Mechanical Damping Research Articles

Effect of nickel electroplating on the mechanical damping and storage modulus of metal matrix composites

The mechanical damping and the storage modulus of the nickel electroplated metal matrix composites have been studied using dynamic mechanical analyzer at different frequencies (0.1, 1 and 10 Hz) over a continuous heating temperature from room temperature to 150 °C. The rice husk ash (RHA) reinforced composites were fabricated using stir casting route. The nickel (Ni) plating was deposited on the base alloy and the MMC’s using electroplating technique. The nickel plating is characterized using SEM. The results showed that damping performance of the base alloy and their composites was significantly improved by nickel plating. Also, nickel plated composites demonstrate higher damping values than that of the unreinforced and Ni plated base alloy. The mechanical damping for all the samples is frequency dependent over the whole temperature range. The storage modulus found to decrease with increasing temperature. The related mechanisms are explained and presented.

Computational framework for simulating rock burst in shear and compression

This paper presents results from a series of numerical modeling tests conducted with the objective of developing a computational framework for studying rock burst events. A commercially available distinct element code with its explicit time-stepping scheme is adopted for modeling the initial quasi-static and the subsequent dynamic response of rock burst in compression and shear. Ground reaction curves are introduced to discuss criteria for stability of a failure through stress analyses. Energy balance equations are analyzed for assessing the rock burst intensity by estimating radiated seismic energy once conditions of instability emerge. Two methods are discussed for estimating radiated seismic energy: tracking of the energy conversion during failure; recording the kinetic energy that is damped by mechanical damping schemes. Modeling approach and methodologies for studying compressive-type rock burst are developed and calibrated against available analytical solutions with respect to radiated seismic energy and excavation convergence. Factors participating in the intensity of rock burst in compression are examined by modeling a rectangular tabular excavation supported by a single pillar with ductile, semi-brittle, and brittle failure responses under different compressive loading. A shear-type rock burst along a strike-slip fault model is simulated and modeling approach is calibrated by checking the resulting slip distribution, radiated seismic energy, and seismic moment against analytical solutions. Factors contributing to the occurrence and intensity of shear-type rock burst are explored by simulating different slip scenarios under different loading conditions. With presented analyses, this paper provides a computational framework calibrated for studying rock burst events and, as a reference for treatment of more complex cases, shows how Young's modulus of the rock, failure stress drop, rock brittleness, and slip-weakening behaviors of faults govern the rock burst occurrence and intensity.

Damping of Particle-Reinforced Composites Due to Interfacial Sliding

Mechanical damping of composites reinforced by randomly distributed particles due to interfacial sliding is analyzed. The matrix is elastically isotropic, and the particles are assumed rigid and of identical radii. An auxiliary problem is solved at first for the steady-state response of an infinite matrix containing a single inclusion to a harmonic external load. The result is then used to derive the explicit expression of the specific damping capability of the composite by using Mori–Tanaka’s mean-field method. Numerical results are given and discussed in detail. It is concluded that the overall damping of the composite depends on several factors, including volume fraction of particles, Poisson’s ratio of matrix and a dimensionless parameter that incorporates the combined effects of particle size, matrix stiffness, interfacial viscosity and vibration frequency. The result is expected to be helpful in tailoring the damping performance of particle-reinforced composites.

Phenomenon of non-outflow of a non-wetting liquid dispersed in nanoporous medium. The influence of modification and size of granules.

In this paper was studied the non-outflow phenomenon of a non-wetting liquid dispersed in nanoporous medium and the influence of porous medium surface modification and size of porous medium granules. The study of this phenomenon is important for development of mechanical energy dampers and for extraction of medicinal substances under certain conditions devices. The presented results for four commercial hydrophobized porous media Fluka 100 C18 (60756), Fluka 100 C18 (60758), Fluka 100 C8 (60755) and Fluka 100 C8 (60759) with the different thickness of the modifying layer and the size of the granules are show that the less of granules size and more narrow pore size distribution lead to decreasing of non-outflow phenomenon. The study of non-outflow phenomenon of non-wetting liquid from the pores of a nanoporous medium was carried out by time relaxation method and dispersed non-wetting liquid distribution recovery method at different temperatures.

