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The indentation can be cut out in 4 regimes. The first regime is elastic, the second is elastic-plastic the third and the last is respectively plastic and purely plastic. The model of spherical expansion of cavity define by Johnson is often used to describe the elastic plastic behaviour of the indentation. This model is developed starting from a variational study for geometries of auto-similar indenters. This article shows from a volume balance, the equality of relations between the volume moved by the indenter and the elastic compressed volume. We thus use this method to determine the relations for geometries which are not auto-similar, in particular for spherical and power functions. This study shows that one can define a universal parameter to describe the indentation in the plastic elastic mode for all the convex axisymmetric indenteurs. This is finally demonstrated by a study by finite elements. © 2011 EDP Sciences. Source


Greaves G.N.,University of Cambridge | Greaves G.N.,Aberystwyth University | Greer A.L.,University of Cambridge | Lakes R.S.,University of Wisconsin - Madison | Rouxel T.,CNRS Applied Mechanics Laboratory of Rennes University
Nature Materials | Year: 2011

In comparing a material's resistance to distort under mechanical load rather than to alter in volume, Poisson's ratio offers the fundamental metric by which to compare the performance of any material when strained elastically. The numerical limits are set by 1/2 and-1, between which all stable isotropic materials are found. With new experiments, computational methods and routes to materials synthesis, we assess what Poisson's ratio means in the contemporary understanding of the mechanical characteristics of modern materials. Central to these recent advances, we emphasize the significance of relationships outside the elastic limit between Poisson's ratio and densification, connectivity, ductility and the toughness of solids; and their association with the dynamic properties of the liquids from which they were condensed and into which they melt. © 2011 Macmillan Publishers Limited. All rights reserved. Source


Desage S.-F.,University of Savoy | Pitard G.,University of Savoy | Pillet M.,University of Savoy | Favreliere H.,University of Savoy | And 6 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The research purpose is to improve aesthetic anomalies detection and evaluation based on what is perceived by human eye and on the 2006 CIE report.1 It is therefore important to define parameters able to discriminate surfaces, in accordance with the perception of human eye. Our starting point in assessing aesthetic anomalies is geometric description such as defined by ISO standard,2 i.e. traduce anomalies description with perception words about texture divergence impact. However, human controllers observe (detect) the aesthetic anomaly by its visual effect and interpreter for its geometric description. The research question is how define generic parameters for discriminating aesthetic anomalies, from enhanced information of visual texture such as recent surface visual rendering approach. We propose to use an approach from visual texture processing that quantify spatial variations of pixel for translating changes in color, material and relief. From a set of images from different angles of light which gives us access to the surface appearance, we propose an approach from visual effect to geometrical specifications as the current standards have identified the aesthetic anomalies. © 2015 SPIE. Source


Garnier P.,The Innovation Company | Le Cam J.-B.,CNRS Applied Mechanics Laboratory of Rennes University | Grediac M.,CNRS Pascal Institute | Dubois M.,CNRS Pascal Institute | Ababou-Girard S.,University of Rennes 1
Constitutive Models for Rubber VIII - Proceedings of the 8th European Conference on Constitutive Models for Rubbers, ECCMR 2013 | Year: 2013

This study deals with the effects of coupled thermal and cyclic mechanical loadings on the viscoelastic response of carbon black filled nitrile rubber. For this purpose, cyclic loading tests were performed at different temperatures by means of DMTA. The type and level of the thermomechanical loadings applied were chosen in order to determine the relative contribution of each of the mechanical and thermal loadings (and their coupling) to the viscoelastic response during the cyclic tests. XPS and FTIR analyses were used to track the change in the microstructure corresponding to the evolution in the viscoelastic response. Results show that the storage modulus increases with the number of cycles, due to the crosslink increase, and that temperature amplifies this phenomenon. The main result is that the cyclic mechanical loading significantly amplifies the effect of temperature. © 2013 Taylor & Francis Group. Source


Rouxel T.,CNRS Applied Mechanics Laboratory of Rennes University | Sellappan P.,University of Illinois at Urbana - Champaign | Celarie F.,CNRS Applied Mechanics Laboratory of Rennes University | Houizot P.,CNRS Applied Mechanics Laboratory of Rennes University | Sangleboeuf J.-C.,CNRS Applied Mechanics Laboratory of Rennes University
Comptes Rendus - Mecanique | Year: 2014

The microcracking sequence (radial, median, lateral, and ring-like) arising at the glass surface under sharp contact loading and the extent to which these cracks develop is intimately related to the way the material attempts to relax the corresponding stress field. Two processes which are known to occur upon indentation are densification and isochoric shear flow. The contributions of both mechanisms were quantitatively assessed for glasses belonging to different chemical systems in previous papers [1-3]. In the present study, indentation cracking maps are provided, which offer guidelines to the design of glasses with better surface damage resistance based on their elastic properties and hardness. © 2013 Académie des sciences. Source

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