento termico.

Surface Contact Fatigue Failure of a Case Hardened Pinion Shaft

An investigation was made to determine the causes of surface contact fatigue failure of a case hardened driver pinion located in the intermediate shaft of a reducer gearbox used in a sugar and alcohol mill. The examination of the component revealed the presence of a cemented layer substantially thicker than that generally specified for pinions devised for this application. This, associated with the massive presence of brittle threadlike carbon-rich cementite phase (Fe 3 C) in prior austenite grain boundaries of the pinion teeth, favored surface crack nucleation and propagation during cyclic loading, leading to spallation of the contact surface with the counterpart gear, which impaired the systems operation. Poor carburization practice was discovered as the root cause of the mechanical failure, thus demanding the implementation of a new manufacturing route to avoid problems in similar load-bearing rotating components.

Study on friction and wear behavior of SAE 1045 steel, reinforced nylon 6.6 and NBR rubber used in clutch disks

The friction and wear properties of AISI 1045 steel, nylon 6.6 composites with different types and percentages of reinforcement and a nitrile rubber, Alpha 66, were submitted to sliding wear tests. The five types of nylon 6.6 composites tested generated matching, low values for the coefficient of friction. This may be due to the greater influence of the nylon 6.6 matrix on the coefficient of friction. However, the wear in nylon composites showed wide variation, determined by the type of reinforcement added to the composite. The other two materials tested, nitrile rubber and 1045 steel, showed behavior different from that of the composites. The NBR (signifying a norm established by the Brazilian Association of Technical Norms) rubber showed a superior coefficient of friction and greater wear. On the other hand, the steel showed a high coefficient of friction and low wear, suggesting that the coefficient of friction has no direct connection to the wear resistance of the materials studied here.

Micro Abrasive Wear Behaviour Study of Carburization and Ion Plasma Nitriding of P20 Steel

P20 steel, which is mainly used in plastic molds, was thermochemically treated by ion plasma nitriding and solid and gas carburization. In this work, the solid and gas carburization were performed at 925 oC for four different durations. The ion plasma nitriding was performed at 520 oC for four different durations. The thermochemical treatment increased the micro abrasive wear resistance of the studied material. The gas carburizing treatment resulted in a greater surface microhardness. Longer treatment times increased the effectiveness of the thickness layer in all cases. The solid carburization produced a larger thickness layer than the gas carburization and ion nitriding.