2020

Jump to: 2019

9 pages, 4230 KiB

Open AccessArticle

Investigation of 2D Rainbow Metamaterials for Broadband Vibration Attenuation

by Han Meng, Dimitrios Chronopoulos, Nick Bailey and Lei Wang

Materials 2020, 13(22), 5225; https://doi.org/10.3390/ma13225225 - 19 Nov 2020

Cited by 15 | Viewed by 2466

Phononic crystals (PnCs) and metamaterials are widely investigated for vibration suppression owing to the bandgaps, within which, wave propagation is prohibited or the attenuation level is above requirements. The application of PnCs and metamaterials is, however, limited by the widths of bandgaps. The [...] Read more.

Phononic crystals (PnCs) and metamaterials are widely investigated for vibration suppression owing to the bandgaps, within which, wave propagation is prohibited or the attenuation level is above requirements. The application of PnCs and metamaterials is, however, limited by the widths of bandgaps. The recently developed rainbow structures consisting of spatially varied profiles have been shown to generate wider bandgaps than periodic structures. Inspired by this design strategy, rainbow metamaterials composed of nonperiodic mass blocks in two-dimensional (2D) space were proposed in the present study. The blocks were connected by curved beams and tessellated with internal voids to adjust their masses. In order to demonstrate the effects of the rainbow design, two 2D metamaterials, with periodic and nonperiodic units, respectively, were investigated and manufactured using additive manufacturing technologies. Receptance functions, i.e., displacement frequency response functions, of the manufactured metamaterials were calculated with finite element models and measured with a testing system containing a mechanical shaker, an impedance head, and a laser Doppler vibrometer. The obtained numerical and experimental results showed that the metamaterial with rainbow blocks has extended bandgaps compared with the periodic metamaterial. Full article

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14 pages, 3168 KiB

Open AccessArticle

Band Gaps and Vibration Isolation of a Three-dimensional Metamaterial with a Star Structure

by Heng Jiang, Mangong Zhang, Yu Liu, Dongliang Pei, Meng Chen and Yuren Wang

Materials 2020, 13(17), 3812; https://doi.org/10.3390/ma13173812 - 28 Aug 2020

Cited by 30 | Viewed by 3324

Abstract

Elastic metamaterials have promising applications in wave control and vibration isolation, due to their extraordinary characteristics, e.g., negative Poisson ratio, band gaps, effective negative mass density and effective negative modulus. How to develop new functional metamaterials using a special structure has always been [...] Read more.

Elastic metamaterials have promising applications in wave control and vibration isolation, due to their extraordinary characteristics, e.g., negative Poisson ratio, band gaps, effective negative mass density and effective negative modulus. How to develop new functional metamaterials using a special structure has always been a hot topic in this field. In this study, a three-dimensional (3D) star structure is designed to construct metamaterials with both negative static and dynamic properties. The results show that the 3D star structure formed a wide band gap at lower frequency and had a negative Poisson’s ratio. Different from conventional acoustic metamaterials, the main physical mechanism behind the low-frequency band gap of the 3D star structure is the resonance mode formed by the bending deformation of each rib plate, which made it easier to achieve effective isolation of low-frequency elastic waves with a low mass density. In addition, many structural parameters of the 3D star structure can be modulated to effectively adjust the band gap frequency by changing the angle between the concave nodes and aspect ratio. This study provides a new way to design the 3D acoustic metamaterials and develop the lightweight vibration isolation devices. Full article

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24 pages, 4626 KiB

Open AccessArticle

Secondary Resonance Energy Harvesting with Quadratic Nonlinearity

by Guoce Zhang and Bo Zhang

Materials 2020, 13(15), 3389; https://doi.org/10.3390/ma13153389 - 31 Jul 2020

Cited by 3 | Viewed by 2150

Abstract

Piezoelectric energy harvesters can transform the mechanical strain into electrical energy. The microelectromechanical transformation device is often composed of piezoelectric cantilevers and has been largely experimented. Most resonances have been developed to harvest nonlinear vibratory energy except for combination resonances. This paper is [...] Read more.

