Metal Beam Research Articles

Plane-by-Plane Femtosecond Laser Inscription Method for Single-Peak Bragg Gratings in Multimode CYTOP Polymer Optical Fiber

We report on the development and characterization of single peak fiber Bragg gratings (FBGs) in polymer optical fiber (POF). We use a multimode gradient index cyclic transparent optical polymer (CYTOP) fiber, where the FBGs are inscribed with a femtosecond laser. We adapt the direct-write, plane-by-plane inscription method, where the beam is scanned transversely across the core, to create refractive index changes. In order to reduce the number of fiber modes coupling to the grating, we limit the FBG's spatial extent to the central part of the core, in the region where the gradient index profile peaks. In this way, we are able to excite the strongest lower order modes thereby generating single peak POF-FBG spectra. We support our experimental results with modeling using the bi-directional beam propagation method (Bi-BPM). Furthermore, a FBG array is used as a quasi-distributed sensor, recovering the vibration response of a freely suspended metal beam, using a 6-m sensing strand. The FBGs are multiplexed using a high-speed commercial wavelength demodulator, the output of which provides wavelength- and time-dependent displacement information. The results are compared directly with the performance of a silica-fiber-based FBG sensor array, and show a significant sensor sensitivity improvement for the polymer fiber to dynamic strain.

Design and Experimental Validation of an Active Catheter for Endovascular Navigation

Endovascular techniques have many advantages but rely strongly on operator skills and experience. Robotically steerable catheters have been developed but few are clinically available. We describe here the development of an active and efficient catheter based on shape memory alloys (SMA) actuators. We first established the specifications of our device considering anatomical constraints. We then present a new method for building active SMA-based catheters. The proposed method relies on the use of a core body made of three parallel metallic beams and integrates wire-shaped SMA actuators. The complete device is encapsulated into a standard 6F catheter for safety purposes. A trial-and-error campaign comparing 70 different prototypes was conducted to determine the best dimensions of the core structure and of the SMA actuators with respect to the imposed specifications. The final prototype was tested on a silicon-based arterial model and on a 23 kg pig. During these experiments, we were able to cannulate the supra-aortic trunks and the renal arteries with different angulations and without any complication. A second major contribution of this paper is the derivation of a reliable mathematical model for predicting the bending angle of our active catheters. We first use this model to state some general qualitative rules useful for an iterative dimensional optimization. We then perform a quantitative comparison between the actual and the predicted bending angles for a set of 13 different prototypes. The relative error is less than 20% for bending angles between 100 deg and 150 deg, which is the interval of interest for our applications.

A closed-form solution of the interfacial stresses and strains in steel beams strengthened with externally bonded plates using ductile adhesives

Ductile adhesives are known to be beneficial in enhancing the capacity and ductility of bonded joints. However, there is a lack of closed-form analytical solutions for plated metallic beams that account for adhesive plasticity. This paper presents a first order, elastic-plastic bond analysis for beams strengthened with externally bonded fiber reinforced polymer (FRP) plates using ductile adhesives, based on a shear-lag formulation. This model is able to analyze arbitrary mechanical and thermal loading conditions and closed-form solutions under shearing and peeling are given. Following a review of the existing stress-based analytical solutions, a comparison between the existing and proposed analyses is also presented. The shear solution was validated by comparing with the experimental results of carbon fiber reinforced polymer (CFRP) strengthened steel beams under moderately elevated temperatures. A comprehensive parametric study has been conducted to illustrate the effects of different design parameters on the bond behavior. It is found that the adhesive shear toughness is the most critical parameter in determining the debonding failure load while the adhesive Young’s modulus does not significantly affect the bond stresses in the elastic-plastic regime. Further, the magnitude of the peak peeling stresses is self-limiting after shear yielding, and the use of a thinner plate with higher Young’s modulus is beneficial in further reducing the peeling stress.

