Showing papers on "Deflection (engineering) published in 2001"

Interferometry of actuated microcantilevers to determine material properties and test structure nonidealities in MEMS

Abstract: By integrating interferometric deflection data from electrostatically actuated microcantilevers with a numerical finite difference model, we have developed a step-by-step procedure to determine values of Young's modulus while simultaneously quantifying nonidealities. The central concept in the methodology is that nonidealities affect the long-range deflections of the beams, which can be determined to near nanometer accuracy. Beam take-off angle, curvature and support post compliance are systematically determined. Young's modulus is then the only unknown parameter, and is directly found. We find an average value of Young's modulus for polycrystalline silicon of 164.3 GPa and a standard deviation of 3.2 GPa (/spl plusmn/2%), reflecting data from three different support post designs. Systematic errors were assessed and may alter the average value by /spl plusmn/5%. An independent estimate from grain orientation measurements yielded 163.4-164.4 GPa (the Voigt and Reuss bounds), in agreement with the step-by-step procedure. Other features of the test procedure include that it is rapid, nondestructive, verifiable and requires only a small area on the test chip.

Scattering of surface waves by a semi-infinite floating elastic plate

Abstract: A new inner product is developed based on the Fourier analysis to study the scattering of surface waves by a floating semi-infinite elastic plate in a two-dimensional water domain of finite depth. The eigenfunctions for the plate-covered region are orthogonal with respect to this new inner product. The problem is studied for various wave and geometrical conditions. Especially, the influence of different edge conditions on the hydrodynamic behavior is investigated and compared. The edge conditions considered in the present study involve (i) a free edge, (ii) a simply supported edge, and (iii) a built-in edge. The hydrodynamic performance of an elastic plate is characterized for various conditions in terms of wave reflection and transmission, plate deflection, and surface strain. It is observed that the hydrodynamic behavior depends on the wave conditions, the geometrical settings, and the edge conditions. The built-in edge condition induces the maximum wave reflection and the minimum wave transmission. The free edge condition leads to the maximum plate deflection.

A Model for Relations between Needle Deflection, Force, and Thickness on Needle Penetration

Abstract: A force-deflection model of needle penetration is proposed and evaluated experimentally. The force at the fixed end of the needle and the needle deflection were measured using a force sensor and a bi-plane X-ray imaging system, and the model was evaluated with the data. We define a physical quantity ?, which we call infinitesimal force per length, analogous to traction (force per surface area). The model predicts ? to be constant over the length of the inserted portion of the needle. However the results indicate that this assumption does not fully account for the real deflection. It is strongly suggested that there is an additional degree of freedom: a moment or a rotational force acting on the needle.

Three-dimensional tissue and methods for making the same

Abstract: An improved method for imprinting a paper web during a wet pressing event is disclosed which results in asymmetrical protrusions corresponding to the deflection conduits of a deflection member. In one embodiment, differential velocity transfer during a pressing event serves to improve the molding and imprinting of a web with a deflection member. Improved deflection members are also disclosed. Improved tissue webs produced are also disclosed having useful sets of physical and geometrical properties, such as a pattern densified network and a repeating pattern of protrusions having asymmetrical structures.

Quantitative surface stress measurements using a microcantilever

Abstract: A method for calculating the surface stress associated with the deflection of a micromechanical cantilever is presented. This method overcomes some of the limitations associated with Stoney’s formula by circumventing the need to know the cantilever’s Young’s modulus, which can have a high level of uncertainty, especially for silicon nitride cantilevers. The surface stress is calculated using readily measurable cantilever properties, such as its geometry, spring constant, and deflection. The method is applicable to both rectangular and triangular cantilevers. A calibration of the deflection measurement is also presented. The surface stress measurement is accurate to within 4%–7%.

