Search results for "COMPOSITE"
showing 10 items of 4584 documents
Correlation between ball milling conditions and planar effects on Cu-nanostructured powders
2002
It is most often proposed that the process of ball milling introduces a variety of defects (vacancies, dislocations, grain boundaries, stacking faults,...) which raise the free energy of the system making it possible to produce metastable phases. But there are very few investigations that deal with the characterization and quantification of the defects produced in milled powders. XRD is really a valuable technique for a characterization in terms of size and morphology of crystallites and imperfections. In this paper, a new line profile analysis method is proposed in order to take into account the dependence of the crystallite size, of the residual strains as well as of the planar defects, o…
Interphase Model and Phase-Field Approach for Strain Localization
2020
Quasi-brittle materials subjected to a high level of mechanical solicitations see the development in relatively narrow zone of micro-cracks that coalesce into stress free cracks. In this work, the problem of strain localization in elastoplastic materials exhibiting softening has been approached by applying the interphase model together with the phase-field theory. In particular, the narrow zone where strains concentrate, usually named process zone or localization band, is kinematically modeled using the interphase model, while the phase-field variable is introduced to regularize the contact strains at the interface between the plastic strain band and the surrounding material. This correspon…
Replica field theory for anharmonic sound attenuation in glasses
2011
Abstract A saddle-point treatment of interacting phonons in a disordered environment is developed. In contrast to crystalline solids, anharmonic attenuation of density fluctuations becomes important in the hydrodynamic regime, due to a broken momentum conservation. The variance of the shear modulus Δ2 turns out to be the strength of the disorder enhanced phonon–phonon interaction. In the low-frequency regime (below the boson peak frequency) we obtain an Akhiezer-like sound attenuation law Γ ∝ Τω2. Together with the usual Rayleigh scattering mechanism this yields a crossover of the Brillouin linewidth from a ω2 to a ω4 regime. The crossover frequency ωc is fully determined by the boson peak …
The State of a Quantum System as a Subsystem of a Composite System
2020
The notion of state in quantum systems is analized, a non-probabilistic definition of state provided, the Zurek’s concept of envariance is mathematically formulated, and the characterization of a state through its properties is discussed.
Dynamics of a subconstituent picture of weak interactions
1985
We use sum rules in order to discuss the dynamics of the simplest subconstituent model of weak interactions with elementary spin 1/2 fermions and scalar bosons. Vacuum condensates of the scalars play an essential role and lead to features quite different from QCD. With a certain vacuum structure vector dominance of the composite W-mesons is a good approximation, and we also see a clear signal for massless fermions in the two-point function of composite fermions. Thus such a model is in good agreement with standard phenomenology. Composite Higgs particles are also investigated. The effective interaction is evidently of the gauge type.
Direct measurement of forces between particles and bubbles
1999
One of the elementary stages of the flotation process is the formation of an aggregate between the particle and a bubble. This aggregate formation is governed by hydrodynamic, capillary and interparticle forces. During the last four years, techniques have been developed to measure directly the force between a colloidal particle and a bubble. These techniques are closely related to the development of atomic force microscopy. Advantages and possibilities, as well as limits and drawbacks are described.
Relaxation dynamics in orientational glasses
1991
Abstract The multipolar relaxation dynamics observed in dipolar and quadrupolar glasses are reviewed. Special attention is given to the distribution of the relaxation times and to the temperature dependence of the mean relaxation rates. Experimental evidence is provided that orientational glasses can be described in terms of ‘strong glasses’ that are characterized by a low density of configurational states in the potential energy surface. It is suggested that this behavior results from the natural separation of timescales of reorientational and diffusive processes in these crystals.
Shear Modulus of an Irreversible Diblock Copolymer Network from Self-Consistent Field Theory
2019
Using self-consistent field theory, we investigate the stretching-induced microphase separation in an irreversibly cross-linked polymer network composed of diblock copolymer chains and estimate its...
Mechanical and optical properties of continuously spun fibres of a main-chain smectic A elastomer
2012
Oriented smectic liquid crystal elastomer fibres are prepared with a special wet-spinning technique. The continuous spinning process in principle allows the preparation of fibres with arbitrary length. In comparison to ordinary rubbers, they have unique mechanical properties that qualify them as potential candidates for mechanical actuator applications. We demonstrate that these fibres show a remarkable contraction and extension at the transition from the ordered smectic to the disordered isotropic phase. We characterise their most relevant physical properties, viz. the thermally driven shape changes, stress–strain relations and optical birefringence, by optical and mechanical measurements.
Direct observation of a buckling transition during the formation of thin colloidal crystals
2007
We have investigated a colloidal suspension in a thin wedge formed by two glass plates in the presence of a lateral pressure. Starting with a single hexagonal layer, with increasing separation between the glass plates additional layers are added. This process is accompanied by a number of structural transitions necessary to maintain a high packing fraction under the given boundary conditions. Besides the well-known sequence of hexagonal and quadratic phases, we observe two new phases which are identified with the buckling and the rhombic phase recently predicted by other authors.