Internal Tensile Forces Research Articles

The importance of three dimensions in the study of solid armature transition in railguns

It is shown experimentally that the main processes first causing breakdown of the sliding solid contact (SSC) carrying large currents are not two-dimensional processes of the velocity skin-effect type, but pinch instabilities developing in the contact interface. Electromagnetic and electrothermal explosive ejection of ionized material of low-mass pinch waists ignite parasite-shunting arcs behind and ahead of the armature under acceleration. Thus one has to speak of transition into arcing mode not of the SSC alone, but of the launch process as a whole. It has been noted that during the transition into the arcing mode the solid armature begins to behave as a hybrid armature of pulling type. At this operation mode, two stable arcs appear, due to pinch cords moving forward along the contact surfaces, which are fixed to both contact surfaces of the armature near their leading edges. Consequently, the armature main body is accelerated under the action of internal tensile forces originating in its leading part where the I × B forces are applied.

Propagation of force and the induced bending displacement along eukaryotic flagellar axoneme

The mechanical forces responsible for inducing the bending movement of eukaryotic flagellar axonemes have components that propagate at velocities different from those for the displacement of the medium. These forces are subject to the Third Law of Mechanics which states the null-conservation of acting and reacting forces. Experimental demonstration of the propagating internal tensile force along the axoneme, when not accompanied by simultaneous bending displacement, demonstrates that the active force for the bending of the flagellar axoneme is part of the process of counterbalancing the corresponding reactive force to the ATP hydrolysis underlying the force generation.

Tower silo design: Principles and computer implementation

Farm tower silo design in Canada is changing from the use of strictly empirical formulae to analytical methods. This means that several types of structures and a variety of silage materials at a range of moisture contents can be accomodated. This paper attempts to summarize the wall pressures caused by whole plant materials in bottom and top unloading silos. Both dry and wet silages are considered. Guidelines are provided also for determining pressures from high moisture grains. The determination of internal hoop tensile forces is also discussed. A design aid is provided for bottom unloading silos where the internal hoop tensile forces are difficult to calculate. A computer program was developed using the various algorithms to aid in the rapid determination of a pressure diagram and of the resulting hoop forces, given the silo geometry and the specification of the material intended to be stored.

Theoretical Estimation of the Response of Helically Armored Cables to Tension, Torsion, and Bending

This paper concerns the mechanical behavior of ACSR (aluminum conductor steel-reinforced) conductors under static-loading conditions, which may comprise any combination of tension, torsion, and bending. The model described is quite general and can be applied to other types of helically armored cables. A stiffness matrix is developed and relations are given for axial, torsional, and flexural rigidities and for coupling parameters. For small curvatures, the flexural rigidity is comparable to the upper limit accepted in current practice by ACSR users. As the curvature increases, however, frictional forces develop between the outer layers and sliding of wires may occur, with the result that the flexural rigidity decreases. The tension level also influences the flexural rigidity of the conductor. Actually the model does not consider the flexural rigidity of the system as a fixed entity but as directly influenced by local compressive forces and internal radial and tensile forces. The analysis can also apply to situations where a given number of initial constituent wires have failed and the load is transferred to neighboring wires, leaving the conductor unbalanced; it will be seen how internal arrangements manage to accommodate the local perturbation.

SORPTION OF WATER AND ALCOHOL VAPORS BY CELLULOSE

Measurements were made of the amount of water vapor sorbed by beaten and unbeaten samples of kraft, unbleached sulphite and bleached sulphite wood pulps at relative vapor pressures ranging from 0 to 100%. Beating of the pulp made practically no difference to the degree of sorption at any relative vapor pressure. This indicated that beating caused no change in the hydration of the cellulose. Measurements were made of the sorption of methyl alcohol vapor by bleached sulphite, kraft and groundwood, and of the sorption of propyl alcohol vapor by bleached sulphite and cotton, all previously wetted with water and then dried. After sorption of alcohol, evacuation at room temperatures did not completely remove the alcohol. Measurements were also made of sorption of propyl alcohol by bleached sulphite and by cotton which had been dewatered by washing with propyl alcohol. The shape of the sorption curve was different for these samples, and the residual alcohol after evacuation was less. After a sample of cotton had been dried over phosphorus pentoxide in vacuo for a long period it was found to hold 0.35% of water by weight which could be removed by heating the cellulose to 100 °C. This was regained from the pentoxide on cooling the cellulose.The data are explained on the hypothesis that the crystalline submicroscopic elements of the cellulose structure are drawn together by internal tensile forces during the evaporation of the sorbed liquid, and that bonding between these elements may take place by the growing together of the crystal elements, leaving the structure internally stressed. On absorption, dissolution of these bondings takes place and the stresses are relieved as liquid enters the structure.