Evaluation of structural stressmethod and master curve for fatigue life prediction of a weldedjoint

Este artigo apresenta um estudo dos métodos da tensão estrutural hot spot e do método da curva mestre (Battelle) para a determinação da vida à fadiga de uma junta soldada do tipo T. Ambos os métodos utilizam o conceito de tensão estrutural, determinada, normalmente, através de modelos de elementos finitos. Utilizando diferentes tipos de modelos de elementos finitos de casca, os resultados obtidos pelos 2 métodos foram comparados com os obtidos experimentalmente, verificando‐se diferenças significativas entre os métodos. Os níveis de carregamento influenciaram decisivamente na precisão de ambas as metodologias, sendo que, para o caso em estudo, o método hot spot demonstrou ser mais preciso. O maior diferencial constatado para o método de Battelle foi a correção do parâmetro da tensão estrutural, visto que, sem essa correção, as tensões no pé da solda foram muito similares às obtidas pelo método hot spot. Comparando a curva mestre de comportamento à fadiga do método de Battelle com a curva do método hot spot, ambas em função da tensão nominal aplicada no ensaio, verificou‐se que o método hot spot é conservador. Para os diferentes modelos numéricos estudados, apenas uma técnica de modelagem forneceu resultados dispersos das demais. Pelo método de Battelle, o comportamento da componente de flexão da tensão variou consideravelmente de um modelo para o outro, denotando que, sobre um carregamento mais complexo, poderá haver uma variabilidade maior na vida à fadiga calculada.This paper presents a study on the structural hot spot stress method and the master curve method (Battelle) for evaluating the fatigue life of a T‐shaped welded joint. Both methods are based on the concept of structural stress, which is usually determined using finite element models. Using different types of shell finite element models, the results obtained by the two methods were compared to experimental data, verifying significant differences between the studied methods. The loading level had a great deal of influence over the accuracy of both methodologies, but on the other hand the hot spot method revealed to be more precise for the analyzed joint. The main differential for the Batelle method was the correction of the stress amplitude into an equivalent structural stress parameter, since, without this correction, the stresses on the weld toe were very similar between the Battelle and the hot spot methods. Comparing the master curve for the fatigue behavior of the Battelle method to the fatigue curve of hot spot method, with both curves expressed in terms of the nominal stress applied in the experiment, it was verified that the hot spot method is conservative. Among the different modeling techniques used, only one provided results that are not in agreement with the others. Using the Battelle method, the behavior of the bending stress component varied considerably according to the employed numerical model, indicating that can be a greater variability in the expected fatigue life for joints under more complex loading configuration.Peer Reviewe

Miedo a equivocarse y motivación autodeterminada en estudiantes adolescentes

El objetivo de este estudio fue analizar los efectos de la manipulación del clima motivacional, y del feedback positivo, verbal y no verbal, en relación con el miedo a equivocarse, la motivación intrínseca, y la importancia que le concede el estudiante a la Educación Física, teniendo como mediadores las necesidades psicológicas básicas. Se utilizó un diseño cuasi experimental con grupo control no equivalente. La muestra estuvo compuesta por estudiantes de primer curso de Educación Secundaria, con edades entre 12 y 13 años (M = 12.14, DT = .42). En el grupo experimental (n = 20) se transmitió un clima tarea y un grupo control (n = 17) sobre el que no hubo manipulación. La intervención duró 30 sesiones de 50 minutos, con una frecuencia de dos sesiones semanales. Se midió antes y después de la misma. Los resultados revelaron un incremento en el grupo experimental en el feedback positivo, percepción de competencia, motivación intrínseca, en la concesión de importancia a la Educación Física, disminuyendo todas las variables del miedo a equivocarse. Por lo que la intervención fue efectiva ya que hubomejoras en el grupo experimental en las variables motivacionales, viéndose disminuida la del miedo a fallar

