Publications

2010

• Dual integrals in non linear fracture mechanics
  
  • Stolz Claude
  , 2010. We study the invariance of integrals based on free and complementary energy in elastoplasticity.
• A non-isothermal fatigue crack growth law for the A356-T7 aluminium alloy
  
  • Merhy Elias
  • Rémy Luc
  • Maitournam Habibou
  • Augustins Louis
  , 2010, pp.#43. Fatigue crack growth period in cylinder heads of A356-T7 casting alloy has been found to constitute an important part of the structure's total life. Therefore, the fatigue model design should consider crack propagation life. Then, in order to find a new crack growth law, finite element simulations on a cylinder head 3D model and fatigue crack tests have been conducted as to establish the contribution of each loading parameter in governing the crack propagation. SEM, optical microscopy and other metallographic techniques have been used to examine fracture surfaces and to analyze particles cracking. It has been found that the crack growth mechanism changes gradually at the microstructural scale with the increasing of Kmax value. Performing tests at variable frequencies has shown important crack growth time dependence. Negative load ratio tests have revealed a primordial importance of the compressive load part on the crack advance. Using experimental and numerical results, a new "damage tolerant" model design based on a non-isothermal crack growth prediction law has been introduced. The law is based on a corrected linear elastic fracture mechanics stress intensity factor Kp accounting for the cumulative crack tip plasticity. The law figures all of the purely fatigue effect, the crack growth under monotonic loading condition (time dependent parameter) and the effect of the compressive load on the global crack advance.
• Construction and justification of Paris-like fatigue laws from Dugdale-type cohesive models
  
  • Abdelmoula Radhi
  • Marigo Jean-Jacques
  • Weller Thibaut
  Annals of Solid and Structural Mechanics, Springer Berlin Heidelberg, 2010, 1, pp.139-158. We propose a construction of fatigue laws from cohesive forces models in the case of a crack submitted to a mode I cyclic loading. Taking the cumulated opening as the memory variable and the surface energy density associated with Dugdale's model, we explicitly construct the fatigue law which gives the crack growth rate by cycle d'/dN in terms of the stress intensity factor KI. In particular, we recover a Paris law with an exponent 4, i.e., d'/dN = CKI 4, when KI is small, the coefficient C being explicitly expressed in terms of the material parameters. Furthermore, the law can be applied in the full range of values of KI and can be extended to non simple cycles. (10.1007/s12356-010-0011-3)
  DOI : 10.1007/s12356-010-0011-3
• Synthetic description of the piano soundboard mechanical mobility
  
  • Ege Kerem
  • Boutillon Xavier
  , 2010, pp.5. An expression of the piano soundboard mechanical mobility (in the direction normal to the soundboard) depending on a small number of parameters and valid up to several kHz is given in this communication. Up to 1.1 kHz, our experimental and numerical investigations confirm previous results showing that the soundboard behaves like a homogeneous plate with isotropic properties and clamped boundary conditions. Therefore, according to the Skudrzyk mean-value theorem (Skudrzyk 1980), only the mass of the structure M, the modal density n(f), and the mean loss factor eta(f), are needed to express the average driving point mobility. Moreover, the expression of the envelope - resonances and antiresonances - of the mobility can be derived, according to (Langley 1994). We measured the modal loss factor and the modal density of the soundboard of an upright piano in playing condition, in an anechoic environment. The measurements could be done up to 2.5 kHz, with a novel high-resolution modal analysis technique (see the ICA companion-paper, Ege and Boutillon (2010)). Above 1.1 kHz, the change in the observed modal density together with numerical simulations confirm Berthaut's finding that the waves in the soundboard are confined between adjacent ribs (Berthaut et al. 2003). Extending the Skudrzyk and Langley approaches, we synthesize the mechanical mobility at the bridge up to 2.5 kHz. The validity of the computation for an extended spectral domain is discussed. It is also shown that the evolution of the modal density with frequency is consistent with the rise of mobility (fall of impedance) in this frequency range and that both are due to the inter-rib effect appearing when the half-wavelength becomes equal to the rib spacing. Results match previous observations by Wogram (1980), Conklin (1996), Giordano (1998), Nakamura (1983) and could be used for numerical simulations for example. This approach avoids the detailed description of the soundboard, based on a very high number of parameters. However, it can be used to predict the changes of the driving point mobility, and possibly of the sound radiation in the treble range, resulting from structural modifications.
• Vibrational and acoustical characteristics of the piano soundboard
  
