Search results for "Elastic"
showing 10 items of 2162 documents
Mechanical characterisation and 3D fractional viscoelastic modelling of railway sub-ballast rubberised asphalt
Inelastic neutron and low-frequency Raman scattering in a niobium-phosphate glass for Raman gain applications
2011
Abstract We present measurements of the vibrational spectrum of a binary niobium-phosphate glass in the THz frequency range using inelastic neutron and Raman scattering. The spectra of these glasses show a low-frequency enhancement of the vibrational density of states (“boson peak”). Using a recently developed theory of vibrational excitations in disordered solids we are able to reconcile the measured neutron and Raman spectra using fluctuating elastic and Pockels constants as a model concept. As the spontaneous Raman susceptibility is a key parameter for Raman amplification our results suggest a significant gain profile for application of niobium-phosphate glasses in Raman amplifiers.
Mixed finite elements for nonlocal elastic multilayered composite plate refined theories
2020
Abstract A novel mixed finite element formulation for the layerwise analysis of nonlocal multilayered composite plates is presented. The finite elements are formulated starting from the weak form of a set of governing equations for the laminate layers that were deduced via the Reissner Mixed Variational Theorem. The primary variables, namely displacements and out-of-plane stresses, are expressed at layer level as through-the-thickness expansions of suitable selected functions with coefficients approximated by the finite element scheme. The through-the-thickness expansion order is considered as a free parameter. This way, finite elements for different refined higher order plate theories can …
Waves propagation in a fractional viscoelastic continuum
2009
In this paper the analysis of waves scattering in a fractional-type viscoelastic material is analyzed. Such a material involves, in the constitutive equation, the presence of noninteger order derivatives of the strain filed yielding a memory-type behavior of the material model. The presence of such a term has been also justified experimentally reporting the relaxation modulus of polymeric materials, obtained from experimental test, that are well-fitted by a powerlaw of fractional order. Some numerical applications reporting the standing-waves condition of an 1D solid varying the fractional differentiation order has also been reported in the paper.
The finite element implementation of 3D fractional viscoelastic constitutive models
2018
Abstract The aim of this paper is to present the implementation of 3D fractional viscoelastic constitutive theory presented in Alotta et al., 2016 [1]. Fractional viscoelastic models exactly reproduce the time dependent behaviour of real viscoelastic materials which exhibit a long “fading memory”. From an implementation point of view, this feature implies storing the stress/strain history throughout the simulations which may require a large amount of memory. We propose here a number of strategies to effectively limit the memory required. The form of the constitutive equations are summarized and the finite element implementation in a Newton-Raphson integration scheme is described in detail. …
Fractional model of concrete hereditary viscoelastic behaviour
2016
The evaluation of creep effects in concrete structures is addressed in the literature using different predictive models, supplied by specific codes, and applying the concepts of linear viscoelastic theory with ageing. The expressions used in the literature are mainly based on exponential laws, which are introduced in the integral expression of the Boltzmann principle; this approach leads to the need of finding approximated numerical solutions of the viscoelastic response. In this study, the hereditary fractional viscoelastic model is applied to concrete elements, underlining the convenience of using creep or relaxation functions expressed by power laws. The full reciprocal character of cree…
NNLO QED contribution to the µe → µe elastic scattering
2020
We present the current status of the Next-to-Next-to-Leading Order QED contribution to theµescattering. Particular focus is given to the techniques involved to tackle the virtual amplitude and their automatic implementation. Renormalization of the amplitude will be also discuss in details.
Calculation of Proton-Deuteron Elastic Scattering at 10 MeV with a Realistic Potential
1998
We present the first results of a calculation of the differential cross section and of polarization observables for proton-deuteron elastic scattering at 10thinspthinspMeV proton laboratory energy, for the Paris potential. The method used is the {open_quotes}screening and renormalization approach{close_quotes} which allows one to correctly take into account the Coulomb repulsion between the two protons. Comparison is made with the precise experimental data of Sagara {ital et al.}thinspthinsp[Phys.thinspthinspRev.thinspthinspC {bold 50}, 576 (1994)] and of Sperison {ital et al.}thinspthinsp[Nucl.thinspthinspPhys.thinspthinsp{bold A422}, 81 (1984)]. {copyright} {ital 1998} {ital The American …
Effetto dell’invecchiamento idrotermico sulle proprietà termiche e meccaniche di resine epossidiche strutturali
2018
Le resine termoindurenti, utilizzate come matrici per materiali compositi rinforzati con fibre di carbonio, sono caratterizzate da un elevato grado di densità di reticolazione che conferisce loro una elevata fragilità e che allo stesso tempo le espone a significativi effetti di invecchiamento idrotermico durante il loro utilizzo [1]. In particolare si assiste alla diminuzione della temperatura di transizione vetrosa, per effetto di fenomeni di plasticizzazione e degradazione, e alla diminuzione di modulo elastico a flessione. Recentemente gli autori hanno proposto un metodo, Photoelastic Stress Analysis (PSA), molto efficace per monitorare le modifiche del materiale, in termini di swelling …
Nuclear Resonance Scattering Using Synchrotron Radiation (Mössbauer Spectroscopy in the Time Domain)
2010
Conventional Mossbauer spectroscopy (MS) can be considered as “spectroscopy in the energy domain.” It has been widely used since its discovery in 1958 [1]. Nuclear resonant forward scattering (NFS) of synchrotron radiation has been successfully employed as a time-differential technique since 1991 [2]. Another related technique, nuclear inelastic scattering (NIS) of synchrotron radiation [3], can be regarded as an extension of conventional, energy-resolved MS (in the range 10−9 to 10−7 eV) to energies on the order of molecular vibrations (in the range 10−3 to 10−1 eV). So far only a few “Mossbauer” stations for NFS and NIS measurements have become available in synchrotron laboratories, i.e.,…