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Dynamic crack initiation assessment with the coupled criterion
No full textInternational audienceAn extension of the coupled criterion (CC) of finite fracture mechanics is established in order to assess dynamic crack initiation. The main change compared to the classical quasi-static approach consists in considering the crack velocity profile during initiation instead of assuming an instantaneous crack initiation. The proposed approach enables the study of dynamic crack initiation under either quasi-static or dynamic loading. It is illustrated on several examples including transverse cracking in laminates, crack initiation in drilled specimen under quasi-static tension or compression and on a V-notch specimen subjected to time-dependent loading. The dynamic CC predicts crack initiation over a finite length occurring in a given time depending on the crack velocity. The influence of the initiation crack velocity profile is significative provided crack velocity is large enough. Taking into account dynamic effects enables a better representation of experimentally observed variation of initiation stress as a function of hole size under tensile loading in drilled hole specimens
Les défis des formations d'ingénieurs au Maghreb vus par les acteurs décisionnels
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The Satellite Constellation Design Problem via MI(N)LP Boosted with a Genetic Algorithm
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The influence of bearing material on the wear produced, application on the prodisc-C cervical prothesis
No full textInternational audienceCervical disc prostheses are designed to replace the degenerated intervertebral disc and recover movement between the vertebrae. These prostheses are made of at least two elements with a ball and socket design; this allows movement between the elements. The articular surfaces wear out, the polyethylene cores deteriorate (failure of polyethylene), and produce wear debris. This study focused on the Prodisc-C cervical disc prosthesis model with the design ball and socket and three degrees of freedom (3 DOF). The aim is to clarify the difference between the two bearings materials, Metal-on-Polyethylene (MoP) and Metal-on-Poly-ether-ether-ketone (MoPEEK), in terms of contact and wear. We designed this prosthesis model in 3D using Solidworks design software. Then, we imported this model to the Ansys Workbench simulation software to do the numerical analysis. We have fixed the lower plate and a fixed compressive load of 150 N was first applied on the upper plate, Next, this compressive load was combined with a rotational displacement of 7.5° in flexion, 6° in lateral bending, and 4° in axial rotation on the upper plate. After the simulation, we found that the contact pressure for the bearing material MoP is 5.53 MPa and justified this value using the Hertzian theory P0 = 4.9 MPa. Then the contact pressure for the bearing material MoPEEK is 11.09 MPa, justified by the Hertzian theory P0 = 10.74 MPa. The clinical reference polyethylene-on-cobalt alloy (prosthesis with polyethylene core MoP) was 1.05mm3/million cycles, compared to 0.83 mm3/million cycles MoPEEK, a 20.95% discount has been won
Three-dimensional micro-structurally informed in silico myocardium—Towards virtual imaging trials in cardiac diffusion weighted MRI
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Kernel representation of Kalman observer and associated H-matrix based discretization
No full textInternational audienceIn deterministic estimation, applying a Kalman filter to a dynamical model based on partial differential equations is theoretically seducing but solving the associated Riccati equation leads to a so-called curse of dimensionality for its numerical implementation. In this work, we propose to entirely revisit the theory of Kalman filters for parabolic problems where additional regularity results proves that the Riccati equation solution belongs to the class of Hilbert-Schmidt operators. The regularity of the associated kernel then allows to proceed to the numerical analysis of the Kalman full space-time discretization in adapted norms, hence justifying the implementation of the related Kalman filter numerical algorithm with H-matrices typically developed for integral equations discretization
Conception d'une application de soutien à la coéducation pour l'inclusion scolaire des élèves avec des Troubles du Spectre de l'Autisme (TSA)
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Efficient Proofs of Retrievability using Expander Codes
No full textInternational audienceProofs of Retrievability (PoR) protocols ensure that a client can fully retrieve a large outsourced file from an untrusted server. Good PoRs should have low communication complexity, small storage overhead and clear security guarantees. We design a good PoR based on a family of graph codes called expander codes. We use expander codes based on graphs derived from point-line incidence relations of finite affine planes. Høholdt et al. showed that, when using Reed-Solomon codes as inner codes, these codes have good dimension and minimum distance over a relatively small alphabet. Moreover, expander codes possess very efficient unique decoding algorithms. We take advantage of these results to design a PoR scheme that extracts the outsourced file in quasi-linear time and features better concrete parameters than state-of-the-art schemes w.r.t storage overhead and size of the outsourced file
Graded damage in quasi‐brittle solids
No full textInternational audienceA novel approach to damage modeling for quasi-brittle solids is presented relying upon a differential inclusion that is closely related to the one of implicit gradient models. The proposed formulation naturally fits in the socalled non-local standard approach, whereby the framework of GeneralizedStandard Materials is extended to include gradients of internal variables to account for the physics of the fracture phenomenon in a regularized sense, i.e. via extended constitutive equations in which a length scale parameter brings to the macro level information about material microstructure. This concept is fully embodied into the present approach to quasi-brittle fracture, whereby progressive damage occurs in layers of finite thickness where the gradient of damage is bounded and a fully damaged region is understood as a fracture with no ambiguity. Key to the effective implementation of the model are the choice of two constitutive functions and the implicit tracking of regions in a state of progressive damage via Lagrange multipliers acting on internal constraints. The ideas are developed for a general Cauchy continuum and representative numerical simulations are included that demonstrate the model capabilities