Shrinkage, Cracking and Deflection- the Serviceability of Concrete Structures

Abstract: This paper addresses the effects of shrinkage on the serviceability of concrete structures. It outlines why shrinkage is important, its major influence on the final extent of cracking and the magnitude of deflection in structures, and what to do about it in design. A model is presented for predicting the shrinkage strain in normal and high strength concrete and the time-dependent behaviour of plain concrete and reinforced concrete, with and without external restraints, is explained. Analytical procedures are described for estimating the final width and spacing of both flexural cracks and direct tension cracks and a simplified procedure is presented for including the effects of shrinkage when calculating long-term deflection. The paper also contains an overview of the considerations currently being made by the working group established by Standards Australia to revise the serviceability provisions of AS3600-1994, particularly those clauses related to shrinkage.

Optimal design of a flexural actuator

Abstract: A minimum-weight flexural actuator is designed. The actuator comprises a triangular corrugated core with shape memory alloy (SMA) faces. It is clamped at one end and free at the other. For design and optimization, the temperature history of the face sheets upon heating and subsequent cooling is first obtained as a function of the cooling efficiency (Biot number) and the operational frequency deduced. Based upon this response, a phenomenological model is employed to represent the martensite evolution. Thereafter, the end deflection is calculated as a function of temperature. The minimum weight is calculated subject to the provisos that: (i) the end deflection attains a specified value; (ii) the power consumed is less than the upper limit of the supply; and failure is averted by (iii) face/core yielding and (iv) face/core buckling; (v) the operational frequency of the panel achieves a specified limit.

Bending behavior and deformability of glass fiber-reinforced polymer reinforced concrete members

Abstract: In this paper, bending behavior of rectangular concrete beams reinforced with sand-coated and ribbed glass fiber-reinforced polymer (GFRP) bars, including failure mode delineation and deformability response, is presented. Discussion on the bending behavior of the GFRP reinforced concrete members includes the influence of strength, stiffness, and geometric properties of concrete and GFRP bars. Additionally, the limit state of energy absorption is established, which is a ratio of energy absorption at ultimate failure of GFRP reinforced concrete beams under bending to that at a limiting serviceability curvature. The energy absorption concept including the limit state is introduced herein; this satisfies the curvature limit state so that the deflection and crack-width limit states can be unified and deformability factors established to avoid catastrophic failures.

Strength and Ductility of RC Beams Repaired with Bonded CFRP Laminates

Abstract: The objective of this study is to investigate the strength and ductility aspects of reinforced concrete (RC) beams strengthened with an externally bonded carbon fiber reinforced polymer (CFRP) laminate and to examine how such retrofitting affects strength, deflection, curvature, and energy, as exemplified by the area under the load-deflection curve of the strengthened composite beam. Three series of tests on eleven RC beams were carried out and their ultimate load capacities and ductilities evaluated. The variables in the experimental program were longitudinal steel ratio, volume of internal stirrups, and the location and configuration of external anchorages. The results show that both deflection and energy absorption are drastically reduced when beams are strengthened with bonded CFRP plates without external anchorages. Suitably designed and positioned external anchorages allow much of this lost ductility to be regained; however, even then the ductility of the strengthened beam cannot be restored to its original level. It is shown that definitions of ductility based on deflection and energy are able to give a good and rational representation of the physical aspects of ductility of RC beams strengthened with bonded CFRP laminates with or without external anchorages. The results show that the effects on ductility arising from strengthening existing RC beams with CFRP laminates cannot be ignored, even if it is not clear at this stage how to apply the concept of ductility indices and ductility ratios developed in this paper in design practice.

Nonlinear finite-element modeling of batter piles under lateral load

Abstract: In this paper, a finite-element model is developed in which the nonlinear soil behavior is represented by a hyperbolic relation for static load condition and modified hyperbolic relation, which includes both degradation and gap for a cyclic load condition. Although batter piles are subjected to lateral load, the soil resistance is also governed by axial load, which is incorporated by considering the P-Δ moment and geometric stiffness matrix. By adopting the developed numerical model, static and cyclic load analyses are performed adopting an incremental-iterative procedure where the pile is idealized as beam elements and the soil as elastoplastic spring elements. The proposed numerical model is validated with published laboratory and field pile test results under both static and cyclic load conditions. This paper highlights the importance of the degradation factor and its influence on the soil resistance-displacement (p-y) curve, number of cycles of loading, and cyclic load response.

