Impulse Excitation Research Articles

Influence of impulse characteristics on realizing high-energy orbits in hybrid energy harvester

AbstractEnergy harvesters based on non-linear systems are promising devices for extracting energy from mechanical vibrations. This paper presents a new design of energy harvester consisting of two coupled nonlinear systems; the Duffing oscillator and a system with quasizero stiffness. A numerical analysis of the dynamics of the harvester is carried out, presenting coexisting solutions and their energy efficiencies in both chaotic and periodic motion zones. The root mean squared (RMS) voltage results depend on the dimensionless excitation frequency, where high-energy orbits are coexisting with low-energy orbits. Therefore, the second part of the paper focuses on various strategies for jumps between the orbits using impulses. Different impulse characteristics and their sequences for periodic and chaotic zones are analyzed. Therefore, a detailed analysis is presented for many strategies using an impulse excitation diagram (IED) as a numerical tool for accurately estimating the amplitude of the impulse, its duration, and the moment of initiation. The probability of achieving a given solution is also determined. The simulation results show that achieving the most effective orbit with a single impulse, as well as several impulses, requires similar energy. However, the advantage of the step-by-step method is the lower energy required to initiate a single impulse which enables the use of a smaller regulator. This work can be a valuable tool for designing various systems and strategies for changing the orbit of a solution.

Influence of the configuration of elastic and dissipative elements on the energy harvesting efficiency of a tunnel effect energy harvester

Paper presents computer simulations conducted to study the influence of the configuration of an energy harvesting system with tunnel mechanical characteristics in terms of its energy generation efficiency. In this context, numerical simulation experiments were carried out to assess the impact of physical properties and initial conditions on the occurrence of coexisting solutions and its energy efficiency. Chaotic motion zones were identified on the basis of Lyapunov exponent. To be able to choose the best solution in terms of energy efficiency, studies on the use of impulse excitation to change the orbit of the solution were also presented. Results show that modifying the energy harvesting system design with an impulse excitation subsystem can significantly improve (up to tenfold) the amount of energy harvested from vibrating mechanical devices.

Energy Harvesting from Vibrating Cantilever Structure of Different Base Materials using Piezoelectric Material: Theoretical and Experimental Approach

Energy conversion from one form to the other forms the basis for many inventions. Non utilized energy of mechanical vibration has attracted many researchers to focus on energy harvesting from vibrating structures. Piezoelectric material when attached to a vibrating structure converts mechanical energy into electrical energy. Today, harvesting energy ranges from micro level to macro level and has obtained its importance in wide range of real time application such as from low powered electronic devices to solar, wind and hydroelectric energy systems, respectively. The current work presents a detailed theoretical and experimental study on a cantilever type beam structure embedded with piezoelectric material on different base materials to understand micro level energy harvesting. Euler Bernoulli beam theory based mathematical model is excited with an impulse load at the free end for a broader frequency spectrum analysis. Finally, the proposed energy harvesters, cantilever specimens of three different base materials are ranked based on their maximum voltage and maximum instantaneous power outputs experimentally for the given impulse excitation. Out of three base materials considered steel and copper-based energy harvesters generated a maximum voltage output of 0.16mV and 0.13mV, respectively which corresponds to a maximum instantaneous power output of approximately 1.96nW and 1.69nW, respectively. Aluminum-based energy harvester performed the least among the three contributing to 0.81nW.

A two-dimensional nonlinear vibration absorber using elliptical impacts and sliding

Highly flexible structures often exhibit multiple low-frequency modes of vibration in multiple directions that vibrate with relatively high amplitudes. As a result, new two-dimensional vibration absorbers that target the motion of multiple modes are needed to mitigate motion of these structures. This research proposes a novel two-dimensional nonlinear vibration absorber (2D-NVA) as a method of vibration reduction for flexible structures that possess multiple low-frequency modes in multiple directions. The proposed 2D-NVA is composed of two low-mass bodies, called the housing and impactor, that are installed on the linear primary structure using strong and weak coupling stiffness, respectively. The housing is composed of a ring-like rigid body with the cavity in the shape of an ellipse, and the impactor is composed of a rigid body or particle that resides inside the housing. The nonlinearity arises through contact between the interior of the housing and impactor, and both impacts and constrained sliding with friction are allowed. The behavior of the proposed 2D-NVA is investigated both computationally and experimentally, and it is shown to dramatically reduce motion of a two-dimensional linear structure in both directions under varying amplitude of impulsive excitations.

