Showing papers on "Deflection (engineering) published in 1992"

Dynamic pile‐soil‐pile interaction. Part II: Lateral and seismic response

Abstract: SUMMARY A simplified three-step procedure is proposed for estimating the dynamic interaction between two vertical piles, subjected either to lateral pile-head loading or to vertically-propagating seismic S-waves. The starting point is the determination of the deflection profile of a solitary pile using any of the established methods available. Physically-motivated approximations are then introduced for the wave field radiating from an oscillating pile and for the effect of this field on an adjacent pile. The procedure is applied in this paper to a flexible pile embedded in a homogeneous stratum. To obtain analytical closed-form results for both pile-head and seismic-type loading pile-soil and soil-pile interaction are accounted for through a single dynamic Winkler model, with realistic frequency-dependent ‘springs’ and ‘dashpots’. Final- and intermediate-step results of the procedure compare favourably with those obtained using rigorous formulations for several pile group configurations. It is shown that, for a homogeneous stratum, pile-to-pile interaction effects are far more significant under head loading than under seismic excitation.

A detailed analysis of the optical beam deflection technique for use in atomic force microscopy

Abstract: A Michelson interferometer and an optical beam deflection configuration (both shot noise and diffraction limited) are compared for application in an atomic force microscope. The comparison shows that the optical beam deflection method and the interferometer have essentially the same sensitivity. This remarkable result is explained by indicating the physical equivalence of both methods. Furthermore, various configurations using optical beam deflection are discussed. All the setups are capable of detecting the cantilever displacements with atomic resolution in a 10 kHz bandwidth.

Electromechanical deflections of piezoelectric tubes with quartered electrodes

Abstract: The deflection of a piezoelectric tube, with the outer (or inner) metal coating sectioned into four quadrants, is analyzed. We show that by applying a voltage V on one of the quadrants, the electromechanical deflection is (√2d31VL2/πDh), where d31 is the piezoelectric coefficient, L is the length, D the diameter, and h the wall thickness of the tube. The deflections calculated with it agree well with the results of finite‐element calculations and direct experimental measurements. The formula can be used in the design and application of tube scanners in scanning tunneling microscopes and scanning force microscopes.

Mechanical properties of 3C silicon carbide

Abstract: The residual stress and Young's modulus of 3C silicon carbide (SiC) epitaxial films deposited on silicon substrates were measured by load-deflection measurements using suspended SiC diaphragms fabricated with silicon micromachining techniques. The film's residual stress was tensile and averaged 274 MPa while the in-plane Young's modulus averaged 394 GPa. In addition, the bending moment due to the residual stress variation through the thickness of the film was determined by measuring the deflection of free-standing 3C-SiC cantilever beams. The bending moment was in the range of 2.6 x 10 exp -8 -4.2 x 10 exp-8 N m.

Bending of gel beams: method for characterizing elastic properties and permeability

Abstract: When a saturated gel is deformed, its mechanical response is profoundly influenced by the flow of liquid in its pores. For example, if a gel bar is suddenly deformed in 3-point bending, the liquid cannot immediately flow out of the pores, so the gel initially responds incompressibly; consequently, its deflection provides a measure of its shear modulus, G p , rather than Young's modulus, E p . In this paper, the kinetics of deformation of such a rod are analyzed, showing that it is possible to obtain the permeability, D , of the gel from the time-dependence of the load, as well as finding both G p and E p . Analyses are presented for the time dependence of the load at constant deflection for a square and cylindrical beam, and for load at constant deflection rate for a square beam. The method is applied to determine G p , E p , and D for a silica gel made from tetraethoxysilane.

Analysis and Design of Doweled Slab‐on‐Grade Pavement Systems

Abstract: This paper provides an in‐depth synthesis of knowledge acquired over the last several decades pertaining to the analysis and design of doweled slab‐on‐grade pavement systems. This task is accomplished on the basis of rigorous, theoretically sound engineering principles, and relies extensively on the application of dimensional analysis for the interpretation of finite element data pertaining to the behavior of doweled joints. A design procedure is derived that allows, for the first time, the determination of the dowel diameter and spacing required to achieve a desired level of load transfer, or a threshold value of dowel‐concrete bearing stress. The proposed approach eliminates the need for any a priori assumptions with respect to the distribution of dowel shear forces. An efficient and general method for the backcalculation of the modulus of dowel reaction, K, from deflection data is also suggested. These research findings constitute a mechanistic structural model for JPCP and contribute significantly tow...

