In situ stable fracture of ceramic interfaces

The fracture toughness of ceramics is often dominated by the structure of their grain boundaries. Our capacity to improve the performance of ceramic components depends on our ability to investigate the properties of individual grain boundaries. This requires development of new fracture testing methods providing high accuracy and high spatial resolution. Recently, several techniques have been developed using small scaled mechanical testing, based within a nanoindenter, using a variety of tip and sample geometries, including: micropillar compression, microcantilever bending and double-cantilever compression. However, the majority of the published work relies on load-displacement curves for the identification of crack initiation and the geometries can result in a complex analysis of force distribution and stress intensity factor. Our approach uses a double cantilever geometry to obtain stable crack growth and we calculate the fracture energy under a constant wedging displacement. The tests are carried out within an SEM, this has two benefits: the sample is well aligned for a controlled test and images are recorded during the test for later analysis. Crucially this allows us to use beam deflection and crack length rather than critical load to measure fracture toughness. Our tests have proved it is possible to initiate and stably grow a crack in a controlled manner in ceramic materials for several microns. This approach has been validated on SiC where it gives a good approximation of the surface energy and then extended to SiC bi-crystals along with Ni-Al2O3 interfaces where crack blunting and bridging mechanism can be observed and measure

In-situ fracture tests of brittle materials at the microscale

The fracture toughness of ceramics is often dominated by the structure of their grain boundaries. Our ability to improve life of ceramic components depends on our ability to investigate properties of individual grain boundaries. This requires development of new fracture testing methods allowing high spatial resolution and high control over the area to test. Further benefits of these ‘small scale’ approaches will enable testing of specimens for which big volumes are not available (e.g. thin films, coating, or simply samples of dimensions limited by production process). Recently, several techniques have been developed using small scaled mechanical testing, based within a nanoindenter, changing tip and sample geometries, including: micropillar compression [1]; microcantilever bending [2,3]; and double-cantilever compression [4]. However, the majority of the published works utilises complex geometries resulting into complex analysis of force distribution and stress intensity factor and rely on load-displacement curves for the identification of crack initiation, with the added complication of friction. Our approach builds upon the work of Lawn [5], who showed that a practical test geometry to obtain stable crack growth and calculate the fracture energy G is that of a double-cantilever beam (DCB) under constant wedging displacement. We replicate this configuration in our tests fabricating double-cantilever beams of micrometric dimensions by focused ion beam (FIB) milling and loading them in-situ in an SEM using a nanoindenter with a wedge-shaped tip. This has two benefits: the sample is well aligned for a controlled test; images are recorded during the test for later analysis. This allows us to use beam deflection and crack length rather than critical load to measure fracture toughness. Our tests have proved it is possible to initiate and stably grow a crack in a controlled manner in ceramic materials (fig. 1) and our fracture energy results have been validated against prior macro-scale fracture data. This approach is being extended to multi-phase materials with unknown materials properties and extends our arsenal of small-scale characterisation techniques required to generate new processing strategies for the next generation of materials design

Modelling Environmental Fate and Transport of POPs and Metal Usig the Fugacity/Aquivalence approach: Two Acquatic Environments as a Case Study.

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Fabrizio Monaco

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Micromechanisms of compressive failure of fibre reinforced polymers

Fibre reinforced polymers benefit from high flexural strength, corrosion resistance and low density. These qualities make them a candidate to substitute the conventional rigid steel pipelines for subsea transport of oil and gas. However, deep water pipelines are subject to high external hydrostatic compressive stresses alongside variable internal fluid pressure that can result in high compressive hoop, radial and axial stress. For aligned fibre reinforced composites, compressive strength is generally lower than the tensile strength and a design limiting factor. Therefore, failure mechanisms and conditions need to be well understood in order to design safe and cost-effective structures. Please click Additional Files below to see the full abstract

