Search Results (95)

Lattice-based metamaterials have attracted much attention due to their excellent mechanical properties. Nevertheless, designing lattice materials with desired properties is still challenging, as their mesoscopic topology is extremely complex. Herein, the bidirectional evolutionary structural optimization (BESO) method is adopted to design lattice structures with maximum bulk modulus and elastic isotropy. Various lattice configurations are generated by controlling the filter radius during the optimization processes. Afterwards, the optimized lattices are fabricated using Stereo Lithography Appearance (SLA) printing technology. Experiments and numerical simulations are conducted to reveal the mechanical behavior of the topology-optimized lattices under quasi-static compression, which are compared with the traditional octet-truss (OT) and body-centered cubic (BCC) lattice structures. The results demonstrate that the topology-optimized lattices exhibited superior mechanical properties, including modulus, yield strength, and specific energy absorption, over traditional OT and BCC lattices. Moreover, apart from the elastic modulus, the yield stress and post-yield stress of the topology-optimized lattice structures with elastically isotropic constraints also present lower dependence on the loading direction. Accordingly, the topology optimization method can be employed for designing novel lattice structures with high performance. Full article

This work focuses on characterizing structured metamaterials by assessing their elastic law and ultimate strength using finite elements and limit analysis applied to a representative volume element. The elastic and plastic behavior of a reference geometry—the octet truss lattice—is obtained by calculating the response of the representative volume element subjected to prescribed tensor strain bases, namely pure normal strain and pure shear, along the cube symmetry directions. The geometry of the body centered cubic and pure cubic phases of the representative volume element has been analyzed, highlighting that the elastic isotropic behavior depends on the ratio between the stiffnesses of the two phases. The ultimate behavior of the structure has been analyzed through the direct application of the lower bound method of limit analysis. The method has been implemented in a direct finite element environment using the limit analysis procedure developed by the authors. The method was already used and described in previous publications and is briefly recalled. It is based on the identification of the linear operator linking the self-equilibrated stress set to a discrete parameter manifold, accounting for the piecewise continuous distribution of the permanent strain. In the paper, it is highlighted that for different aspect ratios between the body-centered cubic and the pure cubic phase geometry, different ratios between limit shear stress and normal stress arise, the isotropic one assumed to coincide with the von Mises result, where ${\displaystyle \frac{{\sigma }_0}{{\tau }_0}}=\sqrt{3}$. Full article

In this study, a terahertz microfluidic multi-band sensor was designed. Unlike previous microfluidic absorption sensors that rely on dipole resonance, the proposed sensor uses a physical mechanism for absorption by exciting higher-order lattice resonances in microfluidic structures. With a Fabry–Perot cavity, the sensor can form an absorption peak with a high quality factor (Q) and narrow full width at half maximum (FWHM). A high Q value and a narrow FWHM are valuable in the field of sensing and provide strong support for high-precision sensing. On this basis, the sensing performance of the device was investigated. The simulation results clearly show that the absorption sensor has ultra-high sensitivity, which reaches 400 GHz/Refractive Index Unit (RIU). In addition, the sensor generates three absorption peaks, overcoming the limitations of a single frequency band in a composite resonance mode and multidimensional frequency response, which has potential application value in the field of volatile organic compound (VOC) sensing. Full article

This study presents a novel method for dynamically tuning singular states in one-dimensional (1D) photonic lattices (PLs) using air-slit-based structural modifications. Singular states, arising from symmetry-breaking-induced resonance radiation, generate diverse spectral features through interactions between resonance modes and background radiation. By strategically incorporating air slits to break symmetry in 1D PLs, we demonstrated effective control of resonance positions, enabling dual functionalities including narrowband band pass and notch filtering. These singular states originate from asymmetric guided-mode resonances (aGMRs), which can be interpreted by analytical modeling of the equivalent slab waveguide. Moreover, the introduction of multiple air slits significantly enhances spectral tunability by inducing multiple folding behaviors in the resonance bands. This approach allows for effective manipulation of optical properties through simple adjustments of air-slit displacements. This work provides great potential for designing multifunctional photonic devices with advanced metamaterial technologies. Full article

