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Sinou J.-J.,CNRS Tribology and Dynamic Systems Laboratory | Faverjon B.,CNRS Contacts and Structural Mechanics Laboratory
Journal of Sound and Vibration | Year: 2012

The aim of this paper is to investigate the effects of the presence of a transverse crack in a rotating shaft under uncertain physical parameters in order to obtain some indications that might be useful in detecting the presence of a crack in rotating system. The random dynamic response of the cracked rotor is evaluated by expanding the changing stiffness of the crack (i.e. the breathing mechanism) as a random truncated Fourier series. To avoid the use of the Monte Carlo simulations (MCS), an alternative procedure that is based on a combination of the Harmonic Balance Method and the Stochastic Finite Element Method (SFEM) using the Polynomial Chaos Expansion (PCE) is proposed. So the response of the Fourier components of the cracked rotor is expanded in the polynomial chaoses. The random dynamic response obtained by applying this procedure is compared with that evaluated through numerical integration based on the Harmonic Balance Method and the Monte Carlo simulations. © 2011 Elsevier Ltd. All rights reserved.


Mollon G.,CNRS Contacts and Structural Mechanics Laboratory | Zhao J.,Hong Kong University of Science and Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2014

The inability of simulating the grain shapes of granular media accurately has been an outstanding issue preventing particle-based methods such as discrete element method from providing meaningful information for relevant scientific and engineering applications. In this study we propose a novel statistical method to generate virtual 3D particles with realistically complex yet controllable shapes and further pack them effectively for use in discrete-element modelling of granular materials. We combine the theory of random fields for spherical topology with a Fourier-shape-descriptor based method for the particle generation, and develop rigorous solutions to resolve the mathematical difficulties arising from the linking of the two. The generated particles are then packed within a prescribed container by a cell-filling algorithm based on Constrained Voronoi Tessellation. We employ two examples to demonstrate the excellent control and flexibility that the proposed method can offer in reproducing such key characteristics as shape descriptors (aspect ratio, roundness, sphericity, presence of facets, etc.), size distribution and solid fraction. The study provides a general and robust framework on effective characterization and packing of granular particles with complex shapes for discrete modelling of granular media. © 2014 Elsevier B.V.


Rethore J.,University Claude Bernard Lyon 1 | Rethore J.,CNRS Contacts and Structural Mechanics Laboratory
International Journal for Numerical Methods in Engineering | Year: 2010

Constitutive parameter identification has been greatly improved by the achievement of full-field measurements. In this context, noise sensitivity has been shown to be of great importance. It is crucial to incorporate noise sensitivity minimization in the design of robust identification procedures. In this paper, we investigate noise sensitivity reduction techniques for constitutive parameter identification based on Finite Element Model Updating. After examining the existing strategies, we propose a single step algorithm based on a mixed optical/mechanical cost function. The key point of this novel procedure is that no boundary conditions are needed. A first example on a real case illustrates the advantages of the proposed methodology in terms of noise sensitivity. A second example shows its capabilities to identify a non-linear consitutive law. © 2010 John Wiley & Sons, Ltd.


Rethore J.,CNRS Contacts and Structural Mechanics Laboratory
International Journal for Numerical Methods in Engineering | Year: 2015

With the development of full-field measurement techniques, it has been possible to analyze crack propagation experimentally with an increasing level of robustness. However, the analysis of curved cracks is made difficult and almost unexplored because the possible analysis domain size decreases with crack curvature, leading to an increasing uncertainty level. This paper proposes a digital image correlation technique, augmented by an elastic regularization, combining finite element kinematics on an adapted mesh and a truncated Williams' expansion. Through the analysis of two examples, the proposed technique is shown to be able to address the experimental problems of crack tip detection and stress intensity factors estimation along a curved crack path. © 2015John Wiley & Sons, Ltd.


Gu X.,CNRS Contacts and Structural Mechanics Laboratory | Velex P.,CNRS Contacts and Structural Mechanics Laboratory
Mechanism and Machine Theory | Year: 2013

Eccentricity errors are incorporated into a planetary gear lumped parameter model in which deflections, errors and gear geometry are coupled. In the presence of errors, rigid-body positions and motions are perturbed leading to initial separations between tooth flanks and inertial excitations caused by unsteady rotational speeds. The equations of motion are solved by combining a time-step scheme, a contact algorithm and a fixed-point method, which make it possible to determine and use mesh instantaneous characteristics in the calculations of tooth loads. A number of quasi-static and dynamic results are presented which show that eccentricities can be highly influential on planetary gear dynamic behaviour. Finally, the interest of floating members in equalizing planet dynamic loading is demonstrated and commented upon. © 2012 Elsevier Ltd.


