Impulse Excitation Research Articles

Asymptotic method and wave theory of motion in studying the effect of periodic impulse forces on systems characterized by longitudinal motion velocity

A methodology for researching dynamic processes of one-dimensional systems with distributed parameters that are characterized by longitudinal component of motion velocity and are under the effect of periodic impulse forces has been developed. The boundary problem for the generalized non-linear differential Klein–Gordon equation is the mathematical model of dynamics of the systems under study in Euler variables. Its specific feature is that the unexcited analogue does not allow applying the known classical Fourier and D'Alembert methods for building a solution. Non-regularity of the right part for the excited non-linear analogue is another problem. This study shows that the dynamic process of the respective unexcited motion can be treated as overlapping of the direct and reflected waves of different lengths but equal frequencies. Analytical dependencies have been obtained for describing the aforesaid parameters of the waves. They show that the dynamic process in such mechanical systems depends not only on their main physical and mechanical parameters and boundary conditions, but also on the longitudinal motion velocity (relative momentum). As relative momentum increases, the frequency of the process decreases. To describe excited motion, we use the principle of single frequency of oscillations in non-linear systems with concentrated masses and distributed parameters as well as regularization of periodic impulse excitations. The main idea of asymptotic integration of systems with small non-linearity into the class of dynamic systems under study has been generalized. A standard equation for the resonance and non-resonance cases has been obtained. It has been established that for the first approximation, in the non-resonance case, impulse excitation affects only the partial change of the form of oscillations. Resonance processes are possible at a specific relation between the impulse excitation period, the motion velocity of the medium, and physical-mechanical features of the body. The amplitude of transition through resonance becomes higher when impulse actions are applied closer to the middle of the body. As the longitudinal motion velocity increases, it initially increases and then decreases.

Experimental study of the semi-active mass damper under impulse excitation.

Mass dampers usually aim to control the steady state vibration of harmonic excitation, but few efforts have focused on suppressing the transient vibration caused by impulse excitation. To obtain the optimum tuning parameters of the semi-active tuned mass damper (TMD) under impulse, optimization analysis of the transient vibration response is carried out. The analytical solutions of transient response are obtained. The transient response of the primary system is attenuated effectively by optimizing three parameters of the TMD, namely, the stiffness, initial displacement, and initial velocity. Three experimental setups are built to achieve different values of the parameters to verify the simulation results. The stiffness of the TMD is modeled analytically and experimentally, and the vibration magnitude denotes that there are several fluctuations when the stiffness of the TMD changes. The results also show that initial displacement and initial velocity of the TMD can lead to different transient vibration magnitudes for the primary system. The optimum parameters of the semi-active TMD can be obtained by the proposed method, and the transient response can be controlled by optimizing the stiffness, initial displacement, and initial velocity of the TMD.

A Comparative Study of the Preamplifiers in Electrostatic Sensors Through Analytical Modeling and Experimental Evaluation

Electrostatic sensors have been used to monitor a diverse range of processes and systems that involve movement of charged objects. Several types of preamplifiers are available for signal conditioning of electrostatic sensors, which differ in many aspects. This paper presents a comprehensive comparative study of four types of preamplifiers, namely trans-resistance amplifier, charge amplifier, current sense amplifier and potential amplifier, in order to clarify their differences for correct selection and facilitate proper cabling and electrode design. An equivalent circuit model that quantifies the interaction between the charged object and the electrode using coupling capacitance is established. The voltage outputs of the four preamplifiers are expressed analytically using the potential of the charged object and the object-electrode capacitance that varies as the object moves. In order to produce repeatable and controllable inputs to the electrostatic sensor, a fluctuating electric field is actively generated by applying an excitation voltage signal on an emitting electrode. Under impulse excitation, similarities in the signal waveforms are found between the trans-resistance and current sense amplifiers as well as between the charge and potential amplifiers, apart from the opposite polarities. Both impulse and frequency responses show that the current sense and potential amplifiers are significantly affected by the parasitic capacitances that depend on electrode structure and cabling and measures should be taken to reduce their effects.

