Elastic Structures Research Articles

A Cost-Effective and Easy-to-Fabricate Conductive Velcro Dry Electrode for Durable and High-Performance Biopotential Acquisition.

Compared with the traditional gel electrode, the dry electrode is being taken more seriously in bioelectrical recording because of its easy preparation, long-lasting ability, and reusability. However, the commonly used dry AgCl electrodes and silver cloth electrodes are generally hard to record through hair due to their flat contact surface. Claw electrodes can contact skin through hair on the head and body, but the internal claw structure is relatively hard and causes discomfort after being worn for a few hours. Here, we report a conductive Velcro electrode (CVE) with an elastic hook hair structure, which can collect biopotential through body hair. The elastic hooks greatly reduce discomfort after long-time wearing and can even be worn all day. The CVE electrode is fabricated by one-step immersion in conductive silver paste based on the cost-effective commercial Velcro, forming a uniform and durable conductive coating on a cluster of hook microstructures. The electrode shows excellent properties, including low impedance (15.88 kΩ @ 10 Hz), high signal-to-noise ratio (16.0 dB), strong water resistance, and mechanical resistance. After washing in laundry detergent, the impedance of CVE is still 16% lower than the commercial AgCl electrodes. To verify the mechanical strength and recovery capability, we conducted cyclic compression experiments. The results show that the displacement change of the electrode hook hair after 50 compression cycles was still less than 1%. This electrode provides a universal acquisition scheme, including effective acquisition of different parts of the body with or without hair. Finally, the gesture recognition from electromyography (EMG) by the CVE electrode was applied with accuracy above 90%. The CVE proposed in this study has great potential and promise in various human-machine interface (HMI) applications that employ surface biopotential signals on the body or head with hair.

Mechanism design and mechanical analysis of pipeline inspection robot

Purpose This study aims to address the issues of limited pipe diameter adaptability and low inspection efficiency of current pipeline inspection robots, a new type of pipeline inspection robot capable of adapting to various pipe diameters was designed. Design/methodology/approach The diameter-changing mechanism uses a multilink elastic telescopic structure consisting of telescopic rods, connecting rods and wheel frames, driven by a single motor with a helical drive scheme. A geometric model of the position relationships of the hinge points was established based on the two extreme positions of the diameter-changing mechanism. Findings A pipeline inspection robot was designed using a simple linkage agency, which significantly reduced the weight of the robot and enhanced its adaptive pipe diameter ability. The analysis determined that the robot could accommodate pipe diameters ranging from 332 mm to 438 mm. A static equilibrium equation was established for the robot in the hovering state, and the minimum pressing force of the wheels against the pipe wall was determined to be 36.68 N. After experimental testing, the robots could successfully pass a height of 15 mm, demonstrating the good obstacle capacity of the robot. Practical implications This paper explores and proposes a new type of multilink elastic telescopic variable diameter pipeline inspection robot, which has the characteristics of strong adaptability and flexible operation, which makes it more competitive in the field of pipeline inspection robots and has great potential market value. Originality/value The robot is characterized by the innovative design of a multilink elastic telescopic structure and the use of a single motor to drive the wheel for spiral motion. On the basis of reducing the weight of the robot, it has good pipeline adaptability, climbing ability and obstacle-crossing ability.

Dynamical mixed boundary-transmission problems of the generalized thermo-electro-magneto-elasticity theory for composed structures

Abstract In the present paper we investigate three-dimensional dynamical mixed boundary-transmission problems for composed body consisting of two adjacent anisotropic elastic components having a common interface surface. The two contacting elastic components are subject to different mathematical models: Green–Lindsay’s model of generalized thermo-electro-magneto-elasticity in one component and Green–Lindsay’s model of generalized thermo-elasticity in the other one. We assume that the composed elastic structure under consideration contains an interfacial crack. We prove the uniqueness and existence theorems in appropriate function spaces.

Finite element analysis for the Navier-Lamé eigenvalue problem

The present paper introduces the analysis of the eigenvalue problem for the elasticity equations when the so-called Navier-Lamé system is considered. This system incorporates the displacement, rotation, and pressure of a linear elastic structure. The analysis of the spectral problem is based on the compact operator theory. A finite element method using polynomials of degree k≥1 is employed to approximate the eigenfrequencies and eigenfunctions of the system. Convergence and error estimates are presented. An a posteriori error analysis is also performed, where the reliability and efficiency of the proposed estimator are proven. We conclude this contribution by reporting a series of numerical tests to assess the performance of the proposed numerical method for both a priori and a posteriori estimates.

