317 research outputs found
Constitutive modeling and thermoviscoplasticity
Development and solution of coupled thermomechanical equations at elevated temperature and/or high strain rates are discussed. Three main considerations are presented: development of the coupled thermomechanical equations by means of the rational theory of thermodynamics, development of a thermoviscoplastic constitutive equation which is congruous with the developed coupled equations, and the applicability of the developed equations to the treatment by the finite element method
Two different fractional Stefan problems which are convergent to the same classical Stefan problem
Two fractional Stefan problems are considered by using Riemann-Liouville and
Caputo derivatives of order such that in the limit case
() both problems coincide with the same classical Stefan problem.
For the one and the other problem, explicit solutions in terms of the Wright
functions are presented. We prove that these solutions are different even
though they converge, when , to the same classical solution.
This result also shows that some limits are not commutative when fractional
derivatives are used.Comment: 14 pages, 1 figur
ââCooling by Heatingââ- Demonstrating the Significance of the Longitudinal Specific Heat
Heating a solid sphere at its surface induces mechanical stresses inside the sphere. If a finite amount of heat is supplied, the stresses gradually disappear as temperature becomes homogeneous throughout the sphere. We show that before this happens, there is a temporary lowering of pressure and density in the interior of the sphere, inducing a transient lowering of the temperature here. For ordinary solids this effect is small because c_{p}â
c_{V}. For fluent liquids the effect is negligible because their dynamic shear modulus vanishes. For a liquid at its glass transition, however, the effect is generally considerably larger than in solids. This paper presents analytical solutions of the relevant coupled thermoviscoelastic equations. In general, there is a difference between the isobaric specific heat c_{p} measured at constant isotropic pressure and the longitudinal specific heat c_{l} pertaining to mechanical boundary conditions that confine the associated expansion to be longitudinal. In the exact treatment of heat propagation, the heat-diffusion constant contains c_{l} rather than c_{p}. We show that the key parameter controlling the magnitude of the âcooling-by-heatingâ effect is the relative difference between these two specific heats. For a typical glass-forming liquid, when the temperature at the surface is increased by 1Â K, a lowering of the temperature at the sphere center of the order of 5Â mK is expected if the experiment is performed at the glass transition. The cooling-by-heating effect is confirmed by measurements on a glucose sphere at the glass transition
The constitutive tensor of linear elasticity: its decompositions, Cauchy relations, null Lagrangians, and wave propagation
In linear anisotropic elasticity, the elastic properties of a medium are
described by the fourth rank elasticity tensor C. The decomposition of C into a
partially symmetric tensor M and a partially antisymmetric tensors N is often
used in the literature. An alternative, less well-known decomposition, into the
completely symmetric part S of C plus the reminder A, turns out to be
irreducible under the 3-dimensional general linear group. We show that the
SA-decomposition is unique, irreducible, and preserves the symmetries of the
elasticity tensor. The MN-decomposition fails to have these desirable
properties and is such inferior from a physical point of view. Various
applications of the SA-decomposition are discussed: the Cauchy relations
(vanishing of A), the non-existence of elastic null Lagrangians, the
decomposition of the elastic energy and of the acoustic wave propagation. The
acoustic or Christoffel tensor is split in a Cauchy and a non-Cauchy part. The
Cauchy part governs the longitudinal wave propagation. We provide explicit
examples of the effectiveness of the SA-decomposition. A complete class of
anisotropic media is proposed that allows pure polarizations in arbitrary
directions, similarly as in an isotropic medium.Comment: 1 figur
Thermo-mechanical response FEM simulation of ceramic refractories undergoing severe temperature variations
T. K Papathanasiou and F. Dal Corso gratefully acknowledge support from the European Union FP7 project âMechanics of refractory materials at highâtemperature for advanced industrial technologiesâ under contract number PIAPPâGAâ2013â609758. A. Piccolroaz would like to acknowledge financial support from the European Unionâs Seventh Framework Programme FP7/2007-2013/ under REA grant agreement number PITN-GA-2013-606878-CERMAT2
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