367 research outputs found
A MODEL FOR THE MIXED MODE CRACK PROPAGATION IN COMPOSITE LAMINATES UNDER CYCLIC LOADINGS
No full textStructural collapse of a wind turbine blade. Part A: static test and equivalent single layered models
No full textThe overall objective is a top-down approach to structural instability phenomena in wind turbine blades, which is used to identify the physics governing the ultimate strength of a generic wind turbine blade under a flap-wise static test. The work is concerned with the actual testing and the adoption of a phenomenological approach, and a discussion is conducted to assess and evaluate the wind turbine blade response during loading and after collapse by correlating experimental findings with numerical model predictions. The ultimate strength of the blade studied is governed by instability phenomena in the form of delamination and buckling. Interaction between both instability phenomena occurs causing a progressive collapse of the blade structure
Utopia i kryzys. Lars T. Lih i rozważania wokół komunizmu wojennego
No full textThe article concerns the policy of ‘war communism’ in Soviet Russia during the civil war. In historiography, there are two dominant views regarding this phenomenon – while some researchers argue that it was a crisis policy (pragmatic and determined by external circumstances), others are inclined to claim that it was a utopian policy (a frantic attempt to immediately implement the communist ideal). Based on the revisionist works by Lars T. Lih, the author argues with the interpretation of the Bolshevik utopian policy, focusing on the analysis of three basic elements of this interpretation, namely: the contingent policy in the countryside, Leon Trotsky’s book entitled Terrorism and Communism and the work entitled The ABC of Communism by Nikolai Bukharin and Yevgeni Preobrazhensky. Thus, the article is an attempt to create a different picture of the Bolshevik policy in the first years after the revolution from the one that is popular in the Polish historical discourse
The Collapse of a Large Laminated Composite Wind Turbine Blade with Multiple Local Buckling-driven Delaminations
No full textInvestigation of failure mechanisms in GFRP sandwich structures with face sheet wrinkle defects used for wind turbine blades
No full textWrinkle defects can be formed during the production of wind turbine blades consisting of composite monolithic and sandwich laminates. Earlier studies have shown that the in-plane compressive strength of a sandwich panel with wrinkle defects may decrease dramatically. This study focuses on the failure modes of sandwich specimens consisting of thick GFRP face sheets with a wrinkle defect and a balsa wood core subjected to in-plane compression loading. Three distinct modes of failure were found, and the strain distributions leading up to these failures were established by use of digital image correlation (DIC). Finite element analyses were subsequently conducted to model the response of the test specimens prior to failure, and generally a very good agreement was found with the DIC measurements, although slight differences between the predicted and measured strain fields were observed in the local strain values around the wrinkle defect. The Northwestern University (NU) failure criterion was applied to predict failure initiation, and a good correlation with the experimental observations was achieved
Interlaminar/interfiber failure of unidirectional glass fiber reinforced composites used for wind turbine blades
No full textA unidirectional glass fiber/epoxy composite was characterized under multi-axial loading by testing off-axis specimens under uniaxial tension and compression at various angles relative to the fiber direction. Iosipescu shear tests were performed with both symmetric and asymmetric specimens. Tests were performed on both 1-2 and 1-3 material coordinate planes. Strain gauges and Digital Image Correlation were used to record the stress–strain responses. A new approach was used to define a ‘failure initiation strength’ by analyzing the recorded stress–strain curves. The experimentally determined failure stresses were compared with the predictions of the maximum stress, Tsai-Wu and Northwestern University failure criteria. It was found that using the approach of analyzing the stress–strain curve to define a point of material failure initiation, it was possible to obtain good correlation between the experimental data and predictions by both the Tsai-Wu and the NU failure criteria
Solution Strategy for Large Three-dimensional Composite Structures with Geometric and Material Induced Instability under Mixed-mode Loading
No full textDoes remediation save lives? On the cost of cleaning up arsenic-contaminated sites in Sweden