Mechanical characterization of high-speed rubber ball impacts applied for impulse excitation

This paper is concerned with the material modelling of rubber balls applied for impulse excitation of high-speed rotating milling tools, which is essential for understanding the dynamics of various machining processes. For this purpose, a novel ball-shooter device was developed. The accurate finite element (FE) prediction of the ball impacts requires the complete understanding of the rubber ball’s mechanical behavior during impact, which involves high strain-rate deformations. We propose a damped-hyperelastic constitutive model, which is based on an Ogden’s hyperelastic model in combination with Rayleigh-damping. The material parameters of the long-term hyperelastic behavior are obtained using compression tests on the rubber balls. The Rayleigh-damping parameters were determined using inverse FE-based strategy, in which error of the experimental results (high-speed camera recordings) and the prediction of the FE-simulations is minimized. Our fitted model, in combination with the proposed finite element model, can be used effectively used to predict various quantities during impact excitations of machine tools.

Research on inductive neuron model and its dynamic characteristics

The size of neuron is on a mesoscopic scale. In this paper, considering the inductance characteristics of the neuron, the classical circuit model and mesoscopic circuit model of neuron including neuron membrane inductance, membrane capacitance, potassium ion memristor and chloride ion resistance are established. Based on the classical circuit theory and the quantum theory of mesoscopic circuit, the expression of neuron membrane voltage response under external impulse excitation is derived. Substituting the electrophysiological parameters of the squid neuron into the expression of membrane voltage, we find that the membrane voltages in both models first increase and then decrease, and finally reach their corresponding resting states of zero value, and their energy values are concentrated mainly in a range of 0–30 Hz in which the brainwave frequency is. Further comparisons show that the peak value of membrane voltage and the time required to reach the peak value (peak time) in the mesoscopic circuit model are lower than those in the classical circuit model, and are closer to the experimental results after the squid axon has been stimulated, indicating that the mesoscopic circuit model can better reflect the physiological characteristics of the stimulated neurons. Based on the mesoscopic circuit model, the peak value of membrane voltage increases and the peak time decreases with the increase of external excitation intensity. Parameters such as membrane voltage peak and peak time are more sensitive to the neuron membrane capacitance. The mesoscopic circuit model of the neuron is of great significance in understanding the excitability of the stimulated neuron and also in promoting the development of quantum neural networks inspired by brain function.

Damage detection based on output-only measurements using cepstrum analysis and a baseline-free frequency response function curvature method

Low-severity multiple damage detection relies on sensing minute deviations in the vibrational or dynamical characteristics of the structure. The problem becomes complicated when the reference vibrational profile of the healthy structure and corresponding input excitation, is unavailable as frequently experienced in real-life scenarios. Detection methods that require neither undamaged vibrational profile (baseline-free) nor excitation information (output-only) constitute state-of-art in structural health monitoring. Unfortunately, their efficacy is ultimately limited by non-ideal input excitation masking crucial attributes of system response such as resonant frequency peaks beyond first (few) natural frequency(ies) which can better resolve the issue of multiple damage detection. This study presents an improved frequency response function curvature method which is both baseline-free and output-only. It employs the cepstrum technique to eliminate [Formula: see text] decay of higher resonance peaks caused by the temporal spread of real impulse excitation. Long-pass liftering screens out the bulk of low-frequency sensor noise along with the excitation. With more visible resonant peaks, the cepstrum purified frequency response functions (regenerated frequency response functions) register finer deviation from an estimated baseline frequency response function and yield an accurate damage index profile. The simulation and experimental results on the beam show that the proposed method can successfully locate multiple damages of severity as low as 5%.

The Feasibility Study of Quantitative Flaw Detection of Grouted Sleeve Connection by Ultrasonics

Grouted sleeve connection has been widely used to connect rebars in prefabricated concrete (PC) structures. Due to the complexities of materials and internal configurations, the flaws or defects are inevitable, which may cause the negative impact on the mechanical properties of reinforcement sleeve connection, ultimately leading to the hidden risk in the PC structures. It is challenging to explore a reliable and efficient flaw detection method for the grouting sleeve. In this paper, an active grout defects detection approach for grouted sleeve connectors using UT wave measurement is proposed, where piezoelectric-lead-zirconate-titanate (PZT) transducer are mounted on surface of the sleeve as transmitter and receivers; and experimental study is carried out to validate the feasibility of the proposed method. In order to investigate the effect of grout defects on UT wave measurement, five grouted sleeve specimens with different degrees of the artificial grout defects are designed and analysis on the PZT transducer was used for measurement. By comparing the PZT transducers measurement of different specimens with different grout defects under an identical impulse excitation signal, the grout defect is detected. Experimental results indicate grout defect leads to decrease in PZT transducers measurement UT energy, the relationship between the UT energy ratio and the internal grouting flaws is established: the UT energy decreases with the increment of flaw size. Therefore, the UT method provides a feasible option to evaluate the internal flaws of grouted sleeve connection.

