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Claudio De Rosa - One of the best experts on this subject based on the ideXlab platform.

  • Mechanical properties and Elastic Behavior of high-molecular-weight poorly syndiotactic polypropylene
    Macromolecules, 2003
    Co-Authors: Claudio De Rosa, And Finizia Auriemma, Odda Ruiz De Ballesteros
    Abstract:

    An analysis of the mechanical properties and Elastic Behavior of low-stereoregular and nearly amorphous syndiotactic polypropylene (sam-PP), prepared with heterocycle-fused indenyl silyl amido dimethyltitanium complexes, is presented. High-molecular-weight poorly syndiotactic sam-PP samples show good Elastic Behavior at room temperature in a large range of deformation. While highly stereoregular and crystalline syndiotactic polypropylene shows good Elastic properties only for previously stretched oriented fibers, sam-PP samples present good Elasticity even for unoriented compression-molded films during the first stretching. Because of the very low crystallinity, these samples experience a negligible irreversible plastic deformation and show a typical Behavior of thermoplastic elastomers. The small crystalline domains in the amorphous matrix act as physical knots of the elastomeric lattice, preventing the viscous flow of the amorphous chains. The Elastic Behavior is associated with a reversible polymorphic...

  • Origin of the Elastic Behavior of Syndiotactic Polypropylene
    Macromolecules, 2001
    Co-Authors: Finizia Auriemma, Odda Ruiz De Ballesteros, Claudio De Rosa
    Abstract:

    An analysis of the mechanical properties and a detailed structural study of samples of syndiotactic polypropylene (sPP) are presented in order to clarify the origin of the Elastic Behavior of sPP. Samples of sPP having different stereoregularity and showing different polymorphic Behavior have been analyzed. The present study allows to establish that the Elastic properties of unoriented specimens of sPP are poor, since the initial dimensions are only partially recovered upon the release of the stress. Good Elastic properties are, instead, shown by sPP fibers, which have been previously oriented (for instance, uniaxially drawn at 400% and at 600% their initial length and then stress-relaxed). Tension set values less than 10% are attained for these fibers. The Elastic properties of sPP mainly originate from a reversible crystal−crystal phase transition which occurs during the stretching and when the tension is removed. The stable crystalline modification of sPP with chains in the helical conformation transfo...

Odda Ruiz De Ballesteros - One of the best experts on this subject based on the ideXlab platform.

  • Mechanical properties and Elastic Behavior of high-molecular-weight poorly syndiotactic polypropylene
    Macromolecules, 2003
    Co-Authors: Claudio De Rosa, And Finizia Auriemma, Odda Ruiz De Ballesteros
    Abstract:

    An analysis of the mechanical properties and Elastic Behavior of low-stereoregular and nearly amorphous syndiotactic polypropylene (sam-PP), prepared with heterocycle-fused indenyl silyl amido dimethyltitanium complexes, is presented. High-molecular-weight poorly syndiotactic sam-PP samples show good Elastic Behavior at room temperature in a large range of deformation. While highly stereoregular and crystalline syndiotactic polypropylene shows good Elastic properties only for previously stretched oriented fibers, sam-PP samples present good Elasticity even for unoriented compression-molded films during the first stretching. Because of the very low crystallinity, these samples experience a negligible irreversible plastic deformation and show a typical Behavior of thermoplastic elastomers. The small crystalline domains in the amorphous matrix act as physical knots of the elastomeric lattice, preventing the viscous flow of the amorphous chains. The Elastic Behavior is associated with a reversible polymorphic...

  • Origin of the Elastic Behavior of Syndiotactic Polypropylene
    Macromolecules, 2001
    Co-Authors: Finizia Auriemma, Odda Ruiz De Ballesteros, Claudio De Rosa
    Abstract:

    An analysis of the mechanical properties and a detailed structural study of samples of syndiotactic polypropylene (sPP) are presented in order to clarify the origin of the Elastic Behavior of sPP. Samples of sPP having different stereoregularity and showing different polymorphic Behavior have been analyzed. The present study allows to establish that the Elastic properties of unoriented specimens of sPP are poor, since the initial dimensions are only partially recovered upon the release of the stress. Good Elastic properties are, instead, shown by sPP fibers, which have been previously oriented (for instance, uniaxially drawn at 400% and at 600% their initial length and then stress-relaxed). Tension set values less than 10% are attained for these fibers. The Elastic properties of sPP mainly originate from a reversible crystal−crystal phase transition which occurs during the stretching and when the tension is removed. The stable crystalline modification of sPP with chains in the helical conformation transfo...