Battery pack casings with a total energy of 12.432 kWh were designed using two types of materials: aluminum alloy and carbon fiber reinforced composite filament based on polyphthalamide or high-performance/high-temperature nylon (PPA-CF). The effectiveness of mechanical metamaterials (lattice and auxetic structures) in mitigating the levels of random vibrations in the battery pack casings was studied using a numerical method. Both structures demonstrate outstanding capabilities with a 97% to 99% reduction in vibration levels in the aluminum casing. However, the capabilities of these structures in mitigating vibration levels in the PPA-CF casing are very limited, in that they can only mitigate approximately 63.8% and 92.8% of the longitudinal vibrations at the top cover of the casing and center of its front and back walls, respectively. Compared to PPA-CF, aluminum alloy shows better vibration mitigation performance with or without structural modification. Full article

The current limitations in predicting mechanical properties arise from an incomplete understanding of surface-induced size effects in variable-density polymer lattice metastructures. Through large-scale, high-fidelity finite element simulations, we identify a novel variable-density surface law governing the surface intrinsic length at the macroscopic scale. Capitalizing on this surface law discovery, we propose a surface-enhanced computational homogenization framework. By incorporating the surface intrinsic length parameters with the variable-density surface law and an offline database constructed through high-throughput numerical simulations, we develop an efficient predictive model capable of online analysis for the mechanical behavior of variable-density polymeric lattice metastructures. This innovative approach preserves critical configuration-dependent surface effects while achieving both efficiency and precision in predicting the macro-scale mechanical performance of such metastructures. Full article

Tunable thermal expansion metamaterials exhibit superior shock absorption performance in the field of high-precision equipment, but the applications are currently restricted by the unclear quantitative relationship of temperature-induced deformation. Herein, this work leverages the virtual work principle and the deformation geometric relationship to establish a generic temperature-induced deformation control model for bi-materials by utilizing the key variable coverage ratio under the condition of no deformation in the vertical direction. The feasible region regarding flexibility for the internal serpentine unit and lattice structure with different coverage ratios is given. The combination of the finite element and experimental methods is adopted to examine temperature-induced deformation, which presents tunable thermal expansion performances associated with the coverage ratio and temperature. This work, based on the established deformation coordination relationship of dual-material temperature-sensitive metamaterials, achieves temperature-induced deformation control and provides a reference for structural design adaptable in various working conditions such as vibration isolation and vibration reduction in complex engineering such as aerospace and so on. By strategically designing the coverage of the two structures within the specified range to maintain equivalent flexibility, the ultimate deformation of the serpentine unit is reduced by one-half due to deformation induced by temperature variations. Full article

Metamaterials are pushing the limits of traditional materials and are fascinating frontiers in scientific innovation. Mechanical metamaterials (MMs) are a category of metamaterials that display properties and performances that cannot be realized in conventional materials. Exploring the mechanical properties and various aspects of vibration and damping control is becoming a crucial research area. Their geometries have intricate features inspired by nature, which make them challenging to model and fabricate. The fabrication of MMs has become possible because of the emergence of additive manufacturing (AM) technology. Mechanical vibrations in engineering applications are common and depend on inertia, stiffness, damping, and external excitation. Vibration and damping control are important aspects of MM in vibrational environments and need to be enhanced and explored. This comprehensive review covers different vibration and damping control aspects of MMs fabricated using polymers and other engineering materials. Different morphological configurations of MMs are critically reviewed, covering crucial vibration aspects, including bandgap formation, energy absorption, and damping control to suppress, attenuate, isolate, and absorb vibrations. Bandgap formation using different MM configurations is presented and reviewed. Furthermore, studies on the energy dissipation and absorption of MMs are briefly discussed. In addition, the vibration damping of various lattice structures is reviewed along with their analytical modeling and experimental measurements. Finally, possible research gaps are highlighted, and a general systematic procedure to address these areas is suggested for future research. This review paper may lay a foundation for young researchers intending to start and pursue research on additive-manufactured MM lattice structures for vibration control applications. Full article

