Using a cohesive damage model to predict the tensile behaviour of CFRP single-strap repairs

This work addresses both experimental and numerical analyses regarding the tensile behaviour of CFRP single-strap repairs. Two fundamental geometrical parameters were studied: overlap length and patch thickness. The numerical model used ABAQUS® software and a developed cohesive mixed-mode damage model adequate for ductile adhesives, and implemented within interface finite elements. Stress analyses and strength predictions were carried out. Experimental and numerical comparisons were performed on failure modes, failure load and equivalent stiffness of the repair. Good correlation was found between experimental and numerical results, showing that the proposed model can be successfully applied to bonded joints or repairs.

Role of abrasive material on micro-abrasion wear tests

Micro-abrasion wear tests with ball-cratering configuration are widely used. Sources of variability are already studied by different authors and conditions for testing are parameterized by BS EN 1071-6: 2007 standard which refers silicon carbide as abrasive. However, the use of other abrasives is possible and allowed. In this work, ball-cratering wear tests were performed using four different abrasive particles of three dissimilar materials: diamond, alumina and silicon carbide. Tests were carried out under the same conditions on a steel plate provided with TiB2 hard coating. For each abrasive, five different test durations were used allowing understanding the initial wear phenomena. Composition and shape of abrasive particles were investigated by SEM and EDS. Scar areas were observed by optical and electronic microscopy in order to understand the wear effects caused by each of them. Scar geometry and grooves were analyzed and compared. Wear coefficient was calculated for each situation. It was observed that diamond particles produce well-defined and circular wear scars. Different silicon carbide particles presented dissimilar results as consequence of distinct particle shape and size distribution.

Influence of the abrasive particles size in the micro-abrasion wear tests of TiAlSiN thin coatings

Ball rotating micro-abrasion tribometers are commonly used to carry out wear tests on thin hard coatings. In these tests, different kinds of abrasives were used, as alumina (Al2O3), silicon carbide (SiC) or diamond. In each kind of abrasive, several particle sizes can be used. Some studies were developed in order to evaluate the influence of the abrasive particle shape in the micro-abrasion process. Nevertheless, the particle size was not well correlated with the material removed amount and wear mechanisms. In this work, slurry of SiC abrasive in distilled water was used, with three different particles size. Initial surface topography was accessed by atomic force microscopy (AFM). Coating hardness measurements were performed with a micro-hardness tester. In order to evaluate the wear behaviour, a TiAlSiN thin hard film was used. The micro-abrasion tests were carried out with some different durations. The abrasive effect of the SiC particles was observed by scanning electron microscopy (SEM) both in the films (hard material) as in the substrate (soft material), after coating perforation. Wear grooves and removed material rate were compared and discussed.

Semi-destructive in situ tests as support to the assessment of a conservation process

This paper refers to the assessment on site by semi-destructive testing (SDT) methods of the consolidation efficiency of a conservation process developed by Henriques (2011) for structural and non-structural pine wood elements in service. This study was applied on scots pine wood (Pinus sylvestris L.) degraded by fungi after treatment with a biocidal product followed by consolidation with a polymeric product. This solution avoids substitutions of wood moderately degraded by fungi, improving its physical and mechanical characteristics. The consolidation efficiency was assessed on site by methods of drill resistance and penetration resistance. The SDT methods used showed good sensitivity to the conservation process and could evaluate their effectiveness. (C) 2015 Elsevier Ltd. All rights reserved.

Adherend thickness effect on the tensile fracture toughness of a structural adhesive using an optical data acquisition method

Adhesive bonding is nowadays a serious candidate to replace methods such as fastening or riveting, because of attractive mechanical properties. As a result, adhesives are being increasingly used in industries such as the automotive, aerospace and construction. Thus, it is highly important to predict the strength of bonded joints to assess the feasibility of joining during the fabrication process of components (e.g. due to complex geometries) or for repairing purposes. This work studies the tensile behaviour of adhesive joints between aluminium adherends considering different values of adherend thickness (h) and the double-cantilever beam (DCB) test. The experimental work consists of the definition of the tensile fracture toughness (GIC) for the different joint configurations. A conventional fracture characterization method was used, together with a J-integral approach, that take into account the plasticity effects occurring in the adhesive layer. An optical measurement method is used for the evaluation of crack tip opening and adherends rotation at the crack tip during the test, supported by a Matlab® sub-routine for the automated extraction of these quantities. As output of this work, a comparative evaluation between bonded systems with different values of adherend thickness is carried out and complete fracture data is provided in tension for the subsequent strength prediction of joints with identical conditions.