Mechanical characteristics of abrasive composite materials characterized by the Impulse Excitation Technique

Mechanical characteristics of abrasive composite materials characterized by the Impulse Excitation Technique

Influence of porosity to dynamic Young’s modulus of sintered iron. Bayesian approach

In this paper Young’s modulus against porosity relation E/Eo = f(P) for sintered Fe and steel powder compacts is discussed. For the experiment beam like (5 × 10 × 50 mm3) compacts, in density range 6.6–7.0 g/cm3 (P = 0.12–0.09), prepared from Fe powder (ASC100.29) are sintered in industrial conditions. Elastic constants E, G, ν are calculated from experimentally obtained fundamental mode shape frequencies, specimen mass and dimensions, using impulse excitation technique (IET). To ensure free beam boundary conditions, supports are placed in mode shapes nodal points. Popular model equation is fitted to experimental data. A Bayesian approach is used for parameter estimation. Fitted model equation predicts reasonably well the data from our and another researchers experiments with pre-alloyed Fe-Cr-Mo powder compacts, but fails for sintered steels prepared from powder mixtures and diffusion alloyed powders with Cu additions.

Investigating the Effects of Building Direction on the Dynamic Elastic and Damping Properties of Electron Beam Melted Ti-6AL-4V Parts Using Impulse Excitation Technique

Investigating the Effects of Building Direction on the Dynamic Elastic and Damping Properties of Electron Beam Melted Ti-6AL-4V Parts Using Impulse Excitation Technique

Mechanical characteristics of abrasive composite materials characterised by the impulse excitation technique

Abrasive composites are widely used in industrial machining, for example as grinding tools. Grinding wheel hardness expresses the retention capacity that the binder has over the abrasive grains and is important to optimise grinding processes, and can associate the stages of grinding and cut off. The hardness of the abrasive tools can be characterised by the determination of Young's modulus using the impulse excitation technique (IET). In this work, Young's modulus is determined with the IET, which is a non-destructive method with good objectivity, low equipment expenditure, and short measuring time. The results were compared to destructive bending tests. Resin bond composite abrasives with different grit/resin ratio structures were prepared and evaluated on microstructure and density. It was observed that increasing the grit/resin ratio also increases Young's modulus, except for higher porosity samples, where the hardness decreases because of the larger binder volume within the sample.

A Comparative Analysis of Selected Methods for Determining Young's Modulus in Polylactic Acid Samples Manufactured with the FDM Method.

The objective of this study was to compare three methods for determining the Young’s modulus of polylactic acid (PLA) and acrylonitrile-butadiene-styrene (ABS) samples. The samples were manufactured viathe fused filament fabrication/fused deposition modeling (FFF/FDM) 3D printing technique. Samples for analysis were obtained at processing temperatures of 180 °C to 230 °C. Measurements were performed with the use of two nondestructive techniques: the impulse excitation technique (IET) and the ultrasonic (US) method. The results were compared with values obtained in static tensile tests (STT), which ranged from 2.06 ± 0.03 to 2.15 ± 0.05 GPa. Similar changes in Young’s modulus were observed in response to the processing temperatures of the compared methods. The values generated by the US method were closer to the results of the STT, but still diverged considerably, and the error exceeded 10% in all cases. Based on the present findings, it might be concluded that the results of destructive and nondestructive tests differ by approximately 1 GPa.

Modal Identification of Ultralow-Frequency Flexible Structures Based on Digital Image Correlation Method

Traditional modal testing has difficulty accurately identifying the ultralow-frequency modes of flexible structures. Ultralow-frequency excitation and vibration signal acquisition are two main obstacles. Aiming at ultralow-frequency modal identification of flexible structures, a modal testing method based on Digital Image Correlation method and Eigensystem Realization Algorithm is proposed. Considering impulse and shaker excitation are difficult to make generate ultralow-frequency vibration of structures, the initial displacement is applied to the structure for excitation. The ultralow-frequency accelerometer always has a large mass, which will change the dynamics performance of the flexible structure, so a structural vibration response was obtained through the Digital Image Correlation method. After collecting the free-decay vibration signal, the ultralow-frequency mode of the structure was identified by using the Eigensystem Realization Algorithm. Ground modal tests were conducted to verify the proposed method. Firstly, a solar wing structure was adopted, from which it was concluded that the signal acquisition using Digital Image Correlation method had high feasibility and accuracy. Secondly, an ultralow-frequency flexible cantilever beam structure which had the theoretical solution was employed to verify the proposed method and the theoretical fundamental frequency of the structure was 0.185 Hz. Results show that the Digital Image Correlation method can effectively measure the response signal of the ultralow-frequency flexible structure, and obtain the dynamics characteristics.