Atomic force microscope having cantilever with piezoresistive deflection sensor

Abstract: A microminiature cantilever structure is provided having a cantilever arm with a piezoresistive resistor embedded in at least the fixed end of the cantilever arm. Deflection of the free end of the cantilever arm produces stress in the base of the cantilever. That stress changes the piezoresistive resistor's resistance at the base of the cantilever in proportion to the cantilever arm's deflection. Resistance measuring apparatus is coupled to the piezoresistive resistor to measure its resistance and to generate a signal corresponding to the cantilever arm's deflection. The microminiature cantilever is formed on a semiconductor substrate. A portion of the free end of the cantilever arm is doped to form an electrically separate U-shaped piezoresistive resistor. The U-shaped resistor has two legs oriented parallel to an axis of the semiconductor substrate having a non-zero piezoresistive coefficient. A metal layer is deposited over the semiconductor's surface and patterned to form an electrical connection between the piezoresistive resistor and a resistance measuring circuit, enabling measurement of the piezoresistive resistor's resistance. Finally, the semiconductor substrate below the cantilever arm is substantially removed so as to form a cantilevered structure, and a tip is connected to the free end of the cantilever arm to facilitate the structure's use in an atomic force microscope.

Super-elasticity and thermal behavior of Ni-Ti alloy orthodontic arch wires.

Abstract: Bending properties and thermal behavior of twenty commercial Ni-Ti alloy orthodontic arch wires were investigated quantitatively to characterize their suitability for clinical use. There was substantial difference among the load-deflection curves obtained by a three-point bending test. Some wires exhibited super-elasticity; load decreased little with decreasing deflection. Others showed good spring-back properties only; load was nearly proportional to deflection. Thermal behavior due to phase transformation of the alloy was examined by differential scanning calorimetry (DSC). Some of the wires did not have the correct transformation temperatures to exhibit super-elasticity at body temperature. Moreover, thermal behavior was closely related to super-elasticity. There were clear thermal peaks in the DSC curves of the super-elastic wires. However, wires without super-elasticity had no peak in the DSC curves.

Compensating Lags in Head-Coupled Displays Using Head Position Prediction and Image Deflection

Abstract: Images on head-coupled systems are delayed by latencies in measuring head position and generating computer graphics. The objectives of this study were 1) to investigate the effects of time delays on head tracking performance; 2) to evaluate the use of an image deflection technique to reduce deleterious effects of delayed images; and 3) to investigate the application of a head position prediction algorithm to enhance the benefits of image deflection. There were significant decreases in head tracking performance when lags of 40 ms or more were added to a system with an inherent 40 ms lag. Lag compensation by image deflection significantly improved tracking performance with lags up to 380 ms. However, by deflecting the delayed image back to its prelag angular position, part of the picture was displaced beyond the edge of the screen. The amount of deflection required was reduced by a simple means of predicting the position of the head before applying deflection. Improved means of predicting head position would further reduce the required image deflection.

Solutions of the heat conduction equation in multilayers for photothermal deflection experiments

Abstract: Analytical expressions for temperature and laser beam deflection in multilayer medium is derived using Green function techniques. The approach is based on calculation of the normal component of heat fluxes across the boundaries, from which either the beam deflections or the temperature anywhere in space can be found. A general expression for the measured signals for the case of four-quadrant detection is also presented and compared with previous calculations of detector response for finite probe beams.

Mechanical Behaviour of Wood Exposed to Humidity Variations.

Abstract: The effects on wood of simultaneous mechanical and moisture loading are studied. In order to clarify the mechano-sorptive behaviour of wood, a review of different phenomena presented in the literature is included. Compressive tests have been performed on spruce. The tests have been performed with both constant load and varying load. The humidity has been varied during the tests. The properties of the material used have been investigated both before and after the main testing was performed. Based on the review of mechano-sorptive phenomena and the test results presented in this study, a constitutive model is developed. The model was quantified on the basis of test results presented both in this thesis and in the literature. The validity of the model was checked independently against other tests. Finally a number of practical load situations were studied. In these simulations both humidity and load were varied. The calculations show that the model is capable of describing the response of wood with reasonable accuracy. The simulations indicate that the response of small test specimens is more difficult to describe than that of larger beams. Some differences in behaviour are found to depend on loading mode and nature of moisture cycling. Very large and fast moisture cycles seem to give larger mechano©sorption than smaller variations. The results of the simulations show that there is a significant influence of strain on the shrinkage and swelling response. Studies of the effect of varying load show that a temporarily applied load has little effect on the long term deflection of structural timber. A simulation of snow load variation shows that the long term deflections are rather small in comparison with the case when the characteristic load is assumed to be constant over time. (Less)

Vibration of shear-deformable beams using a spline-function approach

Abstract: B-spline functions are used as trial functions in a Rayleigh-Ritz analysis of the free vibration of shear-deformable Timoshenko beams. In a first approach it is demonstrated in numerical applications that when the lateral deflection and the cross-sectional rotation are represented by functions of equal order the calculated natural frequencies are of good accuracy for stocky beams but can overestimate the true frequencies very considerably for slender beams. This is identified as a shear-locking difficulty and consideration of its causes points clearly to the adoption of a new displacement field in which the deflection is represented by a B-spline function which is one order higher than that used to represent the rotation. Numerical results using this new displacement field demonstrate good accuracy for both stocky and slender beams: the shear-locking difficulty is completely eliminated. This has clear significance for the analysis of shear-deformable plates and shells when using B-spline functions.