Failure regime in (1+1) dimensions in fibrous materials

In this paper, we introduce a model for fracture in fibrous materials that takes into account the rupture height of the fibers, in contrast with previous models. Thus, we obtain the profile of the fracture and calculate its roughness, defined as the variance around the mean height. We investigate the relationship between the fracture roughness and the fracture toughness.Comment: 4 pages, 4 figures.eps, Revte

Testing the interaction of dark energy to dark matter through the analysis of virial relaxation of clusters Abell Clusters A586 and A1689 using realistic density profiles

Interaction between dark energy and dark matter is probed through deviation from the virial equilibrium for two relaxed clusters: A586 and A1689. The evaluation of the virial equilibrium is performed using realistic density profiles. The virial ratios found for the more realistic density profiles are consistent with the absence of interaction.Comment: 16pp 1 fig; accepted by GeR

Space-filling and benthic competition on coral reefs

Reef-building corals are ecosystem engineers that compete with other benthic organisms for space and resources. Corals harvest energy through their surface by photosynthesis and heterotrophic feeding, and they divert part of this energy to defend their outer colony perimeter against competitors. Here, we hypothesized that corals with a larger space-filling surface and smaller perimeters increase energy gain while reducing the exposure to competitors. This predicted an association between these two geometric properties of corals and the competitive outcome against other benthic organisms. To test the prediction, fifty coral colonies from the Caribbean island of Curaçao were rendered using digital 3D and 2D reconstructions. The surface areas, perimeters, box-counting dimensions (as a proxy of surface and perimeter space-filling), and other geometric properties were extracted and analyzed with respect to the percentage of the perimeter losing or winning against competitors based on the coral tissue apparent growth or damage. The increase in surface space-filling dimension was the only significant single indicator of coral winning outcomes, but the combination of surface space-filling dimension with perimeter length increased the statistical prediction of coral competition outcomes. Corals with larger surface space-filling dimensions (Ds > 2) and smaller perimeters displayed more winning outcomes, confirming the initial hypothesis. We propose that the space-filling property of coral surfaces complemented with other proxies of coral competitiveness, such as life history traits, will provide a more accurate quantitative characterization of coral competition outcomes on coral reefs. This framework also applies to other organisms or ecological systems that rely on complex surfaces to obtain energy for competition

Recent improvements in the Broadband seismic networks in Portugal

Portugal, in spite of the significant earthquake region, (e.g.: Borges et al., 2001) has been operating a limited number of broadband digital seismic instruments. The older BB seismic station in a systematic and continuous operation on the country is MTE, belonging to GEOFON and locally supported by IM, which is working since 1997. To efficiently carry out the task of develop the Broadband Portuguese seismic network, there is a collaboration between some national institutions, such as Institute of Meteorology (IM), Geophysics Center of Évora University (CGE/UE), Geophysics Center of University of Lisbon (CGUL/IGIDL) and Instituto Superior Técnico (IST), with governmental support from the National Science and Technology Foundation (Rede Nacional de Geofísica, RNG). From this collaboration we expect shortly to assist the emergence of a high quality infrastructure, significant to real-time monitoring the earthquake activity for use by governmental authorities, and of paramount importance to scientific research. The installation of this network is to be carried out in narrow connection with international institutions as GEOFON, EMSC, ROA, ORFEUS, with who we saw to establish collaborations. Data from some stations are already being exported to international data centers, such as DMC and ORFEUS, and will be used for an upcoming prototype of an Early Warning Tsunami System to be developed for Cadiz Gulf coastal area and southwestern coasts of Portugal mainland, within the framework of the NEAREST project. Conclusions While the broadband network is developed they elapse investigation projects that request short period data. Of these projects we highlight the Seismic Tomography of the Continental Lithosphere of Algarve (Portugal) that involve the installation of a Portable seismic network consisting of 30 short- period stations, including a subnet of 7 telemetry stations, in operation since January 200