Characteristics of intense multispecies metallic ion beams extracted from plasma of a pulsed cathodic arc

The energy spectra of a metallic ion beam extracted by a three-grid extractor from the plasma of a pulsed vacuum arc (pulse duration of 200 μs, discharge current Id of up to 100 A and ion current of up to 0.6 A) are studied by means of an electrostatic energy analyzer in a range of the extraction voltage Uext of up to 10 keV. It is found that the most probable ion energy Em/Z is markedly less than eUext, and the difference between these values as well as the width of the spectra decrease with increasing Uext or/and decreasing Id. It is found as well that the spectra contain “tails” of ions with energies significantly exceeding Em/Z. The shape of the spectra differs at various phases of the pulse, so that Em/Z in the initial transition phase is considerably more than that in the quasi-stationary phase. As possible causes of these effects, the nonmatched ion optics of the extraction gap and the action of the non-neutralized space charge of the extracted ion beam moving through the drift gap are considered.

Damage identification in beam structure based on thresholded variance of normalized wavelet scalogram

In this paper, a damage identification algorithm based on continuous wavelet transform of one-dimensional structures exploiting mode shapes is presented. Numerical models of aluminium and carbon composite beams, containing a mill-cut and impact damage, respectively are considered for this study. Wavelet scalogram is used to obtain the transform coefficients at different wavelet scales and is subsequently normalized in order to emphasize locations with largest coefficients. Variance of normalized wavelet scalogram is computed along the axis of the beam yielding sharp peaks in the zones corresponding to damage in beams. This operation excludes wavelet scale factors as variables for damage localization problems. The universal threshold is applied to filter out lower amplitude peaks that do not indicate damage. These results are summed up for all nodes of beams and all wavelet functions that are analysed in this paper in order to also exclude the number of different wavelet functions as another variable for damage localization. The universal threshold is applied the second time to yield the final result on the locations of damage. Results suggest that the proposed damage localization method is a fast and reliable tool for damage detection in one-dimensional metal and composite beam structures.

Dynamic properties of unbonded, multi-strand beams subjected to flexural loading

Abstract Beam-like structures, constructed from many long strands that are constrained rather than bonded together, can provide appreciable levels of structural damping through friction between individual strands. This paper describes experimental and numerical studies, carried out on square-section metal beams, which are aimed at improving understanding of the relationship between construction and performance. A beam is formed from a pack of square-section strands that is held together at various compression loads with pre-calibrated clamps. Flexural deformation of the assembled beam is simulated using standard finite element analysis employing simple Coulomb friction at the interfaces. The validity of the assumptions used in the models is confirmed by comparison with three point bend tests on a regular nine strand construction at several different clamp loads. Dynamic loss factors for this beam are obtained by conducting forced vibration tests, which show that the damping is insensitive to frequency. Subsequent numerical studies are used to investigate the effects of increasing the number of strands whilst maintaining the overall cross-section geometry of the beam. It is found that the system stiffness drops and loss factor increases when more strands are used for a maintained beam cross-section. Interestingly, the energy dissipated by each beam construction is almost the same. These results provide a vital and necessary insight into the physics for stranded structures and materials that are largely prevalent in mechanical (e.g. cables) and electrical (e.g. wires) elements.

Experimental study of local and modal approaches to active vibration control of elastic systems

Two different methods, local and modal, are suggested to control systems with distributed parameters, each of them having its own advantages and drawbacks. The aim of the present research is to carry out experiments aiming in comparison of these 2 methods for the problem of suppression of forced bending vibrations of a thin metal beam. Two pairs of piezoelectric sensors and actuators are attached to the beam in each control system considered. Their locations are chosen so as to provide the most efficient measurement and excitation of the first and second vibration modes of the beam. Frequency methods of the automatic control theory are employed to design stable control systems that can efficiently suppress bending vibrations of the beam with the first and second resonance frequencies. As a result, control systems with the desired performance are created on the basis of both local and modal methods. The obtained modal system works efficiently for both resonances, whereas the local systems demonstrate appropriate performance either at the first or at the second resonance frequency only. This difference is due to the fact that in the case of modal control, each control loop corresponds to a particular vibration mode and can be designed to provide optimal performance at the required frequency. The performed benchmark study demonstrates the advantages of the modal method over the local one for the cases where it is necessary to suppress vibrations in the frequency range that contains more than one resonance frequency of the control object.

