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The dynamic indentation response of sandwich panels with a corrugated or Y-frame core
The dynamic indentation response of stainless steel sandwich panels with a corrugated core or a Y-frame core has been explored using the finite element method to gain insight into the potential of the cores to mitigate against collisions over a wide range of impact velocities pertinent to land and sea-borne vehicles. Back-supported sandwich panels were impacted on the front face by a flat-bottomed or a circular punch at constant velocity ranging from quasi-static loading to 100 m/s. At velocities below 10 m/s the forces on the front and back faces are equal but inertia stabilisation raises the peak load above its quasi-static value. This strength elevation is greater for the corrugated core than for the Y-frame core, and more pronounced for the flat-bottomed punch than for the circular punch. For velocities greater than 10 m/s, the indentation force applied to the front face exceeds the force transmitted to the back face due to plastic-shock effects. In this regime, the force transmitted to the back face by the Y-frame core is markedly less than for the corrugated core, and this brings a performance benefit to the Y-frame, i.e. it protects the underlying structure in the event of a collision.This research was carried out under the project number MC2.06261 in the framework of the Research Program of the Materials innovation institute M2i (www.m2i.nl). The authors are also grateful for the financial support of the Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT).This is the accepted manuscript of a paper publishing in the International Journal of Mechanical Sciences (L St-Pierre, NA Fleck, VS Deshpande, International Journal of Mechanical Sciences 2015, 92, 279–289
Spectroscopy of doubly charmed baryons
We study the mass spectrum of baryons with two and three charmed quarks. For
double charm baryons the spin splitting is found to be smaller than standard
quark-model potential predictions. This splitting is not influenced either by
the particular form of the confining potential or by the regularization taken
for the contact term of the spin-spin potential. We consistently predict the
spectra for triply charmed baryons.Comment: 6 pages, 1 figure, accepted for publication in Phys. Rev.
The predicted compressive strength of a pyramidal lattice made from case hardened steel tubes
AbstractA sandwich panel with a core made from solid pyramidal struts is a promising candidate for multifunctional application such as combined structural and heat-exchange function. This study explores the performance enhancement by making use of hollow struts, and examines the elevation in the plastic buckling strength by either strain hardening or case hardening. Finite element simulations are performed to quantify these enhancements. Also, the sensitivity of competing collapse modes to tube geometry and to the depth of case hardening is determined. A comparison with other lattice materials reveals that the pyramidal lattice made from case hardened steel tubes outperforms lattices made from solid struts of aluminium or titanium and has a comparable strength to a core made from carbon fibre reinforced polymers
Magnetism in the complex cobaltates Y1−xSrxCoO3−δ (0.7 ≤ x ≤ 0.95) and Ca3Co2O6
The magnetic phases in the complex cobaltates Y1−xSrxCoO3−δ (0.7 ≤ x ≤ 0.95)
and Ca3Co2O6 have been investigated by susceptibility, heat capacity, X-ray and
neutron scattering techniques. These measurements have shown that the super-
structure ordering in the perovskite cobaltate Y1−xSrxCoO3−δ which evolves as a
function of temperature heavily influences the ferrimagnetic behaviour of this mate-
rial. Neutron scattering has also been used to probe the unusual time and magnetic
field dependent behaviour of the spin-chain compound Ca3Co2O6, and to further
our understanding of the magnetic phase diagram of this system.
Both polycrystalline and single crystal samples have been used in this study.
High quality single crystals of the A-site (Sr/Y) and oxygen vacancy ordered form
of the perovskite Y1−xSrxCoO3−δ have been produced using the floating zone technique and characterised using EDAX and TGA. The single crystals produced were
large enough to perform polarised and inelastic neutron scattering experiments
on this compound for the first time, revealing anisotropic quasi-elastic scattering
above the magnetic transition temperature. In addition, diffraction experiments on
these samples found evidence of coincident structural and magnetic transitions in
Y1−xSrxCoO3−δ at both 370 and 280 K.
