Search

Abstract: Thin composite films consisting of a matrix with embedded particles are currently being developed both as hard, wear resistant coatings and as functional surfaces. The effect of stiff particles in the film are studied for systems where the film is under residual tensile stresses. The particles, when they are fully bonded to the matrix, increase the stiffness of the composite film. In cases where the particles debond from the matrix material, the stiffness of the composite film decreases. The conditions under which the debonding process is stable are studied. For systems properly designed, a controlled debonding process of the particles can thus be used to reduce the stress levels in composite film lowering the risk for delamination of the composite film from the substrate as well as the risk of through cracks in the film. The work includes finite element based unit cell calculations of interface debonding between spherical particles and the film, and the release of residual stresses following this. The three dimensional unit cell calculations assume a periodic distribution of particles in the plane parallel to the substrate interface with equi-biaxial tension and periodicity with zero overall stress perpendicular to the substrate interface. [Copyright &y& Elsevier]

Abstract: A recent method by Steffensen et al. (2013) to estimate the fracture toughness of thin, hard films uses closed-form linear elastic fracture mechanical models for an edge crack in a semi-infinite plane to calculate the energy release rate for a circumferential crack propagating from the surface of the film. Also, in the proposed model the in-plane shear stress was neglected, and it was assumed that the crack propagates perpendicular to the surface. In this paper, the accuracy of the previously proposed method for calculating the energy release rate for axisymmetric circumferential crack during indentation is investigated. Also, neglecting the in-plane shear stress and the assumed direction of crack propagation are investigated. The J-integral and the virtual crack closure technique are used to calculate the energy release rate on the basis of results from a large scale axisymmetric finite element model. Thereby, the proper geometry of the circumferential crack, plasticity in the substrate, material mismatch across the interface are included. In general, it was found that the closed-form linear elastic fracture mechanics model is sufficient for the method. [Copyright &y& Elsevier]

Abstract: In this paper, a method to estimate fracture toughness, , from the first indenter-induced circumferential crack in a thin film is suggested. The method is based on the stresses in the film and finite element simulations are used to estimate these stresses. The film is taken to be linear elastic while plasticity is included in the substrate. Delamination is not taken into account in the method and the film is perfectly bonded to the substrate. The stress in the film is used to estimate the location where the circumferential crack will initiate from a defect in the film surface. The location is found to be at a distance away from the indenter which correlate with experiments. Also, the stress is used to calculate the stress intensity factor and the energy release rate for a plane strain crack. The energy release rate for the plane strain crack is then used to calculate the energy release for a crack channeling around the indenter forming the circumferential crack. By the energy release rate for the channeling crack fracture toughness is estimated independent of the initial defects in the film provided such defects exist. If the initial defects are smaller than a required minimum value, fracture toughness is overestimated by this method and this overestimation is calculated. Besides fracture toughness, the energy release rate for the channeling crack is used to estimate the depth of the plane strain crack which is found to be smaller than the film thickness. The method is used to estimate the fracture toughness, , for an alumina ( ) film using the critical indentation depth. In order to verify the result the estimated crack radius is compared to the actual radius of the circumferential crack in the alumina. The differences between the two radius is found to be within a few percent. [Copyright &y& Elsevier]

Abstract: The bovine digital vasculature contractility has been implicated in the development of laminitis. To investigate the effect of hypoxia/reoxygenation on the contractility of isolated peripheral bovine digital veins (BDVs), vessel rings were studied under isometric conditions and submitted to 30min of hypoxia (95%N2–5%CO2) and reoxygenation (95%O2–5%CO2) conditions, respectively. The BDVs contracted with a high K+ depolarizing solution, developed hypoxia-induced relaxation, followed by an increase in tension upon reoxygenation. In contrast, phenylephrine-contracted BDVs displayed a rapid, sustained and reversible hypoxia-induced contraction. Reoxygenation caused a rapid relaxation in phenylephrine-contracted BDVs. The presence of the endothelium did not modify the hypoxia/reoxygenation effects and hypoxia-induced contraction was still observed in a nominal Ca2+-free Krebs, however, the last effect was not maintained over time. The hypoxia-induced contraction in an isolated peripheral vein may contribute to the understanding of the physiology and pathophysiology of superficial venous smooth muscle contractility, particularly in the alteration of bovine digital haemodynamics under hypoxia/reoxygenation conditions. [Copyright &y& Elsevier]

Abstract: The Arrau turtle (Podocnemis expansa) is an endangered species, as a result of long-lasting, unsustainable exploitation. To obtain reference haematological values from the wild Podocnemis expansa during post-laying, 20 turtles were captured in the Orinoco River. Blood was obtained from the dorsal cervical sinus in lithium heparin tubes. Red blood cells (RBC), white blood cells (WBC), thrombocytes (TC), packed cell volume (PCV), plasmatic protein (PP), haemoglobin (Hgb), mean corpuscular volume (MCV) and differential leukocyte count were determined. Haematological values were: RBC 0.9×109/L, WBC 5.7×109/L, TC 5.4×109/L, PCV 35.6%, PP 4.2g/dL, Hgb 11.8g/dL, MCV 411fL. The differential leukocyte count comprised: 71% heterophils, 23% lymphocytes, 3% eosinophils, 1.6% basophils, and 1% monocytes. The reports of reference haematology values for the wild P. expansa are limited; therefore, the results presented herein contrast with those values obtained in captivity. This study represents a contribution to the referential haematological values of the wild P. expansa. [Copyright &y& Elsevier]