Local effects in the vicinity of inserts in sandwich panels

The paper considers local bending effects induced in the vicinity of inserts in sandwich panels. Such local bending effects are associated with an increase of bending stresses in the sandwich faces and normal and shear stresses in the sandwich core. An earlier developed analytic model [Proceedings of the Sixth International Conference on Sandwich Structures (ICSS-6) (2002) 551] is adapted for the case of a sandwich panel with circular insert, with elastic properties differing from those of the core. The locally induced stresses in the faces and core due to presence of the insert are expressed via simple analytic relations (and charts) enabling an estimation of these local stresses. Finite element analysis is employed to demonstrate the applicability of the analytic model, and a good correspondence between the numerical and the analytical data is found. A study case related to marine applications, namely a circular insert in a sandwich deck panel used for mounting of a rigging fixture, is considered, and optimization of an existing design is carried out.     

An improved model for the prediction of intra-cell buckling in CFRP sandwich panels under in-plane compressive loading

Local instability in the form of “intra-cell buckling” or “dimpling” is a well-known failure mode in honeycomb-cored sandwich panels with very thin faces. Most work reported on the subject suggests relatively simple design formulae for the estimation of the intra-cell buckling load. It is however widely known that these classical design formulae in some cases considerably underpredict the intra-cell buckling load. In this paper a series of experimental results obtained for different CFRP/honeycomb sandwich panel configurations loaded in compression are presented. The results confirm that the “classical” design formulae provide overly conservative results. During the tests the intra-cell buckling patterns were monitored carefully, and it was observed that the hitherto assumed buckling patterns did not correspond to the experimental observations. Based on these findings a new simplified design formula is suggested, which for the investigated CFRP/honeycomb sandwich panels provides significantly more accurate predictions than the “classical” design formulae.     

Numerical Solution of Fractional Advection-Dispersion Equation

Numerical schemes and stability criteria are developed for solution of the one-dimensional fractional advection-dispersion equation (FRADE) derived by revising Fick’s first law. Employing 74 sets of dye test data measured on natural streams, it is found that the fractional order F of the partial differential operator acting on the dispersion term varies around the most frequently occurring value of F = 1.65 in the range of 1.4 to 2.0. Two series expansions are proposed for approximation of the limit definitions of fractional derivatives. On this ground, two three-term finite-difference schemes?“1.3 Backward Scheme” having the first-order accuracy and “F.3 Central Scheme” possessing the F-th order accuracy?are presented for fractional order derivatives. The F.3 scheme is found to perform better than does the 1.3 scheme in terms of error and stability analyses and is thus recommended for numerical solution of FRADE. The fractional dispersion model characterized by the FRADE and the F.3 scheme can accurately simulate the long-tailed dispersion processes in natural rivers.     

Multipurpose modular experimental station for the DiProI beamline of Fermi@Elettra free electron laser

We present a compact modular apparatus with a flexible design that will be operated at the DiProI beamline of the Fermi@Elettra free electron laser (FEL) for performing static and time-resolved coherent diffraction imaging experiments, taking advantage of the full coherence and variable polarization of the short seeded FEL pulses. The apparatus has been assembled and the potential of the experimental setup is demonstrated by commissioning tests with coherent synchrotron radiation. This multipurpose experimental station will be open to general users after installation at the Fermi@Elettra free electron laser in 2011.     

Vertrauensvolle E-Mail-Kommunikation

Der ?elektronische Brief“ bzw. die elektronische Mail (E-Mail) ist seit über 30 Jahren im privaten wie beruflichen Umfeld im Einsatz. Behörden, Steuerbüros, Krankenhäuser, Finanzinstitute und viele weitere Gruppen versenden und empfangen E-Mails, um Informationen auszutauschen. Innerhalb kurzer Zeit findet eine E-Mail ihren Weg vom Sender in Deutschland zum Empfänger in beispielsweise den USA. Wie funktioniert das? Und was hat es mit E-Mail-Verschlüsselung auf sich? Dieser Artikel betrachtet die grundlegende technische Funktionsweise der E-Mail sowie Hintergründe und Funktionsweise der Verschlüsselung mit S/MIME und PGP.     

Holistic process planning chain for robot machining

Today, machining of large, integral constructed structural parts requires expensive machining centers. In contrast, modern industrial robots are suitable for a wide field of applications and are characterized large working spaces and low capital investment. Therefore, they provide high economical potential for machining applications in aerospace industry, especially for the machining of near to shape pre-products like extruded profiles. However, their constructive characteristics like low stiffness and high sensitivity to vibrations lead to disadvantages compared with conventional machining centers and have to be considered during process planning. Therefore, several methods for offline and online optimization of robot machining processes were developed and integrated in a new process chain for manufacturing of structural fuselage parts. Thereby, the conventional CAD–CAM process planning chain was extended with simulation based analysis and optimization methods and a load-depending trajectory planning. These methods for offline process optimization within this novel process chain are presented in this paper.