Thermal vapor sulfurization of Ti3C2TX MXene to TiS2/carbon nanosheet cathode for long-life and high-loading all-solid-state lithium batteries

Stable and fast operation of all-solid-state lithium batteries (ASSBs) depends on durable and sufficient interfacial contacts between electrode components, especially when the loading and content of electrode active materials are high. Here, we propose promoting ionic/electronic transportations and contacts in sulfide electrolyte-based ASSBs by using TiS2/carbon nanosheets (TiS2/C-s) with large area-to-thickness aspect ratios as the cathode, which are prepared by simple thermal vapor sulfurization of exfoliated Ti3C2Tx MXene. The elastic 2D structure of the TiS2/C-s material can substantially improve interfacial contact with the solid electrolyte, minimize the diffusion distance of lithium ions, and buffer volume/stress changes during cycling, thereby ensuring the electro-chemo-mechanical stability and fast reaction kinetics of electrodes. Consequently, a 50 wt% TiS2/C-s cathode without any conductive carbon additives demonstrates a high discharge capacity (295 mAh g−1), long-term cyclic stability (94.7 and 74.7 % capacity retention after 250 cycles at 0.1 mA cm−2 and after 2300 cycles at 1 mA cm−2, respectively), and decent rate capability (126.0 mAh g−1 at 3 mA cm−2). Moreover, stable cycling with a high areal capacity (5.95 mAh cm−2) can also be achieved.

Natural Vibrations and Stability of Composite Cylindrical Shells Containing a Quiescent Fluid

This paper presents the results of investigation of the natural vibrations and stability of circular vertical multilayered cylindrical shells, fully or partially filled with a quiescent compressible fluid subjected to hydrostatic and external static loads. The behavior of the elastic structure and fluid medium is described based on the classical shell theory and Euler’s equations. The linearized equations of motion of the shell, together with the corresponding geometrical and physical relations are reduced to a system of ordinary differential equations with respect to new unknowns. The acoustic wave equation is transformed to a system of differential equations using the method of generalized differential quadrature. The solution of the formulated boundary value problem is developed using Godunov’s orthogonal sweep method. The dependences of the lowest vibration frequencies and critical external pressure on the ply angle and the filling level of two-layer and three-layer cylindrical shells are analyzed in detail. It is demonstrated that, in contrast to the ply angle and a given combination of boundary conditions, the lay-up scheme of composite materials plays different parts in the problems of maximizing the fundamental frequency of vibrations and extending the stability boundaries.

Characterization of caseinate-pectin complex coacervates as a carrier for delivery and controlled-release of saffron extract

In this work, microcapsules were developed by the complex coacervation of sodium caseinate and pectin as a carrier for saffron extract. Parameters such as Zeta potential, dynamic light scattering, and microscopic techniques were investigated for their influence on the formation of these complexes. Furthermore, Fourier transform infrared (FTIR) analysis confirmed the reaction mechanism between the protein and tannic acid or saffron extract. The study revealed that core/shell and protein/polysaccharide (Pr/Ps) ratios play a role in the encapsulation efficiency (EE) and loading capacity (LC) of saffron extract, with EE and LC ranging from 48.36 to 89.38% and 1.14 to 5.55%, respectively. Thermal gravimetric analysis revealed that the degradation temperature of saffron increased significantly with microencapsulation. The use of tannic acid for hardening the microcapsules led to an increase in size from 13 μm to 27 μm. Rheological findings indicated that shear-thinning behavior in the coacervates, with cross-linking, has a minor effect on the interconnected elastic gel structures. However, cross-linking improved the microcapsules' thermal and structural properties. The increase in polymer chain length due to cross-linking and the presence of the guest molecule (saffron extract) resulted in higher rheological moduli, reflecting enhanced entanglements and correlating well with the thermal, structural, and microstructural properties of the coacervates. Kinetic release studies showed a slower release in the gastric phase compared to the intestinal phase, with the Ritger–Peppas model effectively describing saffron extract release, highlighting a dominant swelling and dissolution release mechanism. Therefore, the NaCas/HMP coacervate wall materials made saffron stable in the gastric stage and sustainably release. It in the intestinal stage, promoting excellent absorption of saffron in simulated digestion.Graphical