No full textSwedish environmental policy is based on 16 environmental quality objectives (Gov. Bill 2000/01:130 and Gov.Bill 2004/05:150).1 One of the most challenging objectives,‘A non toxic environment’, has two interim targets that concern remediation of contaminated sites. In sum, they state that the highest priority should be given to sites posing the highest risks to human health and the environment.2 By eliminating pollutants in soil, groundwater and sediment, the interim targets aim to reduce risks to human health and the environment. In Sweden, 83,000 sites are potentially contaminated due to previous industrial activities. According to the Swedish Environmental Protection Agency (EPA), the administrator of the governmental funds for remediation, approximately 1500 of these sites contain contaminant concentrations that could seriously harm human health and the environment (Swedish EPA, 2008a). To reach the interim targets, all these sites need to be remediated by 2050. Remediation of contaminated sites has so far cost more than SEK 3,000 million.3 The approximated cost to mitigate the potential risks at the most harmful sites is estimated at SEK 60,000 million.4 The Swedish government’s funding for remediation presently comes in the form of a directed grant (sakanslag). The directed grant, administrated by the Swedish EPA, subsidises remediation of contaminated sites that were contaminated prior to modern environmental legislation (in 1969) or for which no liable party can be found. The directed grant amounts to approximately 455 millions annually, which corresponds to about 10 percent of the annual national funds for environmental protection (Gov. Bill 2007/08:1). To make it possible to prioritise among contaminated sites, the Swedish EPA has developed a method for risk assessment called the ‘MIFO’ (i.e. the Method for Inventory of Contaminated Sites). The risk assessment does not take into account the actual exposure at a contaminated site. Risk is instead assessed based on divergence from guideline values for acceptable concentrations given a standardised (i.e. worst case) exposure situation on an individual level. This means that a site can be remediated without any individuals actually being exposed. The expected risk reduction is consequently not quantified. This eliminates the possibility of valuing the risk reduction, which should be weighed against the remediation cost. The purpose of this paper is to analyse how health effects, in the form of cancer risks, from sites contaminated by arsenic are valued implicitly in remediation. By using an environmental medicine approach that takes exposure into account, and without underestimating the potential health consequences of arsenic exposure, our purpose is to place arsenic risk management in the overall picture of live-saving interventions. In the case of cancer prevention, it is necessary to recognise that focus on an environmental carcinogen like arsenic may draw public attention – and funding – away from mental health risks like ambient air pollution and indoor radon. Although environmental pollution accounts for less than ten percent of all cancer cases (Harvard Centre for Cancer Prevention, 1996; Saracci and Vineis, 2007), environmental factors are important to recognize since they may be preventable. We emphasise, however, the inefficiency in becoming overly concerned about small risks while, at the same time, losing sight of the large risks. If society’s spending on lifesaving measures with small effects (i.e. a small number of lives saved) crowds out spending on lifesaving measures with large effects, then remediation can, in fact, even be said to waste lives. By using data on 23 arsenic-contaminated sites in Sweden, we estimate the sitespecific cancer risks and calculate the cost per life saved by using the sites’ remediation costs. Our results show that the cost per life saved through remediation is much higher than that associated with other primary prevention measures, indicating that the ambition level of Swedish remediation may be too high.
Ivan Krylóv: Fabler
No full textThis is a serious edition of Krylov's fables. It is complete and careful to follow Krylov's order of fables. About every six pages there is a good black-and-white illustration. The only colored illustration (12) repeats the cover's portrait of Krylov. The text margins are generous and the illustrations large. Fables and illustrations that caught my attention on this viewing of the book include The Trigamist (I 20); The Bag (III 7); Author and Robber (VI 24); and The Crow (VII 26). I do not yet understand the fit between fable and image in Leaves and Roots (IV 2). It strikes me that Krylov's illustrators present his fables as quite stark. For all their seriousness, Aesop and La Fontaine seem to draw more fun out of artists. The key fables in Krylov, both borrowed and new, tend to have illustrations here, as is only right. Each fable has a comment in a section near the book's end. That section is followed by an acknowledgement of the eight artists -- Brjullov, Kandaurov, Panov, Petrov, Popov, Sapozjnikov, Serov, and Trutovskij -- and four institutions whose art is presented here. The last two elements of the book are a T of C and an AI of fables. This is one of the heavier books that made my Scandinavian burden a challenge flying home from Europe!This is a hardbound book (hard cover)Language note: DanishPa dansk ved Lars P. Poulsen-Hansen & Holger Scheibe
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