Papers by Keyword: Initial Tension

Abstract: The tension spring with initial tension is a coil spring with unique properties not found in other springs. It is often used to eliminate backlash, compensate for wear or thermal expansion, and hold parts in contact. While such tension springs have wide industrial applications, the academic literature on their properties and manufacturing is limited. Therefore, this study focuses on the computer numerical control (CNC) coiling machines commonly used to produce coil springs, and explores their process principles and the effects of settings on the geometry and initial tension of the springs through finite element analysis and experimental validation. As a result, the spring diameter can be controlled by adjusting the rake angle of the coiling pin and the distance to the mandrel wire feed opening using an empirical formula derived in this study to determine the parameters associated with a desired diameter. The plane of inclination applied to the mandrel is only used to initially deflect the wire when forming the first spring coil, without significantly affecting the initial stress. On the other hand, the transverse displacement of the mandrel is positively correlated with the pitch of the open compression spring and the initial tension of the tightly wound extension spring.

Abstract: This study explores the curvature and mechanical sensitivity of a pre-stressed layered plate embedded with a piezoelectric layer in large deflection. Piezoelectric effect was included in deriving the nonlinear governing equations but the arising nonlinear terms are neglected, yielding a standard Bessel equation or a modified Bessel equation for the lateral slope. Analytical solutions are developed and further manipulated to obtain lateral curvature and mechanical sensitivity. The results for a nearly monolithic plate under low pretension and low voltage applied across the piezoelectric layer agree well with those of CPT for a single-layered plate under pure mechanical loading. For typical symmetric 3-layered piezoelectric plates, the solutions show that, piezoelectric effect is apparent only up to a moderate initial tension. Beyond a moderate threshold value, the pretension turns to be dominant, resulting in nearly zero curvature and uniform mechanical sensitivity throughout the entire plate.

Abstract: Taking the free vibration system of a submerged floating tunnel tether as research object, the non-linear free vibration equation was set up. By means of Galerkin method, the partial differential equation was transformed into a set of ordinary ones. The damping ratios of the first four modes were obtained after complex eigenvalue analysis. Subsequently, effects of inclination, sag, initial tension force and length of tether on its modal damping ratios were analyzed. The results show that inclination and sag of tether merely affect the damping ratio of first in-plane mode; they have no effect on the damping ratios of higher order in-plane modes and out of plane modes; the first in-plane modal damping ratio of tether is in direct proportion to its inclination, whereas in inverse proportion to its sag; the first modal damping ratio of tether (both in-plane and out of plane) is in direct proportion to its length, whereas in inverse proportion to its initial tension.

Abstract: The present authors have invented a new method of changing coil orientation of a coil spring. The major merit of coil orientation change for SMA are reduction of space and control of two way shape memory effect. For instance, when a coil is heated above Af temperature with a load, the coil contracts. There is unrecovered strain which is attributed to elastic deformation by the load. The elastic strain can be eliminated by changing coil orientation. By removing elastic strain, the necessary space can be reduced. Besides generation and control of two way shape memory effect is presented using the reverse of coil orientation.

Abstract: The nonlinear problem of large deflection of an elastically-bossed layered plate under pretension due to lateral load is studied. The approach follows von Karman plate theory for large deflection for a symmetrically layered isotropic case. The thus derived nonlinear governing equations are solved using a numerical finite difference method with the aid of an iteration scheme. For a nearly monolithic plate with a thin boss, the obtained solutions correlate well with those available in literature for a single-layered flat plate, thus validates the presented approach. For three layered symmetric plates made of typical silicon based materials, various initial tension and lateral pressure are implemented. The results indicate that, edge behavior may appear at both the boss edge and the clamped end of the plate, thereby revealing severe variations for the structural responses. Varying the central boss size and relative thickness may have a sensible influence upon the behavior of the bossed layered plate. Furthermore, lateral pressure appears to have a sensible effect upon the nonlinear behavior of the bossed layered plate. For a relatively large initial tension, however, the pretension effect dominates, yielding a total membrane behavior for the bossed plate, regardless of the size of the center boss, except in the vicinity of the clamped edge.

Abstract: To discuss the surface characteristics and friction properties of PTFE yarn, the longitudinal structure and cross section were analyzed, it were investigated that the influence on friction coefficient of running speed, guide material and initial tension on ring spinning for producing PTFE film yarn. The results show that the longitudinal section of PTFE yarn was regular cylinder, the cross section was polygon, the yarn surface was very smooth, not easy to absorb dust, PTFE yarn had very good self-cleaning function. The friction coefficient of PTFE yarn was decreased at first with the increase of running speed but increased later, and the friction coefficient of PTFE yarn was reduced with the increase of initial pressure. The friction coefficient between PTFE yarn and plastic was very small, it can be said that plastic was the best guide material for ring spinning of PTFE yarn. Introduction

Abstract: A new type of flexible suspension tension structure (FSTS) is presented in this paper, which has the advantages of high-efficiency, convenient construction and wide application sphere, and it is also a kind of green and low carbon structure. In order to investigate the mechanical behavior of FSTS under the vertical load, series of structures under 10 groups of upward loads and 8 groups of downward loads are calculated with the matrix analysis method. The results show that the passive tensions of cables and displacement in the middle of span present approximate linear features under the downward loads. However, there are double broken linear features in FSTS under the upward loads. So this regularity can be utilized for the simple analysis and two-stage design calculation. Finally, the reliability of FSTS with the initial tension is investigated with the interval method. 81 kinds of structures with different initial tension are calculated, and the influence regularity of the initial tension in the back cable and the bottom cable are given. It is found that the deformation of FSTS is more sensitive to the initial tension of cables. Consequently, the initial tensions of cables are dominated by deformation of structures under design and construction.

Abstract: The guyed mast structure consists of a vertical shaft supported along its height by several layers of inclined pre-tensioned guys. The central shaft is generally made of lattice steel structure, and the guys are spaced at equal angles around the mast to ensure the vertical shaft’s stability. By taking a 102 m meteorological guyed tower in Hainan as an example, this paper made two design proposals using steel pipe and round steel material for the shaft respectively. According to the requirements of the project, this paper then did non-linear static analysis and buckling analysis of the structure by finite element software SAP2000, and compared the results of the two proposals so as to find the optimal one. The results show that steel pipe material is more economical when used for the mast shaft and more reasonable for bearing forces. The choice of the number and the initial tension of guys, as well as the wind vibration coefficient, which have a great effect on a guyed mast, are also discussed in this paper.

Abstract: Mechanical sensitivity of a bossed and clamped layered isotropic circular plate with pretension in large deflection is evaluated. The approach extends Von-Karman’s plate theory for large deflection to a symmetrically layered plate with a center boss. The derived nonlinear governing equations are solved using a finite difference method incorporating a numerical iteration scheme in finding the lateral slope and radial force resultant. The obtained geometrical responses are further manipulated to calculate the associated mechanical sensitivity. For a 3-layered plate with nearly the same layer moduli, the results correlate well with those following available formulation for a single-layer isotropic plate. The developed approach is then implemented for various initial tensions, lateral pressures as well as different boss sizes and ratios between the layer moduli. The obtained numerical results show that, initial tension appears to have the strongest influence upon the radial variation of mechanical sensitivity over the top surface of the bossed layered plate. While both the size of center boss and magnitude of lateral pressure can still have a significant effect, the mechanical sensitivity seems to be insensitive to the change of the ratio between layer moduli for a bossed and symmetrically layered plate.