4,819 research outputs found
An Equation of State for Anisotropic Solids under Shock Loading
An anisotropic equation of state is proposed for accurate extrapolation of
high-pressure shock Hugoniot states to other thermodynamics states for shocked
single crystals and polycrystalline alloys. The proposed equation of state
represents mathematical and physical generalization of the Mie-Gr\"{u}neisen
equation of state for isotropic material and reduces to this equation in the
limit of isotropy. Using an anisotropic nonlinear continuum framework and
generalized decomposition of a stress tensor [Int. J. Plasticity \textbf{24},
140 (2008)], the shock waves propagation along arbitrary directions in
anisotropic solids of any symmetry can be examined. The non-associated strength
model includes the distortion effect of the yield surface which can be used to
describe the anisotropic strength differential effect. A numerical calculation
showed that the general pulse shape, Hugoniot Elastic Limits (HELs), and
Hugoniot stress levels for aluminum alloy 7010-T6 agree with the experimental
data. The results are presented and discussed, and future studies are outlined.Comment: 6 pages, 2 figure
Modelling Stress Wave Propagation and Triaxial Compression Test using Smoothed Particle Hydrodynamics
Smoothed Particle Hydrodynamics (SPH) is used to model stress wave propagation and compression tests in elastic solids under triaxial loading conditions. It builds on our previous studies of deformation of elastic solids under uniaxial and biaxial loading. A laboratory scale triaxial compression test is used to demonstrate the generation, propagation and reflection of the elastic waves in the specimen. To verify the SPH based approach, the results are compared to matching results using the Finite Element Method (FEM). The solutions predicted by SPH are found to agree well. This paper illustrates the potential of SPH for accurate modelling of solid materials that are subjected to triaxial compression, and of the resulting elastic wave propagation
Molecular Dynamics Simulations of Weak Detonations
Detonation of a three-dimensional reactive non-isotropic molecular crystal is
modeled using molecular dynamics simulations. The detonation process is
initiated by an impulse, followed by the creation of a stable fast reactive
shock wave. The terminal shock velocity is independent of the initiation
conditions. Further analysis shows supersonic propagation decoupled from the
dynamics of the decomposed material left behind the shock front. The dependence
of the shock velocity on crystal nonlinear compressibility resembles solitary
behavior. These properties categorize the phenomena as a weak detonation. The
dependence of the detonation wave on microscopic potential parameters was
investigated. An increase in detonation velocity with the reaction
exothermicity reaching a saturation value is observed. In all other respects
the model crystal exhibits typical properties of a molecular crystal.Comment: 38 pages, 20 figures. Submitted to Physical Review
Rupture by damage accumulation in rocks
The deformation of rocks is associated with microcracks nucleation and
propagation, i.e. damage. The accumulation of damage and its spatial
localization lead to the creation of a macroscale discontinuity, so-called
"fault" in geological terms, and to the failure of the material, i.e. a
dramatic decrease of the mechanical properties as strength and modulus. The
damage process can be studied both statically by direct observation of thin
sections and dynamically by recording acoustic waves emitted by crack
propagation (acoustic emission). Here we first review such observations
concerning geological objects over scales ranging from the laboratory sample
scale (dm) to seismically active faults (km), including cliffs and rock masses
(Dm, hm). These observations reveal complex patterns in both space (fractal
properties of damage structures as roughness and gouge), time (clustering,
particular trends when the failure approaches) and energy domains (power-law
distributions of energy release bursts). We use a numerical model based on
progressive damage within an elastic interaction framework which allows us to
simulate these observations. This study shows that the failure in rocks can be
the result of damage accumulation
Theoretical and numerical modeling of Rayleigh wave scattering by an elastic inclusion
This work presents theoretical and numerical models for the backscattering of
two-dimensional Rayleigh waves by an elastic inclusion, with the host material
being isotropic and the inclusion having arbitrary shape and crystallographic
symmetry. The theoretical model is developed based on the reciprocity theorem
using the far-field Green's function and the Born approximation, assuming a
small acoustic impedance difference between the host and inclusion materials.
The numerical finite element (FE) model is established to deliver relatively
accurate simulation of the scattering problem and to evaluate the
approximations of the theoretical model. Quantitative agreement is observed
between the theoretical model and the FE results for arbitrarily-shaped
surface/subsurface inclusions with isotropic/anisotropic properties. The
agreement is excellent when the wavelength of the Rayleigh wave is larger than,
or comparable to, the size of the inclusion, but it deteriorates as the
wavelength gets smaller. Also, the agreement decreases with the anisotropy
index for inclusions of anisotropic symmetry. The results lay the foundation
for using Rayleigh waves for quantitative characterization of
surface/subsurface inclusions, while also demonstrating its limitations.Comment: 25 pages, 8 figures. The article has been submitted to The Journal of
the Acoustical Society of America. After it is published, it will be found at
https://asa.scitation.org/journal/ja
Dynamic problems for metamaterials: Review of existing models and ideas for further research
Metamaterials are materials especially engineered to have a peculiar physical behaviour, to be exploited for some well-specified technological application. In this context we focus on the conception of general micro-structured continua, with particular attention to piezoelectromechanical structures, having a strong coupling between macroscopic motion and some internal degrees of freedom, which may be electric or, more generally, related to some micro-motion. An interesting class of problems in this context regards the design of wave-guides aimed to control wave propagation. The description of the state of the art is followed by some hints addressed to describe some possible research developments and in particular to design optimal design techniques for bone reconstruction or systems which may block wave propagation in some frequency ranges, in both linear and non-linear fields. (C) 2014 Elsevier Ltd. All rights reserved
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