Showing papers on "Deflection (engineering) published in 2009"

Impact Response of Reinforced Concrete Beam and Its Analytical Evaluation

Abstract: This paper examines the impact responses of reinforced concrete (RC) beams through an experimental study and presents an analytical model developed to predict the maximum midspan deflection and maximum impact load, which aids as an important performance index to evaluate the damage levels of RC beams when subjected to impact loadings. The experimental study involves a drop hammer impact test and investigates the influence of drop height and the effect of the amount of longitudinal steel reinforcement contributes to the response of RC beams. The RC beam specimens used in the experiment comprised of under-reinforced sections provided with sufficient amount of transverse reinforcements to allow for an overall flexural failure. The experimental impact responses of the RC beams were simulated with two-degree-of-freedom mass-spring-damper system model, in which the loading rate effects were duly considered. The analytical results are in good agreement with the experimental results for the RC beams that exhibited overall flexural failure.

A Pseudorigid-Body 3R Model for Determining Large Deflection of Cantilever Beams Subject to Tip Loads

Abstract: In this paper, a pseudo-rigid-body (PRB) 3R model which consists of four rigid links joined by three revolute joints and three torsion springs is proposed for approximating the de∞ection of a cantilever beam subject to a general tip load. The large de∞ection beam equations are solved through numerical integration. A comprehensive atlas of the tip de∞ection for various load modes is obtained. A three-dimensional search routine has been developed to flnd the optimal set of characteristic radius factors and spring stifiness of the PRB 3R model. Detailed error analysis has been done by comparing with the pre-computed tip de∞ection atlas. Our results show that the approximation error is much less than that of the conventional PBR 1R model. The beneflts of the PRB 3R model include (a) load independence which is critical for analysis/synthesis applications where loads vary signiflcantly, (b) high accuracy for large de∞ection beams, and (c) explicit kinematic and static constraint equations which are simpler to solve compared with the flnite element model. To demonstrate the use of the PRB 3R model, a compliant 4-bar linkage is studied and verifled by a numerical example. The result shows a maximum tip de∞ection error of 1:2% compared with the FEA model.

Optimizing the signal-to-noise ratio of a beam-deflection measurement with interferometric weak values

Abstract: The amplification obtained using weak values is quantified through a detailed investigation of the signal-to-noise ratio for an optical beam-deflection measurement. We show that for a given deflection, input power and beam radius, the use of interferometric weak values allows one to obtain the optimum signal-to-noise ratio using a coherent beam. This method has the advantage of reduced technical noise and allows for the use of detectors with a low saturation intensity. We report on an experiment which improves the signal-to-noise ratio for a beam-deflection measurement by a factor of 54 when compared to a measurement using the same beam size and a quantum-limited detector.

Flexural Behavior of Concrete Beams Reinforced with Hybrid (GFRP and Steel) Bars

Abstract: Reinforcing concrete with a combination of steel and glass fiber-reinforced polymer (GFRP) bars promises favorable strength, serviceability, and durability. To verify its promise and to support design of concrete structures with this hybrid type of reinforcement, we have experimentally and theoretically investigated the load-deflection behavior of concrete beams reinforced with hybrid GFRP and steel bars. Eight beams, including two control beams reinforced with only steel or only GFRP bars, were tested. The amount of reinforcement and the ratio of GFRP to steel were the main parameters investigated. Hybrid GFRP/steel-reinforced concrete beams with normal effective reinforcement ratios exhibited good ductility, serviceability, and load carrying capacity. Comparisons between the experimental results and the predictions from theoretical analysis showed that the models we adopted could adequately predict the load carrying capacity, deflection, and crack width of hybrid GFRP/steel-reinforced concrete beams.

Wideband low-noise optical beam deflection sensor with photothermal excitation for liquid-environment atomic force microscopy.

Abstract: I developed a wideband low-noise optical beam deflection sensor with a photothermal cantilever excitation system for liquid-environment atomic force microscopy The developed sensor has a 10 MHz bandwidth and 47 fm/Hz deflection noise density in water The theoretically limited noise performance (ie, the noise level limited only by the photodiode shot noise) has been achieved in liquid for the first time Owing to the wide bandwidth and the replaceable focus lens design, the sensor is applicable to cantilevers with various dimensions The deflection noise densities of less than 78 fm/Hz have been achieved in water for cantilevers with lengths from 35 to 125 μm The ideal amplitude and phase versus frequency curves without distortion are obtained with the developed photothermal excitation system The excitation system is applicable to relatively stiff cantilevers (>20 N/m) in liquid, making it possible to obtain true atomic-resolution images in liquid True atomic-resolution imaging of mica in water is

