Bending Mode Research Articles

Ultrafast Time-Domain Spectroscopy Reveals Coherent Vibronic Couplings upon Electronic Excitation in Crystalline Organic Thin Films.

The coherent coupling between electronic excitations and vibrational modes of molecules largely affects the optical and charge transport properties of organic semiconductors and molecular solids. To analyze these couplings by means of ultrafast spectroscopy, highly ordered crystalline films with large domains are particularly suitable because the domains can be addressed individually, hence allowing azimuthal polarization-resolved measurements. Impressive examples of this are highly ordered crystalline thin films of perfluoropentacene (PFP) molecules, which adopt different molecular orientations on different alkali halide substrates. Here, we report polarization-resolved time-domain vibrational spectroscopy with 10 fs time resolution and Raman spectroscopy of crystalline PFP thin films grown on NaF(100) and KCl(100) substrates. Coherent oscillations in the time-resolved spectra reveal vibronic coupling to a high-frequency, 25 fs, in-plane deformation mode that is insensitive to the optical polarization, while the coupling to a lower-frequency, 85 fs, out-of-plane ring bending mode depends significantly on the crystalline and molecular orientation. Comparison with calculated Raman spectra of isolated PFP molecules in vacuo supports this interpretation and indicates a dominant role of solid-state effects in the vibronic properties of these materials. Our results represent a first step toward uncovering the role of anisotropic vibronic couplings for singlet fission processes in crystalline molecular thin films.

Infrared spectra of solid-state ethanolamine: Laboratory data in support of JWST observations

Ethanolamine (NH$_2$CH$_2$CH$_2$OH; EA) has been identified in the gas phase of the interstellar medium within molecular clouds. Although EA has not been directly observed in the molecular ice phase, a solid-state formation mechanism has been proposed. However, the current literature lacks an estimation of the infrared band strengths of EA ices, which are crucial data for quantifying potential astronomical observations and laboratory findings related to their formation or destruction via energetic processing. We conducted an experimental investigation of solid EA ice at low temperatures to ascertain its infrared band strengths, phase transition temperature, and multilayer binding energy. Since the refractive index and the density of EA ice are unknown, the commonly used laser interferometry method was not applied. Infrared band strengths were determined using three distinct methods. In addition to evaluating EA band strengths, we also tested the advantages and disadvantages of different approaches used for this purpose. The obtained lab spectrum of EA was compared with the publicly available MIRI MRS James Webb Space Telescope observations towards a low-mass protostar. We used a combination of Fourier-transform transmission infrared spectroscopy and quadrupole mass spectrometry. The phase transition temperature for EA ice falls within the range of 175 to 185 K. Among the discussed methods, the simple pressure gauge method provides a reasonable estimate of band strength. We derived a band strength value of about $1 $ cm molecule$^ $ for the NH$_2$ bending mode in the EA molecules. Additionally, temperature-programmed desorption analysis yielded a multilayer desorption energy of 0.61pm 0.01 eV. By comparing the laboratory data documented in this study with the JWST spectrum of the low-mass protostar IRAS 2A, an upper-limit for the EA ice abundances was derived. This study addresses the lack of quantitative infrared measurements of EA at low temperatures, crucial for understanding EA's astronomical and laboratory presence and formation routes. Our approach presents a simple yet effective method for determining the infrared band strengths of molecules with a reasonable level of accuracy.

Digital dynamic modeling and topology optimized design of shell face mills

This paper presents digital modeling of shell face mills in milling cylinder heads. The cutter's structural dynamics and its mode shapes are predicted using a Finite Element system. The geometries of the cutter body and inserts are imported from their Computer Aided Design (CAD) models. The insert edge is discretized into small segments to model its varying normal rake and inclination angles, which affect the cutting mechanics. The cutter is dynamically assembled with the target machine tool spindle using the receptance coupling method. A general dynamic cutting force model, which considers the varying edge geometry and inserts’ run-outs, is developed and used to predict cutting forces and chatter stability diagrams. The proposed model is experimentally verified to demonstrate the feasibility of the systematic application of physics-based digital design and analysis of tools for the mass machining of specific parts. The cutter body shape is optimized to increase the stiffness of the bending mode shape that caused chatter via topology optimization, which led to five-fold increase in the absolute stable depth of cut.