05.08: Lateral‐torsional buckling of beams of monosymmetrical cross‐sections loaded perpendicularly to the axis of symmetry: Theoretical analysis

ABSTRACTDetermination of the critical moment is a crucial step of the process of assessment of the buckling resistance of a metal beam with no intermediate restraints between supports. The critical moment of an ideal beam depends, among others, on support conditions and variation of the bending moment along the span of the beam. It can be found as a solution of the eigenvalue problem of differential equations of bending. This complex procedure can generally provide a formula for the calculation of the critical moment with certain coefficients varying depending on the variation of the bending moment along the span and support conditions of the beam. The formula for the critical moment and numerical values of the coefficients taking into account the type of supports and variation of the bending moment for some common cases can be found in literature.The paper focuses on process of derivation of the formula for calculation of the elastic critical moment of beams of double symmetrical and monosymmetrical cross‐sections (channels) loaded perpendicularly to the plane of symmetry. Based on classical Vlasov's theory and variational method, a formula for the elastic critical moment of beams of double symmetrical cross‐sections and channels loaded perpendicularly to the plane of symmetry and coefficients for not only simple cases of loads but also selected special cases are derived using mathematical methods and presented in the paper. Numerical values of the above mentioned coefficients are summarized in tables and charts.

Ultrasonic guided wave sensing characteristics of large area thin piezo coating

This paper reports on the characterization method and performance enhancement of thin piezo coating for ultrasonic guided wave sensing applications. We deposited the coatings by an in situ slurry coating method and studied their guided wave sensing properties on a one-dimensional metallic beam as a substrate waveguide. The developed piezo coatings show good sensitivity to the longitudinal and flexural modes of guided waves. Sensing voltage due to the guided waves at various different ultrasonic frequencies shows a linear dependence on the thickness of the coating. The coatings also exhibit linear sensor output voltage with respect to the induced dynamic strain magnitude. Diameter/size of the piezo coatings strongly influences the voltage response in relation to the wavelength. The proposed method used a characterization set-up involving coated sensors, reference transducers and an analytical model to estimate the piezoelectric coefficient of the piezo coating. The method eliminates the size dependent effect on the piezo property accurately and gives further insight to design better sensors/filters with respect to frequency/wavelength of interest. The developed coatings will have interesting applications in structural health monitoring (SHM) and internet of things (IOT).

Phase influence of combined rotational and transverse vibrations on the structural response

Abstract The planar dynamic response of a cantilever metallic beam structure under combined harmonic base excitations (consisting of in-plane transverse and rotation about the out-of-plane transverse axis) was investigated experimentally. The important effect of the phase angle between the two simultaneous biaxial excitations on the beam tip displacement was demonstrated. The experiments were performed using a unique six degree-of-freedom (6-DoF) electrodynamic shaker with high control accuracy. The results showed that the beam tip displacement at the first flexural mode was amplified when the phase angle between the rotational and translational base excitations was increased. The beam nonlinear stiffness, on the other hand, simultaneously: (i) decreased due to fatigue damage accumulation, and (ii) increased due to an increase in the phase angle. The results were compared to the uniaxial excitation technique, where the principle of superposition was applied (mathematical addition of the structural response for each uniaxial excitation). The principle of superposition was shown to overestimate the structural response for low phase angles. Thus, the application of the superposition vibration testing as a substitute for multiaxial vibration testing may lead to over-conservatism and erroneous dynamic and reliability predictions.

First trial of the muon acceleration for J-PARC muon g-2/EDM experiment

Muon acceleration is an important technique in exploring the new frontier of physics. A new measurement of the muon dipole moments is planned in J-PARC using the muon linear accelerator. The low-energy (LE) muon source using the thin metal foil target and beam diagnostic system were developed for the world’s first muon acceleration. Negative muonium ions from the thin metal foil target as the LE muon source was successfully observed. Also the beam profile of the LE positive muon was measured by the LE-dedicated beam profile monitor. The muon acceleration test using a Radio-Frequency Quadrupole linac (RFQ) is being prepared as the first step of the muon accelerator development. In this paper, the latest status of the first muon acceleration test is described.

The plastic behavior of sandwich beams with core gradation

The objective of this paper is to establish yielding criteria for a slender sandwich beam with two-layer metal foam cores under transverse loading. A unified yielding criterion for this geometrical or physical asymmetry four-layer metallic sandwich beam is established. Based on the yield criteria, an analytical solution for large deformation of fully clamped multilayer sandwich beams under transverse loading is presented. Comparisons of present solutions with numerical results are given and good agreements are obtained. Finally, the effects of core strength and thickness ratios on the large deflection responses of the sandwich beams with core gradation are discussed in detail. It is demonstrated that the present analytical model can reasonably predict the behavior of the plastic deformation of four layer sandwich beams.