Tailoring pea proteins gelling properties by high-pressure homogenization for the formulation of a model spreadable plant-based product

This study investigated the impact of high-pressure homogenization (HPH) at varying intensities on the gelling properties of a commercial pea protein concentrate for the formulation of emulsion-filled gels as a model spreadable plant-based product. As a preliminary characterization, pea protein dispersions (10%-15%–20% w/w) underwent HPH treatments, 60 and 150 MPa for 5 cycles. Mechanical characteristics of heat-set gels were evaluated through rheological measurements. Emulsion-filled gels were then produced, starting from a common primary emulsion, incorporating either native or treated pea protein suspensions, and characterized with frequency and amplitude sweep tests, back extrusion, texture profile analysis (TPA) and confocal laser scanning microscopy (CLSM). Results revealed that HPH treatments had a significant influence on the aggregation state of protein suspensions reducing residue size, but inducing the formation of new, albeit smaller, agglomerates, with a direct impact on gel network formation. Treatment at 150 MPa consistently produced a stiffer, compact, and elastic gel structure, as confirmed by frequency sweep, back extrusion and TPA tests. Additionally, when this structure was disrupted, it exhibited creamy-viscous characteristics, as verified by amplitude sweep analyses. CLSM micrographs showed the formation of a more structured and compact gel matrix with the increase of the pressure applied.

Elasticity Mapping of Colloidal Glasses Reveals the Interplay between Mesoscopic Order and Granular Mechanics.

Colloidal glasses (CGs) made of polymer (polymethylmethacrylate) nanoparticles are promising metamaterials for light and sound manipulation, but fabrication imperfections and fragility can limit their functionality and applications. Here, the vibrational mechanical modes of nanoparticles are probed to evaluate the nanomechanical and morphological properties of various CGs architectures. Utilizing the scanning micro-Brillouin light scattering (µ-BLS), the effective elastic constants and nanoparticles' sizes is determined as a function of position in a remote and non-destructive manner. This method is applied to CG mesostructures with different spatial distributions of their particle size and degree of order. These include CGs with single-sized systems, binary mixtures, bilayer structures, continuous gradient structures, and gradient mixtures. The microenvironments govern the local mechanical properties and highlight how the granular mesostructure can be used to develop durable functional polymer colloids. A size effect is revealed on the effective elastic constant, with the smallest particles and ordered assemblies forming robust structures, and classify the various types of mesoscale order in terms of their mechanical stiffness. The work establishes scanning µ-BLS as a tool for mapping elasticity, particle size, and local structure in complex nanostructures.

Rayleigh-type wave in non-planar pre-stressed nearly incompressible elastic structure

The primary objective of the current work is to establish the impacts of planar boundary and non-planar boundary on the displacement components (DCs) of Rayleigh-type wave propagation in an elastic structure. The elastic structure, precisely, incorporates a pre-stressed nearly incompressible elastic material in the half-space along with the non-planar boundary at the free surface. The methodology applied features variable separable technique and Taylor’s series expansion along with substitution method to establish the expressions for DCs and frequency relation. The frequency relation of Rayleigh-type wave is obtained for the situation considering planar free surface, which is further reduced as a special case of the study and validated with the classical result present in the literature. The DCs of Rayleigh-type wave have been numerically computed, and their reliance on wave number have been exhibited graphically. In addition to this, the influences of affecting parameters viz., hydrostatic stress, principal Cauchy stress and curvature parameter on DCs have been traced out. The computational result also manifests the domain of existence of Rayleigh-type wave propagating in the considered model in the presence of planar free surface.

Caffeine weakens the astringency of epigallocatechin gallate by inhibiting its interaction with salivary proteins

The astringency of green tea is an integrated result of the synergic and antagonistic effects of individual tea components, whose mechanism is highly complex and not completely understood. Herein, we used an epigallocatechin gallate (EGCG)/caffeine (CAF)/saliva model to simulate the oral conditions during tea drinking. The effect of CAF on the interaction between EGCG and salivary proteins was first investigated using molecular docking and isothermal titration calorimetry (ITC). Then, the rheological properties and the micro-network structure of saliva were studied to relate the molecular interactions and perceived astringency. The results revealed that CAF partially occupied the binding sites of EGCG to salivary proteins, inhibiting their interaction and causing changes in the elastic network structure of the salivary film, thereby reducing astringency.