Compressive Mechanical Properties and Energy Absorption of Cubic Spherical Hollow Cellular Material Based on the Rod and Curved Surface Structure

Cellular materials, such as lattices and honeycombs, were widely used for structural protection owing to their excellent mechanical properties. By combining the excellent characteristics of lattice and honeycomb curved surface structures, this study designed a cell called Cubic Spherical Hollow (CSH), which had the advantages of orthogonal isotropy and better spatial connectivity. Inspired by the micro-structural arrangement of bamboo fiber and conch shell, we designed the new CSH cellular materials through the interlayer offset strategy. Then, the effects of interlayer offset on the mechanical properties and compression deformation behavior were explored experimentally and simulatively. Compared with other cellular materials, CSH cellular materials exhibited excellent mechanical properties with higher specific strength and specific modulus. The arrangement offsets of the CSH cells between different layers led to a change in the deformation mechanism from a rod’s compressive mode to a combination of a rod’s compressive mode and curved surface’s bending mode. The initial peak stress and plateau stress decreased with the increased arrangement offsets of the CSH since the extruded protrusions of the structure filled the holes and reduced the lateral expansion behavior of the material in the pressurized environment. This phenomenon also reduced the transverse expansion and prevented the sudden change in stress in the constrained space, indicating that the structural deformation was stable and had excellent cushioning and energy absorption properties. In this study, the cellular material design strategy opens a new avenue for energy absorption.

Bending response and energy absorption of sandwich beams with combined reinforced auxetic honeycomb core

This study introduces a reinforced star-shaped auxetic honeycomb (RSSAH) sandwich beam, enhanced with hollow thin-walled tubes to improve bending resistance and energy absorption performance. The bending performance of the RSSAH is systematically investigated through quasi-static three-point bending tests and finite element numerical simulations. The findings suggest that when subjected to mid-span stress, the RSSAH displays both localized indentation and overall bending deformation, accompanied by notable negative Poisson’s ratio (NPR) impact under bending loads. Parametric studies are undertaken by numerical simulations to investigate the impact of compression position, auxetic angle, and face sheet thickness on the bending mode of the auxetic honeycomb sandwich beam. The analysis shows that the RSSAH can exhibit excellent bending performance and, at one of the compression positions, displays double-plateau stress characteristics. It is also found that altering key geometric parameters, such as the auxetic angle and panel thickness ratio, can greatly improve the bending capabilities of the RSSAH, achieving stable plastic deformation and high energy absorption. Finally, compared to star-triangle honeycomb (STH) sandwich beam, traditional reentrant honeycomb (RH) sandwich beam and star-shaped auxetic honeycomb (SSAH) sandwich beam, the RSSAH demonstrates superior bending performance and energy absorption capacity. This study offers insights and references for the development of innovative reinforced auxetic honeycomb sandwich beams.

Mixed Mode‐I/II interlaminar fracture toughness Characterization of woven Carbon–Kevlar interyarn hybrid textile composites

AbstractIn actual service conditions, the composite structures are subjected to the combined effect of Mode‐I and Mode‐II loadings. It has great significance in the aerospace, defense, military, automobile, and marine sectors. This study aims to determine the Mixed Mode‐I/II interlaminar fracture toughness (ILFT) of plain and twill woven carbon, Kevlar monolithic, and interyarn hybrid textile composites under several hybridization schemes. The tailored properties are obtained using the interyarn hybridization of high stiff carbon yarn and high tough Kevlar yarn. The effect of individual yarn in the length direction in different hybrid composite laminates is carefully investigated. The Mixed Mode‐I/II ILFT characterization is experimentally performed using a mixed mode bending (MMB) test specimen on the Instron 8862 system under 45%, 55%, and 65% Mixed Mode ratios (MMRs). The increase in mode mixture percentage decreases the lever length, increases the load‐bearing capacity, and increases the Mixed Mode‐I/II ILFT of the MMB test specimen. Plain woven composites exhibited a higher ILFT than twill woven textile composites. The plain woven carbon–Kevlar hybrid composite laminate with carbon yarn‐in‐length direction shows the highest Mixed Mode‐I/II ILFT after CP laminates. Hybridization significantly increases the Mixed Mode‐I/II ILFT compared to monolithic Kevlar fabric‐reinforced composites. Moreover, the failure mechanisms are investigated using scanning electron microscopy.Highlights Mixed Mode‐I/II ILFT of carbon–Kevlar interyarn hybrid textile composites. ILFT at nonlinearity (NL), VIS, and 5%/Max load points for 45%, 55%, and 65% MMR. Advantage of placing carbon yarn‐in‐length direction in hybrid configurations. Effect of carbon–Kevlar interyarn hybridization on Mixed Mode‐I/II ILFT. Fractography of tested specimens to investigate several failure mechanisms.