Design and analysis of an automotive bumper beam in low-speed frontal crashes

Abstract: In this paper, the most important parameters including material, thickness, shape and impact condition are studied for design and analysis of an automotive front bumper beam to improve the crashworthiness design in low-velocity impact. The simulation of original bumper under condition impact is according to the low-speed standard of automotives stated in E.C.E. United Nations Agreement, Regulation no. 42, 1994. The bumper beam analysis is accomplished for composite and aluminum material to compare the weight and impact behavior. The strength in elastic mode is investigated with energy absorption and impact force in maximum deflection situation. A good design of this part of automotives must prepare for the safety of passengers; meanwhile, should have low weight. Beside the role of safety, fuel efficiency and emission gas regulations are being more important in recent years that encourage manufacturer to reduce the weight of passenger cars. In this research, a front bumper beam made of three materials: aluminum, glass mat thermoplastic (GMT) and high-strength sheet molding compound (SMC) is studied by impact modelling to determine the deflection, impact force, stress distribution and energy-absorption behavior. The mentioned characteristics are compared to each other to find best choice of material, shape and thickness. The results show that a modified SMC bumper beam can minimize the bumper beam deflection, impact force and stress distribution and also maximize the elastic strain energy. In addition, the effect of passengers in the impact behavior is examined. The time history of the calculated parameters is showed in graphs for comparison. Furthermore, beside the above-mentioned benefits, some more advantages like easy manufacturing due to simple shape without-ribs, economical aspects by utilizing low-cost composite material and reducing weight with respect to others can be achieved by SMC material.

Railway Track Stiffness Dynamic Measurements and Evaluation for Efficient Maintenance

Abstract: Railway track stiffness (vertical track load divided by track deflection) is a basic parameter oftrack design which influences the bearing capacity, the dynamic behaviour of passing vehiclesand, in ...

A short pulse (7 μs FWHM) and high repetition rate (dc-5kHz) cantilever piezovalve for pulsed atomic and molecular beams

Abstract: In this paper we report on the design and operation of a novel piezovalve for the production of short pulsed atomic or molecular beams. The high speed valve operates on the principle of a cantilever piezo. The only moving part, besides the cantilever piezo itself, is a very small O-ring that forms the vacuum seal. The valve can operate continuous (dc) and in pulsed mode with the same drive electronics. Pulsed operation has been tested at repetition frequencies up to 5 kHz. The static deflection of the cantilever, as mounted in the valve body, was measured as a function of driving field strength with a confocal microscope. The deflection and high speed dynamical response of the cantilever can be easily changed and optimized for a particular nozzle diameter or repetition rate by a simple adjustment of the free cantilever length. Pulsed molecular beams with a full width at half maximum pulse width as low as 7 μs have been measured at a position 10 cm downstream of the nozzle exit. This represents a gas pulse with a length of only 10 mm making it well matched to for instance experiments using laser beams. Such a short pulse with 6 bar backing pressure behind a 150 μm nozzle releases about 1016 particles/pulse and the beam brightness was estimated to be 4× 10 22 particles/ (s str). The short pulses of the cantilever piezovalve result in a much reduced gas load in the vacuum system. We demonstrate operation of the pulsed valve with skimmer in a single vacuum chamber pumped by a 520 l/s turbomolecular pump maintaining a pressure of 5× 10-6 Torr, which is an excellent vacuum to have the strong and cold skimmed molecular beam interact with laser beams only 10 cm downstream of the nozzle to do velocity map slice imaging with a microchannel-plate imaging detector in a single chamber. The piezovalve produces cold and narrow (Δv/v=2%-3%) velocity distributions of molecules seeded in helium or neon at modest backing pressures of only 6 bar. The low gas load of the cantilever valve makes it possible to design very compact single chamber molecular beam machines with high quality cold and intense supersonic beams. The high speed cantilever piezovalve may find broad applicability in experiments where short and strong gas pulses are needed with only modest pumping, the effective use of (expensive) samples, or the production of cold atomic and molecular beams. © 2009 American Institute of Physics.

A Continuum-Based Model for Analysis of Laterally Loaded Piles in Layered Soils

Abstract: An analysis is developed to calculate the response of laterally loaded piles in multilayered elastic media. The displacement fields in the analysis are taken to be the products of independent functions that vary in the vertical, radial and circumferential directions. The governing differential equations for the pile deflections in different soil layers are obtained using the principle of minimum potential energy. Solutions for pile deflection are obtained analytically, whereas those for soil displacements are obtained using the one-dimensional finite difference method. The input parameters needed for the analysis are the pile geometry, the soil profile, and the elastic constants of the soil and pile. The method produces results with accuracy comparable with that of a three-dimensional finite element analysis but requires much less computation time. The analysis can be extended to account for soil non-linearity.