Characterization of the viscoelasticity of pharmaceutical tablets using impulse excitation technique

Pharmaceutical tablets can be produced on different kinds of presses that may have very different compaction kinematics. Strain rate sensitivity (SRS) is thus an important property for the powders used to produce pharmaceutical tablets. Viscoelasticity is one of the aspects of the SRS and can be sometimes difficult to characterize. In this work, impulse excitation technique was used as an easy-to-implement method for characterizing viscoelasticity using the fact that this property induces damping which can be detected on resonance spectra as peak enlargements. A damping ratio, related to the first flexural vibration mode, was determined on impulse excitation frequency spectra using the half-power bandwidth method on tablets made with different products. This method made it possible to obtain reproducible results for the damping ratio. As viscoelasticity is not the only phenomena that can promote damping, tests were made in order to assess the influence of other parameters: viscoplasticity, porosity and tablet dimensions. Results indicated that the influence of these phenomena could be considered as negligible. Finally, the damping ratios determined were in good accordance with the known viscoelastic behavior of the studied products. This made it possible to confirm that impact resonance is an easy and quick way to characterize the viscoelastic nature of pharmaceutical tablets.

Global dynamics and performance of vibration reduction for a new vibro-impact bistable nonlinear energy sink

A new vibro-impact bistable nonlinear energy sink (VI-BNES) with relatively light weight attached to a damped linear oscillator (LO) is proposed to form a two-degree-of-freedom nonlinear mechanical system with bilateral rigid constraints. The state of the system after instantaneous impact is described by the simplified shock theory and the momentum conservation. When the LO subjected to impulse excitations with different levels is considered as the driver of the VI-BNES, a two-dimensional non-smooth reduced impact system with a harmonic perturbation and an irrational nonlinear restoring force is obtained to study the threshold for the homoclinic bifurcations and chaotic responses of the VI-BNES. Bistability of this mechanical model makes the reduced unperturbed system have a pair of symmetric homoclinic orbits as the pseudo-separatrix for in-well and cross-well oscillations. The Melnikov method developed by us for non-smooth planar systems with bilateral rigid constraints is firstly employed to detect the threshold of the amplitude of excitations of the LO for the onset of chaotic oscillations. Furthermore, cubic polynomial approximation of the restoring force on the premise of maintaining the equilibria of the system is carried out such that the analytical Melnikov analysis for the global dynamics becomes possible. The performance of the VI-BNES is also studied and compared with other NESs in detail through numerical analysis and experiments to show the high efficiency of vibration reduction of the VI-BNES due to the dual beneficial role of the bistability and the impacts with the bilateral rigid constraints.

Laser Self-Mixing Sensor for Simultaneous Measurement of Young’s Modulus and Internal Friction

The Young’s modulus and internal friction are two important parameters of materials. Self-mixing interferometry (SMI) is an emerging non-destructive sensing method that has been employed for various applications because of its advantages of simple structure, ease of alignment and high resolution. Some recent works have proposed the use of SMI technology to measure the Young’s moduli and/or internal frictions by measuring the resonance frequencies and damping factors of specimen vibrations induced by impulse excitation. However, the measurement results may be affected by frequencies of SMI fringes, and the implementation requires extra signal processing on SMI fringes. In this work, we developed an all-fiber SMI system without SMI fringes to measure the Young’s modulus and internal friction simultaneously. Simulations and experiments were carried out to verify the feasibility of the proposed method. Two specimens of brass and aluminum were tested. The experimental results show that the standard deviations of Young’s moduli for brass and aluminum are 0.20 GPa and 0.14 GPa, and the standard deviations of internal frictions are 4.0×10−5 and 5.4×10−5, respectively. This method eliminates the influences of the SMI fringe frequency on the resonant frequency and requires no signal processing on SMI fringes, contributing to its simplicity as a method for the measurement of the Young’s modulus and internal friction.

