Evaluation of the fretting fatigue behaviour of commercially pure titanium

Fretting fatigue occurs when the contact surfaces of two components undergo small oscillatory movement while they are subjected to a clamping force. A cyclic external load gives rise to the early initiation of fatigue cracks, thus reducing their service life. In this paper, the fretting fatigue behaviour of commercially pure titanium flat samples (1.5 mm thick) is evaluated. A fretting device composed of a frame, load cell, and two screw-mounted cylindrical fretting pads with convex extremities was built and set to a servo-hydraulic testing machine. The fatigue tests were conducted under load control at a frequency of 10 Hz and stress ratio R = 0.1, with various contact load values applied to the fretting pads. Additional tests under inert environment allowed assessing the role of oxidation on the wear debris formation. The fracture surfaces and fretting scars were analysed via scanning electron microscopy in order to evaluate the surface damage evolution and its effect on the fatigue crack features. The effect of the fretting condition on the S-N curve of the material in the range of 10(4)-10(6) cycles is described. Fatigue crack growth calculations allowed estimating the crack initiation and propagation lives under fretting conditions. The effect of the fretting condition in fatigue life is stronger for the lower values of cyclic stress and does not seem to depend on the contact loading value.

Population persistence in weakly-coupled sinks

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

RELATIONSHIPS BETWEEN THE PLASMA ENVIRONMENT AND THE COMPOSITION AND OPTICAL-PROPERTIES OF PLASMA-POLYMERIZED THIN-FILMS PRODUCED IN RF DISCHARGES OF C2H2-SF6 MIXTURES

Polymer films were grown in rf discharges containing different proportions of C2H2 and SF6. Quantitative optical emission spectrometry (actinometry) was used to follow the trends in the plasma concentrations of the species H and F, and more tentatively, of CH, CF, and CF2, as a function of the feed composition. Infrared spectroscopy revealed the density of CH and CF bonds in the deposited material. As the partial pressure of SF6 in the feed was increased, the degree of fluorination of the polymer also rose. The form of the dependency of the deposition rate on the proportion of SF6 in the feed was in good qualitative agreement with the activated growth model. From transmission ultraviolet visible spectroscopy data the refractive index and the absorption coefficient of the polymers were calculated as a function of the deposition parameters. Since the optical gap depended to some extent upon the degree of fluorination, it could, within limits, be determined by a suitable choice of the proportion of SF6 in the feed. A qualitative explanation of this relationship is given.

On the equivalence of the mechanisms governing switching and hysteresis phenomena

The nucleation and growth model, which is usually applied to switching phenomena, is adapted for explaining surface potential measurements on the P(VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene) copolymer obtained in a constant current corona triode. It is shown that the growth is one-dimensional and that the nucleation rate is unimportant, probably because surface potential measurements take much longer than the switching ones. The surface potential data can therefore be accounted for by a growth model in which the velocity of growth varies exponentially with the electric field. Since hysteresis loops can be obtained from surface potential measurements, it is suggested that similar mechanisms can be used when treating switching and hysteresis phenomena, provided that account is taken of the difference in the time scale of the measurements.

Two decades of adjustment and agricultural development in Latin America and the Caribbean

Includes bibliography

Two decades of adjustment and agricultural development in Latin America and the Caribbean

Includes bibliography

Development of sustainable precision farming systems for swine: Estimating realtime individual amino acid requirements in growing-finishing pigs

