Influence Of Geometrical Parameters Research Articles

Low frequency bandgap and high stiffness of innovative auxetic metamaterial with negative thermal expansion

Achieving multifunctional integration is crucial in mechanical metamaterials to meet the requirements of structures and equipment serving in complex environments across various engineering fields. In this study, we propose two novel bi-material and tri-material metamaterials based on the original edge-shared quadrangle (EQ/EQO) metamaterial, which exhibit negative thermal expansion (NTE), negative Poisson's ratio (NPR), and bandgap characteristics. The effective thermoelastic properties, including coefficient of thermal expansion (CTE), Poisson's ratio (PR), and Young's modulus, are compared and analyzed through theoretical formulation based on Timoshenko beam theory and numerical simulation using continuum elements with Abaqus. Additionally, finite element analysis is employed to calculate the energy band structures of these metamaterials based on Bloch's theorem, while the transmission characteristic curve verifies the validity of the obtained band structure. We systematically discuss the bandgap characteristics, coupling relationship between bandgaps and thermoelastic properties, as well as the influence of geometrical parameters on both bandgaps and thermoelastic properties. Our results demonstrate that the effective thermoelastic properties of these metamaterials are primarily determined by their frame structure's geometrical parameters, particularly the incline angle. Furthermore, for bi-material metamaterials, their specific stiffness closely relates to their bandgaps; however, for tri-material metamaterials, only the central local resonant unit determines their bandgap behavior. Notably, planar and 3D tri-material metamaterials can concurrently achieve a low-frequency bandgap along with high stiffness as well as NTE/NPR behavior. This work presents a new design strategy for optimizing multifunctional metamaterials' bandgaps while incorporating NTE behavior.

A synergistic approach to optimizing the performance of a concentrating solar segmented variable area leg thermoelectric generator using numerical methods and neural networks

AbstractThis study presents an optimized design for segmented variable area leg thermoelectric modules using finite element methods and Bayesian regularized neural networks. We explored the impact of geometry and thermal parameters on module performance using ANSYS software, identifying optimal parameters for power output and efficiency. Key findings revealed the higher influence of geometric parameters and confirmed the advantages of segmented thermoelectric generators for high-temperature applications like concentrated solar systems. With this optimization, power output and efficiency of the module increased by 875% and 165%, respectively, under 25 Suns. To refine the optimization process, a Bayesian regularized neural network was utilized, proving effective in predicting module performance with a low mean squared error and high coefficient of determination. This research provides important insights into high-performance thermoelectric modules for sustainable energy applications, demonstrating the significant role of advanced computational methods in energy solutions.

Reusable energy-absorbers design harnessing snapping-through buckling of tailored multistable architected materials

Abstract Multistable metamaterials are artificially engineered materials that possess microarchitectures capable of maintaining multiple stable configurations. However, the realization of mechanical metamaterials with numerous programmable stable configurations using Double-Curved Beam (DCB) elements remains an ongoing challenge. In this study, we exploit the snapping-through buckling phenomenon exhibited by architected DCB structures to devise a mechanical metamaterial with a unique deformation mode, encompassing Multi-stability, Multi-path, Multi-platform, and Multi-step characteristics, hence referred to as a 4M mechanical metamaterial. By employing DCB as fundamental building block elements, architected metamaterials with two-dimensional (2D) series or parallel lattices are successfully constructed, as well as three-dimensional (3D) tubular geometries, denoted as DCB-n-m-C and DCB-n-m-M metamaterials, respectively. These metamaterials exhibit reversible energy absorption characteristics and the stiffness can be transformed from positive to negative under both small and large elastic deformations. Functional gradient design and tailored deformation capability are given by adjusting the wall thickness of each layer of double-curved beams, thereby demonstrating the multi-path deformation features inherent in 4M metamaterials. DCB-n-m-M metamaterials has multiple energy platforms in the process of snapping-through, which reflects the multi-platform characteristics of 4M metamaterial. Consequently, novel properties such as multistability, programmability, and reusable energy absorption characteristics are achieved. To comprehensively understand the mechanical response of the metamaterials, a thorough investigation into the influence of geometric parameters is conducted, including the number of polygonal edges, the number of the layers, and the aspect ratio Q. This investigation involves a combination of theoretical analyses, numerical simulations, and experimental verifications. The introduced design strategy paves a way for the innovative design of multistable, multi-step, tailored, and reversible deformation metamaterials.