Managing the commons in the knowledge economy

The work leading to this publication has received funding from the European Union’s Seventh Framework Programme (FP7/2007- 2013) under grant agreement n° 610349.This report presents an in-depth analysis of the concept of common goods and of possible political and management variation in the context of a knowledge-based economy. The research presents an initial critical review of the literature together with a concrete analysis of the development of the commons and common goods.The report will be organised in three sections. In the first, entitled "From the theory of public goods to the new political economy of the commons" we will see how, for Ostrom's new theory of the commons, what remains as a central element defining common goods is the particular nature of certain goods, in continuity with the ahistorical and static approach to classification of goods (private, public, common, belonging to a club) driven by neo-classical inspired economic theory.In the second section we will develop the approach of Common in the singular drawn up with the contribution of numerous studies in the theoretical framework of cognitive capitalism.The third will deal with the historic and empirical analysis of the origin, sense and principal stakes at play in the dynamics of the common, starting from the key role of the transformations of labour at the foundation of a knowledge-based economy.Throughout this journey, in the three sections different crucial aspects relating to the forms of regulation open to guarantee the sustainability of the commons and promote its development as a new central form of economic and social organisation will be faced systematically.This research offers an exhaustive theoretical framework, tackling all the conceptual and historical issues on the evolution of the theory of common goods. At the same time however, it offers practical and regulative examples of models of self-governance of commons, in the context of the knowledge-based economy. This analysis offers the D-CENT project possible models of democratic management of resources and common infrastructures that are at the base of the experience of shared democracy in Spain, Iceland and Finland, with the aim of achieving middle and long-term sustainability. Specifically speaking, the analysis submitted here reports: (1) research into the market of identity and the opposing claim of social data as digital common goods and the need for public and common infrastructures of information and communication not based on the logic of the market and surveillance (D3.3); (2) models to implement a commons currency of the common that can support the activities of social movements and productive communities (D3.5); (3) the final report (D1.3) on models of sustainability and the general impact of this project.Many of the examples proposed here, from the re-municipalisation of water, the self-management of cultural spaces to the free software and makers’ movement, illustrate collective practices that establish new spaces, institutions or norms of participative and democratic sharing. These examples represent practices of re-appropriation and management of the common, new practices of labour, creation and production based on collaboration and sharing.Moreover, from the concrete experiences analysed here, the idea emerges that the concept of common goods can constitute a concrete alternative, and that includes on a legal footing (Rodotà, 2011). Therefore the common is the product of a social and institutional structure that demonstrates forms of governing and social co-operation that guarantee its production, reproduction and spread. The new institutions of the common that emerge from these constituent practices constitute a general principle of self-governance of society and self-organisation of socialproduction, proposing a new division between common, public and private.Obviously, the success of these new practices is a complex process that must rely on institutions which accord and guarantee reproduction over time and space of the commons and common goods: ways of management based on self-governance and collaborative economics; relationships of exchange based on reciprocity and gratuitousness; legal regimes that, like the invention of copyleft for free software, guarantee the accumulation of a stock of common-pool resources (CPR); distribution norms that permit the active involvement of the commoners in the development of the commons, guaranteeing a basic income, for example.In this context, it becomes more and more essential and urgent to define the terms of an alternative model of regulating a knowledge-based society and economy at the centre of which the logic of the commons would perform an essential role

Using coupled micropillar compression and micro-Laue diffraction to investigate deformation mechanisms in a complex metallic alloy Al13Co4

In this investigation, we have used in-situ micro-Laue diffraction combined with micropillar compression of focused ion beam milled Al13Co4 complex metallic alloy to study the evolution of deformation in Al13Co4. Streaking of the Laue spots showed that the onset of plastic flow occured at stresses as low as 0.8 GPa, although macroscopic yield only becomes apparent at 2 GPa. The measured misorientations, obtained from peak splitting, enabled the geometrically necessary dislocation density to be estimated as 1.1 x 1013 m-2

Small scale fracture of bone to understand the effect of fibrillar organization on toughness

Fracture toughness is a critical component of bone quality and derives from the hierarchical arrangement of collagen and mineral from the molecular level to the whole bone level. Molecular defects, disease, and age affect bone toughness, yet there is currently no treatment to address deficits in toughness. Toughening mechanisms occur at every length scale, making it difficult to isolate the influence of specific components. Most experimental studies on the fracture behaviour of bone use milled samples of bone or whole bones. Toughness deficits can be identified but may be caused by a multitude of parameters across length-scales, making it difficult to develop targeted therapies. Herein, we measure the toughness of bone in micropillars where porosity and heterogeneities are minimized, allowing us to determine the role of fibril anisotropy on fracture toughness. Double cantilever beam micromechanical tests were conducted in a scanning electron microscope on 4x6x15 mm pillars of mouse bone femorae produced in the longitudinal and transverse orientations. Subsequent transmission electron microscopy of the fractured pillars revealed a role of the local organization of the mineralized collagen fibrils in influencing crack propagation. We demonstrate that fibril orientation is a critical factor in deflection during crack propagation, significantly contributing to fracture toughness