The objective of this study was to develop and evaluate a mathematical model used to estimate the daily amino acid requirements of individual growing-finishing pigs. The model includes empirical and mechanistic model components. The empirical component estimates daily feed intake (DFI), BW, and daily gain (DG) based on individual pig information collected in real time. Based on DFI, BW, and DG estimates, the mechanistic component uses classic factorial equations to estimate the optimal concentration of amino acids that must be offered to each pig to meet its requirements. The model was evaluated with data from a study that investigated the effect of feeding pigs with a 3-phase or daily multiphase system. The DFI and BW values measured in this study were compared with those estimated by the empirical component of the model. The coherence of the values estimated by the mechanistic component was evaluated by analyzing if it followed a normal pattern of requirements. Lastly, the proposed model was evaluated by comparing its estimates with those generated by the existing growth model (InraPorc). The precision of the proposed model and InraPorc in estimating DFI and BW was evaluated through the mean absolute error. The empirical component results indicated that the DFI and BW trajectories of individual pigs fed ad libitum could be predicted 1 d (DFI) or 7 d (BW) ahead with the average mean absolute error of 12.45 and 1.85%, respectively. The average mean absolute error obtained with the InraPorc for the average individual of the population was 14.72% for DFI and 5.38% for BW. Major differences were observed when estimates from InraPorc were compared with individual observations. The proposed model, however, was effective in tracking the change in DFI and BW for each individual pig. The mechanistic model component estimated the optimal standardized ileal digestible Lys to NE ratio with reasonable between animal (average CV = 7%) and overtime (average CV = 14%) variation. Thus, the amino acid requirements estimated by model are animal- and time-dependent and follow, in real time, the individual DFI and BW growth patterns. The proposed model can follow the average feed intake and feed weight trajectory of each individual pig in real time with good accuracy. Based on these trajectories and using classical factorial equations, the model makes it possible to estimate dynamically the AA requirements of each animal, taking into account the intake and growth changes of the animal. © 2012 American Society of Animal Science. All rights reserved.

Modelo de programação matemática para controle do crescimento da vegetação sob redes de distribuição de energia elétrica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Trade and investment flows between the Caribbean and the rest of the hemisphere in the context of the FTAA

Includes bibliography

Taxa de câmbio e estratégia de crescimento econômico de longo prazo da China

Pós-graduação em Economia - FCLAR

Determinação da taxa de propagação de trinca por fadiga dos aços SAE-1050 e SAE-4130 empregados na fabricação de eixos ferroviários

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeito da fadiga cíclica na resistência, crescimento subcrítico de trincas e tempo de vida de cerâmicas a base de alumina infiltradas por vidro

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A periodization of Latin American development in the Robinsonian tradition

This paper analyzes Joan Robinson's growth model and then adapts it in order to provide an explanatory taxonomy of Growth Eras. The Growth Eras or Ages were for Robinson a way to provide logical connections between output growth, capital accumulation, the degree of thriftiness, the real wage and illustrate a catalogue of growth possibilities. This modified taxonomy follows the spirit of Robinson's work, but it takes different theoretical approaches. which imply that some of the classifications do not fit perfectly the ones here suggested. Latin America has moved from a Golden Age in the 1950s and 1960s to a Leaden Age in the 1980s, having two traverse periods, one of which the process of growth and industrialization accelerated in the late 1960s and early 1970s, which is referred to as a Galloping Platinum Age, an one in which a process of deindustrialization and reprimarization and maquilization of the productive structure took place, starting in the 1990s, which could be referred as the Creeping Platinum Age.

CEPAL Review no.88

Celso Furtado’s contributions to structuralism and their relevance today / Ricardo Bielschowsky. -- Has investor protection been rendered obsolete by the Argentine crisis? / Michael Mortimore and Leonardo Stanley. -- The rights-based approach in development policies and strategies / Victor Abramovich. -- Can the Latin American and Caribbean countries emulate the Irish model of FDI attraction? / Ruth Rios-Morales and David O’Donovan. -- The slow comeback of industrial policies in Latin America and the Caribbean / Wilson Peres. -- A low-growth model: informality as a structural constraint / Mario Cimoli, Annalisa Primi and Maurizio Pugno. -- The Argentine labour market in a financially globalized world / Mario Damill and Roberto Frenkel. -- Social precarity in Mexico and Argentina: trends, manifestations and national trajectories / María Cristina Bayón. -- The Fiscal Covenant in Guatemala: lessons learned from the negotiations / Juan Alberto Fuentes K. and Maynor Cabrera. -- Changes in Chile’s production structure, 1986-1996: output and industrial interdependence / José Miguel Albala-Bertrand. -- Guidelines for contributors to the CEPAL Review. -- CEPAL Review on the Internet. -- Recent ECLAC publications.

O emprego na transição para uma economia verde: cenários para o Brasil com base no consumo de energia pela indústria

Pós-graduação em Economia - FCLAR