Characterization of Ice Adhesion: Approaches and Modes of Loading

Airborne structures are vulnerable to atmospheric icing in cold weather operation conditions. Most of the ice adhesion-related works have focused on mechanical ice removal strategies because of practical considerations, while limited literature is available for a fundamental understanding of the ice adhesion process. Here, we present fracture mechanics-based approaches to characterize interfacial fracture parameters for the tensile and shear behavior of a typical ice/aluminum interface. An experimental framework employing single cantilever beam, direct shear, and push-out shear tests were developed to achieve near mode-I and near mode-II fracture conditions at the interface. Both analytical (beam bending and shear-lag analysis), and numerical (finite element analysis incorporating cohesive zone method) models were used to extract mode-I and II interfacial fracture parameters. The combined experimental and numerical results, as well as surveying published results for the direct shear and push-out shear tests, showed that mode-II interfacial strength and toughness could be significantly affected by the test method due to geometrically induced interfacial residual stress. As a result, the apparent toughness of the zero-angle push-out test could reach an order of magnitude higher than those derived from direct shear tests. Moreover, it was found that the interfacial ice adhesion is fracture mode insensitive and roughness insensitive for tensile and shear modes, for the observed modes of failures in this stud

Intramolecular forces: the molecular structure and conformation of 2-cyclopropylpyridine and 4-cyclopropylpyridine

The molecular structure and conformation of 2-cyclopropylpyridine and 4-cyclopropylpyridine have been studied experimentally by gas-phase electron diffraction as well as by ab initio quantum chemical calculations. 2-Cyclopropylpyridine appears exclusively in the bisected form, with the cyclopropyl group pointing towards the nitrogen atom. The 4-cyclopropylpyridine molecules are, however, present as a mixture of conformers, dominated by the bisected one (71.0(6.5)%) along with the perpendicular conformer. The energies of the two cyclopropylpyridines are being compared to the energy of cyclopropylbenzene. The presence of the nitrogen atom is generally found to lower the energy of these molecules. When the orbitals of the cyclopropyl group may interact with the nitrogen lone-pair electrons, as in one of the bisected 2-cyclopropylpyridine conformers, this has a profound effect on the stability of the molecule, resulting in a lowering of the energy by ca. 3 kcal mol(-1). The expected shortening of the distal cyclopropyl C-C bond length is observed in 2-cyclopropylpyridine, while the calculated difference between vicinal and distal C-C bonds had to be assumed in the experimental study of 4-cyclopropylpyridine. (c) 2004 Elsevier B.V. All rights reserved

The strain rate and temperature dependence of Young's modulus of ice

Measurements were made of Young's modulus of polycrystalline ice over the strain rate range of 10[-8] to 5 x 10[-3] s[-1] at temperatures of -10, -19.3, -29 and -39.5 degrees C on two types of ice: naturally formed granular ice and laboratory grown columnar-grained ice. Load was applied at constant rate of cross-head movement until the stress was about 5 kg/cm[2], and then removed immediately at the same rate. Young's moduli were determined from the linear portion of the stress-strain curve during loading. The modulus for both types of ice increased with increasing strain rate over the full range of strain rate covered in the investigation.Les auteurs mesurent le module de Young de la glace polycristalline \ue0 des viteses de d\ue9formation entre 10[-8] et 5 x 10[-3] s[-1] et \ue0 des temp\ue9ratures de -10, -19.3, -29 et -39.5 degr\ue9s C pour deux genres de glace: la glace granulaire naturelle et la glace colonnaire obtenue en laboratoire. La charge est appliqu\ue9e \ue0 une vitesse de traverse constante jusqu'\ue0 une contrainte d'environ 5 kg/cm[ 2], puis enlev\ue9e imm\ue9diatement \ue0 la m\ueame vitesse. On d\ue9 termine le module de Young d'apr\ue8s la partie lin\ue9aire de la courbe contrainte/d\ue9formation durant le chargement. Le module des deux genres de glace augmente en m\ueame temps que la vitesse de d\ue9formation augmente \ue0 toutes les vitesses de d\ue9formation \ue9tudi\ue9es.Peer reviewed: NoNRC publication: Ye

The structure of betaxolol from single crystal X-ray diffraction and natural bond orbital analysis

The structure of betaxolol obtained from ethanol:water solution was studied by X-ray diffraction. The geometrical parameters needed to define the structure are tabulated. The X-ray data show the existence of two conformers in the unit cell differing only in the conformation of the cyclopropylmethoxy fragment. Differences in the bond lengths angles and dihedral between both conformations are observed. The cyclopropyl groups lie in approximately perpendicular planes.http://www.sciencedirect.com/science/article/B6TGS-4SBY517-4/1/903bcc11f3a4623410c907f8bf4d39f