Showing papers on "Cantilever published in 1985"

Distributed Piezoelectric-Polymer Active Vibration Control of a Cantilever Beam

Abstract: An active vibration damper for a cantilever beam was designed using a distributed-parameter actuator and distributed-parameter control theory. The distributed-parameter actuator was a piezoelectric polymer, poly (vinylidene fluoride). Lyapunov's second method for distributed-parameter systems was used to design a control algorithm for the damper. If the angular velocity of the tip of the beam is known, all modes of the beam can be controlled simultaneously. Preliminary testing of the damper was performed on the first mode of the cantilever beam. A linear constant-gain controller and a nonlinear constant-amplitude controller were compared. The baseline loss factor of the first mode was 0.003 for large-amplitude vibrations (± 2 cm tip displacement) decreasing to 0.001 for small vibrations (±0.5 mm tip displacement). The constant-gain controller provided more than a factor of two increase in the modal damping with a feedback voltage limit of 200 V rms. With the same voltage limit, the constant-amplitude controller achieved the same damping as the constant-gain controller for large vibrations, but increased the modal loss factor by more than an order of magnitude to at least 0.040 for small vibration levels.

Vibration Tailoring of Advanced Composite Lifting Surfaces

Abstract: This paper discusses the free-vibration characteristics of directionally stiffened, laminated composite beamlike structures such as high-aspect-ratio lifting surfaces. A bounded nondimensional parameter, , is defined to describe the degree of elastic coupling between bending curvature and twist rate for a laminated beam. In addition, three different stiffness models commonly used to model laminated beam/tube deformation are described and compared. Using one of these models, the ability of the laminate design to control mode shape or node line characteristics is illustrated for a cross-coupled laminated cantilever beam. Finally, the effect of the nondimensional cross-coupling parameter, i/s on cantilever beam free-vibration node line positions and frequencies is illustrated, independent of a specific laminate design.

Mode I Interlaminar Fracture Toughness of Composites Using Slender Double Cantilevered Beam Specimens

Abstract: The use of slender double cantilever beam specimens for measuring the mode I in terlaminar fracture toughness was critically evaluated. Experiments were performed with unidirectional composites to ...

Nonuniform Bending‐Stress Distribution (Shear Lag)

Abstract: Nonuniform normal longitudinal stress distribution in a trapezoidal box beam with lateral cantilever is discussed. The problem is solved by the variational method assuming as unknown the displacement of the beam axis and three functions which describe the warping of the horizontal flanges; the unknowns are reduced in case of vertical walls. The state of stress of stress in each structural element is analyzed and an example is given to illustrate the results.

An exact solution for the stress intensity factor for a double cantilever beam

Abstract: An exact solution for the stress intensity factor for a double cantilever beam (DCB) specimen loaded by opposing point loads has been obtained by the Wiener-Hopf technique. A simple approximate formula is given for the stress intensity factor that is accurate to within 1.1 percent for all crack lengths with a large uncracked ligament.

Measurement of apparent young's modulus in the bending of cantilever beam by heterodyne holographic interferometry

Abstract: Detection of micromechanical phenomena in material requires a sufficiently high-accuracy measurement This paper shows the possibility of applying heterodyne holographic interferometry to such experimental verification The effects of the ratios of thickness to grain size on the apparent Young's modulus are evaluated based on the deflection patterns of the cantilever beam The characteristic length l of couple-stress theory is calculated by applying the analytical results of Koiter to our experimental results This value is about one fifth of the grain size

Bending Theory for Fiber-Reinforced Beams:

Abstract: The Saint-Venant theory of beams cannot account for constraints against cross- sectional warping, and for this reason it gives results that are inaccurate near fixed ends and at points where the warping changes abruptly, as under concentrated side loads. In highly anisotropic materials such as fiber-reinforced composites, the cumulative effect of such inaccuracies may be significant in some circumstances.In the present paper we present an approximate theory of the bending of cross-ply fiber-reinforced composites that is simpler than the exact theory of elasticity but is capable of accommodating any given displacement boundary conditions and arbi trarily varying side loads. As an illustration, the theory is applied to the problem of a tip-loaded cantilever with a fixed end. In this problem the theoretical results agree with elementary beam theory (with a particular choice of the shear correction factor) except in a relatively long end-effect region near the clamped end.To test the theory, cantilever specim...

A statistical analysis of the frictional forces generated between monofilaments during intermittent sliding

Abstract: The friction between poly(ethylene terephthalate) monofilaments (about 20 mu m diameter), known by the acronym PET, with a range of titanium contents has been measured. In addition, some experiments were carried out with PET fibres sliding over glass and human hair. The configuration used produces a nominal point contact and involves a taut fibre against which a second fibre is brought to form a cantilever. Movement of the first fibre invariably generates discontinuous or stick-slip motion in the cantilevered fibre. The equipment developed for friction measurements was capable of recovering and storing data from a large number of stick-slip events. Much of the static frictional force data could be fitted (at the 95% confidence limit of the chi 2 goodness-of-fit test) to the gamma, Weibull or log-normal distributions. The exact form of the distribution depended on the conditions of the experiment and, additionally in the case of human hair, on the direction of sliding. Some of the data which could not be modelled by these distributions were found to be associated with time-dependent effects. This non-stationarity, which arises from a low-level wear process, increased with the imposed sliding velocity and the total load at the contact point. By the use of simple regression models of frictional force against time, it was possible to 'correct' some of the non-stationary data so that they became (nominally) stationary. Distributions fitted to these modified data showed good continuity in both the functionality and the numerical values of the distribution parameters with the distributions fitted to the stationary data. The study also revealed the occurrence of a type of microslip prior to gross slip. This microslip manifests itself as a continuous velocity of the contact point of the fibre. Microslip was found to occur under nearly all circumstances and is dependent on a large number of factors. There was a close relationship between the extent of microslip and the degree of non-stationarity.

