Generalized equation for transient-wave propagation in continuous inhomogeneous rigid-frame porous materials at low frequencies

International audienceThis paper provides a temporal model for the propagation of transient acoustic waves in continuous inhomogeneous isotropic porous material having a rigid frame at low frequency range. A temporal equivalent fluid model in which the acoustic wave propagates only in the fluid saturating the material, is considered. In this model, the inertial effects are described by the inhomogeneous inertial factor [A.N. Norris., J. Wave Mat. Interact. 1 365 (1986)]. The viscous and thermal losses of the medium are described by two inhomogeneous susceptibility kernels which depend on the viscous and thermal permeabilities . The medium is one dimensional and its physical parameters (porosity, inertial factor, viscous and thermal permeabilities) are depth dependent. A generalized wave propagation equation in continuous inhomogeneous material is established and discussed

Measuring static viscous permeability of porous absorbing materials

International audienceConventional acoustical methods for measuring the permeability or flow resistivity of a porous material require a priori estimation of the porosity. In this work, an acoustical method is presented in which a simplified expression (independent of both the frequency and porosity) for the transmitted waves at the Darcy’s regime (low frequency range) is derived, and used for the inverse determination of both the viscous static permeability (or flow resistivity) and the thickness of air-saturated porous materials. The inverse problem is solved based on the least-square numerical method using transmitted waves in time domain. Tests are performed using industrial plastic foams. Experimental and numerical validation results of this method are presented, which show theadvantage of measuring the viscous permeability and thickness of a porous slab, without the required prior knowledge of the porosity, but by simply using the transmitted waves

Microstructure and mechanical behavior of ultrafine-grained Ni processed by different powder metallurgy methods

Ultrafine-grained samples were produced from a Ni nanopowder by hot isostatic pressing (HIP) and spark plasma sintering (SPS). The microstructure and mechanical behavior of the two specimens were compared. The grain coarsening observed during the SPS procedure was moderated due to a reduced temperature and time of consolidation compared with HIP processing. The smaller grain-size and higher nickel-oxide content in the SPS-processed sample resulted in a higher yield strength. Compression experiments showed that the specimen produced by SPS reached a maximal flow stress at a small strain, which was followed by a long steady-state softening while the HIP-processed sample hardened until failure. It was revealed that the softening of the SPS-processed sample resulted from microcracking along the grain boundaries

Résistance au feu des profils creux en acier remplis de béton

Les colonnes en profil creux en acier rempli de béton sont largement utilisées dans le domaine du génie civil et en particulier dans la construction d’immeuble de grande hauteur. De nombreux travaux de recherche consacrés à la résistance au feu de ces profilés ont été réalisés en Europe et en Amérique du Nord. Bien que des méthodes de calcul soient désormais proposées par des codes et règlements, des outils plus pratiques sont nécessaires pour les ingénieurs de conception. Il n’est pas facile de développer de telles méthodes et cela en raison de la grande dispersion des résultats expérimentaux. Dans cet article, trois méthodes basées sur des procédures très différentes sont utilisées tout en examinant leurs potentialités mais aussi leurs domaines de validité et les résultats obtenus ont été comparés avec les résultats expérimentaux

Chloro complexes of cobalt(II) in aprotic solvents: stability and structural modifications due to solvent effect

Cobalt(II) chloro complexes were studied in aprotic solvents, namely, dimethylsulfoxide (DMSO), dimethylformamide (DMF), and propylene carbonate (PC). The measurements were performed spectrophotometrically in UV–visible–IR region at 25°C and at constant ionic strength: I = 1 mol L−1 in DMSO and DMF, and 0.1 mol L−1 in PC. Different models were tested and the model 1, 2, 3, 4, i.e., that of four mononuclear successive complexes was retained. Stability constants of the identified complexes were determined and they increase inversely with the Gutmann\u27s donor number of the solvents. Calculated electronic spectra are reported and the effect of solvents on the spectral properties are discussed. The symmetry of tetrachlorocobaltate is strictly Td

Synthesis, microstructural and tribological characterization of calcined nano-bioceramic α- al2o3, sintered at different temperatures

The current research was undertaken to study the improvement of the tribological behavior of nanocrystalline bioceramic, α-alumina sample, produced by the calculations of gibbsite at different temperatures (300 to 1200°C), followed by uniaxial pressing, sintering and HIP treatment. The improved friction and wear resistance is attributed to the fine microstructure of the sample calcined at 1400 °C

The progress of early phase bone healing using porous granules produced from calcium phosphate cement

<p>Abstract</p> <p>Objective</p> <p>Bone grafting is a vital component in many surgical procedures to facilitate the repair of bone defects or fusions. Autologous bone has been the gold standard to date in spite of associated donor-site morbidity and the limited amount of available donor bone. The aim of this study was to investigate the progress of bone regeneration and material degradation of calcium phosphate granules (CPG) produced from a calcium phosphate self-setting cement powder compared to the use of autologous bone grafting in the treatment of "critical size defects" on load-bearing long bones of minipigs.</p> <p>Methods</p> <p>A critical size defect in the tibial metaphysis of 16 mini-pigs was filled either with autologous cancellous graft or with micro- and macroporous carbonated, apatic calcium phosphate granules (CPG) produced from a calcium phosphate self-setting cement powder. After 6 weeks, the specimens were assessed by X-ray and histological evaluation. The amount of new bone formation was analysed histomorphometrically.</p> <p>Results</p> <p>The semi-quantitative analysis of the radiological results showed a complete osseous bridging of the defect in three cases for the autograft group. In the same group five animals showed a beginning, but still incomplete bridging of the defect, whereas in the CPG group just two animals developed this. All other animals of the CPG group showed only a still discontinuous new bone formation. Altogether, radiologically a better osseous bridging was observed in the autograft group compared to the CPG group.</p> <p>Histomorphometrical analysis after six weeks of healing revealed that the area of new bone was significantly greater in the autograft group concerning the central area of the defect zone (p < 0.001) as well as the cortical defect zone (p < 0.002). All defects showed new bone formation, but only in the autograft group defects regenerated entirely</p> <p>Conclusions</p> <p>Within the limits of the present study it could be demonstrated that autologous cancellous grafts lead to a significantly better bone regeneration compared to the application of calcium phosphate granules (CPG) produced from a calcium phosphate self-setting cement powder after 6 weeks. In the early phase of bone-healing, the sole application of CPG appears to be inferior to the autologous cancellous grafts in an <it>in vivo </it>critical size defect on load-bearing long bones of mini-pigs.</p