Viscoelastic modelling and analysis of two-dimensional woven CNT-based multiscale fibre reinforced composite material system

Carbon nanotube (CNT) has fostered research as a promising nanomaterial for a variety of applications due to its exceptional mechanical, optical, and electrical characteristics. The present article proposes a novel and comprehensive micromechanical framework to assess the viscoelastic properties of a multiscale CNT-reinforced two-dimensional (2D) woven hybrid composite. It also focuses on demonstrating the utilisation of the proposed micromechanics in the dynamic analysis of shell structure. First, the detailed constructional attributes of the proposed trans-scale composite material system are described in detail. Then, according to the nature of the constructional feature, mathematical modelling of each constituent phase or building block’s material properties is established to evaluate the homogenised viscoelastic properties of the proposed composite material system. To highlight the novelty of this study, the viscoelastic characteristics of the modified matrix are developed using the micromechanics method of Mori–Tanaka (MT) in combination with the weak viscoelastic interphase (WI) theory. In the entire micromechanical framework, the CNTs are considered to be randomly oriented. The strength of the material (SOM) approach is used to establish mathematical frameworks for the viscoelastic characteristics of yarns, whereas the unit cell method (UCM) is used to determine the viscoelastic properties of the representative unit cell (RUC). Different numerical results have been obtained by varying the CNT composition, interface conditions, agglomeration, carbon fibre volume percentage, excitation frequency, and temperature. The influences of geometrical parameters like yarn thickness, width, and the gap length to yarn width ratio on the viscoelasticity of such composite material systems are also explored. The current study also addresses the issue of resultant anisotropic viscoelastic properties due to the use of dissimilar yarn thickness. The results of this micromechanical analysis provide valuable insights into the viscoelastic properties of the proposed composite material system and suggest its potential applications in vibration damping. To demonstrate the application of developed novel micromechanics in vibration analysis, as one of the main contributions, comprehensive numerical experiments are conducted on a shell panel. The results show a significant reduction in vibration amplitudes compared to traditional composite materials in the frequency response and transient response analyses. To focus on the aspect of micromechanical behaviour on dynamic response and for the purpose of brevity, only linear strain displacement relationships are considered for dynamic analysis. These insights could inform future research and development in the field of composite materials.

Numerical modeling and analysis of fluid-filled truncated conical shells with ring stiffeners

This study uses a hybrid finite element method to predict dynamic behavior of truncated conical shells with ring stiffeners under fluid loading. The proposed approach combines classical shell theory and the finite element method, making use of displacement functions derived from exact solutions of Sanders’ shell equilibrium equations for conical shells. The analysis of the shell-fluid interface involves leveraging the velocity potential, Bernoulli’s equation, and impermeability conditions to determine an explicit expression for fluid pressure. To the best of our knowledge, this paper is the first to compare the methods applied to ring-stiffened shells against other numerical and experimental findings. Our results on conical shells in various conditions, with and without ring stiffeners, are largely consistent with previous findings. This study also explores the influence of geometric parameters, stiffener quantity, cone angle, and applied boundary conditions on the natural frequency of fluid-loaded ring-stiffened conical shells. The paper concludes with a discussion of several useful implications for further research.

