Publications

2000

• On viscous fluid flow near the moving crack tip
  
  • Bui Huy Duong
  • Guyon Corinne
  • Thomas Bernadette
  , 2000, 76, pp.63-74. We consider a crack partially filled with a fluid. We show that the presence of a lag avoids the appearance of pressure and velocity singularities. For the static equilibrium, we recall the previous result on the Capillary Stress Intensity Factor which provides a purely mechanical explanation of the Rehbinder effect, according to which the toughness of the material can be lowered by humidity. For the steady state propagation of a crack due to viscous fluid flow, we set the coupled system of non-linear equations. (10.1007/0-306-46946-4_4)
  DOI : 10.1007/0-306-46946-4_4
• Infrared thermography of the tensile behavior of natural gut string
  
  • Luong M. P.
  , 2000, pp.423-430. No abstract provided
• Genetic Programming and Domain Knowledge: Beyond the limitations of grammar-guided Machine Discovery
  
  • Ratle Alain
  • Sebag Michèle
  , 2000, pp.211-220. Application of Genetic Programming to the discovery of empirical laws is often impaired by the huge size of the domains involved. In physical applications, dimensional analysis is a powerful way to trim out the size of these spaces This paper presents a way of enforcing dimensional constraints through formal grammars in the GP framework. As one major limitation for grammar-guided GP comes from the initialization procedure (how to find admissible and sufficiently diverse trees with a limited depth), an initialization procedure based on dynamic grammar pruning is proposed. The approach is validated on the problem of identification of a materials response to a mechanical test. (10.1007/3-540-45356-3_21)
  DOI : 10.1007/3-540-45356-3_21
• Modelisation of dynamic crack propagation criteria
  
  • Karimzada T.
  • Maigre H.
  Journal de Physique IV Proceedings, EDP Sciences, 2000, 10, pp.461-466. The aim of this study is the analysis of the dynamic crack propagation criteria in materials under impact loading. We want to define which mechanical quantities monitor the propagation, then use these parameters in numerical simulations and finally compare the results with dynamic propagation experiments. First, we propose a 1D semi-analytical model. In this model several mechanical quantities can be used to define the propagation criterion, like the energy release rate... The effect of the applied loading and the reflections of waves is also very important, leading sometimes to a stick-slip propagation. Next, we present a 2D modelisation. In this case, it is not possible to study analytically the effect each criterion and we need to use a numerical simulation. We propose a numerical method based on finite element. The propagation is simulated by releasing nodes with a the release criterion defined from the propagation criterion. The numerical scheme is chosen to respect the equivalence between the total dissipation and the fracture dissipation. In parallel, we have performed dynamic propagation experiments on PMMA. The samples are DCB specimens loading with a wedge in a Kolsky set-up. During each test, the location of the crack has been recorded 4 times with high speed cameras (1 microsecond shutter). (10.1051/jp4:2000977)
  DOI : 10.1051/jp4:2000977
• Spatial localization of the error of constitutive law for the identification of defects in elastic bodies
  
  • Bui Huy Duong
  • Constantinescu Andreï
  Archives of Mechanics, Polish Scientific Publishers Pwn, 2000, 52, pp.511-522. The error on constitutive law (ECL) is a cost functional currently used in inverse problems for identifying interior distribution of coefficients of partial differential equations from overspecified boundary conditions. In previous works, different authors have shown that the ECL permits a good spatial localization of the perturbations of the coefficients. The purpose of this paper is to justify this spatial localization property. The result is obtained for the elliptic equations of elasticity using boundary integral representations of the solutions and comparing the linear and the perturbed solution of the problem.
• Usure induite par vibrations sous écoulement: le cas des grappes de commande des réacteurs a eau pressurisée. Des études théoriques aux applications industrielles
  
  • Zbinden M.
  • Dragon-Louiset M.
  Mechanics & Industry, EDP Sciences, 2000, 1, pp.581-592. Différents composants internes des réacteurs à eau pressurisée (REP), et en particulier les grappes de commande, subissent un endommagement par usure sous l'action des vibrations induites par les écoulements. Pour faire face à ce problème, un important programme de R&D a été lancé par EDF et ses partenaires. Afin de permettre des calculs prédictifs, un modèle industriel d'usure a été développé, fondé à la fois sur des résultats expérimentaux et sur la cinétique d'usure réelle observée en réacteur. La modélisation de l'usure proprement dite est le maillon final d'une suite de calculs qui commence par la détermination des excitations hydrauliques, se poursuit par le calcul de la réponse dynamique de la structure et des chargements dans les zones de contact, pour s'achever par l'estimation des volumes et des profondeurs d'usure. Des travaux plus théoriques, visant à comprendre et à modéliser les phénomènes mis en jeu ont également été entrepris. Une démarche pour la simulation des phénomènes d'usure douce est proposée, en annexe, associant une étude thermodynamique globale à un modèle de l'interface des deux corps en contact. Elle permet de tenir compte de l'influence de ce milieu complexe sur le chargement et l'usure des solides. L'originalité de ce travail réside dans la prise en compte de la perte de matière et de la physique de l'interface dans un modèle macroscopique.
• A BEM- and adjoint variable-based approach to crack shape sensitivity analysis
  
  • Bonnet Marc
  • Burczynski T.
  • Nowakowski M.
  , 2000, pp.169-176. This communication addresses a computation strategy, based on the adjoint variable approach and BIE/BEM formulations of the direct problem, for evaluating crack or void shape sensitivities of objective functionals. Boundary-only expressions for such sensitivities are sought, in the context of linear elastodynamics. In the case of a void, boundary-only expressions for sensitivities of integral functionals defined on (part of) the external boundary are easy to obtain by the standard adjoint variable approach. When the void degenerates to a crack, the previous result ceases to be applicable, however, because non-integrable terms arise due to crack-tip singularities. We show, for two classes of crack perturbations, that boundaryonly sensitivity expressions using an adjoint state can still be obtained: (1) simple transformations (translation, rotation or expansion of the crack) of arbitrarily shaped domains, and (2) general two-dimensional geometries and crack perturbations. In the latter case, the shape sensitivity is expressed using the primal and adjoint stress intensity factors. Numerical tests of the latter kind of sensitivity expression are presented for a 2-D body with an internal crack, in plane-strain elastodynamics. The influence of crack shape perturbations on an objective functional is examined. The sensitivity results obtained using the present strategy compare well with finite difference evaluations.