Estimation Of Useful Life Research Articles

Aplicación de enfoques de análisis y criterios de rotura en ensayos de fatiga y su influencia en la predicción de la vida útil de la capa de rodadura asfáltica en la estructura del pavimento

The obtaining of fatigue models of asphalt mixtures, are part of the procedures of advanced characterization of the material and are used for the design of pavements. However, there are several approaches to analysis and failure criteria that can be used. These approaches and criteria may not produce the same models of fatigue, resulting in different thicknesses of the asphalt surface in the pavement structure. This study presents the results of the influence of two approaches of analysis (phenomenological and accumulated dissipated energy) and two criteria of rupture (conventional and Pronk & Hopman) in obtaining fatigue models of the asphalt mixture, and its repercussion in the estimation of useful life of the asphalt surface in the pavement structure. The results show that the phenomenological approach is more conservative than the accumulated dissipated energy, as well as the Pronk & Hopman criterion in relation to the conventional criterion, that is, the type of approach and the criterion of rupture adopted will directly affect the final thickness of the projected asphalt surface.

Contribuição para estimativa do grau de saturação a partir das condições ambientais aplicada à análise de confiabilidade de estruturas de concreto sujeitas ao ataque por cloretos

A durabilidade de elementos estruturais de concreto armado sujeitos a condições ambientais de severa agressividade apresenta-se como um dos principais problemas enfrentados na construção civil. Dentre os agentes de deterioração dessas estruturas destacam-se os íons cloretos, amplamente difundidos em ambiente marinho, que causam a corrosão de armaduras. A estimativa de vida útil de elementos de concreto armado surge como uma temática fundamental na avaliação da durabilidade das estruturas. Embora outros processos causem penetração de íons cloreto no concreto, é praticamente consenso que a difusão é o mecanismo predominante. Um modelo clássico de caracterização da penetração de cloretos é a 2ª Lei de Fick. Guimarães (2000) demonstrou que o grau de saturação (GS) do concreto é um parâmetro que exerce forte influência sobre o coeficiente de difusão de cloretos (D). Embora tenham sido desenvolvidas metodologias de medição do GS, estas se apresentam onerosas em termos de tempo e recursos. O objetivo deste trabalho é apresentar estimativas de GS com base nas condições ambientais a que o material é exposto e posteriormente analisar a influência deste parâmetro na avaliação da estimativa de vida de elementos estruturais através da confiabilidade. São utilizados dados meteorológicos e de medição do GS obtidas em duas regiões litorâneas: Rio Grande, Brasil e Santa Pola, Espanha. Obteve-se modelos de estimativa do GS a partir das variáveis ambientais de cada região e também de ambas em conjunto. Avaliou-se então a influência destes modelos na estimativa de vida útil através da probabilidade de falha da estrutura.

Estimation of useful life in turbines blades with cracks in corrosive environment

Geothermal turbines of 110MW were installed in the Federal Electricity Commission in Cerro Prieto Mexico, which operating time exceeds 150,000h. Therefore, the critical components which determine the useful life of the turbine should be evaluated to determine the rehabilitation or replacement of them. The critical components are the blades of the last stage in the steam turbine. It has been observed that different blades of the turbine of 110MW with cracks presented corrosion products, which resulted in a failure for corrosion fatigue mechanisms. In this paper, it was studied the effect of crack propagation produced in a geothermal turbine blade of the last stage, L-0, which is made of stainless steel AISI 410 exposed to corrosion under a sea water solution. The corrosion phenomena including localized corrosion suffered by the cracking sample were studied through the electrochemical noise technique in current and potential and polarization curves. The tests were conducted on pieces of blades subjected to fatigue. The results indicated that the exposure to the corrosion solution modified the width and the length of the cracks. Using a scanning electron microscopy (SEM), the surface of the crack was observed, showing that the corrosion mechanism produced a significant increment of the velocity of crack propagation and therefore, a decrement of the useful life of the material. This research will allow us to understand the corrosion process in addition to estimate the useful life of the blades when they are subjected to load cycles.

Estimativa do tempo de vida útil de represa de pequeno porte

The purpose of this work is to compare two methods for time estimation of useful life for a small and shallow reservoir, located at Pirassununga's Municipal District, in São Paulo State/Brazil: sedimentometry and bathymetry. The model indicated a useful lifetime around 50 years for the studied dam. The values are between 51 year for the initial years of 1998/1999, and 46 year for the final years of 2004/2005, having an oscillation between years of 1999/2000, of 27 years, and 2000/2001, of 76 years. These differences probably are due to global climatic changes phenomena, and anthropomorphic activities in the region. The obtained results showed that it is possible to foresee useful lifetime for small dams through the sedimentometric method knowing the correction coefficient value (K'). The coefficient is calculated using time values of useful lifetime calculated by the sedimentometric and batimetric methods simultaneously, during the period of one year.

Induction period in the aging of polypropylene

AbstractThe ordinary methods for obtaining a rapid estimate of the useful life of a plastic, extrapolations from tests conducted at higher temperatures or at lower stabilizer concentrations than those of actual use, lead to serious errors in estimating the useful life of some stabilized polypropylene compositions. Two methods for obtaining more reliable rapid estimates of useful life have been explored and are reported here: (1) measurement of physical and chemical changes, such as weight loss, stabilizer loss, density increase, dyeability increase, and formation of carbonyl or hydroperoxide groups, which occur during the prefailure stages of oxidative deterioration at the temperature of interest (of these, measurements of stabilizer loss appear the most promising); (2) thermal development of the prefailure oxidative damage initiated at the temperature of interest. This method needs further exploration.