This paper focuses on the theoretical and analytical modeling of a novel seismic isolator termed the Passive Friction Mechanical Metamaterial Seismic Isolator (PFSMBI) system, which is designed for seismic hazard mitigation in multi-story buildings. The PFSMBI system consists of a lattice structure composed of a series of identical small cells interconnected by layers made of viscoelastic materials. The main function of the lattice is to shift the fundamental natural frequency of the building away from the dominant frequency of earthquake excitations by creating low-frequency bandgaps (FBGs) below 20 Hz. In this configuration, each unit cell contains an inner resonator that slides over a friction surface while it is tuned to vibrate at the fundamental natural frequency of the building. This resonance enhances the energy dissipation capacity of the PFSMBI system. After deriving the governing equations for four selected lattice configurations (i.e., Cases 1–4), a parametric study is performed to optimize the PFSMBI system for a wide range of harmonic ground motion frequencies. In this study, we examine how key parameters, such as the mass ratios of the cells and resonators, tuning frequency ratios, the number of cells, and the coefficient of friction, affect the system’s performance. The PFSMBI system is then incorporated into the dynamic model of a six-story base-isolated building to evaluate its effectiveness in reducing the floor acceleration and inter-story drift under actual earthquake ground motion records. This dynamic model is used to investigate the effect of stick–slip motion (SSM) on the energy dissipation performance of a PFSMBI system by employing the LuGre friction model. The numerical results show that the optimized PFSMBI system, through its lattice structure and frictional resonators, effectively reduces floor acceleration and inter-story drift by leveraging FBGs and frictional energy dissipation, particularly when SSM effects are properly accounted for. Finally, a small-scale prototype of the PFSMBI system with two cells is developed to verify the effect of SSM. This experimental validation highlights that neglecting SSM can lead to an overestimation of the energy dissipation performance of PFSMBI systems. Full article

In semiconductor inspection equipment, a chuck used to hold a wafer is equipped with a cooling or heating system for temperature uniformity across the surface of the wafer. Surface temperature uniformity is important for increasing semiconductor inspection speed. Triply periodic minimal surfaces (TPMSs) are proposed to enhance temperature uniformity. TPMSs are a topic of increasing research in the field of additive manufacturing and are a type of metamaterial inspired by nature. TPMSs are periodic surfaces with no intersections. Their continuous curve offers self-support during the additive manufacturing process. This structure enables the division of a single space into two domains. As a result, the heat transfer area per unit volume is larger than that of general lattice structures, leading to a superior heat transfer performance. This paper proposes a new structure called a double-wall TPMS. The process of creating a double-walled TPMS by adjusting the thickness of the sheet TPMS was investigated, and its thermal performance was studied. Finally, a double-wall TPMS was applied to the chuck. The optimal designs for the diamond and gyroid structures exhibited a difference in surface temperature uniformity of 0.23 °C and 0.66 °C, respectively. Accordingly, the models optimized with the double-wall TPMS are proposed. Full article

Seismic metamaterials are an emerging vibration-damping technology, yet concentrating the bandgap in the low-frequency range remains challenging due to the constraints imposed by lattice size. In this study, we numerically investigated seismic metamaterials connected by auxetic (negative Poisson’s ratio) slender strips, which exhibit an exceptionally wide low-frequency band gap for vibration isolation. Using a finite element method, we first performed a comparative analysis of several representative seismic metamaterial configurations. The results showed that the auxetic thin strip-connected steel column structure demonstrated outstanding performance, with the first complete band gap starting at 1.61 Hz, ending at 80.40 Hz, spanning a width of 78.79 Hz, and achieving a relative bandwidth of 192.15%. Notably, while most existing designs feature lattice constants in the ten-meter range (with the smallest around two meters), our proposed structure achieves these results with a lattice constant of only one meter. We further analyzed the transmission characteristics of the steel column structure, both with and without concrete filling. Interestingly, significant vibration attenuation, approaching 70 dB, was observed below the first complete band gap (approximately 0.22–1.17 Hz), even without the use of concrete. By comparing the flexural wave band gap with the transmission spectrum, we attributed this attenuation primarily to the presence of the band gap, a phenomenon often overlooked in previous studies. This attenuation at lower frequencies highlights the potential for effectively reducing low-frequency vibration energy. To further enhance the attenuation, the number of periods in the propagation direction can be increased. Additionally, we systematically explored the influence of geometric parameters on the first complete band gap. We found that optimal results were achieved with a slender strip length of 0.05 m, its width between 0.05 and 0.1 m, and a steel structure width of 0.1 m. Our findings underscore the critical role of auxetic thin strips in achieving broadband low-frequency vibration isolation. The approach presented in this study, along with the discovery of low-frequency flexural wave band gaps, provides valuable insights for seismic engineering and other applications requiring effective vibration reduction strategies. Full article