Fretting Fatigue Life Model Under Combined Loading

ABSTRACTThis paper evaluates the capability of the theory of critical distances (TCD) coupled with the Fatemi–Socie (FS), Smith–Watson–Topper (SWT), and normal stress range (S‐N) criteria for the lifetime estimation of combined fretting fatigue, that is, the combination of bending and axial loading modes, for 316L stainless steel along with the effect of increasing the grain size of the material. After evaluating the stress field, the point, line, area, and volume methods have been implemented to estimate the lifetimes of fretting fatigue experiments based on the dependency of the critical distance on the number of cycles to failure. Whereas the area and volume methods were overestimating the lifetimes, the point and line methods were more accurate. FS and SWT criteria were proper in lifetime estimation, but the normal stress range (S‐N) criterion was not a safe criterion. At the same time, increasing the grain size of the material leads the TCD to be more conservative.

Analytical model analysis of suspension bridges with tower-girder-connected dampers

Recently the tower-girder-connected damper has been utilized to suppress multi-mode vertical vortex-induced vibration (VIV) of long-span suspension bridges. In this paper, an analytical solution is proposed for the damping ratio of vertical bending modes of a single-span suspension bridge, with a vertical or/and a rotational damper mounted near the end of the stiffening girder, which significantly simplifies the design procedure for tower-girder-connected dampers on suspension bridges. The damping effect and the accuracy of the analytical solution are validated for Humen Bridge. It is found that both the vertical and rotational damper with an appropriate parameter selected can supply significantly additional damping ratio to multiple bending modes of the suspension bridge. The rotational and vertical dampers work in a similar way and provide nearly the same maximum additional damping ratio for each mode. In particular, for the first two symmetric modes, regions of reduced motion near the ends of the stiffening girder are developed due to the effects of cable geometry and elasticity, and this reduces the effect of the tower-girder-connected damper. Excluding these modes, the damper effect on a suspension bridge is similar to that on a tension beam with the same beam stiffness and horizontal tension forces.

How do the successive buckling events affect a galaxy bar and stellar disc? Potential observable signatures for spotting the buckling action – I

ABSTRACT Until now, observations have caught up only a handful of galaxies in ongoing buckling action. Interestingly, N-body simulations over the past several decades show that almost every bar buckles or vertically thickens as soon as it reaches its peak strength during its evolution and leads to box/peanut/x (BPX) shapes. In order to understand the effect of multiple buckling events on the observable properties of galactic bar and disc, we perform an N-body simulation of a Milky Way-type disc. The axisymmetric galaxy disc forms a bar within a Gyr of its evolution and the bar undergoes two successive buckling events. We report that the time-spans of these two buckling events are 220 Myr and 1 Gyr, which have almost similar strengths of the bending modes. As a result of these two buckling events, the full lengths of BPX shapes are around 5.8 and 8.6 kpc, which are around two-thirds of the full bar length at the end of each buckling event. We find that the first buckling occurs at a smaller scale (radius $\lt $3 kpc) with a shorter time-span affecting the larger length-scales of the disc, which is quantified in terms of changes in $m=$2 and $m=$ 4 Fourier modes. While the second buckling occurs at larger scales (radius $\approx$6 kpc) affecting the inner disc the most. Finally, we provide observable kinematic signatures (i.e. quadrupolar patterns of the line-of-sight velocities), which can potentially differentiate the successive buckling events.

Intramolecular Vibrational Energy Redistribution in the Reaction H3+ + CO → H2 + HCO.