  • Ege Kerem
  • Boutillon Xavier
  , 2010, pp.427. The vibrations of the soundboard of an upright piano in playing condition are investigated. It is first shown that the linear part of the response is at least 50 dB above its nonlinear component at normal levels of vibration. Given this essentially linear response, a modal identification is performed in the mid-frequency domain [300-2500] Hz by means of a novel high resolution modal analysis technique (Ege, Boutillon and David, JSV, 2009). The modal density of the spruce board varies between 0.05 and 0.01 modes/Hz and the mean loss factor is found to be approximately 2%. Below 1.1 kHz, the modal density is very close to that of a homogeneous isotropic plate with clamped boundary conditions. Higher in frequency, the soundboard behaves as a set of waveguides defined by the ribs. A numerical determination of the modal shapes by a finite-element method confirms that the waves are localised between the ribs. The dispersion law in the plate above 1.1 kHz is derived from a simple waveguide model. We present how the acoustical coincidence scheme is modified in comparison with that of thin plates. The consequences in terms of radiation of the soundboard in the treble range of the instrument are also discussed.
• A Modeling Approach to Predict Fretting Fatigue on Highly Loaded Blade Roots
  
  • Wackers Patrick Yves
  • Arrieta Victor Hernan
  • Alquezar-Getan Marcel
  • Constantinescu Andrei
  • Maitournam Habibou
  Journal of Engineering for Gas Turbines and Power, American Society of Mechanical Engineers, 2010, 132 (8), pp.pages : 082101-1 082101-9. A lifing technique for predicting fretting fatigue on highly loaded blade-disk attachments has been developed and calibrated. The approach combines extensive testing on nickel and titanium based alloys using a specially devised multiaxial fretting test machine and an analytical lifing procedure, based on finite element contact calculations and multiaxial shakedown fatigue models. In order to reproduce realistic operational conditions and standardize testing conditions, a special fretting fatigue testing machine with high temperature testing capabilities was developed. The machine was employed to perform systematic testing under prescribed load and displacement conditions at representative temperatures. Making use of FEA, the rig test results were calculated to identify relevant parameters such as friction coefficient, slip conditions, and machine compliance. The computation procedure involves the calculation of several major loading cycles until a stabilized response of the structure is achieved. The material response is assumed to be elastoplastic, and a nonlinear friction law (space and time) was applied. From the computed mechanical variables, several life prediction models are benchmarked to establish their capabilities to predict fretting fatigue life. Finally, a most promising life estimation procedure was applied to predict life in a real compressor blade-disk attachment. Predicted failure location and number of cycles to failure are compared against engine test results. The experimental-analytical approach has the potential to predict fretting fatigue risk during the design phase on highly loaded joints, as well as estimating the preventive overhaul intervals for parts already in service. (10.1115/1.3205026)
  DOI : 10.1115/1.3205026
• Procédé et dispositif d'analyse d'interactions moléculaires et utilisations
  
  • Türkcan Silvan
  • Allain Jean-Marc
  • Alexandrou Antigoni
  , 2010. L'invention se rapporte à un procédé d'analyse d'une interaction entre une première molécule et une deuxième molécule liée à une particule, comprenant les étapes suivantes : - mettre en contact la première molécule et la deuxième molécule liée à la particule dans des conditions rendant possible leur interaction, - appliquer un flux liquide déterminé sur la particule liée à la deuxième molécule, - observer un déplacement de la particule liée à la deuxième molécule sous l'action du flux appliqué, - analyser l'interaction en fonction du déplacement observé et du flux appliqué, la particule ayant une résistance hydrodynamique supérieure à celle de la première et/ou de la deuxième molécule, et un nombre de Péclet massique supérieur à 1 L'invention se rapporte également à un dispositif d'analyse d'une interaction entre une première molécule et au moins une deuxième molécule, ainsi qu'à l'utilisation du procédé ou du dispositif dans un criblage d'une molécule candidate pour le développement d'un médicament.
• A thermodynamical approach of contact wear and friction
  