Microstructure Evaluation of Ductile Cast Iron and Numerical Modal Analysis

This work is closely connected with the evaluation of the microstructure of the cast iron with the spherical shape of graphite. The given work is mainly focused on mechanical properties, chemical composition and microstructure, which are important to be known as an input parameters for computational modelling and numerical analysis. The external factors, influencing the measure of the mechanical damping, include the measure of the mechanical loading, loading frequency and temperature. These factors have the influence on the process of the mechanical energy distribution in materials. Eigenshapes as well as eifenfreguencies were investigated by modal analysis using finite element method (FEM).

Open-cell poly(vinylidene fluoride) foams with polar phase for enhanced airborne sound absorption

Open-cell foams of polyvinylidene fluoride (PVDF) homopolymer were fabricated with the content of polar phase being changed by thermal treatment, and their airborne acoustic absorption performance properties were measured comparably in an acoustic tube. The experimental results showed that the sample with the more polar phase and hence a stronger local piezoelectric effect exhibited a significantly larger acoustic absorption coefficient. In addition to the conventional visco-inertial, thermal and materials damping effects, our analysis indicated that the thin and polar struts of PVDF foams with the polar phase and the local piezoelectric effect may further enhance the mechanical damping by converting the excited mechanical vibration to electricity through the local piezoelectric effect and increasing the friction and viscous loss at the fluid-solid interface in the presence of electrical charges. The open-cell polymer foams with high content of the polar phase and the local piezoelectric effect have great potential for passive airborne noise mitigation applications.

Realization of an Energy-Efficient Adjustable Mechatronic Spring

Although semi-active variable mechanical dampers are well-known and highly developed concepts, creating an efficient variable stiffness has remained a challenge. In this paper, a brushless dc motor combined with a mechanical motion converter is utilized to synthesize the behavior of a mechanical spring. It is shown that synthesizing resistive and inductive elements in the motor shunt circuit can create damping and stiffness behaviors, respectively. The actuator shunt is digitally controlled by a bidirectional boost converter, which uses a sliding-mode algorithm. Using the proposed approach, the actuator can exhibit independent damping and stiffness effects in real-time. Analytic studies regarding the power requirements and criteria for controller convergence are presented and verified through experimental studies.

Compression response of Ni–Mn–Ga/silicone composite and study of three-dimensional deformation of particles

Ni–Mn–Ga particles/silicone composite was fabricated for a mechanical investigation. The characteristic twinning structure of particles and soft enough matrix provide the conditions enabling the possibility for particles to deform by the twin boundaries motion mechanism under applied stress and/or magnetic field. On the macroscopic scale, the large hysteretic loops in the stress–strain curves for composite evidence about its high energy absorption capability. On the microscopic scale, the in situ compression test was performed using an x-ray micro-computed tomography to study the individual deformation of particles. The strain behavior of individual particles in the three different configuration of groups was disclosed as a function of the compression degree of composite showing large reversible deformation of particles, signature of the twin structure rearrangement. The unusual drop of particles strains at very high compression degrees of composite is explained in terms of the non-uniform stress field in polymer produced by the neighbor particles interactions affected by barreling. The obtained results support the reason that the particles in composite should be arranged in single chains to avoid their interaction which is a way to improve the composite performance in the mechanical damping and magnetic actuator applications.