Piezoelectric energy harvesters can transform the mechanical strain into electrical energy. The microelectromechanical transformation device is often composed of piezoelectric cantilevers and has been largely experimented. Most resonances have been developed to harvest nonlinear vibratory energy except for combination resonances. This paper is to analyze several secondary resonances of a cantilever-type piezoelectric energy harvester with a tip magnet. The conventional Galerkin method is improved to truncate the continuous model, an integro-partial differential equation with time-dependent boundary conditions. Then, more resonances on higher-order vibration modes can be obtained. The stable steady-state response is formulated approximately but analytically for the first two subharmonic and combination resonances. The instability boundaries are discussed for these secondary resonances from quadratic nonlinearity. A small damping and a large excitation readily result in an unstable response, including the period-doubling and quasiperiodic motions that can be employed to enhance the voltage output around a wider band of working frequency. Runge–Kutta method is employed to numerically compute the time history for stable and unstable motions. The stable steady-state responses from two different methods agree well with each other. The outcome enriches structural dynamic theory on nonlinear vibration. Full article

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14 pages, 6680 KiB

Open AccessArticle

Experimental Study on Temperature Effects on NiTi Shape Memory Alloys under Fatigue Loading

by Caikui Lin, Zeqiang Wang, Xin Yang and Haijun Zhou

Materials 2020, 13(3), 573; https://doi.org/10.3390/ma13030573 - 25 Jan 2020

Cited by 15 | Viewed by 2390

Abstract

NiTi Shape Memory Alloy (SMA) has been widely studied in the field of structural vibration control, and the results show that the fatigue life of the SMA is a key factor of the vibration control system. In this paper, the fatigue test is [...] Read more.

NiTi Shape Memory Alloy (SMA) has been widely studied in the field of structural vibration control, and the results show that the fatigue life of the SMA is a key factor of the vibration control system. In this paper, the fatigue test is carried out in Dynamic Mechanical Analyzer (DMA + 1000) to analyze how the changes of temperature and strain amplitude affecting the main fatigue parameters. The test results show that when the test temperature is higher than Austenite finish temperature (A_f), the fatigue properties of SMAs are significantly affected by temperature. With the increase of temperature, the fatigue life becomes shorter and the energy consumption decreases, while the area of hysteresis curve, the stress amplitude, and effective modulus increase. Full article

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2019

Jump to: 2020

12 pages, 3551 KiB

Open AccessArticle

Low Temperature Influence on the Behavior of Viscoelastic Layer of the Pounding Tuned Mass Damper

by Peng Zhang, Jinwei Jiang and Guangtao Lu

Materials 2019, 12(23), 3986; https://doi.org/10.3390/ma12233986 - 01 Dec 2019

Cited by 6 | Viewed by 2306

Abstract

In previous studies, the pounding tuned mass damper (PTMD) has been successfully demonstrated to mitigate the undesired vibration of a variety of structures at room temperature. The advantages of the PTMD over the traditional tuned mass damper (TMD) has been verified through theoretical [...] Read more.

In previous studies, the pounding tuned mass damper (PTMD) has been successfully demonstrated to mitigate the undesired vibration of a variety of structures at room temperature. The advantages of the PTMD over the traditional tuned mass damper (TMD) has been verified through theoretical analysis and experimental investigations. However, the PTMD relies on an impact layer made of viscoelastic material to improve its vibration control performance and robustness against detuning effect. The energy dissipation of the viscoelastic material can be affected by the changes of environmental temperature. Therefore, this paper aims to study the impact damping behavior of the viscoelastic material in the low temperature environment of the sea bed where the PTMD is expected to control vibrations of subsea pipelines. The experimental apparatus fabricated in the previous study to generate and measure the lateral impact was housed inside a refrigerator. The experimental results indicate that the pounding stiffness decreased whereas the energy dissipation increased in the low temperature environment. Moreover, an impact fatigue test was also performed in the low temperature environment and compared with the room temperature case. Experimental results from a previous study show that the viscoelastic material was damaged after 36,000 cycles of impacts in the room temperature and a cyclic hardening–softening process was observed. However, in the low temperature environment, the viscoelastic material was damaged after 50,000 cycles of impacts and the cyclic hardening–softening process was not observed. As the impact cycle grew, the pounding stiffness decreased from 53,000 N/m^1.5 to 17,000 N/m^1.5 and the energy dissipation increased from 46.12 J/m per cycle to 65.4 J/m per cycle. Full article