  • Stolz Claude
  , 2010.
• Stability of non localized responses for damaging materials
  
  • Marigo Jean-Jacques
  • Pham Kim
  Vietnam Journal of Mechanics, Viện Hàn Lâm Khoa học và Công nghệ Việt Nam, 2010, 30 (4), pp.1-11. This work is devoted to the analysis of the stability of the homogeneous states of a bar made of a brittle strain softening material submitted to a tensile loading. We distinguish two types of damage models: local damage models and gradient damage models. We show that a local damage model necessarily leads to the unstability of the homogeneous response once the first damage threshold is reached. On the contrary, in the case of a gradient damage model, viewed as a regularization of the underlying local model, the homogeneous damage states of “sufficiently small” bars are stable.
• Identification of honeycomb sandwich properties by high-resolution modal analysis
  
  • Rébillat Marc
  • Boutillon Xavier
  , 2010, pp.452. A method is proposed to identify the mechanical properties of the skin and core materials of honeycomb sandwich. All the elastic coefficients and loss-factors that matter in the dynamics of a panel in the thick-plate approximation are identified. To this end, experimental natural modes (i.e. eigenmodes of the damped system) are compared to the numerical modes of a large sandwich panel (lx,y/h ≃ 80). The chosen generic model for the visco-elastic behaviour of the materials is E(1 + jd). The numerical modes are computed by means of a Rayleigh-Ritz procedure and their dampings are predicted according to the visco-elastic model. The frequencies and dampings of the natural modes of the panel are estimated experimentally by means of a high-resolution modal analysis technique. An optimisation procedure yields the desired coefficients. A sensitivity analysis assess the reliability of the method.
• Experimental characterisation of damage in SiC/SiC minicomposites
  
  • Chateau Camille
  • Gélébart L.
  • Bornert Michel
  • Crépin Jérôme
  • Caldemaison Daniel
  • Boller Elodie
  • Sauder C.
  • Langer M.
  • Ludwig Wolfgang
  , 2010, 6 (200002), pp.8 p.. SiC/SiC composites are studied for their potential use in the next generation of nuclear reactors. A multiscale approach is under development to construct a predictive modelling of their complex damageable mechanical behaviour due to their heterogeneous microstructure. This paper focuses on the damage characterisation of the composite at the scale of the tow at room temperature, both in terms of its spatial distribution and its chronology. Such observations are necessary to validate a multiscale damage modelling at the microscopic scale. The nonlinear behaviour is related to the accumulation of damages such as matrix cracking, fibre/matrix debonding and finally fibre breaking. Therefore, in-situ tensile tests were carried out on SiC/SiC minicomposites using scanning electron microscopy. Specific procedures could be used to get statistical data on the crack evolution. The first results especially show that the growth of the crack openings over the global strain is related to inter-crack distance. This test was complemented by a microtomographic investigation, conducted at the ESRF, performed on a minicomposite submitted to a tensile load. An analysis conducted on the 3D image of a crack shows a slow propagation of the matrix cracking through the minicomposite section. (10.1051/epjconf/20100620002)
  DOI : 10.1051/epjconf/20100620002
• Multiscale surface and volume full-field strain measurements for improved insights on the micromechanics of materials - Application to rock salt
  
  • Bornert Michel
  • Bourcier M.
  • Dimanov A.
  • Raphanel J.
  • Héripré E.
  • Caldemaison D.
  , 2010.
• A simple experimental procedure to quantify image noise in the context of strain measurements at the microscale using DIC and SEM images
  
  • Wang Linlin
  • Héripré E.
  • El Outmani S.
  • Caldemaison Daniel
  • Bornert Michel
  , 2010. Image noise is an important factor that influences the accuracy of strain field measurements by means of digital image correlation and scanning electron microscope (SEM) imaging. We propose a new model to quantify the SEM image noise, which extends the classical photon noise model by taking into account the brightness setup in SEM imaging. Furthermore, we apply this model to investigate the impact of different SEM setting parameters on image noise, such as detector, dwell time, spot size, and pressure in the SEM chamber in the context of low vacuum imaging. (10.1051/epjconf/20100640008)
  DOI : 10.1051/epjconf/20100640008
• In-situ analysis of strain localization related to structural heterogeneities of carbonate rocks
  