Identification procedure in the modal control of a distributed elastic system

It is necessary to provide the separation of the eigenmodes of elastic objects from the sensor signals and to make it possible to independently affect the modes with the use of actuators when realizing the modal system of controlling an elastic object with distributed parameters. The present paper puts forward an identification procedure which allows separating the vibration modes of the object in measured and control signals in the absence of the object model simulation. The control operability of this procedure was verified by experiment through making a system of active suppression of forced bending vibrations of a metal beam. The experiment showed the high control efficiency of the realized modal system.

Electromagnetic actuators for controlling flexible cantilever beams

Electromagnetic actuators are very important for scientific and industrial applications. Their use may vary within a wide range of possibilities due to their most important feature: the ability to apply known and controllable forces to elements or structures without contact. In this article, an application within this range is analyzed: a proportional-integral-derivative (PID) controller is used with a pair of actuators to control the dynamic forced response of a flexible cantilever metallic beam and to keep it at a given reference position. In order to achieve this objective, both the actuators and the controller need to be adjusted. For the actuators, the main parameters evaluated consider mounting particularities, such as the differential assembly and the influence of the air-gap distance over the magnetic flux density and the magnetic force provided. Next, a brief review of PID controllers is presented, highlighting 5 tuning methods, and their effects on relevant parameters of the electromagnetic system (such as the cutoff frequency). Finally, results focus on the comparative efficiency of the PID tuning methods to reduce the vibration amplitude of the beam bending modes. The results show that the Ziegler–Nichols modified for some-overshoot and no-overshoot methods are the best choices.

Dynamic responses of metal sandwich beams under high velocity impact considering time inhomogeneity of core deformation

The objective of this paper is to establish a yielding criterion for a sandwich beam by considering the time inhomogeneity of foam core deformation, which results in the time-varied neutral surface and cross-sectional area. Taking into account of the bending and axial stretching, a unified dynamic yielding criterion for metallic sandwich beams considering the mass redistribution along with the core compression is established. A membrane factor is proposed and an analytical solution for the large deflection of the beam under high velocity impact is given. Different from the traditional yielding surface, when the core is partially densified, the yielding surface is asymmetric. Comparison of analytical solutions with numerical ones reveals that the present model improves the prediction accuracy of high-velocity impact responses of fully clamped sandwich beams. The present method can also be degenerated to predict the low velocity/energy impact responses of sandwich beams.

A periodic piezoelectric smart structure with the integrated passive/active vibration-reduction performances

The paper proposes a new piezoelectric smart structure with the integrated passive/active vibration-reduction performances, which is made of a series of periodic structural units. Every structural unit is made of two layers, one is an array of piezoelectric bimorphs (PBs) and one is an array of metal beams (MBs), both are connected as a whole by a metal plate. Analyses show that such a periodic smart structure possesses two aspects of vibration-reduction performance: one comes from its phonon crystal characteristics which can isolate those vibrations with the driving frequency inside the band gap(s). The other one comes from the electromechanical conversion of bent PBs, which is actively aimed at those vibrations with the driving frequency outside the band gap(s). By adjusting external inductance, the equivalent circuit of the proposed structure can be forced into parallel resonance such that most of the vibration energy is converted into electrical energy for dissipation by a resistance. Thus, an external circuit under the parallel resonance state is equivalent to a strong damping to the interrelated vibrating structure, which is just the action mechanism of the active vibration reduction performance of the proposed smart structure.

Mechanical rainbow trapping and Bloch oscillations in chirped metallic beams

The mechanical rainbow trapping effect and the mechanical Bloch oscillations for torsional waves propagating in chirped mechanical structures are here experimentally demonstrated. After extensive simulations, three quasi-one-dimensional chirped structures were designed, constructed and experimentally characterized by Doppler spectroscopy. When the chirp intensity vanishes, a perfect periodic system, with bands and gaps, is obtained. The mechanical rainbow trapping effect is experimentally characterized for small values of the chirp intensity. The wave packet traveling along the structure is progressively slowing down and is reflected back at a certain depth, which depends on its central frequency. For larger values of the chirping parameter the rainbow trapping yields the penetration length where the mechanical Bloch oscillations emerge. Numerical simulations based on the transfer matrix method show an excellent agreement with experimental data.

