Metamaterials are man-made substances with unique spatial alternations in their constituent components. They are widely used in modifying elastic, acoustic, or electromagnetic properties of materials. Metamaterials induce low/high-frequency band gaps to control wave propagations with different wavelengths and are also frequently applied in microwave engineering, waveguides, dispersion compensation, smart antennas, and lenses. For instance, permittivity and permeability of the metamaterials can take positive or negative values. Due to smaller single-cell dimensions than their wavelength, the selective frequency of surface-based metamaterials is used for waveguiding. The need for adjustable bandgaps can also lead to a plethora of research into metamaterials’ tunability for structures that operate at different speeds. In this article, recent studies in the field of metamaterials and their applications are reviewed. The piezoelectric metamaterials and the electromagnetic metamaterials are introduced that is followed by a review of new types of chiral metamaterials. Additionally, absorber, nonlinear, terahertz, tunable, photonic, selective surface-based frequency in acoustic metamaterials are comparedand some remarks on tuning bandgaps methods in locally resonant metamaterials are provided.

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Hybrid nanotubes composed of carbon and boron-nitride nanotubes have manifested as innovative building blocks to exploit the exceptional features of both structures simultaneously. On the other hand, by mixing with other types of materials, the fabrication of relatively large nanotubes would be feasible in the case of macroscale applications. In the current article, a nonlinear finite element formulation is employed to deal with the nonlocal vibrational behavior of carbon/boron-nitride nano-hetero-tubes in the presence of magneto-thermal environment. Euler–Bernoulli beam model in conjunction with the Eringen’s nonlocal theory of elasticity is adopted to derive the governing equation of motion. In order to conduct a nonlinear frequency analysis, the von-Kármán nonlinearity associated with moderate rotations is also considered. It is well known that temperature gradients can significantly change the dynamic behavior of nanotubes. On the other hand, the coefficients of thermal expansions of carbon and boron-nitride nanotubes are quite different that may affect the structural stability of hybrid nanotubes. Hence, to explore the vibration characteristic of such composite structures, the influence of magneto-thermal environment is also taken into account. Finally, the eigenvalue analysis is performed to exhibit the nonlinear mode shapes and natural frequencies of the system due to initial displacement. It is expected that the recognition of dynamic behavior of such hybrid nanotubes may open the doors to the creative design of next-generation nano-devices.

In engineering processes, residual stresses can be intense once high plastic deformation and temperature gradient are involved. This is exactly the case for friction stir welding (FSW) in which both rotational and translational movements of the tool induce extreme temperature gradient and plastic deformation. In this research, the extents of longitudinal and transverse residual stresses are measured within the AA7075-T6 plates welded through FSW process using ultrasonic method. According to the obtained results, it can be found that the residual stress is of the tensile type adjacent to the welding line whereas it is of the compressive type far from the welding line. Another observation is that the longitudinal residual stresses are considerably greater than the transverse residual stresses. Furthermore, with the aim of investigating the effects of rotation and traverse velocities of the tool on residual stress, experiments are carried out at three different rotation and traverse velocities. Based on the acquired results, it is observed that upon increasing the rotation and traverse velocities, the longitudinal and transverse residual stresses decrease and increase, respectively.

The accurate assessment of fatigue damage is a crucial issue for the design of marine pipelines. In this study, we modified the approach of Zheng et al. (2007) to simulate the random wave elevations for the fatigue assessment of marine pipelines applied to intermediate seas, e.g., the Persian Gulf. The cumulative fatigue damage due to the bending stresses and the linear and nonlinear acting wave forces was estimated on the basis of the finite element program for free-spanning sections. The results showed that the fatigue damage is highly dependent on both the wave characteristics and the modeling approach for the irregular wave.