D. Wolf - One of the best experts on this subject based on the ideXlab platform.

  • Tailored Elastic Behavior of multilayers through controlled interface structure
    Journal of Computer-Aided Materials Design, 1994
    Co-Authors: D. Wolf, J. A. Jaszczak
    Abstract:

    Atomistic simulations are reviewed that elucidate the causes of the anomalous Elastic Behavior of thin films and composition-modulated superlattice materials. The investigation of free-standing thin films and of superlattices, composed of grain boundaries, shows that the Elastic anomalies are not an electronic but a structural interface effect that is intricately connected with the local atomic disorder at the interfaces. The consequent predictions that (i) coherent strained-layer superlattices should show the smallest Elastic anomalies and (ii) making the interfaces incoherent should enhance all anomalies, are validated by simulations of dissimilar-material superlattices. Such simulations can be an effective aid in tailoring the Elastic Behavior of composite materials because, in contrast with experiments, they allow one to systematically investigate simple, but well-characterized model systems with increasing complexity. This unique capability of simulations has enabled us to elucidate the underlying driving forces and, in particular, (i) to deconvolute the distinct effects due to the inhomogeneous atomic disorder, localized at the interfaces from the consequent interface-stress-induced anisotropic lattice-parameter changes and (ii) to separate the homogeneous effects of thermal disordering from the inhomogeneous effects due to the interfaces.

  • Surface-stress-induced structure and Elastic Behavior of thin films
    Applied Physics Letters, 1991
    Co-Authors: D. Wolf
    Abstract:

    Computer simulations of unsupported (111), (001), and (011) thin films of gold, using an embedded‐atom‐method potential, demonstrate a direct correlation between the bulk‐surface stress and the film dimensions. The considerably more complex Elastic Behavior, by contrast, appears to be dominated by the atomic structure of the film surfaces, and not by the stress‐induced anisotropic lattice parameter changes.

  • Anomalous Elastic Behavior in superlattices of twist grain boundaries in silicon
    Journal of Applied Physics, 1990
    Co-Authors: Simon R. Phillpot, D. Wolf, James F. Lutsko
    Abstract:

    The Elastic constants and moduli of superlattices of high‐angle twist grain boundaries on the two densest crystallographic planes of silicon are calculated using Stillinger and Weber’s three‐body potential. While in both cases the Young’s and shear moduli are found to be softened, the Poisson ratios and some Elastic constants, in particular C33 (in the direction of the interface‐plane normal), are found to be hardened. It is shown that the Elastic Behavior is determined by the structural disorder at the interfaces, and that it cannot be understood in terms of the dimensional changes of the system alone. A comparison with similar calculations for metallic superlattices elucidates the role of the covalent nature of bonding of silicon on its Elastic Behavior.

Antonino Valenza - One of the best experts on this subject based on the ideXlab platform.

  • Visco-Elastic Behavior through fractional calculus: An easier method for best fitting experimental results
    Mechanics of Materials, 2011
    Co-Authors: M. Di Paola, Antonina Pirrotta, Antonino Valenza
    Abstract:

    In capturing visco-Elastic Behavior, experimental tests play a fundamental rule, since they allow to build up theoretical constitutive laws very useful for simulating their own Behavior. The main challenge is representing the visco-Elastic materials through simple models, in order to spread their use. However, the wide used models for capturing both relaxation and creep tests are combinations of simple models as Maxwell and/or Kelvin, that depend on several parameters for fitting both creep and relaxation tests. This paper, following Nutting and Gemant idea of fitting experimental data through a power law function, aims at stressing the validity of fractional model. In fact, as soon as relaxation test is well fitted by power law decay then the fractional constitutive law involving Caputo’s derivative directly appears. It will be shown that fractional model is proper for studying visco-Elastic Behavior, since it may capture both relaxation and creep tests, requiring the identification of two parameters only. This consideration is assessed by the good agreement between experimental tests on creep and relaxation and the fractional model proposed. Experimental tests, here reported are performed on two polymers having different chemical physical properties such that the fractional model may cover a wide range of visco-Elastic Behavior.

Vincent Langlois - One of the best experts on this subject based on the ideXlab platform.

  • Elastic Behavior of weakly cemented contact
    International Journal for Numerical and Analytical Methods in Geomechanics, 2014
    Co-Authors: Vincent Langlois
    Abstract:

    Summary We investigate the Elastic Behavior of weakly cemented contact. We show that the radial distribution of stresses and the stiffnesses of a cemented contact are governed by the ratio a/RΛ, where R, a, and Λ are, respectively, the grain radius, the contact size, and the ratio of the Elastic moduli of cement and grains. Moreover, we show that a cemented contact is always less stiff than a Hertzian contact having a similar size. Finally, we propose accurate approximate expressions of the contact stiffnesses. Copyright © 2014 John Wiley & Sons, Ltd.

  • Elastic Behavior of weakly cemented contact
    International Journal for Numerical and Analytical Methods in Geomechanics, 2014
    Co-Authors: Vincent Langlois
    Abstract:

    We investigate the Elastic Behavior of weakly cemented contact. We show that the radial distribution of stresses and the stiffnesses of a cemented contact are governed by the ratio a/R, where R, a and are respectively the grain radius, the contact size, and the ratio of the Elastic moduli of cement and grains. Moreover, we show that a cemented contact is always less stiff than a Hertzian contact having a similar size. Finally, we propose accurate approximate expressions of the contact stiffnesses.