Acoustic waves in a linear time-invariant medium are generally reciprocal; however, reciprocity can break down in a time-variant system. In this Letter, we report on an experimental demonstration of ...nonreciprocity in a dynamic one-dimensional phononic crystal, where the local elastic properties are dependent on time. The system consists of an array of repelling magnets, and the on-site elastic potentials of the constitutive elements are modulated by an array of electromagnets. The modulation in time breaks time-reversal symmetry and opens a directional band gap in the dispersion relation. As shown by experimental and numerical results, nonreciprocal mechanical systems like the one presented here offer opportunities to create phononic diodes that can serve for rectification applications.
•Theory of lattice metamaterials under sinusoidal distributed static loads•Two basic modes of static damping of distributed pressure waves are identified•Dependence of effective shear modulus on a ...spatial frequency of the load•Pathway toward intelligent mechanical systems able to distinguish load patterns
We discuss response properties of lattice metamaterials to sinusoidal distributed static loads applied on a material edge. Analytical displacement solutions are obtained using a Fourier domain transfer matrix for both essential and natural boundary conditions, which are valid for a state of plane strain in orthorhombic lattices, as well as for planar metasurfaces. These solutions give sinusoidal displacement profiles in the material interior of the same wavenumber (spatial frequency) as the boundary load. Their amplitudes decay in the material interior in one of two possible ways, exponential or oscillatory exponential, depending on the lattice design and on the spatial frequency of the load. There is a tendency for the oscillatory exponential behavior to occur at lower wavenumbers representing smoother boundary loads. As explained on a specific example, comparing the metamaterial’s response amplitudes with those of a homogenous material also allows studying an effective, wavenumber-dependent shear modulus of the lattice, which can take both positive and negative values.
The structural stability, electronic, and mechanical properties of Ti1-xMx (M = Fe, Mo, Nb, Ni) binary alloys were systematically investigated through first-principles calculations based on Density ...Functional Theory (DFT). The results indicate that the formation energy decreased with an increase in the substitutional atomic M content, accompanied by an increase in the values of C11–C12. This observation suggests a significant improvement in the structural stability of the Ti1-xMx alloys considered, with the concentration of substitutional atomic M ranging from 6.25 % to 50 %. Furthermore, the mechanical parameters, including bulk modulus B and shear modulus G, exhibited a linear increase with the concentration of the alloy element M. The Young's modulus E of Ti1-xFex and Ti1-xNbx alloys increased, whereas Ti1-xMox and Ti1-xNbx alloys reached a minimum value. In addition, the B/G ratio and Poisson's ratio ν indicated that β-Ti1-xMx alloys are fundamentally ductile materials. Moreover, using the stretching model, we demonstrate that the tensile strength of Ti1-xMx alloys was significantly improved by increasing the alloy element M concentration. The enhancement in tensile strength was primarily attributed to the enhanced bond strength between Ti and M atoms, as revealed by the analysis of the density state. These findings provide a pragmatic approach for reinforcing the strength-toughness compatibility of Ti-based alloys, rendering them suitable for aerospace industry applications.
•This work suggest that the considered alloying elements M (M = Fe, Mo, Nb, Ni) improve the structural stability of β-phase Ti alloys.•The mechanical parameters, including bulk modulus B and shear modulus G, exhibited a linear increase with the concentration of the alloy element M.•The results indicate that the addition of alloying elements M can enhance the tensile strength of β-Ti alloys while simultaneously maintaining toughness.
•Adding nickel (Ni) and chromium (Cr) to Al6061/SiC composites enhances mechanical properties like strength and hardness.•The inclusion of Ni and Cr leads to increased yield stress, ultimate tensile ...strength, and flexural strength.•While there’s a slight decrease in ductility, the trade-off results in improved material stiffness.•Overall, Ni and Cr show promise as effective reinforcements for engineering applications in Al6061/SiC composites.