Theoretical and Experimental Studies on Vibration Resistance of Composite Plates with Damping Coating

Abstract: This study performs both theoretical and experimental studies on the vibration resistance of composite plates with damping coating subjected to impulse excitation load. A dynamic model is first proposed and the key differential equations are derived to solve the natural frequencies, time-domain vibration response, and dynamic stiffness at any vibration response point regarding the excitation point of such a coated structure. Then, a dynamic experiment system of two plate specimens with and without DC knocked by a hammer excitation is set up. The measured data indicates that the proposed dynamic model is trustworthy for predicting natural frequencies and dynamic stiffness results. Furthermore, based on the calculated dynamic stiffness data associated with the first four modes, the anti-vibration contribution of DC is quantitatively evaluated. It can be found that the coating can indeed improve the vibration resistance of the structure by up to 74.7%. In addition, the vibration suppression effect of DC is found to be closely related to the mode order of such a structure as well as the selected boundary condition.

Effect of Elevated Temperature and Annealing Time on Mechanical Properties of Ti/Cu Bimetal

The paper presents the results of the elastoplastic properties of Ti/Cu bimetallic rods. They were obtained by extrusion and composed of a copper core with a covered titanium layer. Experiments were carried out at room temperature on virgin samples, and samples were subjected to prior annealing in the temperature range of 600-900 °C for 30, 60, and 90 min. The modern technique of impulse excitation of vibration was used to analyze the elastic properties of bimetal, obtaining the temperature and time characteristics of Young's modulus, internal friction, and resonance frequency variability. Subsequently, the samples were stretched to breakage, obtaining information on the values of limit stresses, their deformability, and the energy demand for uniform elastic-plastic deformation in terms of the effect of temperature and annealing time. The influence of thermal processes on the strengthening of the Ti/Cu bimetal was also examined, and microscopic observations and qualitative analysis of the diffusion zone at the interface of the phases were carried out. The research was to answer the question of how a short-term temperature increase in 600-900 °C affects the physical properties of Ti/Cu bimetallic rods. These rods were used as a high-density electric current carrier in metallurgical processes in environments of aggressive chemical compounds. Studies have shown that short-term annealing at elevated temperatures causes a drastic reduction in the strength of the Ti/Cu bimetal, leading to structural changes within the components, and the diffusion zone with the release of intermetallic compounds, leading to structural degradation. Heating at 900 °C for 60 and 90 min caused accelerated interface degradation and destruction of the Ti/Cu bimetal by delamination.

First La2O2S infrared transparent ceramics

Lanthanum oxysulfide (La2O2S) was investigated as infrared transparent ceramic to benefit from stronger chemical bonds and superior mechanical performances to that of non-oxide benchmark infrared materials. La2O2S ceramics were processed by hot-pressing powders prepared by combustion synthesis followed by a sulfurization treatment. Powders and ceramics were characterised through various techniques (XRD, UV-Vis-IR spectroscopy, particle size analysis, SEM, Impulse Excitation Technique, microhardness and fracture toughness tests) to assess their purity, study their microstructure and determine their optical and mechanical properties. The study reports the first IR transmission spectra, Poisson’s ratio, Young’s and shear moduli and fracture toughness values of La2O2S polycrystalline ceramics. The ceramics showed transparency in the 2–11 µm range and their mechanical performances were all superior to that of commercial infrared ceramics. The best transmission (89% of the theoretical transmission) was measured at 7.3 µm for 1 mm-thick ceramics hot-pressed at 1200–1250 °C.