High-flexibility three-dimensional serial folded hinges

High-flexibility three-dimensional serial folded hinges

A flexible, reusable and adjustable high-performance energy absorption system inspired by interlocking suture structures

Energy absorption systems play a very important role in impact protection under complex load conditions. However, traditional protective structures cannot adjust the mechanical properties on demand to accommodate variable load characteristics once manufactured. Therefore, inspired by the superior compression resistance of the diabolical ironclad beetle, a modular energy absorption system is developed by combining the efficient mechanical properties of thin-walled tubes and the robust connectivity of interlocking suture structures, which can be easily assembled from only bio-inspired tubes without external constraints. FEM simulations were performed to systematically investigate the static and dynamic mechanical properties of the developed system, and its crushing performance was demonstrated experimentally. Additionally, the influence of geometric parameters on the mechanical properties of the system has been investigated, and the insensitivity of secondary geometrical parameters and assembly defects has been verified, which shows that the system has a certain safety margin to avoid catastrophic accidents caused by fabrication defects. Moreover, the system exhibits excellent reusability under multi-impact load environments and its energy absorption capacity does not degrade after the primary impact. Furthermore, the system exhibits good designability thanks to the discrete modular structures, its mechanical properties can be tuned by stiffness design without affecting the energy absorption capacity, and its specific energy absorption can be effectively improved by lightweight design. This study provides a novel design strategy for the protection system applied in multiple complex environments.

Failure and Damage of Reciprocating Lip Seals for Pneumatic Cylinders in Dry Conditions

Lip seals are components subjected to high mechanical stress and they are responsible for many out-of-service in pneumatic cylinders. The aim of this work is the development of an experimental methodology to evaluate lifetime duration and analyse failures and damages of rod lip seals for pneumatic cylinders. A dedicated test bench was designed and manufactured which reproduces actual working conditions of the seals i.e., compressed air action (seal pressurisation) and relative linear reciprocating motion. Three types of seals made of two elastomers (NBR and polyurethane) were tested; dry condition was considered to speed up the tests. The influence of geometric parameters like seal seat dimension and seal axis misalignment with respect to the rod axis, was analysed by multiple experimental tests. Results in terms of seal life duration and failure modes are presented which allow comparison of seals performance and provide a helpful tool to end-users in a proper selection of seals geometry, material and key working parameters.

ANALYSIS OF SIMULATION DATA OF A SUPERSONIC FLOW IN A SHORT NOZZLE WITH A NOZZLE

In this paper, we analyzed the influence of the geometric parameters of a shortened nozzle when operating under various conditions - at sea level (at Р=1 bar) and upper atmosphere (Р= 0.1 bar). The influence of geometrical parameters of the nozzle, pressure at the inlet, and the environment on the impulse characteristics of the flow are considered. It is shown that the momentum factor decreases with decreasing inlet pressure, but with increasing flight altitude, i.e. a decrease in the pressure of the external environment, the momentum coefficient decreases to a certain value, and then increases again. This character of the dependence is explained by the wave structure of the flow in a shortened nozzle. The study of simulation data can be used to create new types of nozzles for rocket and space technology.

The Influence of Geometric Parameters for Training an Artificial Neural Network to Predict the Band Structure of 1-D Fishbone Photonic Crystal

With the rising demand for the transmission of large amounts of information over long distances, the development of integrated light circuits is the key to improving this technology, and silicon photonics have been developed with low absorption in the near-infrared range and with sophisticated fabrication techniques. To build devices that work in different functionalities, photonic crystals are one of the most used structures due to their ability to manipulate light. The investigation of photonic crystals requires the calculation of photonic band structures and is usually time-consuming work. To reduce the time spent on calculations, a trained ANN is introduced in this study to directly predict the band structures using only a minimal amount of pre-calculated band structure data. A well-used 1-D fishbone-like photonic crystal in the form of a nanobeam is used as the training target, and the influence of adjusting the geometric parameters is discussed, especially the lattice constant and the thickness of the nanobeam. To train the ANN with very few band structures, each of the mode points in the band structure is considered as a single datapoint to increase the amount of training data. The datasets are composed of various raw band structure data. The optimized ANN is introduced at the end of this manuscript.