Heterodyne Holography Applications in Studies of Small Components

Abstract: Heterodyne hologram interferometry was used to study load-deformation characteristics of computer microcomponents that were surface mounted on a printed circuit board. The board was assembled as a cantilever plate and subjected to cyclic flexure loading according to industry standards. The flexure loading was sinusoidal at 0.1 cps with an amplitude of 1.25 mm (0.050 in.) at the tip of the board. Double-exposure heterodyne holograms were recorded under a number of conditions specified by the magnitude of deflection at the board's tip and the number of accumulated flexure cycles. Data obtained during reconstruction of heterodyne holograms were used to compute displacements and strains along the leads connecting the component to the printed circuit board. The experimental results show that lead displacements were on the order of 1.2 um, while strains were up to 0.054%. The results obtained in this study will be used as input to finite element models of computer microcomponents.

Coupled vibration analysis of blades with angular pretwist of cubic distribution

Abstract: This paper presents a finite element model for the vibration analysis of pretwisted uniform cross-sectional blading. The variation of pretwist along the blade length can be in linear or trigonometric increments. The dynamic stiffness for free vibration of the blade is derived from the strain and kinetic energies using Lagrange's equation. The cubic polynomial approximation of the displacements, in two principal directions, is assumed. This method gives excellent results with the use of only a small number of elements. Good agreement is found with the experimental and theoretical results of other investigators for straight and linearly pretwisted blades. The comparison of theoretical results between the linearly and nonlinearly pretwisted beams shows large deviations when the pretwist angle increases.

Light deflection device

Abstract: A light deflection device is comprised of a cantilever member, a light deflecting element provided near the fixed end of the cantilever member, and a means of imparting deflection to the free end of the cantilever member, so that the angle of inclination of the light deflecting element, and hence the angle of deflection of the light, can be set and controlled with very high precision by the controlled deflection of the cantilever member by said means.

An experimental investigation of the behaviour of thin-walled box beams

Abstract: The purpose of this paper is to present the results of an experimental investigation of the behaviour of four types of thin-walled box beam and to compare the results with those obtained from theoretical analyses. Three steel models consisting of a straight single cell cantilever, a curved single cell cantilever and a simply supported twin box have been constructed, in addition to a continous prestressed concrete two-span double cell beam. Details are given of the methods of construction, instrumentation and experimental procedure for all the models. The behaviour of the individual models has been studied, with particular attention being given to the torsion and distortion of the box sections, the cross-sectional distributions of the longitudinal and transverse bending stresses and the deflections. Appropriate experimental results are presented, therefore, and are compared with those obtained from the specially developed thin-walled box beam finite element which has been presented previously in this journal.

Plastic Response of Cantilevers with Stable Cracks

Abstract: Simple analytical models and experiments are employed to demonstrate the structural response of a cantilever beam with a stable crack subjected to impact loading. The mode of plastic deformation is shown to depend very strongly upon the size and location of the crack; and the permanent damage suffered by a cracked beam is found to be significantly different in magnitude and character from that of a correspondingly‐loaded uncracked beam.

Horizontal furnace with a suspension cantilever loading system

Abstract: A horizontal furnace for processing semiconductor devices having a suspension cantilever which supports workpieces in the furnace tube to achieve particle or dust-free operation while still allowing the loading and unloading of workpieces to be heat-treated. The furnace tube consists of a heating chamber, a connecting chamber and a supporting chamber vertically connected to each other. The chambers correspond to an accommodating portion, a connecting portion and a supporting portion of the cantilever. The supporting chamber is kept at lower temperature than that of the heating chamber during heat processing to prevent deformation or creeping of the suspension cantilever.

Optimal design of thin-walled I beams undergoing torsion

Abstract: The problem of minimum volume design of a thin-walled I beam undergoing torsion is investigated. The behaviour of the beam is described in accord with the theory of thin-walled beams with nondeformable cross-section. The constraint conditions on normal stress level, the magnitude of rotational displacement at a specified cross-section and the extreme values of the cross-section dimensions variable along the beam axis are discussed. An iterative method of solution based upon the optimality condition derived with aid of Pontryagin's maximum principle is developed. A numerical example of a cantilever I beam with variable width of flanges is presented.

Solution of bending of cantilever rectangular plates under uniform surface-load by the method of two-direction trigonometric series

Abstract: The bending of a cantilever rectangular plate is a very complicated problem in the theory of plates. For a long time, there have been only approximate solutions for this problem by energy methods and numerical methods.