883 research outputs found
Being inside or outside the virtuous circle::How news media repertoires relate to political participation repertoires
Being inside or outside the virtuous circle::How news media repertoires relate to political participation repertoires
Microstructural topology effects on the onset of ductile failure in multi-phase materials - a systematic computational approach
Multi-phase materials are key for modern engineering applications. They are
generally characterized by a high strength and ductility. Many of these
materials fail by ductile fracture of the, generally softer, matrix phase. In
this work we systematically study the influence of the arrangement of the
phases by correlating the microstructure of a two-phase material to the onset
of ductile failure. A single topological feature is identified in which
critical levels of damage are consistently indicated. It consists of a small
region of the matrix phase with particles of the hard phase on both sides in a
direction that depends on the applied deformation. Due to this configuration, a
large tensile hydrostatic stress and plastic strain is observed inside the
matrix, indicating high damage. This topological feature has, to some extent,
been recognized before for certain multi-phase materials. This study however
provides insight in the mechanics involved, including the influence of the
loading conditions and the arrangement of the phases in the material
surrounding the feature. Furthermore, a parameter study is performed to explore
the influence of volume fraction and hardness of the inclusion phase. For the
same macroscopic hardening response, the ductility is predicted to increase if
the volume fraction of the hard phase increases while at the same time its
hardness decreases
On Micromechanical Parameter Identification With Integrated DIC and the Role of Accuracy in Kinematic Boundary Conditions
Integrated Digital Image Correlation (IDIC) is nowadays a well established
full-field experimental procedure for reliable and accurate identification of
material parameters. It is based on the correlation of a series of images
captured during a mechanical experiment, that are matched by displacement
fields derived from an underlying mechanical model. In recent studies, it has
been shown that when the applied boundary conditions lie outside the employed
field of view, IDIC suffers from inaccuracies. A typical example is a
micromechanical parameter identification inside a Microstructural Volume
Element (MVE), whereby images are usually obtained by electron microscopy or
other microscopy techniques but the loads are applied at a much larger scale.
For any IDIC model, MVE boundary conditions still need to be specified, and any
deviation or fluctuation in these boundary conditions may significantly
influence the quality of identification. Prescribing proper boundary conditions
is generally a challenging task, because the MVE has no free boundary, and the
boundary displacements are typically highly heterogeneous due to the underlying
microstructure. The aim of this paper is therefore first to quantify the
effects of errors in the prescribed boundary conditions on the accuracy of the
identification in a systematic way. To this end, three kinds of mechanical
tests, each for various levels of material contrast ratios and levels of image
noise, are carried out by means of virtual experiments. For simplicity, an
elastic compressible Neo-Hookean constitutive model under plane strain
assumption is adopted. It is shown that a high level of detail is required in
the applied boundary conditions. This motivates an improved boundary condition
application approach, which considers constitutive material parameters as well
as kinematic variables at the boundary of the entire MVE as degrees of freedom
in...Comment: 37 pages, 25 figures, 2 tables, 2 algorithm
Handreiking bedrijfsuitbreiding Duin- & Bollenstreek : het creëren van kansen voor agrarische bedrijven en het landschap van de Duin- & Bollenstreek : [herziene uitgave]
Instrumentarium om de landschappelijke kwaliteitswinst zichtbaar te maken. De landschappelijke tegenprestaties die in aanmerking komen in dit gebied worden geïnventariseerd. Het betreft de aanleg van houtige beplantingen, de aanleg van biotopen, beschermende maatregelen in het kader van 'bollen en weidevogels', het vergroten van de oppervlakte natuur, verbindingszones aanleggen, het aanpakken van verrommeling, het versterken van zichtlijnen en openheid van het landschap, het aanleggen van bufferzones, het inpassen van cultuurhistorische elementen en de aanleg van recreatieve route
The SONYC survey: Towards a complete census of brown dwarfs in star forming regions
SONYC, short for "Substellar Objects in Nearby Young Clusters", is a survey
program to provide a census of the substellar population in nearby star forming
regions. We have conducted deep optical and near-infrared photometry in five
young regions (NGC1333, rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3),
combined with proper motions, and followed by extensive spectroscopic campaigns
with Subaru and VLT, in which we have obtained more than 700 spectra of
candidate low-mass objects. We have identified and characterized more than 60
new substellar objects, among them a handful of objects with masses close to,
or below the Deuterium burning limit. Through SONYC and surveys by other
groups, the substellar IMF is now well characterized down to ~ 5 - 10 MJup, and
we find that the ratio of the number of stars with respect to brown dwarfs lies
between 2 and 6. A comprehensive survey of NGC 1333 reveals that, down to
~5MJup, free-floating objects with planetary masses are 20-50 times less
numerous than stars, i.e. their total contribution to the mass budget of the
clusters can be neglected.Comment: to appear in the proceedings of the conference 'Brown dwarfs come of
age', May 20-24 2013, Memorie della Societa Astronomica Italian
Fracture initiation in multi-phase materials: a systematic three-dimensional approach using a FFT-based solver
This paper studies a two-phase material with a microstructure composed of a
hard brittle reinforcement phase embedded in a soft ductile matrix. It
addresses the full three-dimensional nature of the microstructure and
macroscopic deformation. A large ensemble of periodic microstructures is used,
whereby the individual grains of the two phases are modeled using equi-sized
cubes. A particular solution strategy relying on the Fast Fourier Transform is
adopted, which has a high computational efficiency both in terms of speed and
memory footprint, thus enabling a statistically meaningful analysis. This
solution method naturally accompanies the regular microstructural model, as the
Fast Fourier Transform relies on a regular grid.
Using the many considered microstructures as an ensemble, the average
arrangement of phases around fracture initiation sites is objectively
identified by the correlation between microstructure and fracture initiation --
in three dimensions. The results show that fracture initiates where regions of
the hard phase are interrupted by bands of the soft phase that are aligned with
the direction of maximum shear. In such regions, the hard phase is arranged
such that the area of the phase boundary perpendicular to the principal strain
direction is maximum, leading to high hydrostatic tensile stresses, while not
interrupting the shear bands that form in the soft phase. The local
incompatibility that is present around the shear bands is responsible for a
high plastic strain. By comparing the response to a two-dimensional
microstructure it is observed that the response is qualitatively similar (both
macroscopically and microscopically). One important difference is that the
local strain partitioning between the two phases is over-predicted by the
two-dimensional microstructure, leading to an overestimation of damage
- …