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19 pages, 1913 KiB

Open AccessArticle

Design, Experimental and Numerical Characterization of 3D-Printed Porous Absorbers

by Tobias P. Ring and Sabine C. Langer

Materials 2019, 12(20), 3397; https://doi.org/10.3390/ma12203397 - 17 Oct 2019

Cited by 11 | Viewed by 3333

Abstract

The application of porous materials is a common measure for noise mitigation and in room acoustics. The prediction of the acoustic behavior applies material models, among which most are based on the Biot-parameters. Thereby, it is expected that, if more Biot-parameters [...] Read more.

The application of porous materials is a common measure for noise mitigation and in room acoustics. The prediction of the acoustic behavior applies material models, among which most are based on the Biot-parameters. Thereby, it is expected that, if more Biot-parameters are used, a better prediction can be obtained. Nevertheless, an estimation of the Biot-parameters from the geometric design of the material is possible for simple structures only. For common porous materials, the microstructure is typically unknown and characterized by homogenized quantities. This contribution introduces a methodology that enables the design and optimization of porous materials based on the Biot-parameters and connects these to microscopic geometric quantities. Therefore, artificial porous materials were manufactured using 3D-printing technology with a prescribed geometric design and the influence of different design variables was investigated. The Biot-parameters were identified with an inverse procedure and it can be shown that different Biot-parameters can be influenced by adjusting the geometric design variables. Based on these findings, a one-parameter optimization procedure of the material is set up to maximize the absorption characteristics in the frequency range of interest. Full article

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22 pages, 6273 KiB

Open AccessArticle

Sound Radiation Analysis of Constrained Layer Damping Structures Based on Two-Level Optimization

by Dongdong Zhang, Yonghui Wu, Jingyue Chen, Shuwen Wang and Ling Zheng

Materials 2019, 12(19), 3053; https://doi.org/10.3390/ma12193053 - 20 Sep 2019

Cited by 9 | Viewed by 2562

Abstract

Constrained layer damping (CLD) is an effective method for suppressing the vibration and sound radiation of lightweight structures. In this article, a two-level optimization approach is presented as a systematic methodology to design position layouts and thickness configurations of CLD materials for suppressing [...] Read more.

Constrained layer damping (CLD) is an effective method for suppressing the vibration and sound radiation of lightweight structures. In this article, a two-level optimization approach is presented as a systematic methodology to design position layouts and thickness configurations of CLD materials for suppressing the sound power of vibrating structures. A two-level optimization model for the CLD structure is developed, considering sound radiation power as the objective function and different additional mass fractions as constraints. The proposed approach applies a modified bi-directional evolutionary structural optimization (BESO) method to obtain several optimal position layouts of CLD materials pasted on the base structure, and sound power sensitivity analysis is formulated based on sound radiation modes for the position optimization of CLD materials. Two strategies based on the distributions of average normalized elemental kinetic energy and strain energy of the base plate are proposed to divide optimal position layouts of CLD materials into several subareas, and a genetic algorithm (GA) is employed to optimally reconfigure the thicknesses of CLD materials in the subareas. Numerical examples are provided to illustrate the validity and efficiency of this approach. The sound radiation power radiated from the vibrating plate, which is treated with multiple position layouts and thickness reconfigurations of CLD materials, is emphatically discussed. Full article

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10 pages, 3979 KiB

Open AccessArticle

Damping Enhancement Using Axially Functionally Graded Porous Structure Based on Acoustic Black Hole Effect

by Weiguang Zheng, Shiming He, Rongjiang Tang and Shuilong He

Materials 2019, 12(15), 2480; https://doi.org/10.3390/ma12152480 - 04 Aug 2019

Cited by 12 | Viewed by 3262

Abstract

The acoustic black hole (ABH) effect for damping flexural waves using axially functionally graded porous (FGP) structure is investigated. With proposed power-law porosity of FGP structure, ABH can be achieved and damping effect is enhanced. The physics are explained from divergent conditions of [...] Read more.