[formula omitted]adaptive resonance ratio control for series elastic actuator with guaranteed transient performance

Series elastic actuator (SEA) technology is promising for the development of compliant robotic joints. Despite advancements in the realization of precise tracking, challenges persist in controlling the vibration and transient performance. This study enhanced the resonance ratio control (RRC) algorithm by integrating it with the L1 adaptive control (L1AC) method to address overshoot, static error, and vibration in SEA position control. Initially, the resonance between the motor and link sides caused by the elastic transmission structure was analyzed, which can result in overshoots and vibrations that affect the transient performance of the SEA control. Subsequently, a control scheme based on L1AC was introduced to enhance the performance. The stability of the proposed algorithm was demonstrated through a comprehensive exploration of key control parameters. Furthermore, the algorithm was augmented with gravity compensation, effectively reducing the predicted and reference errors. Consequently, the transient performance was improved. The efficacy of this enhanced algorithm was validated through simulations and experimental platforms, and comparisons with the RRC and model reference adaptive control algorithms. In all the experiments, the overshoot did not exceed 1.1%, the maximum jitter amplitude on the link side was within 0.2° , and a larger time constant in the controller could effectively eliminate the overshoot and vibration with a small response time delay. Furthermore, the algorithm exhibited a protective response during link side collisions by moderating link velocity and limiting motor current, to safeguard the contact environment, humans, and the SEA itself, which take advantage of the L1AC’s low-pass filter (LPF) properties in disturbance handling.

A mechanical analogue of electromagnetic induction for waves in a chiral elastic structure

Classical Faraday’s law on electromagnetic induction states that a change of magnetic field through a coil wire induces a current in the wire. A mechanical analogue of the Lorentz force, induced by a magnetic field on an electric charge, is the gyroscopic force. Here, we demonstrate a mechanical analogy with a chiral elastic waveguide subjected to gyroscopic forcing. We study waves in an infinite mass-spring ‘gyrocore helix’, which consists of a helix and a central line (gyroscopic elastic core). The helicoidal geometric chirality is considered in conjunction with a physical chirality, induced by gyroscopic forces. It is shown that the interplay between these two chiral inputs leads to the breaking of symmetry of the associated dispersion diagram, resulting in a unidirectional waveform with the direction of propagation being tunable through the gyricity.

Modelling and analysis of imperfect and sliding interfaces on Love-type wave in non-planar non-homogeneous nearly incompressible elastic layered structure

Modelling and analysis of imperfect and sliding interfaces on Love-type wave in non-planar non-homogeneous nearly incompressible elastic layered structure

Observations from the seafloor: ultra-low-frequency ambient ocean-bottom nodal seismology at the Amendment field

SUMMARY Large-scale ocean-bottom node (OBN) arrays of 1000s of multicomponent instruments deployed over 1000s of square kilometres have been used successfully for active-source seismic exploration activities including full waveform inversion (FWI) at exploration frequencies above about 2.0 Hz. The analysis of concurrently recorded lower-frequency ambient wavefield data, though, is only just beginning. A key long-term objective of such ambient wavefield analyses is to exploit the sensitivity of sub-2.0 Hz energy to build long-wavelength initial elastic models, thus facilitating FWI applications. However, doing so requires a more detailed understanding of ambient wavefield information recorded on the seafloor, the types, frequency structure and effective source distribution of recorded surface-wave modes, the near-seafloor elastic model structure, and the sensitivity of recorded wave modes to subsurface model structure. To this end, we present a wavefield analysis of low- and ultra-low-frequency ambient data (defined as <1.0 and <0.1 Hz, respectively) acquired on 2712 OBN stations in the Amendment Phase 1 survey covering 2750 km2 of the Gulf of Mexico. After applying ambient data conditioning prior to cross-correlation and seismic cross-coherence interferometry workflows, we demonstrate that the resulting virtual shot gather (VSG) volumes contain evidence for surface-wave and guided P-wave mode propagation between the 0.01 and 1.0 Hz that remains coherent to distances of at least 80 km. Evidence for surface-wave scattering from near-surface salt-body structure between 0.35 and 0.85 Hz is also present in a wide spatial distribution of VSG data. Finally, the interferometric VSG volumes clearly show waveform repetition at 20 s intervals in sub-0.3 Hz surface-wave arrivals, a periodicity consistent with the mean active-source shot interval. This suggests that the dominant contribution of surface-wave energy acquired in this VSG frequency band is likely predominantly related to air-gun excitation rather than by naturally occurring energy sources. Overall, these observations may have important consequences for the early stages of initial model building for elastic FWI analysis.

