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This paper aims to propose a design method for attenuating stress waves pressure using soft matrix embedded with particles.

Based on the phononic crystal theory, the particle composed of hard core and soft coating can form a spring oscillator structure. When the frequency of the wave is close to the resonance frequency of the spring oscillator, it can cause the resonance of the particle and absorb a lot of energy. In this paper, the resonant phononic crystal with three phases, namely, matrix, particle core and coating, is computationally designed to effectively mitigate the stress wave with aperiodic waveform.

The relationship between the center frequency and width of the bandgap and the geometric and physical parameters of particle core are discussed in detail, and the trend of influence is analyzed and explained by a spring oscillator model. Increasing the radius of hard core could effectively enhance the bandgap width, thus enhancing the effect of stress wave attenuation. In addition, it is found that when the wave is in the bandgap, adding viscosity into the matrix will not further enhance the stress attenuation effect, but will make the stress attenuation effect of the material worse because of the competition between viscous dissipation mechanism and resonance mechanism.

This study will provide a reference for the design of stress wave protection materials with general stress waves.

This study proposes a design method for attenuating stress waves pressure using soft matrix embedded with particles.

This work presents a topology optimization methodology for designing microarchitectures of phononic crystals. The objective is to get microstructures having, as a consequence of wave propagation phenomena in these media, bandgaps between two specified bands. An additional target is to enlarge the range of frequencies of these bandgaps.

The resulting optimization problem is solved employing an augmented Lagrangian technique based on the proximal point methods. The main primal variable of the Lagrangian function is the characteristic function determining the spatial geometrical arrangement of different phases within the unit cell of the phononic crystal. This characteristic function is defined in terms of a level-set function. Descent directions of the Lagrangian function are evaluated by using the topological derivatives of the eigenvalues obtained through the dispersion relation of the phononic crystal.

The description of the optimization algorithm is emphasized, and its intrinsic properties to attain adequate phononic crystal topologies are discussed. Particular attention is addressed to validate the analytical expressions of the topological derivative. Application examples for several cases are presented, and the numerical performance of the optimization algorithm for attaining the corresponding solutions is discussed.

The original contribution results in the description and numerical assessment of a topology optimization algorithm using the joint concepts of the level-set function and topological derivative to design phononic crystals.

The purpose of this paper is to developing a kind of acoustic metamaterial with wide frequency band especially in low frequency region. At the same time, its the tunability of sound insulation frequency is achieved.

A three-dimensional (3D) acoustic metamaterial consisting of rigid frame, spherical attachment and thin film is proposed. The material parameters and the effect of the attachment hole on the forbidden band are investigated by finite element simulation. The sound insulation effect of the structure is validated by the combination of simulation and experiment.

The results show that the elastic modulus of the structural material determines the initial frequency of the forbidden band of the proposed 3D acoustic metamaterials. The lower the elastic modulus of the structural material, the lower the initial frequency of the forbidden band. The material parameters of the frame mainly affect the initial frequency of the first forbidden band, and the material parameters of the attachment will affect both the initial and termination frequency of the first forbidden band. Holes in the attachments reduce the band gap width. The characteristic curve moves down with the increase of subtracted mass.

The findings may greatly benefit the application of the acoustic metamaterials in the fields of sound insulation and noise reduction.

This acoustic metamaterial structure has excellent sound insulation performance. At the same time, the single cell structure can be assembled into any shape. The structure can achieve sound selective filtering and combination control.

The purpose of this paper is to propose a modal method to calculate the band gaps of one-dimensional (1D) phononic crystals.

The phononic crystals have modes with exponential form envelope in the band gaps, however, outside the band gaps the modes are of amplitude modulation periodic form. Thus the start and end frequencies of band gaps can be determined from the existence conditions of periodic modes. So, the band gaps calculation of 1D phononic crystal is transformed into the existence discussion of periodic solution of mode shapes equation. The results are verified by finite element harmonic response analysis.

At the start and end frequencies of the band gap, the mode equation have solution with period of lattice constant.

Compared with the traditional theoretical methods, the proposed modal method has a clearer principle and easier calculation.

In order to improve the computation efficiency of the four-point rainflow algorithm, a new fast four-point rainflow cycle counting algorithm (FFRA) using a novel loop iteration mode is proposed.

In this new algorithm, the loop iteration mode is simplified by reducing the number of iterations, tests and deletions. The high efficiency of the new algorithm makes it a preferable candidate in fatigue life online estimation of structural health monitoring systems.

The extensive simulation results show that the extracted cycles by the new FFRA are the same as those by the four-point rainflow cycle counting algorithm (FRA) and the three-point rainflow cycle counting algorithm (TRA). Especially, the simulation results indicate that the computation efficiency of the FFRA has improved an average of 12.4 times compared to the FRA and an average of 8.9 times compared to the TRA. Moreover, the equivalence of cycle extraction results between the FFRA and the FRA is proved mathematically by utilizing some fundamental properties of the rainflow algorithm. Theoretical proof of the efficiency improvement of the FFRA in comparison to the FRA is also given.

This merit makes the FFRA preferable in online monitoring systems of structures where fatigue life estimation needs to be accomplished online based on massive measured data. It is noticeable that the high efficiency of the FFRA attributed to the simple loop iteration, which provides beneficial guidance to improve the efficiency of existing algorithms.

The aim of the study was to show that a new method, using a look-up table technique, can be used to detect the presence and position of an inclusion embedded in a tissue-like material. Due to the time-consuming nature of the finite element (FE) method or FEM, real-time applications involving FEM as part of a control loop, are traditionally limited to slowly varying systems. By using a simplified two-dimensional FE model and a look-up table, we show by simulations and experiments that it is possible to achieve reasonable computational times in a tactile resonance sensor application.