Impact of steady state and impulse excitations on CuSO4 based memristor

The memristor technology will replace nonlinear resistor applications in suppression of power system overvoltages. A characterization study on Memristance is useful to predict current–voltage characteristics of memristors under different source voltages. A Liquid Memristor (LM) has been chosen in order to study its suitability as a nonlinear resistance for mitigation of an Instrument Transformer overvoltages. The motivation is to investigate the nonlinear property of LM under DC and AC supply voltages in terms of pinching nature and memristance. The simulation response of LM has been validated experimentally for steady state and impulse excitations. The LM is subjected to sinusoidal and triangular supply voltages at 50 Hz and verified for its pinched hysteresis. The response of LM satisfies the standard specifications for (1.2/50) μs lightning and (250/2500) μs switching impulse voltages. The nonlinear resistance of LM shows a varying response for DC voltage instead of single operating point. The memristance of LM is observed to be 1.5 mS under steady state voltage and varied up to 2.89 mS under impulse excitations. The study investigates the dynamic response of LM as a nonlinear system.

Vibration control systems in a building prototype: Application of SMA coil springs in diagonal bracing and TMD

The growing concern with the efficiency and reliability of civil structures that are slim, flexible and highly vulnerable to earthquakes, side winds and impacts can be addressed with the use of smart materials. Among the available techniques, passive control stands out due to its low cost, low maintenance, and no need for an external energy source. In this sense, this work proposes the incorporation of NiTi superelastic SMA springs in a diagonal bracing arrangement and as a secondary device in a Tuned Mass Damper (TMD) to improve the passive vibration control of a 3-DOF building prototype. The study compares the efficiency of the proposed control systems through the modal analysis of the structure under scenarios combining different control types (diagonal bracing or TMD), vibration types (impulse excited or base-forced) and passive attenuation (with or without SMA springs). It was concluded that the length of the SMA spring attenuators has a direct influence on the control capacity, with the shorter springs providing a higher attenuation efficiency, as they generate greater mechanical hysteresis and dissipate more mechanical energy, while adding less mass to the structure. In terms of the amplitudes reached in the experimental modal analysis, the TMD with the SMA springs as a secondary device was the most efficient technique, allowing reductions of up to 74% in impulse excitation and 44% in forced vibration. In terms of added mass, TMD also proved to be more effective, reducing about 63% of NiTi SMA material in impulse excitation and 73% in forced vibration, when compared to diagonal bracing.

Analysis of Texture and Anisotropic Elastic Properties of Additively Manufactured Ni-Base Alloys

Additive manufacturing of metallic materials generates strong crystallographic textures, leading to anisotropic elastic properties on the macroscopic scale. The impact of the processing parameters on the resulting texture requires suitable techniques for the prediction and the experimental determination of elastic properties to exploit the anisotropy in the design process. Within this study mechanical as well as microstructure based approaches are applied on a batch of specimens manufactured from IN718 by selective laser melting to assess the elastic behavior on macroscropic scale. Tensile loading experiments and the impulse excitation technique are applied for the determination of elastic properties without additional constitutive data. Furthermore, the elastic behavior is estimated from single-crystal elastic properties and texture data measured by electron backscatter diffraction and high energy X-ray diffraction. The results of the applied approaches are discussed and compared, allowing also to assess the homogeneity of the elastic properties within the batch of specimens.

