Mostafa Ranjbar

Mn-Cu alloys have attracted considerable attention as structural damping materials because they combine excellent damping capacity with relatively good mechanical properties. However, realizing effective strength-damping synergy still constitutes a critical bottleneck restricting their widespread engineering deployment. In this study, the effects of solution treatment (ST), deep cryogenic treatment (DCT), aging treatment (AT), and their combined routes on the microstructure, mechanical properties, and damping behavior of the M2052 Mn-Cu alloy were systematically investigated. The results show that the ST + DCT + AT route (820 °C/0.5 h + −196 °C/36 h +435 °C/10 h) provides the optimum overall performance. Compared with the as-cast alloy, its tensile strength and hardness are enhanced by ~23.2% and ~36.7%, respectively. Meanwhile, high damping capacity with tanδ ≥ 0.01 can be maintained within a broad temperature window from −100 °C to 200 °C. Microstructural characterization revealed that the ST + DCT + AT treatment generates refined α-Mn precipitates, maximized Mn-rich area fraction, abundant transformation-induced twins, and a relatively high dislocation density. The joint contributions from α-Mn particle refinement, abundant twin boundaries, and dislocation strengthening simultaneously improve mechanical strength and energy-dissipation capability. The results demonstrate that the insertion position of deep cryogenic treatment strongly modulates defect states, precipitate refinement and spinodal decomposition, and serves as a critical factor governing microstructural evolution and strength-damping synergy in Mn-Cu alloys.

In this study, it is aimed to protect underwater vehicles against active sonar systems by anechoic coating. A matrix material with close acoustic impedance to water, resistivity to hydrostatic pressure, suitability for the marine environment, and high material loss factor is selected. At low frequencies, the inclusions in different shapes and sizes are added to the matrix material. Since solid inclusions will increase the coating mass considerably, air cavities are preferred as inclusions. More attention is paid to low-frequency absorption, especially below 1 kHz, because of advancing sonar technology. The acoustic performance of the designed models is compared in three frequency ranges: low (below 3 kHz), middle (3–6 kHz), and high (6–10 kHz). The designed models are constructed by considering hydrostatic pressure; hence, volume of air cavities is tried to decrease, while absorption performance is aimed to increase. Therefore, a conical cavity which commonly used in the literature is optimized by chancing its dimensions and location. Also, novel approaches, gong shape cavity, and sandglass cavities are introduced. The results show that, not only cavity shape, but also its location and dimensions are highly influential on absorption performance. High-volume cavities increase the absorption performance at the low-frequency range, but they are not effective at high frequencies. The gong shape and sandglass air cavities show broadband absorption; also, gong shape cavity volume is less than literature models. Thus, its usability increases at deep waters. The results of this study provide novel underwater acoustic coating models for various applications.

Optical meta-surfaces allow controllable reflection and transmission spectra in both optical and infrared regions. In this study, we explore their potential in enhancing the performance of low-emission glazing designed for improved energy efficiency, for agricultural greenhouses in cold climates. The low-emission glazing employs thin film optics to retain heat by allowing solar radiation while reflecting radiation emitted by room-temperature objects. The incorporation of metamaterials that can be scalably manufactured and designed for capturing solar energy in the mid-infrared spectrum, offers an opportunity to further enhance the glazing’s energy efficiency. Based on existing literature, the finite difference time domain (FDTD) method and the transfer matrix method are utilised to propose a metamaterial structure, with spherical silver nanoparticles and thin-films. We compare the performance of this proposed design against existing materials. The outcome of this study offers insights into the potential of metamaterials in optimizing the energy efficiency of cold-climate agricultural greenhouses.

In this study, it is aimed to protect underwater vehicles against active sonar systems by anechoic metamaterial coating. A mixture of matrix material with close acoustic impedance to water, resistivity to hydrostatic pressure, suitability for the marine environment, and high material loss factor are selected. At low frequencies, the inclusions in different shapes and sizes are added to the matrix material. Since solid inclusions will increase the density considerably, air cavities are preferred as inclusions. More attention is paid to low frequency absorption, especially below 1 kHz, because of advancing sonar technology. The acoustic performance of the designed models is compared in three frequency range: low (0–3 kHz), middle (3–6 kHz), and high (6–10 kHz). The designed models are constructed by considering hydrostatic pressure; hence, volume of air cavities is tried to decrease while absorption performance is aimed to increase. Therefore, a conical air cavity is optimized by chancing its dimensions and location. Also, novel approaches, gong shape air cavity, and sandglass air cavities are introduced. The results show that, not only cavity shape, but also its location and dimensions are highly influential on absorption performance. High volume air cavities increase the absorption performance at the low frequency range, but they are not effective at high frequencies. The gong shape, and sandglass air cavities shows broadband absorption, also, gong shape air cavity volume is less than literature models. Thus, its usability increases at deep waters. The results of this study provide novel underwater meta surfaces for various applications.

Insect wings are an outstanding example of how a proper interplay of rigid and flexible materials enables an intricate flapping flight accompanied by sound. The understanding of the aerodynamics and acoustics of insect wings has enabled the development of man-made flying robotic vehicles and explained basic mechanisms of sound generation by natural flyers. This work proposes the concept of artificial wings with a periodic pattern, inspired by metamaterials, and explores how the pattern geometry can be used to control the aerodynamic and acoustic characteristics of a wing. For this, we analyzed bio-inspired wings with anisotropic honeycomb patterns flapping at a low frequency and developed a multi-parameter optimization procedure to tune the pattern design in order to increase lift and simultaneously to manipulate the produced sound. Our analysis is based on the finite-element solution to a transient three-dimensional fluid–structure interactions problem. The two-way coupling is described by incompressible Navier–Stokes equations for viscous air and structural equations of motion for a wing undergoing large deformations. We 3D-printed three wing samples and validated their robustness and dynamics experimentally. Importantly, we showed that the proposed wings can sustain long-term resonance excitation that opens a possibility to implement resonance-type flights inherent to certain natural flyers. Our results confirm the feasibility of metamaterial patterns to control the flapping flight dynamics and can open new perspectives for applications of 3D-printed patterned wings, e.g. in the design of drones with target sound.

In this paper, we study vibro-acoustic behavior of auxetic sandwich panels subjected to different excitations and boundary conditions. The core of this panel has the auxetic feature (with negative Poisson’s ratio or NPR) with anti-tetrachiral honeycomb structure. Mechanical behavior of the core is formulated using theoretical relations presented for this kind of auxetic. Using the Finite Element Method, the modal analysis and spectral analysis of the structure are accomplished. Different random colored noises are applied as the system excitation. First, a parametric study is performed; and some interesting results are observed from investigating the effects of geometric parameters, boundary conditions, and noise color on the vibro-acoustic behavior of the structure. These parameters affect the natural frequencies, level of radiated sound, and mass of the structure. An optimization algorithm is applied to the geometrical parameters in order to simultaneously reduce the level of radiated sound and preserve the amount of total mass. By the use of the Genetic Algorithm (GA), we could achieve a remarkable noise attenuation gain. It is shown that the GA choses different optimized parameters for the structure according to the location of the load and frequency content of the load spectrum.