Nacre-inspired auxetic interlocking brick-and-mortar composites

We design auxetic 3D interlocking brick-and-mortar composites inspired by nacre - a natural strong and resilient high-performance material. The influences of geometrical parameters and base material properties on their effective elastic properties are systematically investigated by finite element simulations and computational homogenization. The numerical results indicate that the composites exhibit tunable negative Poisson’s ratios by properly tailoring the underlying microstructures. It is revealed that the auxetic behavior therein is attributed to the relative sliding between adjacent bricks with waviness, i.e., the sliding mechanism. These materials, with their auxetic properties and high fracture toughness, are well-suited for a wide range of engineering applications, such as serving as robust auxetic materials.

Influence of dowel group configuration on the stability of reinforced slopes

Introduction. Slope reinforcement with dowels is the most economical and environmentally friendly method of their stabilization. However, the lack of theoretically substantiated schemes for optimal placement of dowels in groups, confirmed by tests in various conditions, leads to inefficient, often excessive use of the material in the arrangement of engineering protection.Aim. To determine the most effective arrangement of dowels in groups with regard to the overall stability of the reinformed soil mass. To assess quantitatively the stability depending on the spacing and shape of dowels in the group.Materials and methods. A review of international and Russian literature on the problem of assessing the influence of geometric parameters of dowel and anchor groups was carried out. According to the results of the review, primary calculations with the use of numerical simulation in the PLAXIS 3D software package was carried out.Results. The available publications mainly analyze configurations of screw anchor groups, paying insufficient attention the use of dowels of cylindrical cross-section. This fact substantiates further research in this field. The conducted numerical simulation allowed the slope stability provided by five dowel group configurations to be compared. The calculation results show that the slope stability depends on the configuration and the number of dowels in the group. The difference between the stability factors for the polygonal and triangular three-row configuration was 0.072 %, with the polygonal configuration requiring three dowels less. Selection of optimal dowel placement contributes to increased landslide control efficiency and reduced costs.Conclusions. The relevance and importance of studying the effect of dowel group configuration on slope stability, emphasizing the need for more in-depth and comprehensive research in this area.

Multi-band tunable electromagnetically induced transparencies based on active metasurface with polarization-independent property

The analogue of an electromagnetically induced transparency (EIT) spectrum is achieved using a metasurface that consists of an array of cross and L-shaped resonators. The mechanism of the EIT-like phenomenon are analyzed, and the influence of geometrical parameters on the effect is discussed. We achieve a multi-band EIT-like through structure configuration. In particular, polarization-independent EIT is realized. A potential application in sensing is suggested and the sensitivity of 65 GHz RIU−1 is obtained. We also investigate the impact of analyte and substrate on the transmission spectrum. We find that when the analyte thickness is higher than 40 μm, the EIT spectral shift is less affected by the analyte thickness. The thickness insensitive characteristics are beneficial for reducing errors caused by analyte dose, thereby improving the accuracy of sensing. By introducing a phase change material, vanadium dioxide, we obtain active control of the EIT effect. Our results provide valuable insights into the development of multi-band tunable compact devices based on metasurfaces.

Strength and failure assessments of 3D printed PLA single lap joints: Experimental and numerical analysis

In this paper, fused deposition modelling (FDM), is either used exclusively or in conjunction with adhesive bonding to manufacture single lap joints (SLJ). The design aspects of 3D printed SLJs are studied to assess their strength and failure mechanisms. Novel tooth-shaped interface joints are developed, leading to stronger and tougher joints. The uniaxial characteristics of Polylactic acid (PLA) were determined through testing on dog-bone samples. Subsequently, numerical models were developed to simulate the strength and failure modes of SLJs, followed by experimental testing. A parametric study was conducted to establish the influence of geometric parameters of tooth-shaped interface joints on failure load of tailored SLJs. Compared to baseline SLJs produced purely by 3D printing, the best performing tooth-shaped interface SLJs exhibit increased strength, failure strain, and toughness of ≈30%, ≈52%, and ≈130% respectively. Computational and experimental results confirm that SLJs with tooth-shaped interfaces can improve strength and failure strain.

