Influence Of Air Pressure Research Articles

Internal friction in metallic foams and some related cellular structures

Abstract Density, pore size and shape, chemical composition, pre-deformation, number of vibration, and air pressure influence damping of cellular metallic materials (CMM: foams with open and closed-cells, sponges and porous sintered metals). At least three ranges of amplitude domains of vibrations are distinguished with respect to internal friction mechanisms. The thermoelastic damping plays an important role in the range of amplitude-independent damping (Al- and Zn-based foams). The amplitude-dependent damping caused by reversible motion of dislocations is enhanced in porous structures by localised stresses. In case of magnetic CMM, the magnetomechanical effect can be an additional source of damping (Ni-based sponges). Up to a certain amplitude of deformation the damping is stable, i.e. practically does not depend on the number of vibrations. Beyond this limit, irreversible microplastic deformation (mpd) enhances the amplitude dependence; a model for damping in porous materials is discussed for this “microplastic” range. An additional time dependence due to fatigue processes is attributed to growth and movement of cracks.

Lateral Buckling Behavior of Pneumatically Stiffened, Reinforced Composite Beams in Bending

The use of inflatable structures has often been proposed for aerospace applications. The advantages of such structures include low weight, easy assembly, and storage. The aim of this study is to investigate the effects of finite inflation on the subsequent buckling response of a carbon-fiber-reinforced composite beam (RCB) in bending. A finite element solution for three incremental beam configurations is developed. The first lateral buckling mode is used to determine the structural efficacy of the inflated beam. For each beam, the bending moment required to induce lateral buckling was determined. A nonlinear material and geometrically nonlinear finite element solution is obtained for the inflation load. A Rik method solution was then obtained to examine the postbuckling response of the RCBs. In addition, an eigenvalue extraction was performed to study the intrinsic influence of air pressure on the structural stability of RCBs. Finally, experimental data were obtained to verify the theoretical results. It is found that a simple eigenvalue extraction provides a conservative estimate of the critical buckling moment for preliminary design purposes. Furthermore, there is good correlation between theory and experiment and there exists noticeable interaction between the beam and pressurized air prior to final buckling for this type of reinforced composite beam.

Commingling Self-Twist Yarn with Filaments1

The air intermingling technique is used to impart filament cohesion in flat and textured multifilament yarns; more recently this technique has been used to combine filaments with spun yarns or elastomers to form composite yarns. In this investigation, a self-twist yarn was commingled with a thin, flat, multifilament yarn using an inter mingling air nozzle. The tensile properties of the commingled yarn were significantly improved in comparison with the self-twist yarn from which the commingled yarn was made. Self-twist yarn is notorious for its structural periodicity, which leads to fabric patterning. This has been reduced to almost invisibility in the commingled yarns. Experiments have also revealed that commingling increases yarn hairiness, which may impose adverse effects on yarn weaveability. Yarn structural examination shows that trapping the ST yarn between the filaments and wrapping the ST and filaments together with a small portion of self-twist yarn surface fibers are the two predominant kinds of bindings formed during commingling. The influences of air pressure in the commingling nozzle, yarn linear speed, and overfeed ratio are also reported.

Influence of the pressure of gaseous media on the relaxation properties of elastomers

A study has been made of the influence of air pressure (up to 30 MPa) at 30–130° on the relaxation properties of a butadiene-methylstyrene elastomer. A pressure increase results in retardation of physical relaxation and leads to some augmentation of the activation energy owing to increased intermolecular interaction and to a free volume reduction. Chemical relaxation is accelerated in a high pressure air medium, and the activation energy is reduced. This reduction is the result of an intensification of thermooxidative processes on account of an increase in the concentration of dissolved ocygen in the elastomer.

A consideration of the effect of air pressure on solids flow from storage vessels

Based on a simplified block-flow model, the mechanism of flow of particles through an aperture is generally analyzed under the influence of air pressure. As a result, the effect of air pressure on the flow criterion and the flow rate of particles can be evaluated in terms of material properties, vessel geometry and operational conditions. Computed results satisfy previous data. Solids flow under air pressure is treated as a fluctuation phenomenon just as under gravity alone or tapping.

Influence of air pressure on erosion of anode and cathode arcs: S Z Bakal, Elektron Obrab Mater, No 5, 1971, 20–21 ( in Russian)

Influence of air pressure on erosion of anode and cathode arcs: S Z Bakal, Elektron Obrab Mater, No 5, 1971, 20–21 ( in Russian)