Split Hopkinson pressure bar testing of 3D woven composites

Results from a series of split Hopkinson pressure bar (SHPB) tests on 3D woven tetxile composites (3DWC) are presented. These tests were done to determine the rate dependent compression response of 3DWC. Three different configurations of the 3DWC, corresponding to compression response in the plane of the material and through-the-thickness direction (out-of-plane) were studied. The rate dependent responses were compared against quasi-static test results and it was found that 3DWC showed an increase in strength in all three directions studied, however, accompanied by a transition in the failure mechanism. The in-plane orientations showed the largest increase in (about 100%) strength at the elevated rates of loading. A follow-on paper provides finite element based results that correspond to the experimental results presented here.     

Reconstructing the parameters of geofields taking measurement noise into account. Part II. Techniques for identification,regularization, and soft computing

Various methods for reconstructing the parameters of geofields taking measurement noise into account are analyzed. Program packages for nonspecialists in the theory of programming are discussed. Recommendations are given regarding the correct choice of method and control parameters for approximating and modelling geofields. The advantages and disadvantages of these methods in different stages of the recovery of the parameters of geofields are examined. It is proposed that fuzzy neural networks be utilized in the early stage when the data are uncertain and limited.     

Dynamic behavior of an aggregate material at simultaneous high pressure and strain rate: SHPB triaxial tests

Low velocity impacts on energetic materials induce plastic deformations and sliding friction which can lead to ignition. If some ignition criteria have been proposed, the remaining difficulty is to characterize the mechanical behavior of the material when submitted to the corresponding solicitations (high pressure and high strain rate). Thus, a technique based on the Split Hopkinson Pressure Bars system is proposed to carry out a triaxial compression test. A cylindrical specimen is placed into a confining ring and is compressed by the system of bars. The ring prevents the radial extension of the specimen and creates a lateral confining pressure. The material and dimensions chosen for the ring maintain a constant radial pressure during the test. Some tests were carried out on an inert aggregate material and proved the validity of this experimental device. The experimental data processing shows the influence of both the pressure and the strain rate. The shear stresses, which contribute to thermal dissipation and then to the ignition threshold, increase according to the pressure.     

Electric conductivity of metal-dielectric-metal structures with dielectric layer formed by spherical metal oxide nanoparticles

The electrical properties of metal-dielectric-metal (MDM) structures with the dielectric layer representing a monolayer of spherical Al₂O₃ or ZrO₂ oxide nanoparticles have been studied. It is established that these heterogeneous structures exhibit electric conductivity according to the mechanism for which the differential resistance dU/dI is negative and reversibly approaches zero with increasing current I. The electric conductivity strongly depends on the polarity of the applied voltage U, provided that electrodes are made of basically different metals or the same metal with different surface conditions. The mechanism of the electric conductivity in the given MDM structure depends on the diameter of nanoparticles in the dielectric layer.     

Failure mechanisms in granular media: a discrete element analysis

This paper attempts to numerically validate the concept of diffuse failure using a discrete element method. First, the theoretical background is reviewed, and it is shown how the kinetic energy of a system, initially at rest after a loading history, is likely to abruptly increase under the effect of disturbances. The vanishing of the second-order work thus constitutes a basic ingredient, related to both the pioneering work of Hill (J Mech Phys Solids (6):236–249, 1958) and the notion of bifurcation applied to geomechanics (Vardoulakis and Sulem in Bifurcation analysis in geomechanics, Chapman & Hall Publisher, London, 1995). Discrete numerical simulations were performed on homogeneous three-dimensional specimens, and the three basic conditions that must be satisfied in order to observe a failure mechanism are numerically checked. Finally, this work illustrates the phenomena that are likely to affect in situ slopes, for instance, when the loading (due to weather conditions or human activities) meets the three basic conditions for a failure mechanism to develop.     

Multilayer Transitions in Spin-3/2 Blume–Capel Model with RKKY Interaction in a Transverse Field

Using mean-field theory, we have studied the effect of quantum transverse field on the magnetic properties and multilayer transitions in the spin-3/2 Blume–Capel model with RKKY interaction. The system is formed by two magnetic multilayer materials, of different thicknesses, separated by a non magnetic spacer of thickness M. It is found that there exist critical transverse fields above which the multilayer transitions occur. This critical value decreases when increasing the thickness of the nonmagnetic spacer M. Phase diagram is established in different plane of space parameter.     

Electron-Hole Asymmetry in the Dynamic Hubbard Model

The two-site dynamical mean field theory (DMFT) is applied to the dynamic Hubbard model. This model takes into account a correction to the Coulomb interaction due to particle double occupancy by using an Ising-like degree of freedom to represent an associated boson field. At finite boson frequency, the appearance of a Mott gap is found to be enhanced even though it shows a metallic phase with the same bare on-site interaction U in the conventional Hubbard model. A lack of electron-hole symmetry is observed through the quasi-particle weight versus particle density.     

Reduction of wine 4-ethylphenol concentration using lyophilised yeast as a bioadsorbent: influence on anthocyanin content and chromatic variables

The present work reports the capacity of lyophilised Saccharomyces cerevisiae G37 and Schizosaccharomyces pombe 936 to adsorb 4-ethylphenol, a compound with a negative impact on the sensorial profile of wine. Using SPME-GC/MS, a strong correlation was detected between the quantity of yeast added and the reduction of the initial wine 4-ethylphenol concentration. The adsorption kinetics for each yeast was determined. The impact of this treatment on wine anthocyanin concentration and chromatic properties was investigated by UV–Vis and HPLC–PDAD/ESI–MS analysis. Large reductions in the anthocyanin concentration were detected when effective 4-ethylphenol-reducing quantities of lyophilised yeast were used.