Skin for a deicer

Abstract: An aircraft deicing assembly 101 for attachment to an airfoil 99 includes a deflection shell 101 disposed over a deflection means 102. The deflection shell is comprised of a primary layer 116 comprised of a high strength fabric reinforced with a phenolic resin and a backing layer 115 comprised of a high strength fabric reinforced with an epoxy resin. The thickness of the backing layer is varied as a function of curvature of the airfoil and spanwise length of the airfoil.

Radiation Of Sound Into A Cylindrical Enclosure From A Point-Driven End Plate With General Boundary Conditions

Abstract: The radiation of sound from a point‐driven circular plate into a hard‐walled cylindrical enclosure is investigated. Emphasis is given on studying the effects of the boundary conditions of the plate, which are modeled as a continuous distribution of edge springs acting against both the deflection and the rotation of the contour of the plate. With this model, both classical and intermediate boundary cases can be simulated by adjusting the elastic stiffness of the springs. A coupled acoustoelastic formulation is developed following a variational approach, with the use of hard‐walled cavity modes. In the analysis, the full interaction between the structure vibration and the internal cavity sound pressure is considered. Numerical results indicate that a significant reduction in noise inside the cavity can be obtained for a relatively wide frequency range by completely relaxing the translational support (zero deflection stiffness) of the plate. This is mainly due to a weakening of the modal radiation efficiency of the flexural modes of the plate. With an increase of the deflection stiffness on the contour of the plate, this beneficial frequency range is shifted to higher frequencies. It is hoped that the findings of the present work will be useful for practical predictions of airplane cabin noise emitted by the rear pressure bulkhead, as well as for noise control in some aerospace structures and mechanical systems involving cylindrical‐shaped cavities.

Load cell for weighing the contents of storage vessels

Abstract: A load cell adapted to be positioned between a foundation and each of several support members for a storage vessel. The load cell includes a circular flex plate having a pair of concentric cylindrical members of different diameters secured to opposite surfaces. A mounting pad adapted to be fastened to the foundation is secured to one of the cylindrical members. A mounting plate is secured to the other cylindrical member. The mounting plate has either a single threaded bore or a threaded stud positioned at the common axis of the cylindrical members for securing the mounting plate to a vessel support member. A strain sensor mounted on the flex plate measures the load-induced deflection of the flex plate.

Response functions of the laser beam deflection probe for detection of spherical acoustic waves

Abstract: Detection of spherical acoustic waves by the laser beam deflection probe is examined. The probe is modeled as a linear system transforming acoustic wave form into transient angular deflection of the probe beam. Transfer and step response functions are derived assuming thin Gaussian laser beam and small deflection angle. It is demonstrated that the probe behaves as a half‐order differentiator when short acoustic transients are detected far from the source. Theoretical predictions are compared to the results of frequency analysis of optoacoustic signals detected by the deflection probe. Good agreement is found.

Joint computational/experimental aerodynamics research on hypersonicvehicle. II - Computational results

Abstract: Parabolized and iterative Navier-Stokes codes are used to predict flowfield solutions around a hypersonic vehicle. Aerodynamic force and moment predictions from the codes are compared with experimental data from the Sandia National Laboratories Mach 8 wind tunnel. The comparisons are made on a spherically blunted cone with a slice parallel to the body axis. On the slice portion of the vehicle, a flap can be attached so that deflection angles of 10, 20, and 30 deg can be obtained. The Sandia parabolized Navier-Stokes code is used to generate solutions for the sliced vehicle with no flap. For the vehicle with a flap, axially separated flow occurs, and a time iterative Navier-Stokes code is used to provide comparisons with the data. Aerodynamic force and moment comparisons are made for laminar flow, and an ideal gas is assumed in the calculations. A detailed study of grid convergence is presented to determine the accuracy of the numerical solutions. Predictions obtained from the codes show very good agreement with the experimental data for force and moment coefficients, except for large flap deflections.

Multi-mode accelerometer

Abstract: An accelerometer (10) having a piezoelectric transducer (22) which produces electrical signals in response to its deflection and comprises an elongated, continuous beam of generally flat configuration and narrow cross section to provide a bending axis which facilitates deflection of the free ends in response to shock in one or more of the linear and torsional modes. The beam is supported intermediate its ends by a mount (29), with the free ends of the beam preferably extending equidistantly in opposite directions from the mount. By laminating a single piece of piezoelectric material to a rigid substrate and forming cantilevers in each deflection direction, an accelerometer with six degrees of freedom may be formed. Also, a compressive type angular accelerometer (122) may be formed from two piezoelectric sensor elements incorporated onto a single piece of piezoelectric polymer (126).