Robotic castheter system input device

Abstract: An input device for a robotic medical system includes a handle configured to be rotatable about a center axis, and to be longitudinally displaceable along the center axis. The input device also includes a deflection control element disposed on the handle and configured to selectively control deflection of the distal end of a flexible medical instrument electrically coupled to the input device. Longitudinal displacement of the handle may cause or result in a corresponding longitudinal motion or deflection of the flexible medical instrument. Rotation of the handle may cause or result in a corresponding rotation of the deflection plane. Longitudinal displacement and rotation of the handle may be detected or sensed electronically.

Deflection, Frequency, and Stress Characteristics of Rectangular, Triangular, and Step Profile Microcantilevers for Biosensors

Abstract: This study presents the deflection, resonant frequency and stress results of rectangular, triangular, and step profile microcantilevers subject to surface stress. These cantilevers can be used as the sensing element in microcantilever biosensors. To increase the overall sensitivity of microcantilever biosensors, both the deflection and the resonant frequency of the cantilever should be increased. The effect of the cantilever profile change and the cantilever cross-section shape change is first investigated separately and then together. A finite element code ANSYS Multiphysics is used and solid finite elements cantilever models are solved. A surface stress of 0.05 N/m was applied to the top surface of the cantilevers. The cantilevers are made of silicon with elastic modulus 130 GPa and Poisson's ratio 0.28. To show the conformity of this study, the numerical results are compared against their analytical ones. Results show that triangular and step cantilevers have better deflection and frequency characteristics than rectangular ones.

Low velocity flexural impact behavior of AR glass fabric reinforced cement composites

Abstract: Fabric–cement composites developed using the pultrusion production process have demonstrated impressive tensile and flexural properties. For instance fabric reinforced composites with bonded Alkali Resistant (AR) glass fabrics exhibit strain-hardening behavior, tensile strength in the range of 20–25 MPa, and strain capacity of the order of 2–5% under static conditions. Properties of these composite systems were investigated under three point bending conditions using an instrumented drop weight impact system. Samples were studied from the viewpoint of the variations of impact load, deflection response, acceleration and absorbed energy. Development of the testing system in terms of components and acceleration response are discussed in detail. Methods of the impact load measurement using three different ways of acceleration response, piezoelectric load washer and conventional strain gage based load cell are discussed. Cement composites with two different fabric contents and four different drop heights of hammer (dropping mass) were tested. Experimental results indicate that for the same drop height, the stiffer beam type specimens have a lower ultimate deflection but a higher load carrying capacity than the plate type specimens. The maximum flexural stress and absorbed energy of composites increase with drop height. In beam specimens, complete fracture does not take place as cracks form and close due to rebound and significant microcracking in the form of radial fan cracking is observed, whereas interlaminar shear is the dominant failure mode in the plate specimens.

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.

Serviceability Limit State criteria based on steel–concrete bond loss for corroded reinforced concrete in chloride environment

Abstract: This paper will focus on the study of reinforced concrete beams stored in a chloride environment for a period of 14–23 years under service loading. According to the experimental results, a Serviceability Limit State (SLS) criteria is proposed based on an excessive steel–concrete bond reduction. Corrosion of reinforcement in chloride environment leads to a specific local steel cross-section loss as well as a steel–concrete bond loss. Experimental results have shown that, in the first stage of corrosion propagation period, the deflection is more sensitive to chloride-induced corrosion than the ultimate capacity due to the effect of the tension steel–concrete bond loss even if both are correlated. Given this high sensibility of the bending stiffness to corrosion pitting attacks, it appears that a Serviceability Limit State (SLS) criteria based on excessive deflection of structural members is an adequate factor for SLS assessment. Later in corrosion propagation period, when the bond is already significantly reduced, only the ultimate capacity is affected by the steel cross-section loss. This does not affect the serviceability, because pitting attacks are very localised with an insignificant influence on the global deflection. Then, once the steel–concrete bond is lost in critical parts of the beams (high bending moment areas), pitting corrosion propagation does not affect anymore serviceability (stiffness reduction, bending or corrosion cracks patterns) but still leads to an ultimate capacity reduction, which is not acceptable. As a result, excessive steel–concrete debonding can be considered as the SLS criteria.

