Search results for "elasticity"

Mössbauer investigations on glass-forming organic liquids

1992

Glycerol forms a molecular glass near 180K. Fe2+ dissolved in glycerol allows the study of the dynamics of the system by Mossbauer spectroscopy. Recently it has been shown that the Mossbauer spectra can be understood in a way consistent with the results of dielectric and ultrasonic viscoelastic relaxation measurements. A jump diffusion model of Sinqwi and Sjolander with a jump rate distribution according to Davidson and Cole allowed us to fit the Mossbauer spectra of Fe in glycerol. First attempts to compare mode coupling theory with Mossbauer spectra are reported.

Molecular Mobility in Glassy Bread: A Multispectroscopy Approach

1999

ABSTRACT The molecular mobility in low-moisture (<9%, web) white bread was studied as a function of temperature using pulsed-proton nuclear magnetic resonance (NMR), and dielectric and dynamic mechanical spectroscopies. The water was mobile, even in glassy samples. Different processes below glass transition temperature (sub-Tg) were observed, and a relaxation map of the studied system was drawn. These results have been interpreted and extrapolated to suggest that the Tg is not a universal predictive parameter for the physical stability of glassy food.

Fractional characteristic times and dissipated energy in fractional linear viscoelasticity

2016

Abstract In fractional viscoelasticity the stress–strain relation is a differential equation with non-integer operators (derivative or integral). Such constitutive law is able to describe the mechanical behavior of several materials, but when fractional operators appear, the elastic and the viscous contribution are inseparable and the characteristic times (relaxation and retardation time) cannot be defined. This paper aims to provide an approach to separate the elastic and the viscous phase in the fractional stress–strain relation with the aid of an equivalent classical model (Kelvin–Voigt or Maxwell). For such equivalent model the parameters are selected by an optimization procedure. Once …

On the Stochastic Response of a Fractionally-damped Duffing Oscillator

2012

A numerical method is presented to compute the response of a viscoelastic Duffing oscillator with fractional derivative damping, subjected to a stochastic input. The key idea involves an appropriate discretization of the fractional derivative, based on a preliminary change of variable, that allows to approximate the original system by an equivalent system with additional degrees of freedom, the number of which depends on the discretization of the fractional derivative. Unlike the original system that, due to the presence of the fractional derivative, is governed by non-ordinary differential equations, the equivalent system is governed by ordinary differential equations that can be readily h…

A numerical integration approach for fractional‐order viscoelastic analysis of hereditary‐aging structures

2019

Analysis of infilled frames using A coupled finite element and boundary element solution scheme

1988

The behaviour of infilled frames subjected to horizontal loads is analysed by an iterative numerical procedure. The stiffness of the structural system is determined with variations in geometrical and mechanical characteristics. The analysis is carried out utilizing the boundary element method (BEM) for the infill and opportunely dividing the frame into finite elements, so as to transform the mutual interactions of the two subsystems into stresses distributed along the boundary for the infill and into nodal actions for the frame. This makes it possible to take into account the separation arising between the two substructures when mutual tensile stresses are involved. At first, infills withou…

General theory for cross-ply laminated beams

1997

We present a general formulation of the elasticity theory of the cross-ply composite laminated beam subjected to various loadings such as axial load, bending moment, shear/bending, and torsion. The formulation is based on the integral equation theory, and a direct approach is employed to obtain the boundary integral equations for the analysis of the laminated beam. The integral equations governing the elasticity problem are directly deduced from the reciprocity theorem, by using the singular solutions of the orthotropic elasticity explicitly derived. The numerical solution is achieved by the boundary element method, which gives, once the traction free boundary conditions and the interfacial…

Moisture dependence on mechanical properties of pine nuts from Pinus pinea L.

2012

Abstract Mechanical properties of pine nut shell are very important in the cracking process. Before industrial cracking shell moisture is adjusted by water soaking in order to avoid the breaking up of the nuts. In this work the moisture dependence of the mechanical properties of pine nut shells were studied in order to improve the industrial cracking process. Relationship between nut size and moisture content was studied and no significant differences were found for shell dimensions at four different moisture levels, 9.79%, 16.71%, 20.98% and 25.05% (dry basis). Compression tests were carried out on pine nuts at nine different moisture contents between 1.38% and 25.48% (db) and their main m…

Seawater carbonate chemistry and shell mineralogy, microstructure, and mechanical strength of four Mediterranean gastropod species near a CO2 seep

2017

Marine CO2 seeps allow the study of the long-term effects of elevated pCO2 (ocean acidification) on marine invertebrate biomineralization. We investigated the effects of ocean acidification on shell composition and structure in four ecologically important species of Mediterranean gastropods (two limpets, a top-shell snail, and a whelk). Individuals were sampled from three sites near a volcanic CO2 seep off Vulcano Island, Italy. The three sites represented ambient (8.15 pH), moderate (8.03 pH) and low (7.73 pH) seawater mean pH. Shell mineralogy, microstructure, and mechanical strength were examined in all four species. We found that the calcite/aragonite ratio could vary and increased sign…

Optimal design of elastic plastic frames accounting for seismic protection devices

2013

The optimal design of elastic perfectly plastic steel frames with or without suitable protection devices and subjected to static as well as seismic loadings is studied. Two minimum volume problem formulations are proposed, on the grounds of the so-called statical approach, accounting for three different resistance limits: the purely elastic limit, the (elastic) shakedown limit and the instantaneous collapse limit. The adopted load combinations are characterized by the presence of fixed loads, of quasi-static perfect cyclic loads and dynamic (seismic) loads. The linear elastic effects of the dynamic actions are studied by utilizing a modal technique. The proposed treatment is referred to the…