An ab initio direct molecular dynamics (MD) calculation at the RS2/aug-cc-pVQZ level, followed by vibration mapping, has been applied to the H3+ + CO → H2 + HCO+ reaction to elucidate the intramolecular vibrational energy redistribution (IVR) processes during the reaction. Direct MD calculations were carried out for 20 K (a typical temperature for interstellar dark clouds) and 330 K (a typical translational temperature for ions in a glow discharge). Under the Cs symmetry constraint, the approach of H3+ turned out to be the H-C stretching mode of the [H···CO]+ part, which invoked the C-O stretching and then the H-C-O bending modes. Under no symmetry constraint, a strong bending mode was first invoked, and the intensities of the subsequent H-C and C-O stretching modes were kept relatively small. The detailed analyses of the IVR during the reaction, in terms of vibration mixing, gave a clue to understanding experimentally observed anomalies in the bending modes, such as population inversion at some bending states. In the MD simulation at 20 K, less than two-thirds of the reaction energy was converted to the vibrational energy of the resultant HCO+ part and one-third to the translational and rotational energies of the leaving H2 molecule. These direct MD simulations, when combined with the experimental spectroscopy data, shed light on a clear understanding of the reaction mechanism, including the IVR during the reaction.

How periodic surfaces bend.

A periodic surface is one that is invariant by a two-dimensional lattice of translations. Deformation modes that stretch the lattice without stretching the surface are effective membrane modes. Deformation modes that bend the lattice without stretching the surface are effective bending modes. For periodic piecewise smooth simply connected surfaces, it is shown that the effective membrane modes are, in a sense, orthogonal to effective bending modes. This means that if a surface gains a membrane mode, it loses a bending mode, and conversely, in such a way that the total number of modes, membrane and bending combined, can never exceed 3. Various examples, inspired from curved-crease origami tessellations, illustrate the results.This article is part of the theme issue 'Origami/Kirigami-inspired structures: from fundamentals to applications'.

Advances in longitudinal equivalent bending stiffness analysis-novel nonlinear characteristics in the assembly process of prefabricated subway stations

The longitudinal bending stiffness of quasi-rectangular prefabricated subway stations plays a great important role in studying their mechanical behavior and conducting safety assessments. To address the issue of immature stress assumptions for existing prefabricated subway stations, three stress assumptions and five bending modes are proposed while considering the coupling effect between axial force and bending moment. The study investigates novel nonlinear characteristics in the longitudinal equivalent bending stiffness and the influencing factors during the assembly of an existing subway station. An effective method for identifying the longitudinal bending modes suitable for the prefabricated subway station is established, the proposed solution has a good agreement with measured longitudinal bending stiffness efficiency. The study demonstrates that the longitudinal bending mode of the prefabricated subway station shifts from "upward convex" to "downward concave" due to the stepwise assembly method. The longitudinal bending stiffness efficiency displays a significant hysteresis curve, eventually stabilizing at approximately 1 %. Upon completion of the monitoring ring assembly, the concrete bears both longitudinal tensile and compressive stress. When assembling 10 rings from the monitoring ring, the longitudinal reinforcing bars bear tensile stress. The longitudinal bending stiffness of the prefabricated subway station exhibits significant time-variable characteristics throughout the assembly process. The research findings can provide effective references for the analysis of longitudinal mechanics and bending performance during the assembly process.

Magneto-viscoelastic rod model for hard-magnetic soft rods under 3D large deformation: Theory and numerical implementation

The main purpose of this work is to develop a three-dimensional (3D) viscoelastic rod model for hard-magnetic soft (HMS) rods under large deformation which are widely used active structures in soft robotics. To do so, the Simo’s viscoelasticity theory has been rationally incorporated into the geometrically exact 3D curved rod model. The proposed model includes the deformation modes of axial tension, shear, bending, and torsion, which is applicable to the HMS rods with arbitrarily initial curved and twisted geometries under 3D large deformation. The viscoelastic constitutive equations of the HMS rod in the present formulation are formulated, which include the general relaxation functions. To obtain the expression for the magnetic load, the rotation-based magnetic free energy density is introduced, and the governing equations of the HMS rod with magnetic load and body force are presented. To obtain the numerical implementation, an implicit time integration algorithm that simply extends the generalized-α method for the rotation group, and the corresponding variational formulation and its linearization of the rod model are derived. To validate the model, five numerical examples, including 2D dynamic buckling, 3D static, and 3D dynamic problem are presented. The dynamic problems include the dynamic snap-through behavior of a bistable HMS arch and damped oscillation of a quarter arc cantilever under 3D deformation. The simulation results show good agreement with the results reported in the literature.