Investigation of sound absorption on a polymeric acoustic metamaterial using 3D printing process

AbstractThis paper presents the design and characterization of DENORMS (Designs for Noise‐Reducing Materials and Structures) cell‐based acoustic metamaterial developed using a 3D printing technique. The metamaterial's acoustic absorption properties were investigated through experimental testing and numerical simulations. The experimental testing of the acoustic metamaterial was conducted in an impedance tube using a two‐microphone method. The numerical simulations were carried out using a thermoviscous module. The simulations allowed for a deeper understanding of the influence of geometric parameters on the absorption coefficient, providing valuable insights for optimizing the design. It was observed that upon increasing the spherical diameter while maintaining the same cylindrical diameter and cylindrical length resulted in an increase in the absorption coefficient throughout the frequency range. It was also observed that upon increasing the cylindrical diameter, there was a significant decrement of absorption coefficient, and upon increasing the length of the cylinder, there was a shift of response toward lower frequency. The augmentation in cell count from 9 to 24 led to a rise in the absorption coefficient and a shift of the response toward lower frequencies. The findings highlight the significance of photopolymer 3D printing in tailoring complex geometries for enhanced performance of the acoustic metamaterial.Highlights Photopolymeric resin used for DENORMS cell‐based acoustic metamaterial. High cleanability and accuracy of digital light processing 3D printing technique. Usage of thermoviscous model for simulation of sound absorption behavior. Use of two microphone impedance tube to determine sound absorption coefficient. Geometric parameters significantly affect the absorption coefficient.

A novel metamaterial with instantaneously sign-switchable coefficient of thermal expansion and Poisson's ratio

Most materials expand when heated and contract when cooled. In contrast, negative thermal expansion materials exhibit the opposite behavior. In this paper, we present a metamaterial that expands both when heated and cooled. The unit cell configuration is crafted by embedding two isosceles triangular structures composed of high thermal expansion materials within a re-entrant hexagonal honeycomb framework. Initially, the bases of the two isosceles triangles are in contact. The metamaterial exhibits two deformation states under different external loads. Analytical formulas for the equivalent parameters were derived based on classical beam theory within the regime of small deformation. Finite element simulations were conducted to validate the accuracy of these analytical formulas. The influence of geometric parameters on the metamaterial is discussed in detail. The results demonstrate that the metamaterial can exhibit excellent multi-functional properties within a small range of deformation, including instantaneous sign-variable coefficients of thermal expansion and Poisson's ratios, along with significantly distinct tensile and compressive stiffnesses. This metamaterial consistently exhibits expansive characteristics regardless of variations in ambient temperature. Additionally, the material always expands laterally regardless of the sign of uniaxial loads. Based on these properties, the metamaterial can be applied to fasteners in the aerospace industry that require permanent locking, ensuring stability in various temperature and mechanical load conditions.

Application of information technology to create the digital acoustic models of VVER

The IT used to create DAMPS is based on an interdisciplinary approach. DAMNR is presented as a self-oscillatory system, belonging to a special class of nonlinear dissipative systems capable of generating undamped oscillations. The use of DAMNR in the design and operation of NPP makes it possible to identify the sources of occurrence of ASW in the coolant, the conditions for their occurrence and frequency, and determine the influence of geometric parameters and the layout of coolant circuit equipment on the interaction of neutronic-physical, thermal–hydraulic and vibroacoustic processes. The use of DAMNR makes it possible to optimize engineering and design solutions when creating NPP by eliminating the conditions that cause the occurrence of unwanted self-oscillations of the coolant and vibroacoustic resonances in normal and emergency operating modes, as well as under conditions of shock impacts and seismic loads. Universal models and analysis methods were verified at Novovoronezh NPP.