Anomalous Behavior During Nano‐Compression Superelastic Tests on Cu‐Al‐Ni Shape Memory Alloy Micro Pillars

Shape memory alloys are one of the most important families of functional materials due to superelasticity and shape memory properties. In particular Cu‐Al‐Ni alloys exhibit these properties at nanoscale, becoming potentially useful to design new smart MEMS. In this work, an anomalous behavior observed during nano‐compression superelastic tests on Cu‐Al‐Ni shape memory alloy micro pillars is reported. The study is approached by nano‐compression tests on micro and nano pillars milled by focused ion beam. The anomalous behavior on the superelastic effect is manifested by a sudden stabilization of the stress‐induced martensite, which does not undergo the reverse transformation. A transition, from superelastic to pseudoelastic‐twinning behavior, takes place during the nano‐compression tests, and is evaluated through the load‐depth curves and quantified by the mechanical damping coefficient η, which undergoes a sharp change from ultra‐high damping, η > 0.1, down to η ≈ 0.01. The stabilization of the martensite occurs under two different experimental conditions, along cycling and by applying a very high stress during superelastic tests. In both cases, a further recovery of the initial superelastic behavior is registered. The mechanisms responsible for the observed stabilization and recovery are discussed, together with the implications and further requirements for technological applications in MEMS.

Dynamic mechanical behavior of WC-Co coated A356.2 aluminum alloy

The effect of WC-Co coating on dynamic mechanical behavior, specifically storage modulus and mechanical damping of A356.2 aluminum alloy was studied. High velocity oxygen fuel (HVOF) is used as deposition technique and the optimum coating thickness was estimated with the aid of a numerical analysis. The experiments were carried using dynamic mechanical analyzer at 0.1, 1 and 10 Hz over an uninterrupted heating temperature from room temperature to 150 °C. It has been found that the damping behavior was significantly improved by depositing WC-Co on the alloy. The interface between the coating and the base alloy plays a vital role in enhancing the damping capacity, however the presence of W2C phase in the coatings due to the de-carburization of WC decreases the storage modulus of alloy.

Roll-to-Roll Processing of Silicon Carbide Nanoparticle-Deposited Carbon Fiber for Multifunctional Composites.

This work provides a proof of principle that a high volume, continuous throughput fiber coating process can be used to integrate semiconducting nanoparticles on carbon fiber surfaces to create multifunctional composites. By embedding silicon carbide nanoparticles in the fiber sizing, subsequent composite fabrication methods are used to create unidirectional fiber-reinforced composites with enhanced structural health monitoring (SHM) sensitivity and increased interlaminar strength. Additional investigations into the mechanical damping behavior of these functional composites reveal a significantly increased loss factor at the glass-transition temperature ranging from a 65 to 257% increase. Composites with both increased interlaminar strength and SHM sensitivity are produced from a variety of epoxy and silicon carbide nanoparticle concentrations. Overall, the best performing composite in terms of combined performance shows an increase of 47.5% in SHM sensitivity and 7.7% increase in interlaminar strength. This work demonstrates successful and efficient integration of nanoparticle synthesis into large-scale, structural applications.

Contactless four-terminal MEMS variable capacitor for capacitive adiabatic logic

This paper reports the design, energy recovery and logical functionality modeling of four-terminal microelectromechanical (MEMS) comb-drive devices for capacitive adiabatic logic (CAL). The proposed electromechanical element consists of the moving mass with two insulated electrodes and two fixed electrodes. The two pairs of fixed and moving electrodes form an input and an output comb-drive capacitive transducer. The voltage across the input port allows us to control the capacitance of the output port. The developed contactless four-terminal design is simulated in Coventor MEMS+ ® software. In order to speed up transient simulation of numerous devices in an electronic Simulation Program with Integrated Circuit Emphasis (SPICE) simulator, the obtained electrical and mechanical characteristics are used to fit our Verilog-A analytical compact model. SPICE simulation results demonstrate CAL logical functionalities using a cascadable power clock scheme, i.e. logic state differentiation and cascadability. We also show that MEMS-based calculation is energy efficient: for example, in a chain of four buffers, 99.1% of the energy transferred to the device is recovered for later use when devices operate at 25 Hz. The non-recoverable energy is mainly dissipated by mechanical damping during the logic state transition from high to low level and can be removed by using retractable power clocks. For this mm-scale device the energy dissipated per operation is of the order of 1 pJ. This is still far from the energy dissipated by a nm-scale field-effect transistor (FET), which is of the order of tens of attojoules. However, for the contactless design constant electric field scaling is possible and the energy dissipation decreases proportionally to the cube of the size. Finally, the limitations of irreversible MEMS-based CAL are discussed.