  • Dautriat Jérémie
  • Bornert Michel
  • Gland N.
  • Dimanov A.
  • Raphanel Jean
  , 2010.
• Discrete volumetric digital image correlation for the investigation of granular type media at microscale : accuracy assessment
  
  • Pannier Yannick
  • Lenoir Nicolas
  • Bornert Michel
  , 2010, 6 (35003), pp.8 p.. The recent development of efficient 3D imaging tools such as X-Rays computed microtomography combined with the extension to volumetric images of Digital Image Correlation (DIC) techniques provide new insights on the analysis of materials and structures. Among many other possible fields of application, geomaterials are good candidates for such investigations, owing to their relative transparency to X-rays and the presence in many samples of a natural contrast suitable for deformation mapping. However, these materials often deform discontinuously at microscale, for instance in the form of the development of a networks of microcracks. Discontinuity is even the dominant rule in granular-type materials such as sand in which the contribution to overall deformation of the microcontinuous phenomena -elastic strains inside grains- are negligible. To investigate deformation at the scale of these discontinuous mechanisms, specific DIC algorithms are required, which override the assumption of continuity of the transformation at the scale of the correlation windows. The recent so-called Discrete-DIC procedure (Hall et al, 2010) is a possible answer. We recall here its general principles and focus on its potential accuracy, from both theoretical and practical points of view. We show that the position and the rotation of individual grains with an average diameter of 500µm can be determined from images recorded with a laboratory microCT scanner, with a 15µm voxel size, with an accuracy of the order of 1µm and 0,1 degree, respectively. (10.1051/epjconf/20100635003)
  DOI : 10.1051/epjconf/20100635003
• Metrological analysis of several algorithms used to demodulate images with spatial carrier
  
  • Molimard J.
  • Badulescu Claudiu
  • Bornert Michel
  • Dupré J.C.
  • Equis S.
  • Grediac Michel
  • Picart Pascal
  • Rotinat R.
  • Valle Valery
  , 2010.
• Optimized optical setup for DIC in rock mechanics
  
  • Yang D.S.
  • Bornert Michel
  • Gharbi H.
  • Valli P.
  • Wang L.L
  , 2010.
• A 12-year long cavern abandonment test.
  
  • Berest Pierre
  • Bérest P.
  , 2010, volume 6, pp.22003.
• Histological and biomechanical study of dura mater applied to the technique of dura splitting decompression in Chiari type I malformation.
  
  • Chauvet Dorian
  • Carpentier Alexandre
  • Allain Jean-Marc
  • Polivka Marc
  • Crépin Jérôme
  • George Bernard
  Neuro Surgical Review, 2010, 33 (3), pp.287-94; discussion 295. Many techniques are described to treat Chiari type I malformation. One of them is a splitting of the dura, removing its outer layer only to reduce the risks of cerebrospinal fluid (CSF) leak. We try to show the effectiveness of this technique from histological and biomechanical observations of dura mater. Study was performed on 25 posterior fossa dura mater specimens from fresh human cadavers. Dural composition and architecture was assessed on 47 transversal and sagittal sections. Uniaxial mechanical tests were performed on 22 dural samples (15 entire, 7 split) to focus on the dural macroscopic mechanical behavior comparing entire and split samples and also to understand deformation mechanisms. We finally created a model of volume expansion after splitting. Dura mater was composed of predominant collagen fibers with a few elastin fibers, cranio-caudally orientated. The classical description of two distinct layers remained inconstant. Biomechanical tests showed a significant difference between entire dura, which presents an elastic fragile behavior, with a small domain where deformation is reversible with stress, and split dura, which presents an elasto-plastic behavior with a large domain of permanent strain and a lower stress level. From these experimental results, the model showed a volume increase of approximately 50% below the split area. We demonstrated the capability of the split dura mater to enlarge for suitable stress conditions and we quantified it by biomechanical tests and experimental model. Thus, dural splitting decompression seems to have a real biomechanical substrate to envision the efficacy of this Chiari type I malformation surgical technique. (10.1007/s10143-010-0261-x)
  DOI : 10.1007/s10143-010-0261-x
• Very slow creep tests on rock samples.,
  