Efficient schedulability tests for real-time embedded systems with urgent routines

Task scheduling is one of the key mechanisms to ensure timeliness in embedded real-time systems. Such systems have often the need to execute not only application tasks but also some urgent routines (e.g. error-detection actions, consistency checkers, interrupt handlers) with minimum latency. Although fixed-priority schedulers such as Rate-Monotonic (RM) are in line with this need, they usually make a low processor utilization available to the system. Moreover, this availability usually decreases with the number of considered tasks. If dynamic-priority schedulers such as Earliest Deadline First (EDF) are applied instead, high system utilization can be guaranteed but the minimum latency for executing urgent routines may not be ensured. In this paper we describe a scheduling model according to which urgent routines are executed at the highest priority level and all other system tasks are scheduled by EDF. We show that the guaranteed processor utilization for the assumed scheduling model is at least as high as the one provided by RM for two tasks, namely 2(2√−1). Seven polynomial time tests for checking the system timeliness are derived and proved correct. The proposed tests are compared against each other and to an exact but exponential running time test.

Syngas production by water electrolysis: preliminary tests on methane production

Master Thesis to obtain the Master degree in Chemical Engineering - Branch Chemical Processes

Geossintéticos em vias de comunicação: influência das condições climáticas

Trabalho de Dissertação de Natureza Científica para obtenção do grau de Mestre em Engenharia Civil na Área de Especialização de Vias de Comunicação e Transportes

Aplicação de um método de correlação de imagem para a determinação da tenacidade à fratura em corte de adesivos estruturais

Qualquer estrutura hoje em dia deve ser resistente, robusta e leve, o que aumentou o interesse industrial e investigação nas ligações adesivas, nomeadamente pela melhoria das propriedades de resistência e fratura dos materiais. Com esta técnica de união, o projeto de estruturas pode ser orientado para estruturas mais leves, não só em relação à economia direta de peso relativamente às juntas aparafusas ou soldadas, mas também por causa da flexibilidade para ligar materiais diferentes. Em qualquer área da indústria, a aplicação em larga escala de uma determinada técnica de ligação supõe que estão disponíveis ferramentas confiáveis para o projeto e previsão da rotura. Neste âmbito, Modelos de Dano Coesivo (MDC) são uma ferramenta essencial, embora seja necessário estimar as leis MDC do adesivo à tração e corte para entrada nos modelos numéricos. Este trabalho avalia o valor da tenacidade ao corte (GIIC) de juntas coladas para três adesivos com ductilidade distinta. O trabalho experimental consiste na caracterização à fratura ao corte da ligação adesiva por métodos convencionais e pelo Integral-J. Além disso, pelo integral-J, é possível definir a forma exata da lei coesiva. Para o integral-J, é utilizado um método de correlação de imagem digital anteriormente desenvolvido para a avaliação do deslocamento ao corte do adesivo na extremidade da fenda (δs) durante o ensaio, acoplado a uma sub-rotina em Matlab® para a extração automática de δs. É também apresentado um trabalho numérico para avaliar a adequabilidade de leis coesivas triangulares aproximadas em reproduzir as curvas força-deslocamento (P-δ) experimentais dos ensaios ENF. Também se apresenta uma análise de sensibilidade para compreender a influência dos parâmetros coesivos nas previsões numéricas. Como resultado deste trabalho, foram estimadas experimentalmente as leis coesivas de cada adesivo pelo método direto, e numericamente validadas, para posterior previsão de resistência em juntas adesivas. Em conjunto com a caraterização à tração destes adesivos, é possível a previsão da rotura em modo-misto.

