15 research outputs found
Polygons vs. clumps of discs: a numerical study of the influence of grain shape on the mechanical behaviour of granular materials
We performed a series of numerical vertical compression tests on assemblies
of 2D granular material using a Discrete Element code and studied the results
with regard to the grain shape. The samples consist of 5,000 grains made from
either 3 overlapping discs (clumps - grains with concavities) or six-edged
polygons (convex grains). These two grain type have similar external envelopes,
which is a function of a geometrical parameter .
In this paper, the numerical procedure applied is briefly presented followed
by the description of the granular model used. Observations and mechanical
analysis of dense and loose granular assemblies under isotropic loading are
made. The mechanical response of our numerical granular samples is studied in
the framework of the classical vertical compression test with constant lateral
stress (biaxial test). The comparison of macroscopic responses of dense and
loose samples with various grain shapes shows that when is considered
a concavity parameter, it is therefore a relevant variable for increasing
mechanical performances of dense samples. When is considered an
envelope deviation from perfect sphericity, it can control mechanical
performances for large strains. Finally, we present some remarks concerning the
kinematics of the deformed samples: while some polygon samples subjected to a
vertical compression present large damage zones (any polygon shape), dense
samples made of clumps always exhibit thin reflecting shear bands. This paper
was written as part of a CEGEO research project www.granuloscience.comComment: This version of the paper doesn't include figures. Visit the journal
web site to download the final version of the paper with the figure
Particle shape dependence in 2D granular media
Particle shape is a key to the space-filling and strength properties of
granular matter. We consider a shape parameter describing the degree of
distortion from a perfectly spherical shape. Encompassing most specific shape
characteristics such as elongation, angularity and nonconvexity, is a
low-order but generic parameter that we used in a numerical benchmark test for
a systematic investigation of shape-dependence in sheared granular packings
composed of particles of different shapes. We find that the shear strength is
an increasing function of with nearly the same trend for all shapes, the
differences appearing thus to be of second order compared to . We also
observe a nontrivial behavior of packing fraction which, for all our simulated
shapes, increases with from the random close packing fraction for disks,
reaches a peak considerably higher than that for disks, and subsequently
declines as is further increased. These findings suggest that a
low-order description of particle shape accounts for the principal trends of
packing fraction and shear strength. Hence, the effect of second-order shape
parameters may be investigated by considering different shapes at the same
level of .Comment: 5 pages, 8 figure
Rapid, low-cost MR imaging protocol to document central nervous system and sinus abnormalities prior to pediatric hematopoietic stem cell transplantation
Patients undergoing bone marrow transplant (BMT) are at risk for infectious complications, including those of the sinus. Central nervous system (CNS) abnormalities related to the chemotherapy or radiation that the patient received for the treatment of underlying malignancy or to transplant-related effects are also commonly seen. the only effective way to differentiate pre- and post-transplant causes is to have a baseline evaluation prior to the admission for transplant. the current method used to evaluate these patients is head CT. However, CT is not accurate to demonstrate CNS abnormalities and exposes the patient to radiation. MRI, despite better sensitivity for white matter abnormalities, has not been routinely used because of the higher cost and longer duration of the exam. Therefore, we designed a fast, low-cost and radiation-free MRI-based protocol to simultaneously evaluate sinus and brain abnormalities.Universidade Federal de São Paulo, Dept Diagnost Imaging, BR-04038002 São Paulo, BrazilUniversidade Federal de São Paulo, Div Pediat Oncol, Dept Pediat, BR-04038002 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Diagnost Imaging, BR-04038002 São Paulo, BrazilUniversidade Federal de São Paulo, Div Pediat Oncol, Dept Pediat, BR-04038002 São Paulo, BrazilWeb of Scienc
Contact angle entropy and macroscopic friction in noncohesive two-dimensional granular packings
Ablation of Ventricular Tachycardia in Chronic Chagasic Cardiomyopathy With Giant Basal Aneurysm Carto Sound, CT, and MRI Merge
Universidade Federal de São Paulo, São Paulo, BrazilUniversidade Federal de São Paulo, São Paulo, BrazilWeb of Scienc