The stress distribution within the struts of lattice metamaterials is non-uniform under compressive loads, with stress concentrations typically occurring at the node regions. Inspired by bamboo, this study proposes a type of body-centered cubic (BCC) lattice metamaterial with tapered prism struts (BCCT). The compressive behavior, deformation modes, mechanical properties, and failure mechanisms of BCCT lattice metamaterials are systematically analyzed using finite element methods and validated through compression tests. Parametric analysis is conducted to investigate the effects of key design parameters, including volume fraction, shape parameter, and material properties. The results reveal that BCCT lattice metamaterials effectively eliminate stress concentration at nodes by redistributing stress toward the center of the struts. This redistribution changes the failure mode from shear band failure to layer collapse, while the struts maintain a bending-dominated deformation mechanism under compression. The mechanical properties of BCCT lattice metamaterials are significantly influenced by the shape factor. Furthermore, the mechanical properties of BCCT lattice metamaterials with different volume fractions and materials are consistently superior to BCC ones, which verifies the effectiveness and adaptability of lattice metamaterials with taper prismatic struts for potential lightweight applications. Full article

The present study assessed the compression performance of four strut lattices manufactured via laser powder bed fusion (LPBF), namely selective laser melting (SLM) from Inconel 625 and Ti-6Al-4V. Static finite element analysis and mechanical testing were performed, and it was concluded that the experimentally determined performance trend was in good agreement with that obtained by numerical methods. The cell type greatly influences the compressive performance of the lattices, regardless of the material used for manufacturing. The best compressive performances were recorded for the octet lattice, followed by the truncated octahedron, Kelvin, and re-entrant lattices. Regarding material performance, for the first maximum compressive strength, similar results were recorded for both materials; a difference was recorded in the case of yield strength, with higher values were recorded for Ti-6Al-4V compared to Inconel 625. The average first maximum compressive strength for the Ti-6Al-4V lattice was between 30.39 and 290.17 MPa, and it was within a range of 16.22–258.71 MPa for Inconel 625. The elastic modulus was between 1.74 and 4.72 GPa for Ti-6Al-4V, and 1.13 and 4.46 GPa for Inconel 625. A more ductile behavior was registered for the nickel-based superalloy than for the titanium alloy; the Inconel 625 specimens were characterized by a bending-dominant damage mode, and Ti-6Al-4V specimens were characterized more by a stretch-dominant damage mode. Full article

The mechanical behavior of the metallic components fabricated by additive manufacturing (AM) technologies can be influenced by adjustments in their microstructure or by using specially engineered geometries. Manipulating the topological features of the component, such as incorporating unit cells, enables the production of lighter metamaterials, such as lattice structures. This study investigates the mechanical behavior of lattice structures created from AlSi10Mg, which were produced using the laser beam powder bed fusion (LB-PBF) process. Specifically, their behavior under pure compressive loading has been numerically and experimentally investigated using ten different configurations. Experimental methods and finite element analysis (FEA) were used to investigate the behavior of body-centered cubic (BCC) lattice structures, specifically examining the effects of tapering the struts by varying their diameters at the endpoints ($d_{\mathrm{end}}$) and midpoints ($d_{\mathrm{mid}}$), as well as altering the height of the joint nodes (h). The unit cells were designed with varying parameters in such a way that $d_{\mathrm{end}}$ is changed at three levels, while $d_{\mathrm{mid}}$ and h are changed at two levels. Significant differences in Young’s modulus, yield strength, and ultimate compressive strength between the various specimen configurations were observed both experimentally and numerically. The FEA underestimated the Young’s modulus corresponding to the configurations with thinner struts in comparison to the higher values found experimentally. Conversely, the FEA overestimated the Young’s modulus of those configurations with larger strut diameters with respect to the experimentally determined values. Additionally, the proposed FE method consistently underestimated the yield strength relative to the experimental values, with notable discrepancies in specific configurations. Full article

Pentamodes are lattice structures composed of beams. Their main property is the low ratio of the shear to bulk modulus, making them suitable for aerospace, antiseismic, and bioengineering applications. At first, in our study, pentamode structures were fabricated using three-dimensional printing and were tested in a laboratory. Then, computational analyses of bulk strength have been performed. In addition, several preliminary computational analyses have been considered, comparing different pentamodes’ dimensions and topologies in order to understand their behaviour under different loading conditions. Experimental results have been compared with the numerical results in order to validate the forces applied to the lattice structures. Our new contribution is that for the first time, the experimental and numerical results are investigated up to the failure of the specimens, the effective Young’s modulus has been calculated for different pentamode lattice structures, and our results are also compared with analytical equations. Full article