Caracterização de perfis pultrudidos Híbridos

A pultrusão é uma técnica já sobejamente conhecida de produção de perfis de secção constante, tais como barras, cantoneiras, perfis estruturais ou tubos, em materiais compósitos de matriz polimérica. A necessidade de, em determinadas aplicações, utilizar perfis que proporcionem melhor isolamento térmico, melhor isolamento acústico ou possuam um momento de inércia ligeiramente superior, sem que o peso próprio seja significativamente afectado, levou à produção de perfis pultrudidos híbridos, com núcleos baseados em pré-formas ou na alimentação contínua de resíduos. Realizados os protótipos seguindo as metodologias acima descritas, urge verificar se as propriedades dos perfis híbridos correspondem às expectativas inicialmente neles depositadas, através de testes destrutivos e não-destrutivos. Assim, foram realizados testes à tracção, à compressão e à flexão, no intuito de verificar os ganhos conseguidos e poder analisar o valor-acrescentado trazido por estes novos perfis em termos estruturais. Estes valores, depois de devidamente validados, permitirão a sua inserção em bases de dados agregadas a programas de cálculo estrutural, que efectuam de forma automática o dimensionamento de estruturas baseadas em perfis desta natureza. Complementarmente, foram realizados testes de isolamento térmico e acústico, com vista a quantificar a melhoria conseguida nestas propriedades, extremamente importantes em determinados tipos de aplicações ligadas à construção civil e obras públicas.

Routine use of point-of-care tests: usefulness and application in clinical microbiology.

Point-of-care (POC) tests offer potentially substantial benefits for the management of infectious diseases, mainly by shortening the time to result and by making the test available at the bedside or at remote care centres. Commercial POC tests are already widely available for the diagnosis of bacterial and viral infections and for parasitic diseases, including malaria. Infectious diseases specialists and clinical microbiologists should be aware of the indications and limitations of each rapid test, so that they can use them appropriately and correctly interpret their results. The clinical applications and performance of the most relevant and commonly used POC tests are reviewed. Some of these tests exhibit insufficient sensitivity, and should therefore be coupled to confirmatory tests when the results are negative (e.g. Streptococcus pyogenes rapid antigen detection test), whereas the results of others need to be confirmed when positive (e.g. malaria). New molecular-based tests exhibit better sensitivity and specificity than former immunochromatographic assays (e.g. Streptococcus agalactiae detection). In the coming years, further evolution of POC tests may lead to new diagnostic approaches, such as panel testing, targeting not just a single pathogen, but all possible agents suspected in a specific clinical setting. To reach this goal, the development of serology-based and/or molecular-based microarrays/multiplexed tests will be needed. The availability of modern technology and new microfluidic devices will provide clinical microbiologists with the opportunity to be back at the bedside, proposing a large variety of POC tests that will allow quicker diagnosis and improved patient care.

Risk factors for positive tuberculin skin tests among migrant and resident children in Lausanne, Switzerland.

SETTING: Ambulatory paediatric clinic in Lausanne, Switzerland, a country with a significant proportion of tuberculosis (TB) among immigrants. AIM: To assess the factors associated with positive tuberculin skin tests (TST) among children examined during a health check-up or during TB contact tracing, notably the influence of BCG vaccination (Bacille Calmette Guérin) and history of TB contact. METHOD: A descriptive study of children who had a TST (2 Units RT23) between November 2002 and April 2004. Age, sex, history of TB contact, BCG vaccination status, country of origin and birth outside Switzerland were recorded. RESULTS: Of 234 children, 176 (75%) had a reaction equal to zero and 31 (13%) tested positive (>10 mm). In a linear regression model, the size of the TST varied significantly according to the history of TB contact, age, TB incidence in the country of origin and BCG vaccination status but not according to sex or birth in or outside Switzerland. In a logistic regression model including all the recorded variables, age (Odds Ratio = 1.21, 95% CI 1.08; 1.35), a history of TB contact (OR = 7.31, 95% CI 2.23; 24) and the incidence of TB in the country of origin (OR = 1.01, 95% CI 1.00; 1.02) were significantly associated with a positive TST but sex (OR = 1.18, 95% CI 0.50; 2.78) and BCG vaccination status (OR = 2.97, 95% CI 0.91; 9.72) were not associated. CONCLUSIONS: TB incidence in the country of origin, BCG vaccination and age influence the TSTreaction (size or proportion of TST > or = 10 mm). However the most obvious risk factor for a positive TST is a history of contact with TB.

