Damage evolution and debonding in hybrid laminates with a cohesive interfacial law

The hybridisation of fibres reinforced laminates, i.e., the combined use of two or more families of fibres, is an effective technique to achieve a pseudo-ductile response and overcome the inherent brittleness which limits the wider use of composite materials. In this paper, a one-dimensional analytical model for unidirectional hybrid laminates is derived. The model considers two elastic–brittle layers bonded together by a cohesive elasto–plastic–brittle interface. This formulation is applied to the study of the debonding and fracture of laminates under uniaxial loading and the results compared to experiments available from the open literature. This study shows that the proposed model provides a close fit to the experimental data and it is able to match accurately the crack patterns seen in the experiments. The model predicts four different failure mechanisms and is able to discriminate among them according to the geometrical and mechanical properties of the layers.

     

Multipole expansions of the electrostatic molecular potential

Multipole expansions of the electrostatic molecular potential up to the hexadecapole terms are examined for H₂O, NH₃ and C₂H₄NH. A reasonable approximation to get unexpensive first order representations of the electrostatic potential for regions outside the van der Waals volume is found.     

Solid State Machinery of Multiple Dynamic Elements in a Metal–Organic Framework

Engineering coordinated rotational motion in porous architectures enables the fabrication of molecular machines in solids. A flexible two-fold interpenetrated pillared Metal-Organic Framework precisely organizes fast mobile elements such as bicyclopentane (BCP) (10⁷ Hz regime at 85 K), two distinct pyridyl rotors and E-azo group involved in pedal-like motion. Reciprocal sliding of the two sub-networks, switched by chemical stimuli, modulated the sizes of the channels and finally the overall dynamical machinery. Actually, iodine-vapor adsorption drives a dramatic structural rearrangement, displacing the two distinct subnets in a concerted piston-like motion. Unconventionally, BCP mobility increases, exploring ultra-fast dynamics (10⁷ Hz) at temperatures as low as 44 K, while the pyridyl rotors diverge into a faster and slower dynamical regime by symmetry lowering. Indeed, one pillar ring gained greater rotary freedom as carried by the azo-group in a crank-like motion. A peculiar behavior was stimulated by pressurized CO_2, which regulates BCP dynamics upon incremental site occupation. The rotary dynamics is intrinsically coupled to the framework flexibility as demonstrated by complementary experimental evidence (multinuclear solid-state NMR down to very low temperatures, synchrotron radiation XRD, gas sorption) and computational modelling, which helps elucidate the highly sophisticated rotor-structure interplay.     

The effect of substitution on the properties of a chemical group

The effect of the substituent R(R = F, OH, NH₂, CH₃) on the electron distribution of the C=C group of ethylene and acrylonitrile may be fairly well represented in terms of classical interactions between the and components of this group and the molecular remainder. A distinction between direct and indirect effects is made, and an estimate of the relative importance of conjugative versus inductive effects is done.This analysis has been performed on a set of 22 SCF wavefunctions calculated with the 4-31G basis set.     

Towards a comprehensive theory of lyoluminescence in alkali halide crystals: Some results and some perspectives for future research

Lyoluminescence is an interesting tool to study irradiation defects in solids and their behaviour after dissolution. A general kinetic scheme of the process valid for alkali halide crystals is presented, and some ideas about structure and properties of the interacting species, in the solid as well as in the liquid phase, are discussed.     

DFT Calculation of Deuterium Quadrupolar Tensor in Crystal Anthracene

A DFT calculation of deuterium nuclear quadrupole tensors of crystal anthracene is presented. After a careful analysis of the DFT functionals and of the basis sets, the B3LYP/6-311+G(d,3p2d) level has been identified as the best compromise between accuracy and computational cost. To account for the crystal environment, three models are proposed: one represented by a cluster of five anthracene arranged as in the crystal, the other formed by an anthracene embedded in a dielectric continuum having the dielectric permittivity of the crystal, and the last represented by an embedded dimer of anthracene. It is shown that the pure continuum model (here represented by the Integral Equation Formalism version of the Polarizable Continuum Model) already accounts for a large part of the crystal effects and that the embedded dimer almost entirely recover all the details of the explicit 5-anthracene cluster.     

Electronic structure of friedel crafts catalysts BF3+HF

SCF MO LCAO calculations using two different gaussian basis sets have been performed for the species HF, F^?, BF₃, BF ₄ ^? and HBF₄ with geometry optimization. Differences in electrophilicity and proton donating capability of HF due to the formation of the adduct with BF₃ are evidenced and discussed.     

Theoretical study of reaction mechanisms for the ketonization of vinyl alcohol in gas phase and aqueous solution

Theoretical ab initio calculations are done on different mechanisms for the conversion of vinyl alcohol to acetaldehyde, both in gas phase and in solution. Several basis sets are used in order to assess the accuracy of the results in gas phase and a continuum model of the solvent is employed to mimic reactions in water solution. The results indicate a catalytic action of water in hydrated clusters in gas phase, whereas in solution, and within the error limits of our calculations, both neutral water-chain and ionic mechanisms appear to be equally probable. Finally, the action of acids or bases is tested through the analysis of the reaction of vinyl alcohol with H₃O⁺ and HO^–. The results of the calculations are shown to be in qualitative agreement with the experimental facts when 6-31++G basis set is used but not when either STO-3G or 4-31G basis sets are employed.