The acoustic black hole (ABH) effect for damping flexural waves using axially functionally graded porous (FGP) structure is investigated. With proposed power-law porosity of FGP structure, ABH can be achieved and damping effect is enhanced. The physics are explained from divergent conditions of the integrated wave phase at composite ends. Numerical results show the damping effect is increased with power law index. The phenomenon is expounded by the characteristics of reflection coefficient and impedance. It indicates that increasing power law index leads to smaller wavelength along to the end, then the wave needs more oscillation cycles to travel, which leads to more energy absorption. Transient analysis for 2D FGP structure also shows the focalization and ABH effect of the flexural waves. Full article

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16 pages, 4503 KiB

Open AccessArticle

Multidimensional Phononic Bandgaps in Three-Dimensional Lattices for Additive Manufacturing

by Waiel Elmadih, Wahyudin P. Syam, Ian Maskery, Dimitrios Chronopoulos and Richard Leach

Materials 2019, 12(11), 1878; https://doi.org/10.3390/ma12111878 - 11 Jun 2019

Cited by 12 | Viewed by 3948

Abstract

We report on numerical modelling of three-dimensional lattice structures designed to provide phononic bandgaps. The examined lattice structures rely on two distinct mechanisms for bandgap formation: the destructive interference of elastic waves and internal resonance. Further to the effect of lattice type on [...] Read more.

We report on numerical modelling of three-dimensional lattice structures designed to provide phononic bandgaps. The examined lattice structures rely on two distinct mechanisms for bandgap formation: the destructive interference of elastic waves and internal resonance. Further to the effect of lattice type on the development of phononic bandgaps, we also present the effect of volume fraction, which enables the designer to control the frequency range over which the bandgaps exist. The bandgaps were identified from dispersion curves obtained using a finite element wave propagation modelling technique that provides high computational efficiency and high wave modelling accuracy. We show that lattice structures employing internal resonance can provide transmissibility reduction of longitudinal waves of up to −103 dB. Paired with the manufacturing freedom and material choice of additive manufacturing, the examined lattice structures can be tailored for use in wide-ranging applications including machine design, isolation and support platforms, metrology frames, aerospace and automobile applications, and biomedical devices. Full article

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16 pages, 4478 KiB

Open AccessArticle

Dynamic Response of Long Rectangular Floors Subjected to Periodic Force Excitation

by Zsuzsa B. Pap and László P. Kollár

Materials 2019, 12(9), 1417; https://doi.org/10.3390/ma12091417 - 30 Apr 2019

Cited by 4 | Viewed by 2534

Abstract

Since damping in lightweight floors is usually low, dynamic amplification can be rather high. Long rectangular plates subjected to concentrated loads are often investigated by a replacement beam with a so called “effective width”. Although this approach is a reliable tool for static [...] Read more.

Since damping in lightweight floors is usually low, dynamic amplification can be rather high. Long rectangular plates subjected to concentrated loads are often investigated by a replacement beam with a so called “effective width”. Although this approach is a reliable tool for static loads, the steady-state dynamic response of beams and long plates subjected to periodic loads are significantly different. The maximum displacements and accelerations of beams (and of not-long rectangular plates) are obtained by using a dynamic amplification factor, which in the case of resonance is equal to

1 / 2 ξ

, where

ξ

is the damping ratio. For long plates (and for not-long orthotropic rib-stiffened plates), as discussed in the paper, the response and the amplification factor are substantially different from those of beams. Hence, design based on effective width may lead to 2–4 times higher acceleration than the real values. In an economic design, to avoid unnecessary damping enhancement, this effect must be taken into account. Full article

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