In this work, a complete rheological characterization of bronchial mucus simulants based on the composition proposed by Zahm et al. (Eur Respir J 1991; 4:311-315) is presented. Dynamic small amplitude oscillatory shear (SAOS) experiments, steady state (SS) flow measurements and three intervals thixotropy tests (3ITT), are carried out to investigate the global rheological complexities of simulants (viscoelasticity, viscoplasticity, shear-thinning, and thixotropy) as a function of scleroglucan concentrations (0.5-2 wt %) and under temperatures of 20 and 37°C. SAOS measurements show that the limit of the linear viscoelastic range as well as the elasticity both increase with increasing sclerogucan concentrations. Depending on the sollicitation frequency, the 0.5 wt % gel response is either liquid-like or solid-like, whereas more concentrated gels show a solid-like response over the whole frequency range. The temperature dependence of gels response is negligible in the 20-37°C range. The Herschel-Bulkley (HB) model is chosen to fit the SS flow curve of simulants. The evolution of HB parameters versus polymer concentration show that both shear-thinning and viscoplasticity increase with increasing concentrations. 3ITTs allow calculation of recovery thixotropic times after shearings at 100 or 1.6 s . Empiric correlations are proposed to quantify the effect of polymer concentration on rheological parameters of mucus simulants. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 386-396, 2018.
The glass industry requires the use of innovative ceramics that enable for long lifetimes. At very high temperatures, one of the key parameters for ceramics is their creep resistance. The characterization of the creep behavior, usually assessed through flexural tests, can be complex when an asymmetry appears between tension and compression. To detect and quantify such asymmetrical behaviors, the use of Digital Image Correlation (DIC) is proposed. First, several challenges are to be tackled for DIC at high temperature, namely, the random pattern stability, the radiation filtering and the heat haze. They are exacerbated by the limited possibilities to heat ceramics, the nonuniform strain fields and their low levels. Beyond several experimental developments, the strain uncertainties are decreased thanks to the use of two global approaches of DIC based on ad hoc finite‐element kinematics. Last, the proposed methodology is applied to the analysis of asymmetric creep at 1350°C of an industrial zircon ceramic designed for its high creep resistance.
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