Increased power output of an electromagnetic vibration energy harvester through anti-phase resonance

Abstract This paper proposes a novel method to increase the power output of a cantilever beam-based electromagnetic vibration energy harvester through anti-phase resonance. A new cantilever beam design is presented to achieve this. By introducing an anti-phase motion between the coil and the magnets at resonance under the same base excitation input, the relative velocity of the coil cutting through the magnetic field is significantly increased and hence its power output. An experiment is performed to compare the proposed method with the conventional method where either the coil or the magnet is fixed onto the vibrating base. Under a base acceleration level of 0.10 g and a natural frequency of 17.24 Hz, results shows a 185% increase in power for the proposed method when compared with the conventional method with a recorded maximum power of 7.4 mW at resonance. The power produced by this method is proven to be higher than the sum of power produced by two individual conventional harvesters under the same velocities. In addition, a 22% increase in frequency bandwidth is also recorded by the proposed method. In terms of the power density, the proposed method indicates a 38% increase when compared with the conventional harvester. Results also show a drastic reduction in the maximum power output and phase difference when the natural frequencies of the coil and the magnets differ by only 1.5%, hence defining the importance of frequency matching. Further analysis indicates that a glass fiber cantilever beam showed a higher decrease in electromagnetic damping as compared to the increase in mechanical damping when small bulk masses were added onto the beam, hence increasing its overall gain.

A Study on Important Issues for Estimating the Effectiveness of the Proposed Piezoelectric Energy Harvesters under Volume Constraints

This study presents theoretical investigations on the effectiveness criteria for piezoelectric energy harvesters (PEHs) under volume constraints. Firstly, the importance of the volume consideration is investigated. The powers of different PEHs of variant volumes are investigated under the same resonance frequency. It is found that the power output is strongly dependent on the volume of the transducer. Secondly, the impact of the mechanical damping, the electrical damping, the volume of motion, the normalized power to the volume, and the applied load resistance on the power output are investigated. The investigations are analyzed to find the optimized conditions of the applied load and the excitation frequency in order to optimize the power output under volume constraints. The proposed procedure for estimating the effectiveness is to compare the performance of the proposed PEHs to a rectangular-shaped PEH of the same volume. An optimized structure for a rectangular-shaped PEH to be used as the reference is investigated. The power output under the optimized conditions is derived. In order to estimate the effectiveness of the proposed PEHs, the average power over a band of frequencies from the proposed structure must be compared to the average power over the same band of frequencies from the optimized reference harvester.

Perception of Mechanical Impedance During Active Ankle and Knee Movement.

During locomotion, energy flow through the legs is governed by the mechanical impedance of each joint. These mechanical properties, including stiffness and damping, have recently been quantified at the ankle joint. However, the relevance of these properties in human sensorimotor control is unclear. An important aspect of sensorimotor control is the ability to sense small changes in stimuli. Thus, we investigated the human ability to detect small changes in the stiffness and damping components of leg joint impedance when interacting with a mechanical system coupled to the ankle or knee. The perception threshold was determined via a psychophysical paradigm that required subjects to compare the mechanical impedance of virtual spring-mass-damper systems. Subjects reliably detected impedance changes of 11% and 12% at the ankle and knee, respectively. Additionally, the perception of stiffness and damping were comparable, indicating that the biomechanical relevance of the stiffness and damping components of impedance may be similar. Finally, these results offer novel insight into the design and control of impedance-based technologies, such as prostheses and exoskeletons.