Impulse mitigation in nonlinear composite-based woodpile phononic crystals

In this work, we study the mitigation of stress waves in composite-based woodpile phononic crystals composed of heterogeneous cylindrical rods, whose bending mode exhibits local resonant behavior that strongly interferes with external perturbation. Impulse excitation in this system is transformed into several modulated wave patterns depending on resonant frequencies and their mechanical properties. Thus, these mechanisms have been a candidate for novel methods of shock mitigation without relying on material dissipation. Here, we suggest the mechanical system consisting of the unit cell's composite configuration as an approach for more efficient shock attenuation. To efficiently analyze the nonlinear wave dynamics of the proposed systems, we present an extended discrete element model (DEM) resulting from a combination of an analytic beam theory with the discretization model. We numerically and experimentally demonstrate extreme dispersive waves for shock mitigation by adjusting the weighted composition ratio of the heterogeneous cylinder. Using the verified DEM, we also investigate the strong attenuation performance of incident impulse in disorder-induced systems with different nonlinear strengths. We, thus, expect that these composite-based mechanical systems could be used to design tunable modulation energy transport and efficient impact protector devices.

Direct-current, long-lasting and highly efficient electret energy harvesting from ultra-low-frequency motions using toothed clutch mechanism

Generally, most wearable energy harvesters generate only a small amount of electrical energy from the low-frequency motions of human body and immediately stop working when the activity ends, resulting in low energy extraction efficiency. Here, we propose an electret rotatory energy harvester (e-REH) with a mechanical tooth-clutch transmission system, converting the ultra-low-frequency irregular human motion (< 0.1 Hz) into a high-speed and long-lasting rotation for boosted energy conversion efficiency. The tooth-clutch transmission system is designed with a compact integration of a linear-to-rotation unit, a tooth-clutch transmission unit and an energy storage unit to generate continuous, stable and highly efficient electrical output. Triggered by impulse excitation of gentle hand tapping, the flywheel can continuously rotate for about 45 s inertially, and the maximum speed of the flywheel can reach about 1500 rpm, indicating the frequency is increased up to 4500 times from 0.022 Hz to 100 Hz. In addition, by introducing the multi-layer phase-shift electrode design, a constant direct-current output with a crest factor down to 1.09 is obtained by the phase coupling effect, avoiding the complicated signal processing circuit. Experimental results show the fabricated e-REH can produce an overall coupling current of 22.1 μA and average output power of 3.95 mW. Thanks to the lightweight, compact and high-efficient transmission design, the e-REH is further integrated into a shoe for wearable energy harvesting and self-powered underground environmental monitoring applications. The research is of considerable significance to the practical applications of e-REH in powering sensors and building self-powered wearable sensor networks.

Thermal Properties of Porous Mullite Ceramics Modified with Microsized ZrO2 and WO3.

Mullite ceramics are well known as materials with a high temperature stability, strength and creep resistance. In this research, the effect of a modification with magnesia-stabilized zirconia and yttria-stabilized zirconia, separately, as well as in a mixture with WO3, in 1:1 and 1:2 ratios on the thermal properties of porous mullite ceramics was investigated. The porous mullite-containing ceramics were prepared by a slip casting of the concentrated slurry of raw materials with the addition of a suspension of Al paste for the pore formation due to the H2 evolution as a result of the reaction of Al with water. The formed samples were sintered at 1600 °C and the holding time was 1 h. The materials were characterized using X-ray diffractometry, scanning electron microscopy, mercury porosimetry, the laser flash contactless method, thermal shock resistance testing and the non-destructive impulse excitation method for determining the elasticity modulus. The modification of the porous mullite ceramic with a mixture of ZrO2 and WO3 oxides had a positive effect by decreasing the thermal conductivity, due to the increased porosity, in comparison to the undoped samples and samples with only ZrO2. The doubling of the WO3 amount in the modifying oxide mixtures improved the ceramic thermal shock resistance. The porous mullite ceramics which were modified with magnesia-stabilized zirconia (2.8 mol% MgO) and WO3 had a lower thermal conductivity and improved thermal shock resistance than the samples with yttria-stabilized zirconia (8 mol% Y2O3) and WO3.