Comparative resilience of clinical perimetric tests to induced levels of intraocular straylight.

PURPOSE: To investigate the effect of intraocular straylight (IOS) induced by white opacity filters (WOF) on threshold measurements for stimuli employed in three perimeters: standard automated perimetry (SAP), pulsar perimetry (PP) and the Moorfields motion displacement test (MDT).¦METHODS: Four healthy young (24-28 years old) observers were tested six times with each perimeter, each time with one of five different WOFs and once without, inducing various levels of IOS (from 10% to 200%). An increase in IOS was measured with a straylight meter. The change in sensitivity from baseline was normalized, allowing comparison of standardized (z) scores (change divided by the SD of normative values) for each instrument.¦RESULTS: SAP and PP thresholds were significantly affected (P < 0.001) by moderate to large increases in IOS (50%-200%). The drop in motion displacement (MD) from baseline with WOF 5, was approximately 5 dB, in both SAP and PP which represents a clinically significant loss; in contrast the change in MD with MDT was on average 1 minute of arc, which is not likely to indicate a clinically significant loss.¦CONCLUSIONS: The Moorfields MDT is more robust to the effects of additional straylight in comparison with SAP or PP.

Performance aux tests d'intelligence : vers une inversion de l'effet Flynn ?

Des nombreuses études ont montré une augmentation des scores aux tests d'aptitudes à travers les générations (« effet Flynn »). Différentes hypothèses d'ordre biologique, social et/ou éducationnels ont été élaborées afin d'expliquer ce phénomène. L'objectif de cette recherche est d'examiner l'évolution des performances aux tests d'aptitudes sur la base d'étalonnages datant de 1991 et de 2002. Les résultats suggèrent une inversion non homogène de l'effet Flynn. La diminution concerne plus particulièrement les tests d'aptitudes scolaires, comme ceux évaluant le facteur verbal et numérique. Cette étude pourrait refléter un changement de l'importance accordée aux différentes aptitudes peu évaluées en orientation scolaire et professionnelle.

Reduction in the use of diagnostic tests in infants with risk factors for early-onset neonatal sepsis does not delay antibiotic treatment.

Despite a low positive predictive value, diagnostic tests such as complete blood count (CBC) and C-reactive protein (CRP) are commonly used to evaluate whether infants with risk factors for early-onset neonatal sepsis (EOS) should be treated with antibiotics. We investigated the impact of implementing a protocol aiming at reducing the number of diagnostic tests in infants with risk factors for EOS in order to compare the diagnostic performance of repeated clinical examination with CBC and CRP measurement. The primary outcome was the time between birth and the first dose of antibiotics in infants treated for suspected EOS. Among the 11,503 infants born at ≥35 weeks during the study period, 222 were treated with antibiotics for suspected EOS. The proportion of infants receiving antibiotics for suspected EOS was 2.1% and 1.7% before and after the change of protocol (p = 0.09). Reduction of diagnostic tests was associated with earlier antibiotic treatment in infants treated for suspected EOS (hazard ratio 1.58; 95% confidence interval [CI] 1.20-2.07; p <0.001), and in infants with neonatal infection (hazard ratio 2.20; 95% CI 1.19-4.06; p = 0.01). There was no difference in the duration of hospital stay nor in the proportion of infants requiring respiratory or cardiovascular support before and after the change of protocol. Reduction of diagnostic tests such as CBC and CRP does not delay initiation of antibiotic treatment in infants with suspected EOS. The importance of clinical examination in infants with risk factors for EOS should be emphasised.