Design of a tunable electromagnetic vibration absorber for transient vibration suppression under impulse

Vibration absorbers usually aim to control the steady-state vibration of harmonic excitation based on the traditional fixed point theory, but few efforts focus on suppressing the transient vibration caused by impulse excitation. In this paper, the excitation is regarded as impulse in modeling, and it can be used for impulse excitation. Thus, the transient vibration absorber is designed to control the transient vibration, and the stiffness of the absorber is a key factor to control the response of the primary system. This paper presents a tunable electromagnetic transient vibration absorber to avoid direct mechanical contact for the absorber. The analytical results of the transient response indicate that the vibration can be attenuated by adjusting the stiffness of the absorber. In order to establish the model of the electromagnetic stiffness, the absorber is divided into three equivalent virtual springs. The circular current loop is equivalent to the rectangular current loop to show the spatial distribution of the magnetic flux density in the air gap. The experimental tests demonstrate that the transient vibration of the primary system can be attenuated by 13% when the current of the coil is 6 A.

EXPERIMENTAL INVESTIGATION OF INTERNAL FRICTION IN RUBBER CONCRETE AND FIBER-REINFORCED RUBBER CONCRETE

Statement of the problem. The paper is devoted to the experimental identification of damping for such materials as butadiene rubber (BR) and cis-butadiene low-molecular weight rubber (SKDN-N) based concrete and fiber-reinforced rubber concrete by means of the Impulse Excitation Technique (IET). Results. It was found that BR based concrete with or without fiber-reinforcement shows more obvious viscoelastic properties than the corresponding materials based on SKDN-N rubber. The addition of steel fiber reduces internal friction in the material, while propylene fiber has the opposite effect. This is due to the fact that the fibrous propylene acts as an additional damping material, which enhances energy dissipation under dynamic loading.Conclusion. The internal friction in the rubber concrete and fiber-reinforced rubber concrete was measured for the first time. The obtained data are the additional microstructural characteristics of polymer concrete, which describes its viscosity. The real values of the investigated quantities have been determined, which makes it possible to use the models with fractional derivatives in the calculations of building structures made of rubber concrete and fiber-reinforced rubber concrete for dynamic loads, taking into account the phenomenon of viscoelasticity.

The Sonic Resonance Method and the Impulse Excitation Technique: A Comparison Study

In this study, resonant frequencies of flexurally vibrating samples were measured using the sonic resonant method (SRM) and the impulse excitation technique (IET) to assess the equivalency of these two methods. Samples were made from different materials and with two shapes (prism with rectangular cross-section and cylinder with circular cross-section). The mean values and standard deviations of the resonant frequencies were compared using the t-test and the F-test. The tests showed an equivalency of both methods in measuring resonant frequency. The differences between the values measured using SRM and IET were not significant. Graphically, the relationship between the resonant frequencies is a line with a slope of 0.9993 ≈ 1.

Nonlinear dynamics of a new energy harvesting system with quasi-zero stiffness

This paper presents the results of modelling a new nonlinear multi-stable QZEH (quasi-zero energy harvester) system for harvesting energy from vibrating mechanical devices. Detailed tests were carried out on the system model, which consisted of a beam and a system of springs, which were used to determine the potential of a quasi-flat well. Two-dimensional distributions of the Lyapunov exponent were output from the numerical model, using the assumed range of variability within the control parameters, and plotted as a map in multi-color. These maps are related to diagrams of the RMS values of the voltage that is induced on the piezoelectric electrodes. To identify the optimal conditions for harvesting energy from mechanical vibrations, a multi-colored map of the RMS voltage values was produced. Its reference to the Lyapunov distribution map, showed that in the chaotic motion zones, energy harvesting is reduced. Based on the established sections of the Lyapunov exponent, diagrams of solutions (DS) showing the number of coexisting solutions and their periodicity were drawn. Multiple solutions and basins of attraction have been identified. On their basis it was possible to estimate the probability of obtaining a solution with the greatest energy harvesting efficiency. Moreover, a method of acting on the solution trajectory, by means of an impulse initiated at a specific moment in time, has been proposed. The results of the model tests were visualized as multi-colored maps of impulse excitations. The direct reference of the results of QZEH model tests to the tristable energy harvesting (TEH) system clearly indicates the advisability of using the QZEH system in terms of higher excitation amplitudes. The QZEH system also shows an improved ability to harvest energy in the low range of values of excitation frequencies.