Deflection (engineering)

About: Deflection (engineering) is a research topic. Over the lifetime, 30862 publications have been published within this topic receiving 298849 citations.

Structural characteristics and applicability of four-span suspension bridge

Abstract: A four-span suspension bridge which has two main 2,000 m spans is investigated with respect to the deformation characteristics. Generally, deformation behavior of the four-span suspension bridge is mainly influenced by rigidity of the center tower. This study is focused on properties such as bending and torsional rigidity of the girder, sag ratio, and dead load. The result of this investigation clarified that the lower rigidity under live load than the three-span bridge is caused by the smaller cable spring coefficient of the main span, which is 1/6 of the side span. Nevertheless, the tendency is stable and can be assisted by stiffened rigidity of the center tower. Live load deflection of the girder can be reduced to less than 1/200 of the main span length, which is useful and economical, by stiffening the bending coefficient of the center tower. Moreover, relatively lower rigidity of the center tower is sufficient for the 2,000 m span suspension bridge than for the 1,000 m span case, keeping the same deflection ratio. Three-dimensional sag geometry of the main cable is effective in limiting the torsional deformation, which is an especially important issue for the four-span suspension bridge caused by twist of the center tower.

Noise in piezoresistive atomic force microscopy

Abstract: The noise performance of piezoresistive atomic force microscopy (AFM) devices is investigated. The total deflection noise of a piezoresistive AFM device comprises vibrational noise from the cantilever, and Johnson and flicker noise from the piezoresistor. The vibrational deflection noise is found to have a minimum when the length of the piezoresistor is of the cantilever length. The minimum vibrational deflection noise is for a free cantilever, whereas a supported cantilever has a minimum vibrational noise of , where K is the spring constant of the device. Taking self-heating of the device into account, it is shown that an optimum power level exists at which the total equivalent displacement noise of a device is minimized. This minimum deflection noise is, for a fixed value of the spring constant, approximately proportional to the cantilever thickness, whereas it varies rather slowly with the length of the piezoresistor.

An effective modelling approach to estimate nonlinear bending behaviour of cantilever type conducting polymer actuators

Abstract: This paper reports on the establishment of an effective yet comprehensive modelling approach that enables (i) to determine the large and nonlinear bending displacements (i.e., deflections) of conducting polymer actuators, widely known as artificial muscles, and (ii) estimate the actuator parameters such as the effective modulus of elasticity. These actuators are fundamentally one-end fixed and the other end free cantilever structures, undergoing large deflections under an electrical potential difference. The classical beam theory fails to predict their bending behaviour such as the tip deflections accurately. Based on the operation principle of the electroactive polymer actuators and the large deflection Euler–Bernoulli equation, the bending displacement models are formulated for a cantilever beam under a continuously distributed load. These nonlinear models have been used to estimate the moduli of elasticity of the actuators, utilizing a nonlinear least square estimation algorithm, and experimentally measured longitudinal and transverse tip deflections. Parametric models relating the voltage input to the cylindrical coordinates of the tip deflection are also identified and experimentally validated. These models were further validated for a new set of experimental data such that the modelling approach is effective enough to estimate nonlinear deflection of the actuators and estimate actuator parameters such as the moduli of elasticity of the materials constituting polymer actuators. The modelling approach can be extended to mimic the bending behaviour of other ionic-type conducting polymer actuators.

Application of the quadrilateral area co-ordinate method: a new element for Mindlin–Reissner plate

Abstract: The quadrilateral area co-ordinate method is used to formulate a new quadrilateral element for Mindlin–Reissner plate bending problem. Firstly, an independent shear field is assumed based on the locking-free Timoshenko's beam formulae; secondly, a fourth-order deflection field is assumed by introducing some generalized conforming conditions; thirdly, the rotation field is determined by the strain–displacement relations. Furthermore, a hybrid post-processing procedure is suggested to improve the stress/internal force solutions. Following this procedure, a new 4-node, 12-dof quadrilateral element, named AC-MQ4, is successfully constructed. Since all formulations are expressed by the area co-ordinates, element AC-MQ4 presents some different, but beneficial characters when compared with other usual models. Numerical examples show the new element is free of shear locking, insensitive to mesh distortion, and possesses excellent accuracy in the analysis of both thick and thin plates. It has also been demonstrated that the area co-ordinate method, the generalized conforming condition method, and the hybrid post-processing procedure are efficient tools for developing simple, effective and reliable finite element models. Copyright © 2005 John Wiley & Sons, Ltd.