Synchronous LoRa sensor nodes for modal identification in footbridge vibration monitoring

AbstractThis article aims at presenting a preliminary investigation of using long-range and low-cost LoRa (Long Range) technology and two synchronous LoRa sensor nodes for cost-effective footbridge structural health monitoring (SHM). Two sensor nodes with LoRa modules and accelerometers were employed for vibration monitoring and a new attempt was made to use synchronous LoRa nodes for modal identification. In this article, a modal identification method based on a lightweight synchronization concept was proposed. This method is able to identify the fundamental mode of vibrating beam structures. Meanwhile, maximum accelerations can also be tracked periodically from the simultaneously recorded acceleration data by the synchronous LoRa nodes. Specifically, synchronization was achieved through the wireless peer-to-peer (P2P) communication between the two LoRa nodes, with the aim of initializing simultaneous acceleration recordings. The fundamental frequency and the phase information derived from the on-board calculation of the synchronized nodes can then be used to effectively identify the vertical bending mode and torsion mode. A series of laboratory tests were also conducted on a beam structure for the purpose of validation. The test results showed that the fundamental mode of the vibrating beam can be obtained rapidly and accurately using the synchronized LoRa nodes, with an average synchronization accuracy of 4.45 ms. The maximum acceleration data recorded by the LoRa nodes also showed high accuracy when compared with the raw acceleration data collected from a commercial Bluetooth accelerometer node. The fundamental frequencies obtained from both types of nodes also compare reasonably. The proposed modal identification method using two synchronous LoRa sensor nodes provides a basis for the development of a low-cost footbridge SHM system with the integration of IoT techniques. An attempt has been made to perform a preliminary field test on a cable-stayed footbridge, where the fundamental frequency and the mode shape type of the footbridge were successfully identified and its serviceability condition was also found to satisfy the code requirements.

Flapping dynamics of a flexible membrane attached to the leading edge of a forward-facing step

An experimental investigation of velocity fields over and wall pressure fluctuations on a forward-facing step (FFS) disturbed by a flexible membrane has been conducted. A two-dimensional flexible membrane of 40mm length and 0.15mm thickness attached to a FFS of 40mm height was tested with oncoming velocity in the range of 7.3 < U < 12.9 m/s, corresponding to Reynolds numbers of 20391 < ReH < 35312 based on the step height. A high-speed camera was used to reconstruct the configuration of the flapping membrane. The flow field velocity dataset in the horizontal-vertical plane and the pressure fluctuation on the step surface were measured by planar particle image velocimetry and pressure sensors, respectively. The flexible membrane displayed two distinct modes, viz. a bending mode or flapping mode. In the bending mode, the membrane elevates the shear layer, thereby delaying the reattachment of separation flow generated by a FFS. In the flapping mode, the membrane periodically generates flapping-induced vortices (FIVs) of different scales with varying Reynolds numbers. The pressure on the FFS also undergoes periodic fluctuations corresponding to these FIVs.

Experimental and numerical analysis of the vibrational behaviour of metallic structures filled with damping materials

This work focuses on characterizing and modeling the vibrational behavior of hollow metallic structures filled with damping material. Vibration tests are first carried on a hollow structure, then two filling materials are considered: a cast viscoelastic material and a granular material composed of epoxy and polyurethane beads. Modal parameters (natural frequencies, modal damping and mode shapes) are extracted from the Frequency Response Functions with experimental modal analysis tools. Damping ratios greater than 5~\% are measured. Given the difference in the nature of the filling materials, dissipation mechanisms are different. The effectiveness of a damping material depends on the type of structural modes (bending, torsion or wall mode) to be damped, and dissipation in filling materials cannot be modelled by a constant loss factor or viscous damping. Consequently, a finite element modeling of the structure filled with viscoelastic material is proposed. Numerical modal parameters of the structure are correlated with experimental measurements. By extension, a bead mix material law, based on a fractional Zener model, is proposed, whose parameters are obtained by inverse identification.