Gu X.,CNRS Contacts and Structural Mechanics Laboratory | Velex P.,CNRS Contacts and Structural Mechanics Laboratory
Journal of Sound and Vibration | Year: 2012

An original lumped parameter model of planetary gears is presented which accounts for planet position errors and simulates their contribution to the quasi-static and dynamic load sharing amongst the planets. A unique feature of the model is that instantaneous gear geometry is used which depends on the combination of deflections and errors. The numerical results compare well with experimental evidence from the literature thus validating the modelling methodology. Simulations are then extended to dynamic tooth loads and trajectories for both fixed and rotating carriers. Finally, the advantages and drawbacks of floating members in high-speed planetary gears are illustrated and commented upon. © 2012 Elsevier Ltd.


Dureisseix D.,CNRS Contacts and Structural Mechanics Laboratory
International Journal of Space Structures | Year: 2012

Origami (paperfolding) has greatly progressed since its first usage for design of cult objects in Japan, and entertainment in Europe and the USA. It has now entered into artistic areas using many other materials than paper, and has been used as an inspiration for scientific and engineering realizations. This article is intended to illustrate several aspects of origami that are relevant to engineering structures, namely: geometry, pattern generation, strength of material, and mechanisms. It does not provide an exhaustive list of applications nor an in-depth chronology of development of origami patterns, but exemplifies the relationships of origami to other disciplines, with selected examples.


Osman T.,CNRS Contacts and Structural Mechanics Laboratory | Velex P.,CNRS Contacts and Structural Mechanics Laboratory
Tribology International | Year: 2012

The main objective of the paper is to study the possible interactions between contact fatigue and dynamic tooth loads on gears. A specific 3D dynamic gear model is combined to contact fatigue models accounting for crack initiation and propagation. The numerical findings compare well with the experimental evidence from a back-to-back test rig. Three characteristic points on a tooth profile are analysed and it is shown that contact fatigue on spur gears clearly depends on dynamic phenomena. Finally, the introduction of profile relief is discussed and its positive influence on the risk of failures at engagement is emphasised. © 2011 Elsevier Ltd.


Bouclier R.,CNRS Contacts and Structural Mechanics Laboratory | Elguedj T.,CNRS Contacts and Structural Mechanics Laboratory | Combescure A.,CNRS Contacts and Structural Mechanics Laboratory
Computer Methods in Applied Mechanics and Engineering | Year: 2012

We are interested in this work in methods that alleviate shear and membrane locking, typically involved in thick plates and shells. We investigate the use of higher order NURBS to address static straight and curved Timoshenko beam with several approaches usually used in standard locking free finite elements. Among theses methods, two main new strategies have been developed for NURBS: selective reduced integration and B projection method. Although the simplicity of implementation and the low computational cost suggest that the first method is attractive, this approach is difficult to be generalized to arbitrary polynomial order and continuity. Conversely, the B one offers a global formalism suitable to tackle every NURBS problem and appears then as the most serious concurrent. The resulting NURBS B element, which happens to be equivalent to a NURBS mixed element, provides robust and accurate results. The performance of the two methods is assessed on several numerical examples, and comparisons are made with other published techniques to prove their effectiveness. © 2012 Elsevier B.V..


Rethore J.,CNRS Contacts and Structural Mechanics Laboratory | Francois M.,CNRS Research Institute in Civil Engineering and Mechanics
Optics and Lasers in Engineering | Year: 2014

This paper presents a digital image correlation method able to detect and measure a contour or silhouette in a digital image, with a sub-pixel precision. A virtual image that describes a simple contour or silhouette roughly similar to the physical object to detect is created. The matching with the physical image of the object is then performed based on digital image correlation. We look for the displacement field which transforms the physical image which is the closest to the virtual one. In order to keep a problem of finite dimension, this field is decomposed on a B-spline basis. The algorithm is close to the digital image correlation method; an efficient implementation is proposed that makes use of levelsets. The full method is tested over both synthesized and real images, one of a star shaped toy and one on an ill-defined image of a high temperature metallic specimen on which no other boundary measurement was possible. The influence of the arbitrary choice of the virtual image contour or silhouette arbitrary parameters is discussed with respect to the precision of the method. This one is shown to be sub-pixel in any case. © 2013 Elsevier Ltd.

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