Mechanical logic gate design based on multi-stable metamaterial with multi-step deformation

Mechanical metamaterials exhibit remarkable design versatility, enabling a series of unconventional mechanical properties via structural modifications. However, it is worth noting that many existing mechanical metamaterials either possess a singular deformation path or only multi-step deformation paths without reusability. This study proposes a novel multi-step deformation metamaterial that possesses multiple stable configurations. This metamaterial produces a unique two-step deformation mode under displacement loading, where the curved beams of the unit cells undergo snap-through and the vertical beams buckling. The influence of geometrical parameters on the multistability of the structure is thoroughly examined, and a theoretical prediction model for the buckling load is formulated. To validate the accuracy of the model, experimental tests and finite element simulations are conducted on the two-step deformation mode of periodic array of the unit cell. Additionally, a bi-material design approach for the unit cell is further introduced to enhance the specific energy absorption of the structure while reinforce the negative stiffness effect. Leveraging the multistable characteristics of the structure, mechanical logic gates such as AND, OR, NOT and NAND are conceptualized and experimentally validated. Through the implementation of rational designs and combinatorial connections within the logic gate structure, more complex logic operations can be realized.

Investigation on the band narrowing and shifting effects of micro-perforated panel absorbers.

Micro-perforated panel (MPP) absorbers exhibit multiple resonance bands with increased bandwidth narrowing and shifting in higher frequencies, limiting their effectiveness. This study investigates the effects of narrowing and shifting in higher-order resonance bands of MPP absorbers. First, an acoustic impedance model for MPP absorbers is introduced, and the narrowing and shifting coefficients are defined and modeled to quantify these effects. It is observed that a larger ratio of acoustic resistance to acoustic mass is favorable for reducing the narrowing and shifting effects. Subsequently, the theoretical model is validated using a numerical model, and a parametric study is conducted to explore the influence of geometric parameters on the narrowing and shifting effects. The study reveals that decreasing aperture and panel thickness, while increasing perforation ratio and cavity depth, reduces the narrowing and shifting coefficients. Remarkably, ultra-micro-perforated panels (UMPPs) with an aperture below 0.1 mm and perforation constant below 0.0046, having relatively larger acoustic resistance and smaller acoustic mass, demonstrate near-zero band narrowing and shifting. Finally, UMPPs are fabricated using micro-electro-mechanical systems (MEMS) technology, and their normal absorption coefficients are measured. Results align with theoretical predictions, confirming UMPPs' ability to achieve zero narrowing and shifting compared to ordinary MPPs and verifying the study's findings.

Design and optimization of a hybrid cooling configuration combining PCM and liquid cooling for Li-ion battery using data-based response surface approximation model

Effective thermal management is crucial for safe operation of electric vehicles. This study proposes a novel hybrid cooling system that using phase change material (PCM) and liquid cooling to address issues such as leakage, non-uniform temperatures under high discharge rates. A comprehensive 3D model was developed to analyze the influence of geometric parameters on the cooling system. Response surface approximation modeling was used to optimize the layout parameters of the PCM. The results show that the hybrid cooling outperforms other methods, maintaining the cell temperature with 35 ℃ and the temperature difference within 4 ℃. The thickness of the PCM is a significant factor, as it increases heat storage capacity and reduces temperature; however, exceeding a certain threshold leads to increased thermal resistance. A non-uniform PCM layout can reduce the temperature difference by 26 %. An optimal PCM thickness of 2.5 mm to 3 mm ensures that the maximum temperature remains below 32.5 ℃, with a temperature difference within 2 ℃. The lowest temperature difference is achieved with a vertical layout height of 70 mm and a horizontal layout thickness of 3 mm. These findings are valuable for enhancing the thermal management of lithium-ion battery.