Estimation of viscoelastic properties in ribbon-shaped homogeneous waveguides by wavenumber analysis and model reduction

Wavenumber based procedures applied to 1D waveguides provide a rigorous framework with an exact signal model that allows for a proper identification of both storage and loss properties independently from the boundary conditions. However, the associated inverse problem is either computationally intense if using a reference solution (e.g. SAFE) or limited to a specific frequency range that depends on the reduced beam model. We propose here to apply the wavenumber-based estimation of isotropic viscoelastic properties to ribbon-shaped homogeneous waveguides, characterized by a rectangular section with slender height-to-width aspect ratio. We show theoretically that considering the ribbon as a thick plate by assuming a model reduction in the height dimension, drastically reduces the wave propagation problem (hence its inverse counterpart) while providing a sufficiently good approximation on the low height-to-wavelength regime. In addition, full-field measurements are performed on an Aluminium and a PVC homogeneous ribbon-shaped waveguide. The experimental dispersive branches (bending and torsion modes) are identified on an ultra-wide frequency range (1 kHz - 1 MHz) using High Resolution Wave Analysis. For both materials, an excellent agreement is observed with the thick plate reduced model, paving the way for wide-band viscoelastic properties identification of ribbon-shaped waveguide.

Prototyping of vibration-sensing-actuation device which is contained high-power electrodynamic speaker for diagnosis of actual water main network

Water leakage and bursting due to deterioration of water distribution mains lead to water outages and economic losses. To prevent the accidents, we are conducting research to develop measurements and diagnostic methods for buried water mains. In this study, we focused on the shift in eigenfrequencies of in-plane bending vibration of rings because of deterioration. Therefore, we are developing the vibration-sensing-actuation device which detects the frequency changes of in-plane bending mode. The water distribution network is mainly composed from cast iron pipe. Moreover, the attached facilities for example fire hydrant and water valve are contained. Since attached facilities are fabricated from cast iron component, actual water main network is heavy facilities which have high rigidity. In order to excite the desired in-plane bending mode in heavy components, the proposed sensing-actuation device requires the high-power actuator. In this study, we introduce the high-power electromagnetic actuator more than 100W output into the proposed device. Furthermore, the fundamental operational tests were conducted under the various input signals in the laboratory situations. In addition, the field operation confirmation was performed in an actual water main network.

Reduction of vortex-induced vibrations of a cantilevered hydrofoil with passive piezoelectric shunt

This work first investigates the ability of a low order fluid-structure model to fit the vortex-induced vibrations (VIV) observed on a truncated hydrofoil in a hydrodynamic tunnel. A particular VIV area is scrutinized, for which a hydrodynamic excitation mechanism due to a Karman-type vortex wake organization successively locks the first torsional and second bending mode of the cantilevered hydrofoil. Coupling two structure oscillators with a Van der Pol wake oscillator satisfactorily reproduces the amplitude response and the lock-in frequency. In order to build a low order model allowing to optimize control strategy, a fourth degree of freedom corresponding to the electric circuit of a resonant piezoelectric shunt has been added. Composed of an inductance and a resistance connected to a piezoelectric patch, the passive shunt was tuned to minimize the vibration amplitude in the frequency lock-in range. Model predictions are finally compared with experimental results.

Toolpath and Tool Design Innovations in Deformation Machining for Superior AA-7075 T6 Fins

Abstract A hybrid manufacturing process, deformation machining (DM) combines subtractive manufacturing with incremental forming. Monolithic components with complex profiles are created through the hybridization of manufacturing technologies, which also reduces the wastage of raw materials. The properties of geometry and surface quality of the fin made from the aluminum alloy Al-7075 T6 using the DM process’s bending mode was examined in this research, as were the effects of various approaches, toolpath methods, and tool design. To achieve the desired shape for the machined fin, various combinations of arcuate and slanting fin toolpath techniques were explored utilizing both top-down and bottom-up methods. The bottom-up method and the arcuate toolpath strategy were used to investigate various tool profiles. Using the best combination of toolpath strategy and tool profile, named as the T3 tool profile, which has a 0.6 mm nose radius and a circular sector, bottom-to-top (BTT)technique, and arcuate toolpath method, components with better geometrical features and surface roughness (SR) were produced. The analysis of the forming force in the bending approach of the DM progression was further carried out using this optimal combination.