Multi-layered Constructions Research Articles

Nondestructive testing of glued joints

The pros and cons are considered for both traditionally applied and special low-frequency acoustic methods of the nondestructive testing of multilayered, glued constructions. The types of defects in glued constructions produced using polymer composite materials are shown; these defects may be revealed by the impedance method when adjusting the device according to the construction being tested. Methods for the nondestructive testing of the glued joints in multilayered constructions are presented and the numbers of the methodical regulation and technical documentation (RTD) developed in the FGUP VIAM are listed.

Sound absorption by multi-layered constructions composed of powder layers and porous sheets

Sound absorption coefficients for powder beds comprised of fine powders (white carbon and vermiculite) were determined using a reverberation room. The characteristic curves showed high peaks in the low-frequency range, due to the excitation of longitudinal vibration modes in the powder beds by random incident sound. Multi-layered constructions composed of powder layers and porous sound-absorbing material (polyurethane foam sheets) were designed, and their sound absorption properties were investigated. Measurements showed that the multi-layered constructions have high sound absorption peaks in the low-frequency range, believed to be due to the combined effects of powder vibration and viscous dissipation in the pores of the polyurethane foam. The combination of two material possessing different sound absorption characteristics results in an expansion of the sound absorption frequency range and indicates the possibility of new sound absorbing materials for low-frequency sound. Sound absorption simulation based on electric transmission line theory was applied to the multi-layered constructions. The calculated results agreed well with the measured results. A simulation using the propagation constant and characteristic impedance of the constituent materials was found to be useful in designing the frequency characteristics of these constructions. © 1998 Scripta Technica. Electr Eng Jpn, 122(2): 1–11, 1998

Simple derivation of the stiffness matrix for axial/torsional coupling of spiral strands

Coupled extensional-torsional behaviour of realistic multi-layered helical strands is addressed. Simplified routines are presented for obtaining the upper and lower bounds to various strand stiffnesses. Such straightforward formulations (aimed at practising engineers) have been derived by extensive theoretical parametric studies on a number of multi-layered spiral strand constructions covering a wide range of cable (and wire) diameters and lay angles. Numerical examples are presented to facilitate the use of the formulations, whose possible practical limitations have been critically addressed.

Transient analysis of air-conditioning load and room conditions considering simultaneous heat and moisture transport of multi-layered constructions

Moisture transport in a building has a major role in condensation problems. It also has much importance in the formation of room air humidity and air-conditioning load. The focal point of this paper is to evaluate room air humidity and air-conditioning load considering moisture transport by desorption and absorption of multi-layered constructions. For this purpose, a computer code has been developed. A brief description of the calculation method and the mathematical background is given. Validation of the procedure is carried out by comparing measured and simulated humidity and temperatures. Simulated examples are shown with the results that the sorption effect keeps air humidity of a storehouse stable and increases air-conditioning loads of an ordinary office room by about 5%.

New Laser Serves Red Light, Straight Up

Researchers have been trying to develop lasers that direct their light up through the top of a chip instead of out the side. But they've had little success in turning such lasers into efficient, practical emitters of the visible light prized for many applications. Now, researchers at Sandia National Laboratories have fashioned tiny surface-emitters that just may pass technological muster. In the 13 May issue of Electronics Letters, Sandia materials scientists Richard Schneider and James A. Lott report a new wrinkle on a technology familiar in the optoelectronics world-that of the so-called vertical cavity surface emitting lasers (VSCELs). To make their VSCEL, the Sandia scientists relied on a fabrication technique known as metalorganic vapor phase epitaxy, which enables them to build up complex multilayered constructions, molecular layer by molecular layer. The light-emitting heart of these constructions is the optical cavity, composed of several 10-nanometer-thick layers of the semiconductor indium-aluminum-gallium-phosphide. The cavity's quantum mechanical properties, which depend partly on the precise thicknesses of its layers, the specific semiconductors used, and the mechanical strain between adjacent layers, turn it into so-called quantum well in which electric charges approaching from the layers above and below it get trapped and recombine to emit redmore » light. Bounding the cavity are complex mirrors made up of alternating sublayers of aluminum arsenide and aluminum gallium arsenide. The mirrors reflect and amplify the emitted light and pave a low resistance pathway into the cavity for electrons and holes - mobile positive charges. The electrical current that drives the laser enters through metal electrodes that are deposited onto the very top and bottom of the multilayered structure.« less