Non-reciprocal transmission of motion is potentially highly beneficial to a wide range of applications, ranging from wave guiding to shock and vibration damping and energy harvesting. To date, large ...levels of non-reciprocity have been realized using broken spatial or temporal symmetries, yet mostly in the vicinity of resonances, bandgaps or using nonlinearities, thereby non-reciprocal transmission remains limited to narrow ranges of frequencies or input magnitudes and sensitive to attenuation. Here, we create a robotic mechanical metamaterials wherein we use local control loops to break reciprocity at the level of the interactions between the unit cells. We show theoretically and experimentally that first-of-their-kind spatially asymmetric standing waves at all frequencies and unidirectionally amplified propagating waves emerge. These findings realize the mechanical analogue of the non-Hermitian skin effect. They significantly advance the field of active metamaterials for non hermitian physics and open avenues to channel mechanical energy in unprecedented ways.
Enhancing the mechanical properties of vibration-damping elastomers with dynamic bonds is crucial for practical applications. Herein, we synthesize recyclable damping elastomers with superior ...mechanical strength through the incorporation of triple dynamic bonds. Firstly, linear polymers with carboxyl and imidazole groups are fabricated by random copolymerization, which consist of dual dynamic bonds (hydrogen bonds and ionic bonds). Then, 1,4-phenylenediboronic acid is introduced by solution blending and can form boron/nitrogen coordination bonds with imidazole groups, thereby converting dual dynamic bonds into triple dynamic bonds. Therefore, the resulting elastomer exhibits remarkable tensile strength of 16.29 MPa, toughness of 73.53 MJ/m3, and damping properties (maintaining tan δ > 0.3 over a temperature range of 75 °C). Furthermore, owning to the triple dynamic bonds, the elastomer retains exceptional mechanical and vibration-damping properties even after three times of recycling. This work provides a simple strategy to fabricate recyclable elastomers with high mechanical performance and vibration-damping property, which have promising and sustainable potential for practical damping applications.
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•A simple method is proposed to develop dynamic-bonds-based vibration-damping elastomers with high mechanical performance.•The mechanical properties of the elastomers are greatly improved via the triple dynamic bonds.•Triple dynamic bonds also endow elastomers with excellent energy dissipation ability, damping properties and recyclability.•The elastomers reach high strength (16.29 MPa), toughness (73.53 MJ/m3) and wide effective damping temperature range (75 °C).
The theoretical study and experimental validation of a nonlinear shunt circuit for piezoelectric vibration damping is investigated here. The circuit consists of a resistor, an inductor and a ...nonlinear cubic voltage source. The shunt acts as an electrical analog to the mechanical nonlinear energy sinks (NESs). These mechanical NESs are passive vibration absorbers that typically have a cubic nonlinear stiffness. They have attractive properties such as saturation of the host system’s vibration amplitude and strongly modulated response. This increases its operational frequency bandwidth and robustness against variations in the properties of host systems compared to linear vibration absorbers. However, the nonlinear nature may induce isolated responses in the host system that induce high vibration amplitudes. This paper investigates if these attractive properties also occur in the electric nonlinear energy sink shunt. An analytical expression for the frequency response is derived through the complexification-averaging method. Bifurcations in the frequency response reveal the occurrence of a quasi-periodic vibration energy exchange between the host system and the voltage over the electrodes of piezoelectric material. This is the main mechanism behind the amplitude saturation of the host system. Other bifurcations also reveal the existence of isolated responses. The nonlinear shunt is then realized with analog multipliers and a synthetic inductor and its performance in vibration damping is experimentally verified for a cantilever beam.