Full-Scale Measurement of Akashi-Kaikyo Bridge during Typhoon

Abstract: Full-scale measurement data observed on the Akashi–Kaikyo Bridge during strong typhoons were analyzed. Power spectral density and spatial correlation of longitudinal velocity fluctuations were analyzed. PSD was well represented by Hino’s formula by changing the scaling parameter. Spatial correlation at two points was well represented not by the exponential formula but by an alternative coherence function based on isotropic turbulence theory. Decay factor in the exponential formula showed a weakly increasing trend with the increase in distance and wind speed. Bridge response of deck lateral deflection was also analyzed. Static deflection at winds with normal to the bridge axis was in good agreement with the analytical value. Gust factors of deck lateral deflection were mostly less than design specification.

Improved model for plate-end shear of CFRP strengthened RC beams

Abstract: In case of RC members strengthened by means of externally bonded reinforcement, a premature failure can be detected in addition to the conventional modes of failure observed in RC unstrengthened beams. The premature failure occurs mainly due to both shear and normal stresses induced in either the external reinforcement–concrete interface or at the level of steel reinforcement. This research is part of a complete programme aiming to set up design formulae to predict the strength of CFRP strengthened beams, particularly when premature failure through laminates-end shear or concrete cover delamination occurs. Series of RC beams were strengthened with carbon-fiber-reinforced plastic (CFRP) laminates and tested to estimate the extent of the applicability of the formulae proposed by the authors, as well as to study the influence of the layout of the external reinforcement in terms of unsheeted length (the distance between CFRP laminates-end and the nearer support) and cross-sectional area, on the behaviour of strengthened beams. The predictions using the proposed formulae are compared with the obtained experimental results, as well as with the calculated design limit states. The interfacial shear stress and the maximum deflection corresponding to the predicted values at maximum and service loads are also studied.

Retrofit hurricane and earthquake protection

Abstract: Retrofit connectors that secure together the outside sheathing and underlying structural members of wood-frame or masonry houses, preventing damage when subjected to lateral stresses from a hurricane, or transverse loads from an earthquake. The connectors have special bushings and bearing surfaces that tie the outside sheathing and underlying structural members together, but allow deflection, and transfer of energy to other structural members. Different embodiments of the connectors allow them to adapt to most wood-frame and masonry homes, and to most roof pitches.

Inelastic analysis of steel frames with composite beams

Abstract: This paper describes a method of inelastic analysis that provides the necessary degree of accuracy for studying the limit-state behavior of steel frames with composite floor beams subjected to the combined action of gravity and lateral loads. An inelastic formulation is proposed to model the composite beams based on the moment-curvature relationship of a composite beam section under positive and negative moments. Steel columns are modeled using the plastic hinge approach. To ascertain the accuracy of the composite beam model, two composite beams and a steel portal frame are analyzed and the results are compared with those obtained from tests and the more established results. Finally, the robustness of the model is demonstrated by studying 2D and 3D building frames using various floor beam models so that their effects on the serviceability deflection and limit load can be compared.

High-frequency mechanical spectroscopy with an atomic force microscope

Abstract: In this article we further develop local mechanical spectroscopy and extend the frequency range over which it can be used. Using a heterodyne method to measure the deflection of the cantilever enables one to measure the probe vibration at any frequency. Since the detection sensitivity of force gradients follows a f2 dependence, extending the frequency range from 1 to more than 5 MHz increases the sensitivity by over an order of magnitude. This setup is combined with a realistic model of the cantilever taking into account the geometry of the cantilever. The model is presented and discussed, and compared with experimental behavior measured on WC–Co and NiTi–epoxy samples. Experimental moduli of 730±50 and 260±40 GPa are obtained for WC and Co, respectively.