This research paper investigates the mechanical characteristics of Al6061/Nickel (Ni) and Al6061/Chromium (Cr) metal matrix composites (MMCs) with varying proportions of Ni and Cr by weight. The proportions of Ni and Cr range from 0% to 2.7% weight. Experimental results reveal that the optimum mechanical properties are achieved at 1.8% weight for Ni. Subsequently, SiC (silicon carbide) particles are added to Al6061/Ni MMCs at varying weight percentages (0%, 1%, 3%, 5%, and 7%) to evaluate their impact on performance. The study demonstrates that the combination of 1.8% Ni and 7% SiC in Al6061 exhibits the most favorable properties. Tensile test is carried out with ASTM D 3552 standard; Flexural strength is assessed through ASTM D790, Microhardness by ASTM E384, and Impact strength by ASTM D256. Overall, Al6061/Ni MMCs exhibit superior mechanical performance compared to Al6061/Cr MMCs, with Al6061/Cr MMCs excelling in elongation, flexural strength, and impact strength. This investigation confirms that the addition of nickel and chromium to the Al6061 alloy induces structural modifications that enhance its mechanical properties. The findings provide valuable insights for optimizing the design and fabrication of MMCs for various engineering applications.
In this article, a multiscale modeling technique is developed to determine the effective elastic moduli of CNT-reinforced epoxy composites containing either well-dispersed or agglomerated carbon ...nanotubes (CNTs). Two aspects of the work are accordingly examined. In the first, molecular dynamics simulations are carried out to determine the atomic-level elastic properties of a representative volume element (RVE) comprised of either epoxy polymer or transversely isotropic CNT-epoxy composite. To study the effect of agglomeration of CNTs on the bulk elastic properties of the nanocomposite, CNT bundles of different sizes were considered. A constant-strain energy minimization method is used to determine the elastic coefficients of the RVEs. In the second, the Mori-Tanaka method is used to scale up the properties of the atomic structure to the microscale level, and the outcome is used to investigate the effect of orientations and agglomeration of CNTs on the bulk elastic properties of the nanocomposite. Our results reveal that as the number of CNTs in the bundle increases, the effective elastic properties of the nanocomposite decrease at the same CNT volume fraction.
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•Developed the novel multiscale model.•MD simulations were used in conjunction with Mori-Tanaka model.•Investigated the effect of orientations and agglomeration of CNTs.•Current MD results are in good agreement with those of ABC results.
This paper presents a stiffening method by which new inclined walls are added to the classical re-entrant honeycomb cell. This modification boosts the in-plane rigidity of the re-entrant cell without ...significant loss from auxetic behaviour. This study focuses on the in-plane elasticity moduli and negative Poisson's ratios along the principal axes. Analytical expressions that calculate the elasticity moduli and negative Poisson's ratios are derived; both finite element modelling and experiments reported in the literature validate the expressions of this work. Further, the variation in the in-plane elastic properties of the core cell is examined by altering the new wall's geometric, sectional, and material parameters. The results from the analytical expressions and the finite element models match very closely and demonstrate the boosted rigidity of the cell proposed in this work. This work also provides a benchmark of the new cell against the classical cell that can be used to tailor the in-plane elasticity moduli and negative Poisson's ratios to suit the needs of different applications.
•Enhancement stiffness of re-entrant honeycomb core cell.•Advanced tunable mechanical properties by new derived analytical expressions.•A benchmark of analytical, numerical and experimental results.
Two-dimensional lattices are ideal candidate for developing artificially engineered materials and structures across different length-scales, leading to unprecedented multi-functional mechanical ...properties which can not be achieved in naturally occurring materials and systems. Characterization of effective elastic properties of these lattices is essential for their adoption as structural elements of various devices and systems. An enormous amount of research has been conducted on different geometry of lattices to identify and characterize various parameters which affect the elastic properties. However, till date we can not control the elastic properties actively for a lattice microstructure, meaning that the elastic properties of such lattices are not truly programmable. All the parameters that control the effective elastic properties are passive in nature. After manufacturing the lattice structure with a certain set of geometric or material-based parameters, there is no room to modulate the properties further. In this article, we propose a hybrid lattice micro-structure by integrating piezo-electric materials with the members of the lattice for active voltage-dependent modulation of elastic properties. A bottom-up multi-physics based analytical framework leading to closed-form formulae is derived for hexagonal lattices to demonstrate the concept of active lattices. It is noticed that the Young’s moduli are voltage-dependent, while the shear modulus and the Poisson’s ratios are not functions of the applied voltage. Thus, the compound mechanics of deformation induced by external mechanical stresses and electric field lead to an active control over the Young’s moduli as a function of voltage. Interestingly, it turns out that a programmable state-transition of the Young’s moduli from positive to negative values with a wide range can be achieved in such hybrid lattices. The physics-based analytical framework for active modulation of voltage-dependent elastic properties on the basis of operational demands provide the necessary physical insights and confidence for potential practical exploitation of the proposed concept in various futuristic multi-functional structural systems and devices across different length-scales.
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