  • Berest Pierre
  • Bérest P.
  • Brouard B.
  • Charpentier J. P.
  • Gharbi Hakim
  • Valès Frédéric
  , 2010, volume 6, pp.22002.
• Mechanosensitive control of growth in plants : stresses , strains or strain rates
  
  • Moulia Bruno B.
  • Der Loughian Christelle C.
  • Martin Ludovic L.
  • Coutand Catherine
  • Julien Jean-Louis J.-L.
  • Fournier-Leblanc Nathalie N.
  • Allain Jean-Marc J.-M.
  , 2010. absent
• Assemblages collés bois-béton : comprendre pour faire durer
  
  • Loulou Louisa
  • Caré Sabine
  • Le Roy Robert
  • Chataigner Sylvain
  • Bornert Michel
  • Nedjar Boumediene
  , 2010. Présentation des objectifs de la thèse de Louisa Loulou : Dans un contexte international qui cherche à préserver l'environnement, les structures composées de matériaux renouvelables comme le bois sont des solutions technologiques intéressantes, vis-à-vis notamment de la réduction de l'émission de CO2, étant donné le puits de carbone que constitue ce matériau. Afin de concevoir des structures de bois et /ou des structures mixtes béton/bois et de proposer des solutions technologiques optimisées, tant sur le plan structurel qu'environnemental, le laboratoire Navier a entamé, depuis quelques années, des recherches théoriques et expérimentales relatives à l'optimisation de telles structures notamment vis-à-vis de leurs dimensionnements. Des systèmes d'assemblage bois/béton par collage ont ainsi été développés et sont apparus comme étant très performants du point de vue de la tenue mécanique en fatigue de structures mixtes pour des conditions thermo-hydriques constantes. En prolongement des travaux effectués, le travail de thèse consiste à prendre en compte les effets différés induits par des sollicitations complexes thermo-hydriques dans l'analyse de la tenue mécanique à long terme de ces structures mixtes bois/béton.
• Analyse multiéchelle par corrélation d'images des champs cinématiques dans les géomatériaux
  
  • Bornert Michel
  • Vales F.
  • Pannier Y.
  • Dautriat J.
  • Yang D.
  • Bourcier M.
  , 2010.
• Dual approach in non-linear fracture mechanics
  
  • Stolz Claude
  International Journal of Fracture, Springer Verlag, 2010, 166, pp.135-143. A dual approach in fracture mechanics based on complementary energy is proposed. The analysis of the dissipation shows that the thermodynamical force associated with the evolution of a crack is an energy release rate, form of which depends on the presence or not of mechanical discontinuties. This energy release rate is given as a integral based on free or complementary energy. The invariance of integrals is analysed and the obtained results in elastoplasticity are discussed. The energy release rate is determined in terms of potential energy or complementary energy, first in elasticity and secondly in elastoplasticity. Associated to these definitions, the laws of propagation of the crack is chosen as a Griffith law and the propagation is governed by a normality rule. In this framework we formulate the evolution problem concerning crack propagation in an elastoplastic material. Variational formulations are obtained in terms of rate of displacement, of stresses and of crack length. (10.1007/s10704-010-9516-3)
  DOI : 10.1007/s10704-010-9516-3
• Initiation of cracks in Griffith's theory: an argument of continuity in favor of global minimization
  
  • Marigo Jean-Jacques
  Journal of Nonlinear Science, Springer Verlag, 2010, 20 (6), pp.831-868. The initiation of a crack in a sound body is a real issue in the setting of Griffith's theory of brittle fracture. If one uses the concept of critical energy release rate (Griffith's criterion), it is in general impossible to initiate a crack. On the other hand, if we replace it by a least energy principle (Francfort-Marigo's criterion), it becomes possible to predict the onset of cracking in any circumstance. However this latter criterion can appear too strong. We propose here to reinforce its interest by an argument of continuity. Specifically, we consider the issue of the initiation of a crack at a notch whose angle $\omega$ is considered as a parameter. The result predicted by the Griffith criterion is not continuous with respect to $\omega$, since no initiation occurs when $\omega>0$ while a crack initiates when $\omega=0$. In contrast, the Francfort-Marigo's criterion delivers a response which is continuous with respect to $\omega$, even though the onset of cracking is necessarily brutal when $\omega>0$