Optimal power, power limit and damping of vibration based piezoelectric power harvesters

Power harvesting describes the process of acquiring the ambient energy surrounding a system and converting it into usable electrical energy. Much of the work over the past two decades has focused on the conversion of ambient vibration energy sources using piezoelectric, electromagnetic and electrostatic transduction. Attempts were made to obtain a general model that could be applied to any transduction mechanism. Of the most interest is an electromagnetic generator model that was used by many researchers to model piezoelectric power harvesters. Two major results from the model are the power limit expression and the equal relationship between the electrically induced damping and the mechanical damping to reach the power limit. However, piezoelectric power harvesters cannot be accurately modeled by this electromagnetic model due to the essential difference in physics. There have also been attempts to obtain the power limit expression based on piezoelectric relationships, but they either neglect the piezoelectric backward coupling to the structure, or assume the power limit occurs at the resonance of the system. This paper obtains the power limit expression based on the piezoelectric coupled equations without those assumptions. In addition, the relationship between the electrically induced damping and mechanical damping at the power limit is studied. Furthermore, a closed-form criterion is derived and proposed to define strongly and weakly coupling power harvesters, whose differences in power characteristics are explained through analytical and numerical analysis. While most of the discussion is focused on linear power harvesters connected to a resistive circuit, the aim of this paper is to provide a comprehensive and deep understanding of this simple configuration, answers to important questions, and a starting point to develop a more general theory on power harvesters because similar system characteristics are observed in power harvesters with more complexities.

Maximum power, optimal load, and impedance analysis of piezoelectric vibration energy harvesters

This paper performs an analysis of maximum power output of piezoelectric energy harvesters. It has been observed that there exists an overall power limit that can be obtained by tuning energy harvesting circuits, including both linear and nonlinear. The significance of the power limit is that it represents the maximum possible power output or capacity of an energy harvester. In other words, the harvested power is always capped by this limit regardless of the type and tuning of the energy harvesting circuit interface. The power limit and the optimal generalized electrical load or impedance to reach this power limit are first obtained directly by using the electromechanically coupled equations of the system, and then obtained by using the equivalent circuit analysis and impedance matching approach. Both are commonly used methods in energy harvesting research. This paper presents an effort to unify them but also offer insights on the power limit from two different perspectives. In the second part of this paper, the power limit and impedance matching results are applied to a linear energy harvesting circuit interface, i.e., resistive energy harvesting (REH) circuit, and a nonlinear circuit interface, i.e., standard AC–DC energy harvesting (SEH) circuit, to study their physical constraints on the impedance matching and clearly explain their power behaviors such as the maximum power and the effect of electromechanical coupling on the power. In addition, closed-form expressions, a relationship between the mechanical damping and the effective electromechanical coupling coefficient, to define the three types of coupling, i.e., weak, critical, strong, are obtained. It is found that the SEH harvesters require about 1.5 times of minimum electromechanical coupling of that of REH harvesters to reach the power limit, and the frequency bandwidth between the two power limit frequencies of a SEH harvester is narrower than that of a REH harvester given the same level of strong electromechanical coupling.

Numerical Investigation on Aeroelastic Behavior of Composite Material Plate Excited by Pulsed Air Jet