CLUSTERIZACIÓN EUCLIDIANA DE LA ESPECTROSCOPÍA MECÁNICA COMPARATIVA EXCITADA POR IMPULSO

ABSTRACT: An alternative methodology is presented to recognize the internal state of a material, which, unlike other methods, it is not necessary to take destructive tests, in addition to the high time and costs involved. The methodology in question is summarized in a technique based on the acoustic-vibrational behaviour of metal alloys, to correlate their acoustic properties and their internal structure. As a case study, a comparison between AISI-SAE 1018 steel and two alloys, one made of aluminum and the other of brass. The specimens are used according to ASTM E1876 for the Impulse Excitation Technique (IET) test. Steel cases were tested in their existing condition and heat treatment according to ASTM E1876 and subjected to a standardized process to compare the acoustic characteristics of the same material with different microstructures. By processing the acoustic response, frequency spectra describe the acoustic behaviour obtained. By processing the acoustic response, frequency spectra describe the vibrational behaviour. The methodology shows results that demonstrate the sensitivity of the test to microstructural changes in metallic materials, demonstrating that the IET test is functional as an alternative method for the identification of materials. Key Words: Mechanical spectroscopy, Impulse excitation, Euclidean clusterization, Non destructive test

Impulsive resistant optimization design of tuned viscous mass damper (TVMD) based on stability maximization

Recently, inerter based dynamic vibration absorbers (IDVAs) have been extensively investigated to control the harmonic and stochastic vibrations. Numerous studies on the theoretical H∞ and H2 optimizations and numerical analysis have been presented for various structures under different excitations. The variance of the stochastic vibration responses can be largely reduced by using these approaches. However, for excitations with non-stationary impulsive characteristics, such as near-fault earthquake and transient gusty wind, the control of peak responses is also concerned. But there are few related investigations on this topic. In order to address this problem, this paper investigates the vibration control performance of tuned viscous mass damper (TVMD) for impulsive stochastic excitations. Firstly, the transfer function (TF) and impulsive response function (IRF) of the vibrating system are analytically derived. Subsequently, the stability maximization (SM) result is obtained by optimizing poles of TF. The control performances of TVMD and TID based on H∞ and SM solutions subjected to impulsive excitations are compared, and the effectiveness of the SM-based TVMD is demonstrated. Considering the practical requirement of TVMD, an integrated optimization procedure that considers the balance of damping force and control performance is proposed. The corresponding empirical formulas for the optimal TVMD design are established. Through a numerical example, the effectiveness of the proposed method and empirical formulas are validated. In addition, the resulting optimal TVMD design outperforms the design based on H∞ optimization. Statistically, the resulting peak responses induced by the impulsive earthquake and wind can be reduced up to 41.0% and 22.1%, respectively.

Curaua-Aramid Hybrid Laminated Composites for Impact Applications: Flexural, Charpy Impact and Elastic Properties.

Curaua, as a leaf-based natural fiber, appears to be a promising component with aramid fabric reinforcement of hybrid composites. This work deals with the investigation of flexural, impact and elastic properties of non-woven curaua–aramid fabric hybrid epoxy composites. Five configurations of hybrid composites in a curaua non-woven mat with an increasing quantity of layers, up to four layers, were laminated through the conventional hand lay-up method. The proposed configurations were idealized with at least 60 wt% reinforcement in the non-alternating configuration. As a result, it was observed that the flexural strength decreased by 33% and the flexural modulus by 56%. In addition, the energy absorbed in the Charpy impact also decreased in the same proportion as the replaced amount of aramid. Through the impulse excitation technique, it was possible observe that the replacement of the aramid layers with the curaua layers resulted in decreased elastic properties. However, reduction maps revealed proportional advantages in hybridizing the curaua with the aramid fiber. Moreover, the hybrid composite produced an almost continuous and homogeneous material, reducing the possibility of delamination and transverse deformation, which revealed an impact-resistant performance.

