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Tarantino M.G.,Polytechnic of Milan | Beretta S.,Polytechnic of Milan | Foletti S.,Polytechnic of Milan | Papadopoulos I.,JRC European Commission
International Journal of Fatigue | Year: 2013

In the present paper, the mechanism of shear crack growth under both pure torsion and mixed mode loadings, simulating rolling contact fatigue testing conditions, has been investigated for a bearing steel and the role of the superimposed compressive stress in subsurface RCF has been clarified both numerically and experimentally. In particular a previous data set of fatigue tests on micro-notched specimens subjected to torsion and out-of-phase loads with |σmin|/τmax ≅ 3.5 (LP1) has been complemented with the new tests onto micro-notched specimens loads with |σmin|/τmax ≅ 0.7 (LP2) and a test under pure compression. The same tests have been also simulated numerically with a non-linear FE analysis of crack advance. The numerical analyses have been conducted with the aim of demonstrating that the compressive stress fully suppresses the tendency to tensile mode growth as the crack extends. Eventually, the competition between tensile and shear mode growth during a fatigue cycle has been investigated theoretically in terms of local branch SIFs. In particular, the conditions for the branch crack growth have been examined on the basis of the effective SIFs: the crack tip shielding effects due to the crack surface interference (both the mode I contribution caused by the asperity mismatch and the shear attenuation produced by the frictional stresses) have been quantified by employing a model for crack sliding interaction under pure mode III and mixed mode I + III loadings. © 2012 Elsevier Ltd. All rights reserved. Source


Bruggemann R.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Restrepo G.,University of Pamplona | Voigt K.,Helmholtz Center for Environmental Research | Annoni P.,JRC European Commission
Match | Year: 2013

Often a ranking based on a multi-indicator system is performed by construction of a composite indicator, which is generally computed as a weighted average of the indicators. The set of weighttuples is introduced: the g-space. Each point of this space represents a tuple of weight values, which lead together with the indicators of an object to a certain value of the composite indicator. The composite indicator induces a weak or linear order, when the associated space of an object set together with a data matrix is available. Each hypercube in the g-space, corresponding to intervals of the weights, can be represented by a partial order which is not necessarily a weak or even a linear order. Changing from one point of the hypercube to another will often not change the partial order. We have a freedom of changing weights according to the dimensionality of the g-space-1 (because of normalization). When other hypercubes are selected, then other partial orders can be found. The boundary between two hypercubes with different partial orders is a lower dimensional sphere, with fewer degrees of freedom. In the current paper we treat these two points: (i) how to use weight intervals to determine the resulting partial orders and (ii) if the number of indicators is not too large and if the focus is on a pair of objects instead on the whole set, then equations are given which can be helpful. As example pesticides are taken, for which three attributes are available. These pesticides are a subset of a set of 50 Italian pesticides, whose leaching potential to groundwater is investigated in Galassi et al.,1996. Source


Annoni P.,JRC European Commission | Bruggemann R.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Saltelli A.,JRC European Commission
Reliability Engineering and System Safety | Year: 2012

A special application of global sensitivity analysis is that on partially ordered sets - posets - that are sets of objects endowed by a binary order relation. In a partial order two objects can be in relation with each other, and are said to be comparable, or not, then they are said to be incomparable. Comparability and incomparability relations between objects can be visualized in a so called Hasse diagram, which is instructive in ranking the objects by multi-criteria/non-compensatory approaches. The interpretation of a Hasse diagram may be difficult even when the number of objects in the set is relatively small. Completely different configurations of the diagram can arise even for small perturbations of the starting data. Global sensitivity indices can shed light on the robustness of the partial order to data value uncertainty. Global measures particularly fit the case since posets are characterized by high number of dimensions and high-order interactions. These distinctive features of sensitivity analysis for posets make quasi-random designs perform almost the same as the random one as it is discussed here with a real test case for comparing the level of competitiveness of EU countries. © 2012 Elsevier Ltd. Source


Annoni P.,JRC European Commission | Bruggemann R.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Saltelli A.,JRC European Commission
Environmental Modelling and Software | Year: 2011

Partial order tools can be used in multiple criteria analysis to prioritize and rank a set of objects. In this setting the starting point is generally a matrix Mnxk of k observed indicators on n objects. Given that indicators are measured at least at the ordinal level, from matrix M its corresponding partially ordered set - poset - is set up to form the basis of multi-criteria ranking. The partial order may be very complex even when the number of objects to be compared is relatively small. The reason of such complexity is often due to the intrinsic nature of partial order which is exclusively based on the ordinal properties of the data matrix. Incomparabilities between objects can be due even to very small differences in the observed values of indicators thus causing 'irrelevant' incomparabilities. Also, objects may have been characterized with a redundant set of variables so that the change in the values of some indicators should not seriously affect the structure of the poset. These two opposite conditions are directly linked to the indicator level of influence and call for an indicator value related sensitivity analysis for testing the robustness of posets. In this work we propose a method to carry out a sensitivity analysis for posets by using variance-based sensitivity indices to detect main effects and interactions between indicators. To this aim, we characterize the poset structure with scalar measures and compute variance-based sensitivity indices according to the most recent practice for a fully exploratory sensitivity analysis. These indices allow for detecting least and most influencing indicators. © 2011 Elsevier Ltd. Source


Lisboa P.,JRC European Commission | Lisboa P.,University of Florence | Valsesia A.,JRC European Commission | Colpo P.,JRC European Commission | And 2 more authors.
Analytical Letters | Year: 2010

The development of advanced biosensor devices for very sensitive detection is highly required for many applications. The careful design of the bio-interface on the transducer surface is known to be one of the major bottlenecks for the development of high performance sensing devices. This paper reviews the emerging role of nanopatterned surfaces as alternative bio interface in the field of bio-detection. The different material used to functionalize this type of surfaces and the fabrication methodologies are described. Finally, the application of these surfaces in bio-detection using different biological systems and detection techniques is presented. In particular, a recent and very promising approach based on the optical interaction of nanoarrays with Surface Plasmon Resonance detection is described. © Taylor & Francis Group, LLC. Source

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