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Clermont-Ferrand, France

Le Cam J.-B.,French Institute for Advanced Mechanics
Rubber Chemistry and Technology | Year: 2010

Elastomeric materials are subjected to significant change in volume during their deformation. This paper proposes to review the change in volume of stretched rubber and to highlight why volume change can be considered as a relevant mechanical quantity to characterize rubbery materials in terms of microstructure evolution. The first part of the present review examines experimental measurements of volume change reported from the end of the 19th century until now. The second part reports the models proposed to predict the change in volume of stretched rubbers. These are formulated for small deformations. Some of them account for the decrease in volume due to crystallization.


Gogu G.,French Institute for Advanced Mechanics
Meccanica | Year: 2011

The paper addresses bifurcation in constraint singularities in connection with structural parameters of parallel mechanisms. The new formulae of mobility, connectivity, overconstraint and redundancy of parallel robots, recently proposed by the author, are used to characterize the bifurcation in constraint singularities. By using these formulae, we have demonstrated that, in a constraint singularity, the instantaneous values of mobility, connectivity of the moving platform and degree of overconstraint increase with no changes in limb connectivity. When bifurcation occurs in a constraint singularity, the mechanism can reach different branches characterized by different independent motions of the moving platform. Bifurcation in constraint singularities is easily identified by inspection with no need to calculate the augmented Jacobian. © 2010 Springer Science+Business Media B.V.


Gogu G.,French Institute for Advanced Mechanics
European Journal of Mechanics, A/Solids | Year: 2012

This paper presents a new family of T2R1-type parallel manipulators with bifurcated planar-spatial motion of the moving platform. In each branch, the moving platform has two independent translations (T) and one rotation (R) driven by three actuators mounted on the fixed base or on a moving link. The rotation axis is perpendicular to the plane of translations or parallel to this plane. In the first case, the moving platform has a planar motion, and in the second case, a spatial motion. The bifurcation between planar and spatial motion occurs in a constraint singularity in which the connectivity between the moving and fixed platforms increases instantaneously with no change in limb connectivity. Overconstrained/isostatic parallel manipulators with decoupled/uncoupled motions and maximally regular solutions with bifurcated planar-spatial motion of the moving platform are presented for the first time. © 2011 Elsevier Masson SAS. All rights reserved.


Gogu G.,French Institute for Advanced Mechanics
Journal of Mechanisms and Robotics | Year: 2011

This paper presents a new family of maximally regular T2R1-type parallel manipulators with bifurcated spatial motion. In each branch, the moving platform has two independent translations (T2) and one rotation (R1) driven by three actuators mounted on the fixed base. The rotation axis is situated in the plane of translation and can bifurcate in two orthogonal directions. This bifurcation occurs in a constraint singularity in which the connectivity between the moving and fixed platforms increases instantaneously, incurring no change in limb connectivity. The Jacobian matrix of the maximally regular solutions presented in this paper is a 3×3 identity matrix in the entire workspace of each branch. This paper presents for the first time a family of maximally regular T2R1-type parallel manipulators with bifurcated spatial motion of the moving platform along with solutions using uncoupled motions. © 2010 American Society of Mechanical Engineers.


Charlet K.,French Institute for Advanced Mechanics | Beakou A.,French Institute for Advanced Mechanics
International Journal of Adhesion and Adhesives | Year: 2011

In order to model the tensile behaviour of flax fibre based composites, the properties of each of the constituents need to be determined. In addition to the fibres, the matrix and the fibre/matrix interface, the fibre/fibre interface present within a bundle of flax fibres is an element which is rather hard to characterize but whose properties also need to be taken into account to understand properly the deformation and rupture modes of the derived composites. In the first part of this study, the protocol used to determine these properties is described; the results of the mechanical tests and the microscopic observations carried out on pairs of fibres are given and exploited to lead to the fibre/fibre interface properties. In the second part, various cohesive zone models will be evaluated using these interface properties and numerical simulations will be performed for the purpose of validation. © 2011 Elsevier Ltd. All Rights Reserved.

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