Cork products have an increasing demand for vibration damping systems due to their good vibration isolation behavior as well as eco-friendly and sustainable properties. In this work, an improvement ...was proposed in the vibration attenuation behavior of multi-layer cork structures by means of two smart materials; shear thickening fluid (STF) and shear stiffening polymer (SSP). The number of layers was varied in the multi-layer cork structures while ensuring a constant thickness for the resultant composites and the smart materials were applied as film layers at the cork layer interfaces. The composites were tested in hammer-based vibration tests and the structural constants of natural frequency and damping ratio were found after modal analyses. In addition to the vibration properties, the thickening/stiffening behavior of the smart materials was also studied in rheological measurements. According to the results, the STF shows a sudden viscosity jump under increasing shear rate while the SSP changes its behavior from viscous to elastic at high rate stimulations. Due to these rheological responses, the smart materials enhance the vibration attenuation performance of the cork layers. Consequently, it is possible to state that the integration of smart materials into cork structures has a promising future to develop eco-friendly and sustainable products as well as improving adaptive properties of passive control systems in vibration damping applications.
•A graded metamaterial beam is proposed for realizing broadband vibration suppression.•The spectral element method (SEM) is used to model the graded metamaterial beam.•Several figures of merit are ...developed for a quantitative analysis.•Criteria towards the tuning of the frequency spacing between local resonators are derived.•A practical implementation of the proposed graded metamaterial beam is demonstrated.
This paper investigates a technique for broadband vibration suppression using a graded metamaterial beam. A series of local resonators with the same mass but different natural frequencies are attached to the beam. The difference between the natural frequencies of neighboring local resonators is defined as the frequency spacing. The spectral element method (SEM) is used to model the graded metamaterial beam, and is verified by the corresponding finite element model (FEM). Three figures of merit are defined to quantitatively evaluate the vibration suppression performance of the proposed metamaterial beam, in terms of the attenuation bandwidth and attenuation strength. Subsequently, a design strategy is proposed, and used to tune the frequency spacing to get a wide attenuation region. A parametric study is conducted to reveal the effects of the frequency spacing and damping ratio on the vibration suppression performance of the graded metamaterial beam: with increasing frequency spacing, the attenuation region first becomes wider, then multiple discrete attenuation regions appear; and with increasing damping ratio, the transmittance response becomes flatter. A piezoelectric metamaterial beam is used to implement the proposed design strategy. Using a synthetic shunt circuit, the ‘stiffness’ of the local resonator can be tuned using a piezoelectric transducer. The FEM simulation results agree well with the developed theory for the graded metamaterial beam: with tuning of the capacitance spacing (2.4 nF), the attenuation bandwidth can be increased by about 172.8% as compared to the conventional one shunted with identical capacitances.
Marine lifting surfaces may undergo flow-induced vibrations due to fluid sources of excitation, leading to shorter life cycles due to structural fatigue and critical to the acoustic performances (e.g ...hydrofoil singing). As such, accurate understanding of the fluid-structure response of marine structures, as well as vibration control and damping, are critical to many maritime applications. In particular, this work investigates the potential of the electromechanical coupling inherent to piezoelectric materials for passive vibration damping of a cantilever blunt flat plate under hydrodynamic flows. A prototype equipped with piezoelectric ceramics connected to an inductor, in order to act as a resonant piezoelectric shunt, is specifically designed for this study. Its flow-induced vibrations are first assessed within the water tunnel of IRENav to identify the natural frequency of interest to control. It shows that the plate is subjected to von Kármán vortex-shedding with two configurations, namely lock-off for the first-bending mode, and lock-in with the first torsional mode. The latter results in the most extreme vibration cases but is also the most difficult to control. Therefore, the first-bending mode is selected for this first experimental assessment. Second, semi-passive control strategies, using the resonant piezoelectric shunt, have been tested on the targeted natural frequency both in air and in still water. Subsequent comparisons show similar coupling factors, meaning that the performances of the resonant shunt should also be similar in air and in still water. Moreover, a numerical model, based on fluid-structure-piezoelectricity coupling, is also set-up to compute the coupling factors. Hence, a valuable numerical tool is provided for future designs of more complex geometries. Finally, experimental vibration mitigation is achieved both for still water and under hydrodynamic flows, experimentally proving the feasibility and relevance of this control solution for maritime applications.