Damping properties of coatings at elevated temperatures

The research reported upon in this paper is an evaluation of the complex modulus (both storage and lose modulus) of a TBC thin coating, 8% stabilized yttrium stabilized zirconium (8YSZ). The specimen incorporated is supported in a free-free fashion and placed in a vacuum chamber surrounded by 200W halogen lamps that allow for an isothermal temperature up to 482°C. The use of a free-free support and the vacuum chamber enclosure is meant to remove external agents which may inject overall effects on the loading dynamic properties. The dynamic excitation was developed with a series of permanent magnets placed strategically, creating a magnetic field developed with up to 7500mA (7500milliamps) current. In order to separate the combined effect of the base material (a titanium beam) from the coating, a method incorporating finite elements was carried out. A strain energy ratio (SER) was used equal to the amount of elastic energy stored in the coating over that stored in the metallic beam. The results led to the dynamic moduli. In order to determine these dynamic coefficients, a vibration ring down technique was incorporated requiring time to reach a steady state. A low value for the loss factor of about 0.02 exists that is applicable across all strain levels, temperatures, and amplitudes. The strain dependency can be approximated using a lower boundary form: ηc=0.00621ln(ε11)+0.021;ε11inmicrostrain. In addition, it was found that 8YSZ is a strain softening material. The material is strongly nonlinear with room temperature values obtained close to those of previous work but varying in strain amount and amplitude of excitation. It has a storage modulus value of 30–35GPa like other references. Similar to previous studies, much variation in results across specimens occurs despite good repeatability. This is due to the variation in the application of the coating.

Large-deflection and post-buckling analyses of laminated composite beams by Carrera Unified Formulation

The Carrera Unified Formulation (CUF) was recently extended to deal with the geometric nonlinear analysis of solid cross-section and thin-walled metallic beams (Pagani and Carrera, 2017). The promising results provided enough confidence for exploring the capabilities of that methodology when dealing with large displacements and post-buckling response of composite laminated beams, which is the subject of the present work. Accordingly, by employing CUF, governing nonlinear equations of low- to higher-order beam theories for laminated beams are expressed in this paper as degenerated cases of the three-dimensional elasticity equilibrium via an appropriate index notation. In detail, although the provided equations are valid for any one-dimensional structural theory in a unified sense, layer-wise kinematics are employed in this paper through the use of Lagrange polynomial expansions of the primary mechanical variables. The principle of virtual work and a finite element approximation are used to formulate the governing equations in a total Lagrangian manner, whereas a Newton–Raphson linearization scheme along with a path-following method based on the arc-length constraint is employed to solve the geometrically nonlinear problem. Several numerical assessments are proposed, including post-buckling of symmetric cross-ply beams and large displacement analysis of asymmetric laminates under flexural and compression loadings.

Paralleled Structure-Based String-Type Fiber Bragg Grating Acceleration Sensor

This paper has presented a novel string-type fiber Bragg grating (FBG) acceleration sensor based on directly utilizing the transversal vibrational property of a tightly suspended optical fiber. This sensor mainly consists of a mass fixed on the middle of an optical fiber embedded with an FBG element and another optical fiber or metal beam in a parallel arrangement mode, which enables to enhance the impact resistance and resonant frequency of the sensor. Compared with existing FBG-based vibration sensors, the proposed sensor possesses an excellent repeatability using a simple structure, and avoids the FBG-pasting process and the associated limitations of chirping failure. The working principle of the proposed FBG vibration sensors with two different configurations has been built with considering the rotational interference of the mass. Static experiments have been completed to show that the sensitivity of the two configurations with paralleled optical fiber and metal beam is 193.6 and 3.275 pm/g, respectively. The paralleled metal beam-based vibration sensor has a working bandwidth of 12~250 Hz, much larger than that of 4~28 Hz for the paralleled string-type optical fiber configuration. The performance of the proposed acceleration sensor can be easily adjusted by arranging different types of the parallel structure and modifying their corresponding physical parameters to satisfy different vibration measurement requirements.