Measurement of Structural Stiffness and Damping Coefficients in a Metal Mesh Foil Bearing

Abstract: Engineered Metal Mesh Foil Bearings (MMFB) are a promising low cost bearing technology for oil-free microturbomachinery. In a MMFB, a ring shaped metal mesh (MM) provides a soft elastic support to a smooth arcuate foil wrapped around a rotating shaft. The paper details the construction of a MMFB and the static and dynamic load tests conducted on the bearing for estimation of its structural stiffness and equivalent viscous damping. The 28.00 mm diameter, 28.05 mm long bearing, with a metal mesh ring made of 0.3 mm Copper wire and compactness of 20%, is installed on a test shaft with a slight preload. Static load versus bearing deflection measurements display a cubic nonlinearity with large hysteresis. The bearing deflection varies linearly during loading, but nonlinearly during the unloading process. An electromagnetic shaker applies on the test bearing loads of controlled amplitude over a frequency range. In the frequency domain, the ratio of applied force to bearing deflection gives the bearing mechanical impedance, whose real part and imaginary part give the structural stiffness and damping coefficients, respectively. As with prior art published in the literature, the bearing stiffness decreases significantly with the amplitude of motion and shows a gradual increasing trend with frequency. The bearing equivalent viscous damping is inversely proportional to the excitation frequency and motion amplitude. Hence, it is best to describe the mechanical energy dissipation characteristics of the MMFB with a structural loss factor (material damping). The experimental results show a loss factor as high as 0.7 though dependent on the amplitude of motion. Empirically based formulas, originally developed for metal mesh rings, predict bearing structural stiffness and damping coefficients agreeing well with the experimentally estimated parameters. Note, however, that the metal mesh ring, after continuous operation and various dismantling and reassembly processes, showed significant creep or sag that resulted in a gradual decrease of its structural force coefficients.Copyright © 2009 by ASME

Thermoelastic analysis of functionally graded plates using the element-free kp-Ritz method

Abstract: In this paper, the static responses of metal and ceramic functionally graded plates subject to thermal and mechanical loads are investigated. The first-order shear deformation plate theory is adopted, and the displacement field is expressed in terms of a set of mesh-free kernel particle functions. It is assumed that the material property of each plate exponentially varies through the thickness. The governing equations are solved to obtain the plate displacements and axial stresses using the element-free kp-Ritz method. The effects of the volume fraction, material property, boundary conditions and length-to-thickness ratio on the plate deflection and axial stress are discussed in detail. The numerical results generated from the proposed method agree well with those in the literature.

Crack Detection and Quantification in Beams Using Wavelets

Abstract: A new method has been proposed to detect the location and also to quantify the crack using the deflection response of the damaged beams alone. The deflection is measured at a particular point for various locations of a concentrated load on the beam. This static deflection profile is used as the input signal for wavelet (Symlet) analysis. Due to variation in deflection at some points, compared to their adjacent points, peaks are seen in the wavelet coefficient (WC) plot. These peak points are identified as damage points along the length of the beam. The peaks can also be seen at sensor point and supports. These can be eliminated by performing wavelet analysis for the deflection profile measured at another point. In a real damaged structure, it is very difficult to measure deflection at several points, as a large amount of instrumentation needs to be installed to measure the response. This practical difficulty can be avoided by minimizing the number of measuring points in the field as explained in the present work. A parametric study has been carried out by varying the damage, location of damage, intensity of load, flexural rigidity, and length of the beam. It has been observed that the WCs change with variations in damage, location of damage, intensity of load, flexural rigidity, and length of the beam. A generalized curve has been proposed to quantify the damage in a fixed beam by taking envelop of all maximum WCs of the deflection response measured at damage points.

How to measure forces with atomic force microscopy without significant influence from nonlinear optical lever sensitivity.

Abstract: In an atomic force microscope (AFM), the force is normally sensed by measuring the deflection of a cantilever by an optical lever technique. Experimental results show a nonlinear relationship between the detected signal and the actual deflection of the cantilever, which is widely ignored in literature. In this study we have designed experiments to investigate different possible reasons for this nonlinearity and compared the experimental findings with calculations. It is commonly assumed that this nonlinearity only causes problems for extremely large cantilever deflections. However, our results show that the nonlinear detector response might influence many AFM studies where soft or short cantilevers are used. Based on our analysis we draw conclusions of the main reason for the nonlinearity and suggest a rule of thumb for which cantilevers one should use under different experimental conditions.

Active aerodynamic blade control design for load reduction on large wind turbines

Abstract: Through numerical simulations that use trailing edge flaps as active aerodynamic load control devices on wind turbines that range from 0.6MW-5MW rated power, a 20-32% reduction in blade root flap bending moments was achieved. This allows the turbine blade lengths to be increased, without exceeding original fatigue damage on the system, resulting in larger swept rotor area. This study developed and simulated several independent flap control designs (including tip deflection and tip rate deflection feedback) that seamlessly integrated with existing pitch control strategies to reduce loads sufficiently to allow 10% rotor extension and increased energy capture (see reference [1] for methodology).