A Study on the Dynamics of an AC Induction Motor Rotor Based on the Analysis of Free Response at Impulse Excitation

Abstract This paper focuses on a topic frequently involved in the dynamics of transient phenomena on rotary machines driven by an AC induction motor supplied by a three-phase four-wire electrical system: the free response of the dynamic system mirrored in the torsional vibrations of its rotor. This dynamic system is reducible at a single degree of freedom system, equivalent of a spring-mass-damper but as a torsional vibratory system composed of the motor rotor (having a moment of inertia) the rotating magnetic field (having a torsional stiffness) and a hypothetical damper (generating a viscous damping mainly due to the air friction). This free response is useful mostly to characterize the transmissibility related to the conversion of information from mechanical to electrical power through this dynamic system. A simple computer-assisted setup is used to describe indirectly and to analyze the free response (generated when the motor is switched-on or after star to delta commutation sequence), using the active electrical power absorbed by the motor.

Mechanical performance of Continuous/Short carbon Fiber-Reinforced Poly(phenylene sulfide) composites

A method for improving the fracture resistance and mechanical strength behavior of polymer composites by incorporating short carbon fibers into continuous fiber/poly(phenylene sulfide) laminate was explored in this manuscript. This method involves the incorporation of short carbon fibers into continuous carbon fiber thermoplastic laminates, by using the hot compression molding technique. Characterization of a continuous and discontinuous carbon fiber composite material with poly(phenylene sulfide) matrix (S-CCF/PPS laminate) was performed by using tensile, V-Notched Iosipescu, combined load compression and impulse excitation tests. According to the found results for this composite material, it was observed that the tensile strength and the elastic modulus values were 41% and 48% lower than a composite reinforced only by continuous fiber, respectively. The shear strength of the mixed material was found to be 32% lower than a continuous carbon fiber composite. These results were expected since it was used a combination of 50% of continuous and 50% of short carbon fiber, in volume. However, the compression strength of the mixed composite was found to be only 11.9% lower than a laminate reinforced with solely continuous carbon fiber, showing a synergic gain in this case. In addition, the impulse excitation results show that the material mechanical properties are within the expected range, but a high dispersion of the values was observed due probably to the random nature of the discontinuous fiber. Furthermore, it was observed that the failure modes for the composite evaluated in this work are similar to those found for composites processed only with continuous reinforcements and that the models used during the simulations presented similar results to what was found experimentally.

Experimental investigation on mechanical properties and free vibration characteristics of epoxy‐based glass/flax laminates

AbstractIn the present study, an attempt is made to replace the synthetic glass fiber used in the FRP structures in terms of natural flax fibers without much sacrifice on static and dynamic stability of the structure. Three types of glass/flax hybrid composite laminates were prepared with different fiber volume fraction of glass and flax fibers. For better understanding purpose, a dedicated glass and dedicated flax laminates were also fabricated. All the laminates were fabricated by vacuum bag molding method with uniform laminate thickness. The mechanical properties of the fabricated laminates, such as tensile strength and flexural strength, were evaluated in accordance with ASTM standards. The impulse excitation technique was used to assess the free vibration characteristics of glass/flax laminates such as modal frequency and material damping. Based on experimentally evaluated mechanical and vibration characteristics a suitable fiber volume fraction for the preferred laminate thickness was suggested to achieve optimum static and dynamic stability.

Fatigue analysis of high-carbon steel at different environmental temperatures considering the blue brittleness effect

Fully-reversed bending fatigue and impulse excitation tests are performed to investigate the behavior of High Carbon Steel (HCS) during cyclic loading at different environmental temperatures. The evolution of the damping, elastic modulus, and frequency for different operating temperatures ranging from 23°C to 135°C is characterized. The results of the damping are related to the rate of damage accumulation and crack growth―both of which are shown to increase with increasing the environmental temperature. It is shown that specimens tend to become more brittle with increasing of environmental temperature due to the so-called blue brittleness effect, and consequently the fatigue life of the specimens decreases. To gain further insight, a finite element model (FEM) is developed to assess the maximum principal stress distribution. The results corroborate the experimental findings.