Smart-Adhesive, Breathable and Waterproof Fibrous Electronic Skins.

For the need of direct contact with the skin, electronic skins (E-skins)should not only fulfill electric functions, but also ensure comfort during wearing, including permeability, waterproofness, and easy removal. Herein, the study has developed a self-adhesive, detach-on-demand, breathable, and waterproof E-skin (PDSC) for motion sensing and wearable comfort by electrospinning styrene-isoprene block copolymer rubber with carbon black nanosheets as the sensing layer and liner copolymers of N, N-dimethylacrylamide, n-octadecyl acrylate and lauryl methacrylate as the adhesive layer. The high elasticity and microfiber network structure endow the PDSC with good sensitivity and high linearity for strain sensing. The hydrophobic and crystallizable adhesive layer ensures robust, waterproof, and detaching-on-demand skin adhesion. Meanwhile, the fiber structure enables the PDSC good air and water permeability. The integration of electric and wearable functions endows the PDSC with great potential for motion sensing during human activities as both the sensing and wearable performances.

Effect of curdlan on the gel properties and interactions of whey protein isolate gels

This study investigated the influence of curdlan on the gel properties of whey protein isolate (WPI). Results demonstrated that curdlan significantly improved the water-holding capacity, gel strength and rheological properties of the WPI gels. Moreover, it promoted the unfolding of the molecular structures of WPI, which was manifested by the transition from α-helix to β-sheet, an increase in free sulfhydryl content and a decrease in surface hydrophobicity. Furthermore, 4 % curdlan promoted the formation of WPI with uniform and compact elastic gel network structures, primarily attributed to disulphide bonds, hydrogen bonds and hydrophobic interactions. However, when the addition of curdlan exceeds 4 %, excessive entanglement of curdlan chains and steric hindrance effects hinder the unfolding and folding of protein structures, weaken their interaction, result in a loose network structure and affect the gel properties. In conclusion, this study demonstrates that curdlan can effectively improve the gelling properties of WPI, suggesting its potential application in low-calorie gel-based dairy products.

A Review on the Dynamic Performance Studies of Gas Foil Bearings

Gas foil bearings have important and wide applications in high-speed turbomachinery, generating low frictional lubricating gas film in series with underlying elastic foil structures to support the rotor system. Their dynamic performance is of vital significance in maintaining the rotor stability as well as in depressing rotor vibrations. This paper conducts a comprehensive review on dynamic performance studies conducted on gas foil bearings, including research on the dynamic stiffness and damping coefficients, bearing stability, nonlinear vibrations of the rotor–bearing system, and active methods for controlling rotor dynamic motions. This review provides clear observations towards the developments and iterations of the models, methods, and experiments of these studies.

Characterization of the Gluten Aggregation, Dough Rheological, and Physicochemical Properties of Flours Used in the Production of Flat Breads in Eskişehir