Nowadays, carbon fiber composite material is becoming more and more popular in aero engine industry due to its high specific strength and stiffness. Laminate carbon fiber composite material is widely used to manufacture the high load wide chord fan blade, containment casing, etc. The aeroelastic behavior of composite product is critical for the optimization of the product design and manufacturing. In order to explore its aeroelastic property, this paper discusses the coupled simulation of aerodynamic excitation applied on laminate composite material plate. Mechanical behavior of composite material plate is different from that of isotropic material plate such as metal plate, because it is anisotropy and has relative high mechanical damping due to resin between plies. These plates to be studied are designed using 4 different layup configurations which follow the design methods for composite fan blade. The numerical simulation of force response analysis mainly uses single frequency mechanical force input to simulate the electromagnetic shakers or other actuators, which could transmit mechanical force to the test parts. Meanwhile, pulsed air excitation is another way to “shake” the test parts. This excitation method induces aero damping into the test part and simulates the unsteady flow in aero engine, which could cause aeroelastic problems, such as flutter, forced response and non-synchronous vibration (NSV). In this study, numerical simulation using coupled method is conducted to explore the characteristics of laminate composite plates and the property of aerodynamic excitation force generated by pulsed air jet device. Modal analysis of composite plate shows that different ply stacking sequences have a significant impact on the plate vibration characteristics. Air pulse frequency and amplitude in flow field analysis are calibrated by hot wire anemometer results. As the air pulse frequency and amplitude are varied, incident angle of flow and layup configurations of plate can be analyzed in details by the simulations. Through the comparisons of all these factors, air pulse excitation property and the aeroelastic behavior of composite material plate are estimated. It would provide a possible way to guide the next-step experimental work with the pulsed air rig. The new composite fan blade design can be evaluated through the process.

SYNTHESIS OF A TWO-MASS ELECTRIC DRIVE WITH AN ASTATIC SYSTEM OF SUBORDINATE REGULATION AT THE ACTION OF VARIABLE FRICTION FORCES

Purpose. The solution of actual problem of active suppression of resilient electromechanical vibrations in an electric drive with the astatic system of automatic control is presented. Methodology. For research of damping properties of electrical drive according to a flow diagram from transmission functions on regulation and indignation a characteristic polynomial is got in the rationed form of parameters that takes into account the physical phenomena and sets intercommunications of parameters in the electromechanical system. As a result of it a characteristic polynomial at a successive dynamic decoupling appears separate interactive electromagnetic and mechanical subsystems. Thus, electromechanical interaction physically means complete extraction of energy of vibrations from a mechanical subsystem in electromagnetic with simultaneous transformation for minimum time. An electric drive for the case of realization of processes of electromechanical interaction is the dynamic extinguisher of vibrations. Results. The active resilient mechanical oscillation damping comes true due to optimization of dynamic inflexibility of mechanical description of electrical drive and as a result the required degree of stability is provided at minimum vibration and high exactness of working off indignations on loading. Originality. For the first time an electrical drive with the astatic system of automatic control at the action of variable forces of friction for the offered optimal parameters of dynamic inflexibility of mechanical description effectively damps vibrations. The synthesis of parameters of regulators according to correlations allowed to realize the maximum indexes of character of attenuation processes at a zero static error. Practical value. The synthesis method is approved in industrial conditions during the adjustment and modernization of the machine tool and is recommended for setting up automatic control systems for the operating and newly designed electric drives of technological machines.

Versatile Behaviors of Electromagnetic Shunt Damper With a Negative Impedance Converter

An electromagnetic shunt damper (EMSD) refers to the electromagnetic device connected to a specially designed shunt circuit that suppresses structural vibration. The analogy between mechanical and electrical systems offers the theoretical possibility of imitating various mechanical dampers using EMSDs. However, the inherent resistance of the whole circuit unfavorably affects the EMSD performance, including the analogous relationship. This study proposes a novel passive solution to address this practical limitation by using a negative impedance converter with voltage inversion (VNIC) to partially cancel the inherent resistance of shunt circuits. The benefit of the VNIC is revealed through theoretical and experimental studies. With the aid of a VNIC, a single electromagnetic device can mimic the versatile behaviors of different types of conventional dampers, such as viscous fluid, viscoelastic, inerter, and tuned inerter dampers, by conveniently adjusting the designs and parameters of shunt circuits. To the best of the authors’ knowledge, the versatility of EMSDs presented in this paper has not been experimentally illustrated in the literature.