Neutron diffraction measurements were also performed on the geometrically
frustrated compound Ca3Co2O6. The low temperature magnetisation process was
found to be accompanied by clearly visible steps in the intensity of the ferromagnetic
and antiferromagnetic Bragg peaks. Detailed measurements have shown that the
presence of short-range correlations cannot account for the reduction in intensity of
the antiferromagnetic Bragg peaks at low temperatures. Instead, the origin of this
drop in intensity was found to be a slow time-dependent magnetic transition from
one long-range ordered antiferromagnetic state to another. This transition occurs
over a timescale of hours and is never complete.
The experimental work detailed in this thesis provides new information about
the phase diagrams of Y1−xSrxCoO3−δ and Ca3Co2O6 and contributes to our overall
understanding of the physics of these complex cobaltate compounds
Spin correlations in Ca3Co2O6: A polarised-neutron diffraction and Monte Carlo study
We present polarised-neutron diffraction measurements of the Ising-like
spin-chain compound Ca3Co2O6 above and below the magnetic ordering temperature
TN. Below TN, a clear evolution from a single-phase spin-density wave (SDW)
structure to a mixture of SDW and commensurate antiferromagnet (CAFM)
structures is observed on cooling. For a rapidly-cooled sample, the majority
phase at low temperature is the SDW, while if the cooling is performed
sufficiently slowly, then the SDW and the CAFM structure coexist between 1.5
and 10 K. Above TN, we use Monte Carlo methods to analyse the magnetic diffuse
scattering data. We show that both intra- and inter-chain correlations persist
above TN, but are essentially decoupled. Intra-chain correlations resemble the
ferromagnetic Ising model, while inter-chain correlations resemble the
frustrated triangular-lattice antiferromagnet. Using previously-published bulk
property measurements and our neutron diffraction data, we obtain values of the
ferromagnetic and antiferromagnetic exchange interactions and the single-ion
anisotropy.Comment: 10 pages, 7 figure
New Lower Bound on Fermion Binding Energies
We derive a new lower bound for the ground state energy of N
fermions with total spin S in terms of binding energies of (N-1) fermions. Numerical examples are provided for some simple
short-range or confining potentials.Comment: 4 pages, 1 eps figur
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High fracture toughness micro-architectured materials
© 2020 We investigate the possibility of achieving high fracture toughness and high strength by the design of lightweight (density below water) metallic micro-architectured materials. The micro-architectured materials were manufactured by drilling a hexagonal array of holes in plates of an aluminum alloy, and the fracture toughness was evaluated via three-point bend tests of single-edge notch specimens. The results show that the fracture toughness of micro-architectured materials increases with increasing relative density and remarkably, a micro-architectured material can be 50% lighter than the parent material but maintain the same fracture toughness. Additional tests on geometrically similar specimens revealed that the fracture toughness increases linearly with the square-root of the cell size. The experiments are complemented by finite element calculations of ductile fracture. In the calculations, the fracture toughness of single-edge notch specimens subjected to three-point bending are evaluated using both, a procedure similar to the experiments and direct computation of the J-contour integral. The fracture toughness as calculated by both methods are consistent with the experimental results. In addition, the calculations are also carried out for single-edge notch specimens subjected to tensile loading, confirming the validity of the measured fracture toughness as a useful material property independent of specimen geometry
Improved Semiclassical Approximation for Bose-Einstein Condensates: Application to a BEC in an Optical Potential
We present semiclassical descriptions of Bose-Einstein condensates for
configurations with spatial symmetry, e.g., cylindrical symmetry, and without
any symmetry. The description of the cylindrical case is quasi-one-dimensional
(Q1D), in the sense that one only needs to solve an effective 1D nonlinear
Schrodinger equation, but the solution incorporates correct 3D aspects of the
problem. The solution in classically allowed regions is matched onto that in
classically forbidden regions by a connection formula that properly accounts
for the nonlinear mean-field interaction. Special cases for vortex solutions
are treated too. Comparisons of the Q1D solution with full 3D and Thomas-Fermi
ones are presented.Comment: 14 pages, 5 figure
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