In this study, the physical, chemical, technological, gluten aggregation, and dough rheological properties of flat bread flours (“Bazlama", "Pide", "Gözleme", "Lavash") produced in Eskişehir were evaluated in detail by comparing them with “Bread” flour. The highest SRC lactic acid and GPI (gluten performance indeks) values (118.1% and 0.648, respectively) were found in "Gözleme" flour; however, "Lavash" and "Pide" flours had values close to “Bread” flour. The lowest SRC lactic acid and GPI values were obtained in "Bazlama" flour (84.13% and 0.531, respectively). The protein content of “Lavash” flour was close to bread flour (10.60%), while the protein content of "Pide" and "Gözleme" flours was higher (11.07% and 10.94%, respectively). The protein content of “Bazlama” flour was significantly lower than that of other flours (9.84%). Again, the sedimentation value of “Gözleme” flour was above that of other flours (65.0 ml). Lavash flour also had a high sedimentation value (60.0 ml). The sedimentation values of “Pide” and “Bread” flour were similar (approximately 53.0 ml) and lower. “Bazlama” flour gave a low sedimentation value (43.0 ml). Unlike bread flour, flat bread flours had a gluten indeks (GI) value higher than 90.0%. The ash content of flat bread flours varied between approximately 0.550 and 0.650%. “Bread” flour had the longest GlutoPeak peak maximum time (PMT) (102.0 s). “Bazlama” flour had the lowest torque 15 s before the maximum torque (BM), maximum torque (BEM), torque 15 s after the maximum torque (PM), energy, and water absorption (19,3 BU; 36,3 BU; 22,0 BU; %9,07; %18,57, 26,0 J ve %53,5, respectively). The BEM value of “Lavash”, “Gözleme” and “Pide” flours was higher than bread flour (around 45 BU). Of these three flours, “Pide” and “Lavash” flours maintained their high BEM after 15 s and gave a high PM (37.7 BU and 31.7 BU, respectively). “Bazlama” flour had the lowest PM value (22.0 BU). Particularly, “Gözleme” and “Pide” flours had high gluten-aggregation properties. Although the gluten and protein content values of “Lavash” flour were similar to those of “Bread” flour, its energy and water absorption values were higher (127.3 J and 58.0%). The difference between “Lavash” and “Pide” flours was a short PMT value (around 50 s). “Gözleme” flour had the highest stability (4.15 min.) and the lowest softening degree (49.5 FU) in the farinograph. Farinograph stability, development time, and softening degree values were also better in “Pide” flour (3.05 min., 2.85 min., and 85.0 BU, respectively). The farinograph qulaity number (FQN) values of these two flours were also high (65.5 and 50.0). “Bazlama” flour had low stability, FQN, and high softening degree. The “Bazlama” flour had the highest softening value (243.5 FU). Farinograph rheological properties of “Lavash” and control “Bread” flour were similar to each other. While the G' value of “Gözleme” and “Pide” flours, which were more stable in the farinograph, was found to be higher (27200 Pa and 24525 Pa), the G' value of “Lavash” flour was the lowest (around 12215 Pa). The G' values of “Bazlama” and “Bread” flour were similar (18050 Pa and 16590 Pa). The “Gözleme” and “Pide” flours with higher storage resistance (G') had higher G'' values (around 12000 Pa). “Lavash” flour had the lowest G'' value (6433.5 Pa). The lowest G'' values of “Bazlama” and “Bread” flour were found to be similar. “Gözleme” flour had the lowest Tanδ value (0.464). It is also low in “Pide” flour (0.491). The dough from these flours had an elastic structure. The “Lavash” and “Bazlama” flours had the highest Tanδ value (0.531 and 0.537). As a result, “Lavash” and “Bazlama” flours were found to have weaker and more extensible viscoelastic properties.

TOP2DFVT: An Efficient Matlab Implementation for Topology Optimization based on the Finite-Volume Theory

The finite-volume theory has shown to be numerically efficient and stable for topology optimization of continuum elastic structures. The significant features of this numerical technique are the local satisfaction of equilibrium equations and the employment of compatibility conditions along edges in a surface-averaged sense. These are essential properties to adequately mitigate some numerical instabilities in the gradient version of topology optimization algorithms, such as checkerboard, mesh dependence, and local minima issues. Several computational tools have been proposed for topology optimization employing analysis domains discretized with essential features for finite-element approaches. However, this is the first contribution to offer a platform to generate optimized topologies by employing a Matlab code based on the finite-volume theory for compliance minimization problems. The Top2DFVT provides a platform to perform 2D topology optimization of structures in Matlab, from domain initialization for structured meshes to data post-processing. This contribution represents a significant advancement over earlier publications on topology optimization based on the finite-volume theory, which needed more efficient computational tools. Moreover, the Top2DFVT algorithm incorporates SIMP and RAMP material interpolation schemes alongside sensitivity and density filtering techniques, culminating in a notably enhanced optimization tool. The application of this algorithm to various illustrative cases confirms its efficacy and underscores its potential for advancing the field of structural optimization.