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Mechanical Relaxation (mechanical + relaxation)
Selected AbstractsCorrelation Between Thermal and Mechanical Relaxation in Chalcogenide Glass FibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009Pierre Lucas Enthalpy relaxation processes in chalcogenide fibers at room temperature are investigated by differential scanning calorimetry and compared with bending-stress relaxation measurements obtained by rolling fibers on a mandrel and recording the viscoelastic relaxation parameters. While the kinetics of the two processes is very different, several qualitative correlations are demonstrated between the enthalpy state and the mechanical properties of chalcogenide glass fibers. It is observed that the ability to undergo stress relaxation is dependent upon the fictive temperature of the glass. Stress relaxation in a glass far from thermodynamic equilibrium is contingent upon its ability to undergo enthalpy relaxation and is minimal in glasses that have already relaxed enthalpy or in which relaxation time is overwhelmingly large. [source] Mechanical relaxation in tetragonal and orthorhombic phases of (Ba,Sr)TiO3 ceramicsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009H. Y. Wang Abstract Two broad relaxation peaks in the tetragonal and orthorhombic phases, respectively, of BaxSr1,xTiO3 (x,=,0.8 and 1) ceramics were investigated via internal friction and modulus measurements. The activation energy calculated from the Arrhenius relation shows that the relaxation process depends on the thermal history. A possible explanation is proposed that the relaxation during heating is associated with the motion of domain walls, the migration of oxygen vacancies and the interaction between oxygen vacancies and domain walls. In addition, the activation energies of Ba0.8Sr0.2TiO3 are smaller than those of BaTiO3, possibly resulting from the larger interspaces of the two neighbouring Ba2+ and Sr2+ along the c -axis. [source] Elementary Mechanisms behind the High-Temperature Deformation Behavior of Lutetium-Doped Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003Giuseppe Pezzotti Intergranular sliding and diffusive mechanisms behind the deformation behavior of a commercially available lutetium-doped silicon nitride were investigated and discussed. A method of locating and separating phenomena critical for mechanical relaxation at elevated temperatures was applied; the method was based on low-frequency forced-vibration damping measurements. The potentiality of lutetium addition for improving the deformation resistance of silicon nitride was clearly reflected in the high-temperature damping behavior of the investigated polycrystal. Softening of intergranular lutetium silicate phases located at multigrain junctions, which resulted in a grain-boundary sliding peak, occurred at remarkably high temperatures (>1725 K). This phenomenon, partly overlapping diffusional flow, was followed by further damping relaxation with the melting of the lutetium silicates. Subsequent grain growth was also detected at temperatures >2100 K. Torsional creep results, collected up to 2100 K, consistently proved the presence of a "locking" effect by lutetium silicates with the sliding of silicon nitride grain boundaries below 1873 K. [source] Dynamic mechanical properties and morphology of poly(benzyl methacrylate)/epoxy thermoset blendsPOLYMER ENGINEERING & SCIENCE, Issue 9 2010Margarita G. Prolongo Poly(benzyl methacrylate) (PBzMA)/epoxy thermoset blends of composition 5 to 25 wt% of PBzMA were prepared curing with 4,4,diaminodiphenylmethane (DDM), to study the influence of composition on the morphology and dynamic-mechanical properties of the blends. The cured blends are phase separated in PBzMA-rich phase and epoxy rich-phase. As the PBzMA content increases, the morphology evolves from nodular, to combined and to totally inverted. The analysis of the ,-mechanical relaxations indicates that the glass transition temperatures (Tg) of PBzMA and of epoxy in the blends are different from the neat polymers, this is related to a noncomplete phase separation on curing. The profiles of the loss modulus-temperature curves are correlated with the change in morphology that appears increasing the PBzMA content. The storage modulus-temperature curves are highly dependent on the morphology of the samples. The storage modulus-composition dependence is predicted using several models for two phase composites. POLYM. ENG. SCI., 50:1820,1830, 2010. © 2010 Society of Plastics Engineers [source] | ||||||||||