Initial failure of mechanically fastened joints with offset loading

In this preliminary study the initial failure of a bolted composite joint was investigated. The results of an experimental program using two simple beams bolted together with offset loading are presented. These test specimens were used to simulate a typical skin-spar attachment in a composite wing undergoing hydraulic shock. Initial failure was found to be due to a prying force induced at the outer sections of the joint leading to transverse shear failure.

Nonharmonic transverse vibration of the H-bonded molecules and the THz spectra in ice and water

A nonlinear equation of motion is found for the dimer comprising two charged H2O molecules. The THz dielectric response to nonharmonic vibration of a nonrigid dipole, forming the hydrogen bond (HB), is found in the direction transverse to this bond. An explicit expression is derived for the autocorrelator that governs the spectrum generated by transverse vibration (TV) of such a dipole. This expression is obtained by analytical solution of the truncated set of recurrence equations. The far infrared (FIR) spectra of ice at the temperature - 7 degrees C are calculated. The wideband, in the wavenumber (frequency) v range 0... 100.0 cm(-1), spectra are obtained for liquid water at room temperature and for supercooled water at -5.6 degrees C. All spectra are represented in terms of the complex permittivity epsilon(v) and the absorption coefficient alpha(v). The obtained analytical formula for epsilon comprises the term epsilon(perpendicular to) pertinent to the studied TV mechanism with three additional terms Delta epsilon(q), Delta epsilon(mu), and epsilon(or) arising, respectively, from: elastic harmonic vibration of charged molecules along the H-bond; elastic reorientation of HB permanent dipoles; and rather free libration of permanent dipoles in 'defects' of water/ice structure. The suggested TV-dielectric relaxation mechanism allows us: (a) to remove the THz 'deficit' of loss epsilon" inherent in previous theoretical studies; (b) to explain the THz loss and absorption spectra in supercooled (SC) water; and (c) to describe, in agreement with the experiment, the low- and high-frequency tails of the two bands of ice H2O located in the range 10...300 cm(-1). Specific THz dielectric properties of SC water are ascribed to association of water molecules, revealed in our study by transverse vibration of HB charged molecules. (C) 2006 Published by Elsevier B.V.

Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 2: performance under shear loading

Validation of a framework for unsaturated soil behaviour has frequently resulted in disagreement with basic propositions. A primary reason for this disparity is considered to be attributable to the anisotropic properties of the soil specimens tested as a result of preparation using one-dimensional compaction. As part of the work presented, comparison is made between tests on samples of unsaturated kaolin prepared at identical specific volumes and specific water volumes using isotropic compression and one-dimensional compression. The suctions in the samples were reduced to predefined values by wetting under low isotropic loading in a triaxial cell. The samples were then taken through various stress paths to failure, defined as the critical state strength, while the suctions were held constant. Stress path tests were also performed on samples without reducing the suction to predefined values. In the latter, constant water mass tests, the suctions were allowed to vary and were measured using a psychrometer. The results of the tests at critical state are compared with the propositions of Wheeler and Sivakumar. The shear strengths of samples with isotropic previous history are shown to be significantly greater than those of samples with one-dimensional stress history when plotted against the mean net stress. The normal compression lines, critical state lines and yield characteristics are also shown to be significantly influenced by the previous stress history and are shown to be different for isotropically and one-dimensionally prepared samples.

Hot Electrons Transverse Refluxing in Ultraintense Laser-Solid Interactions

We have analyzed the coupling of ultraintense lasers (at similar to 2 X 1019 W/cm(2)) with solid foils of limited transverse extent (similar to 10 s of mu m) by monitoring the electrons and ions emitted from the target. We observe that reducing the target surface area allows electrons at the target surface to be reflected from the target edges during or shortly after the laser pulse. This transverse refluxing can maintain a hotter, denser and more homogeneous electron sheath around the target for a longer time. Consequently, when transverse refluxing takes places within the acceleration time of associated ions, we observe increased maximum proton energies (up to threefold), increased laser-to-ion conversion efficiency (up to a factor 30), and reduced divergence which bodes well for a number of applications.