This research explored frictional energy dissipation aspects of electrical discharge machined (EDM) surfaces in the context of passive vibration damping. The effect of discharge current and duration ...was investigated to characterise the damping capability of these surfaces, and to understand the underlying mechanisms. Topographic analyses indicated the damping ratio to be maximised through an interaction between positive skewness and elevated kurtosis of surface height, which facilitates recurrent microslip and plastic deformation at asperity contact edges. This renders EDM textures to be uniquely disposed to vibration control, as demonstrated by their efficacy in enhancing the dynamic performance of a grooving tool.
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•Spark eroded surfaces are uniquely disposed to passive vibration damping.•This is facilitated by the positive skewness and elevated kurtosis of EDM surfaces.•Energy is dissipated by microslip and plastic deformation at asperity contacts.
In recent years, shape memory alloy (SMA) thin films have attracted significant attention from the scientific community and industry for their potential applications in the field of smart sensors and ...actuators, micro- and nano-electromechanical systems, aerospace, automobile, and biomedical. The present article focuses on the recent developments in the field of SMA thin films and their heterostructures with other materials for potential microelectromechanical systems (MEMS) applications. Various microdevices such as microgrippers, micropumps, microvalves, and cantilevers fabricated from binary and ternary SMA films have been discussed in detail. SMA thin films combined with various nitrides, oxides, and ferroelectric layers offer excellent surface modification and vibration damping at microscale for their use in harsh environments. The article encompasses the new paradigms in the field of SMA thin films that have been essentially developed by the authors and co-workers during the past 6 years.
Vibration attenuation and control is a typical topic in mechanical, civil and aeronautical engineering. In recent years, there has been extensive research on smart materials and among all of them, ...the piezoelectrics seem to be the most attractive for passive and active vibration damping applications. Furthermore if multiple modes are concurrently excited, as in case of turbomachinery blades, active damping systems may remarkably increase their life-cycle and outweigh the shortcomings of implementing such systems. However the damping efficiency of the piezoelectric actuators is strictly bound to their driving voltage, size and location on the structure.
In this work, a cantilever piezoelectric bimorph beam under base motion is considered and the analytical expression of the electric potential that nullifies the elastic tip displacement of the beam is derived in case of single and bi-modal excitations.
The model allows to identify for every bi-modal excitations a set of solutions, each of them represented by three parameters: voltage amplitude, left and right corner positions of the piezoelectric actuators pair. As a result, designers can choose the best solution for their specific application demands. For example, if the supply voltage must to be kept as low as possible, then wider actuators should be used and vice versa. It was also found out that the control parameters do not depend on the spectral distribution between the two excited modes. Hence, even if the spectral distribution between the two coupled modes changes over time, it is not necessary to adjust either the voltage or the position of the actuator pair.
The analytical predictions were compared with the results of FEM multi-physics simulations for several base motion excitations and a fair agreement was observed.
•A toe-like structure (TLS) is proposed for low-frequency vibration isolation.•The structure is obtained by imitating toe with nonlinear stiffness and damping.•Adjustable low resonant frequency and ...beneficial damping effect can be obtained.•It provides a feasible way for passive vibration isolation in low frequency band.
Inspired by the cushioning effect of the felid paws in contact with the ground, a novel bio-inspired toe-like structure (TLS) is developed and systematically studied for low-frequency vibration isolation. The TLS consists of two rods with different length (as phalanxes) and a linear spring (as muscle). Based on Hamiltonian principle, the dynamic model is established considering spring deformation and joint rotation damping. The derived equivalent stiffness reveals that the proposed TLS possesses favorable high static and low dynamic stiffness (HSLDS) characteristics in a wide displacement range. Besides, displacement transmissibility suggests that the proposed TLS isolator has low resonance frequency and can effectively isolate base excitation at low frequencies. Comprehensive parameter analysis shows that the inherent nonlinearities in stiffness and damping is conductive to vibration isolation and can be designed/adjusted on demand by selecting suitable structural parameters. This flexibility gives TLS advantages and great potential in extensive engineering applications when subjected to variable vibration loads. A prototype is fabricated and tested for a comprehensive recognize of its advantageous vibration isolation performance in low frequency band. The vibration with excitation frequency higher than 3 Hz can be effectively isolated. This novel bio-inspired TLS provides a feasible approach to passive vibration control and isolation in low frequency band.
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