A piezoelectric disk was placed in the center of a silicone rubber disk (SRD) with viscoelastic properties, where it acted as both sensor and actuator and dissipated radial acoustic waves into the silicone. The look-up table was constructed by calculating the radial Lamb wave transition frequencies in the impedance frequency response of the sensor while varying the position of an inclusion. A position-matching algorithm was developed that matched measured and calculated Lamb wave transitions and thereby identified the presence and position of an inclusion.

In an experiment, the position of a hard inclusion was determined by measuring the Lamb transition frequencies of the first radial resonance in two SRDs. The result of the matching algorithm for Disk 1 was that the matched position was less than 3% from the expected value. For Disk 2, the matching algorithm erroneously reported two false positions before reporting a position that was less than 5% from the expected value. An explanation for this discrepancy is presented. In a verifying experiment, the algorithm identified the condition with no inclusion present.

The approach outlined in this work, adds to the prospect of developing time-sensitive diagnostic instruments. This approach has the potential to provide a powerful technique to quickly present spatial information on detected tumors.

In order to investigate the vibration reduction properties of a three-dimensional elastic metastructure with spherical cavities at low frequencies.

The bandgap characteristics of a three-dimensional elastic metastructure with spherical cavities are studied based on analytical and numerical approaches.

The results of both method revealed that the vibration of the vertexes masses is important for opening bandgaps. The fact that the big sphere cavity radius or short side length of the cube unit leads to a wider bandgap, is noteworthy.

This research provides theoretical guidance for realizing the vibration attenuation application of EMs in practical engineering.

The purpose of this paper is to develop a new formulation using spectral approach, which can predict the wave behavior to uncertain parameters in mid and high frequencies.

The work presented is based on a hybridization of a spectral method called the “wave finite element (WFE)” method and a non-intrusive probabilistic approach called the “polynomial chaos expansion (PCE).” The WFE formulation for coupled structures is detailed in this paper. The direct connection with the conventional finite element method allows to identify the diffusion relation for a straight waveguide containing a mechanical or geometric discontinuity. Knowing that the uncertainties play a fundamental role in mid and high frequencies, the PCE is applied to identify uncertainty propagation in periodic structures with periodic uncertain parameters. The approach proposed allows the evaluation of the dispersion of kinematic and energetic parameters.

The authors have found that even though this approach was originally designed to deal with uncertainty propagation in structures it can be competitive with its low time consumption. The Latin Hypercube Sampling (LHS) is also employed to minimize CPU time.

The approach proposed is quite new and very simple to apply to any periodic structures containing variabilities in its mechanical parameters. The Stochastic Wave Finite Element can predict the dynamic behavior from wave sensitivity of any uncertain media. The approach presented is validated for two different cases: coupled waveguides with and without section modes. The presented results are verified vs Monte Carlo simulations.

The purpose of this paper is to present an optimisation of four-point star-shaped structures produced through additive manufacturing (AM) polylactic acid (PLA). The study also aims to investigate the compression failure mechanism of the structure.

A Taguchi L₉ orthogonal array design of the experiment is adopted in which the input parameters are resolution (0.06, 0.15 and 0.30 mm), print speed (60, 70 and 80 mm/s) and bed temperature (55°C, 60°C, 65°C). The response parameters considered were printing time, material usage, compression yield strength, compression modulus and dimensional stability. Empirical observations during compression tests were used to evaluate the load–response mechanism of the structures.

The printing resolution is the most significant input parameter. Material length is not influenced by the printing speed and bed temperature. The compression stress–strain curve exhibits elastic, plateau and densification regions. All the samples exhibit negative Poisson’s ratio values within the elastic and plateau regions. At the beginning of densification, the Poisson’s ratios change to positive values. The metamaterial printed at a resolution of 0.3 mm, 80 mm/s and 60°C exhibits the best mechanical properties (yield strength and modulus of 2.02 and 58.87 MPa, respectively). The failure of the structure occurs through bending and torsion of the unit cells.

The optimisation study is significant for decision-making during the 3D printing and the empirical failure model shall complement the existing techniques for the mechanical analysis of the metamaterials.

To the best of the authors’ knowledge, for the first time, a new empirical model, based on the uniaxial load response and “static truss concept”, for failure mechanisms of the unit cell is presented.

The purpose of this paper is to demonstrate a novel chiral photonic crystal with thin thickness and small unit cells via numerical calculations. The multi-band circular dichroism is found in a wide frequency range from 400 to 600 THz by studying the transmission properties.

To investigate this chiral photonic structure, refection coefficients are analytically computed using finite element method. Numerical results are given, and physical properties are discussed, including the optical rotation, the circular dichroism and the absorption.

The results of this modeling and simulation under COMSOL multiphysics environment have led the authors to study the scattered parameters such as the coefficient of transmission (S21) and the coefficient of reflection (S11) for a 2D CPC nanostructure. The authors have also developed script under the Matlab environment which studies absorption and circular dichroism and ensure the existence of optical activity. According to the obtained results, the coefficient of transmission is proportional to the parameter of chirality.

The authors have designed a novel chiral photonic structure that exhibits larger circular dichroism. The CD spectrum has typically both positive and negative bands. The design principles defined in this work, which combine the concepts of the photonic crystal with the chiral structure (optical activity, circular dichroism and absorption), represent a model for simulation of the properties of a more complex chiral photonic structure. These results led to realization of novel circularly polarized devices in nanotechnologies.