In-plane mechanical behavior of novel auxetic hybrid metamaterials (original) (raw)
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materials Non-Auxetic Mechanical Metamaterials
The concept of "mechanical metamaterials" has become increasingly popular, since their macro-scale characteristics can be designed to exhibit unusual combinations of mechanical properties on the micro-scale. The advances in additive manufacturing (AM, three-dimensional printing) techniques have boosted the fabrication of these mechanical metamaterials by facilitating a precise control over their micro-architecture. Although mechanical metamaterials with negative Poisson's ratios (i.e., auxetic metamaterials) have received much attention before and have been reviewed multiple times, no comparable review exists for architected materials with positive Poisson's ratios. Therefore, this review will focus on the topology-property relationships of non-auxetic mechanical metamaterials in general and five topological designs in particular. These include the designs based on the diamond, cube, truncated cube, rhombic dodecahedron, and the truncated cuboctahedron unit cells. We reviewed the mechanical properties and fatigue behavior of these architected materials, while considering the effects of other factors such as those of the AM process. In addition, we systematically analyzed the experimental, computational, and analytical data and solutions available in the literature for the titanium alloy Ti-6Al-4V. Compression dominated lattices, such as the (truncated) cube, showed the highest mechanical properties. All of the proposed unit cells showed a normalized fatigue strength below that of solid titanium (i.e., 40% of the yield stress), in the range of 12-36% of their yield stress. The unit cells discussed in this review could potentially be applied in bone-mimicking porous structures.
Normal and shear behaviours of auxetic metamaterials: homogenisation and experimental approaches
Meccanica, 2019
Auxetic metamaterials exhibit attractive mechanical properties, including negative Poisson's ratio and compressional resistance. Although auxetic meta-materials have been extensively investigated using experimental and computational approaches, the consistent estimation of shear properties is unclear. According to Cauchy elasticity, the shear properties of an auxetic structure should be enhanced because of the negative Poisson's ratio. However, this study used homogenisation and experimental approaches to demonstrate that shear elasticity is highly non-linear with respect to the characteristic geometrical parameters of a unit cell and that shear properties are not always improved.
3D Printed Auxetic Mechanical Metamaterial with Chiral Cells and Re-entrant Cores
Scientific Reports, 2018
By combining the two basic deformation mechanisms for auxetic open-cell metamaterials, re-entrant angle and chirality, new hybrid chiral mechanical metamaterials are designed and fabricated via a multi-material 3D printer. Results from mechanical experiments on the 3D printed prototypes and systematic Finite Element (FE) simulations show that the new designs can achieve subsequential cell-opening mechanism under a very large range of overall strains (2.91%–52.6%). Also, the effective stiffness, the Poisson’s ratio and the cell-opening rate of the new designs can be tuned in a wide range by tailoring the two independent geometric parameters: the cell size ratio {{\boldsymbol{c}}}_{{\bf{0}}}{\boldsymbol{/}}{{\boldsymbol{b}}}_{{\bf{0}}}$$ c 0 / b 0 , and re-entrant angle θ. As an example application, a sequential particle release mechanism of the new designs was also systematically explored. This mechanism has potential application in drug delivery. The present new design concepts ca...
Hierarchical Auxetic Mechanical Metamaterials
Scientific Reports, 2015
Auxetic mechanical metamaterials are engineered systems that exhibit the unusual macroscopic property of a negative Poisson's ratio due to sub-unit structure rather than chemical composition. Although their unique behaviour makes them superior to conventional materials in many practical applications, they are limited in availability. Here, we propose a new class of hierarchical auxetics based on the rotating rigid units mechanism. These systems retain the enhanced properties from having a negative Poisson's ratio with the added benefits of being a hierarchical system. Using simulations on typical hierarchical multi-level rotating squares, we show that, through design, one can control the extent of auxeticity, degree of aperture and size of the different pores in the system. This makes the system more versatile than similar non-hierarchical ones, making them promising candidates for industrial and biomedical applications, such as stents and skin grafts.
International Journal of Solids and Structures, 2020
Architected metamaterials exhibit unique properties bestowed by their engineered structure rather than their chemical composition. Extrinsic material properties have been achieved as a result of advances in additive manufacturing. Contemporary fabrication techniques, such as multiphoton lithography and digital light processing, have enabled the fabrication of complex structures with inherent hierarchies at length scales ranging from nanometers to micrometers. However, despite significant insight into the role of buckling in the mechanical behavior of materials reported in earlier studies, particularly strength and energy dissipation, the structural and design principles responsible for the improved mechanical performance were not fully elucidated, thus limiting the design space of these structures. The principal objective of this study was to investigate how controlled three-dimensional assembly and orientation of intertwined lattice members influence localized buckling and the overall mechanical response of such metamaterial structures. The novelty of the present design approach stems from a mechanical metamaterial inspired by the three-compound octahedron and the symmetry variance observed during phase change of crystalline solids. For a specific orientation and tactical joining of the unit cells, this geometry demonstrates unprecedented resilience to large deformations and high energy dissipation capacity. The selective shape modification of specific lattice members is shown to greatly improve the structural integrity of ultralight structures undergoing large deformation. Results from finite element simulations and in situ scanning electron microscopy-microindentation experiments reveal the actual deformation of metamaterial structures with straight and curved lattice members and elucidate the effects of anisotropy and orientation characteristics on the dominant mechanisms affecting the mechanical performance of intertwined lattice structures.
The two-dimensional elasticity of a chiral hinge lattice metamaterial
International Journal of Solids and Structures
We present a lattice structure defined by patterns of slits that follow a rotational symmetry (chiral) configuration. The chiral pattern of the slits creates a series of hinges that produce deformation mechanisms for the lattice due to bending of the ribs, leading to a marginal negative Poisson's ratio. The engineering constants are modelled using theoretical and numerical Finite Element simulations. The results are benchmarked with experimental data obtained from uniaxial and off-axis tensile tests, with an overall excellent agreement. The chiral hinge lattice is almost one order of magnitude more compliant than other configurations with patterned slits and-in contrast to other chiral micropolar media-exhibits an in-plane shear modulus that closely obeys the relation between Young's modulus and Poisson's ratio in homogeneous isotropic linear elastic materials.
Auxetic metamaterials subjected to dynamic loadings
Theoretical and Applied Mechanics
Materials with negative Poisson?s ratio are called auxetics and they present enhanced properties (e.g. damping, indentation resistance, fracture toughness and impact resistance) under external loadings. The auxetic properties are derived from peculiar-shaped microstructures, such as starshaped frames. In the present investigation, several applications are studied using auxetic microstructures. Finite element models are developed for dynamic analysis. First, an application related to auxetic microstructures, for the core of structural panels, is presented. Next, the use of auxetic materials in armor plates in dynamic bullet penetration problems is considered. Finally, a numerical simulation for wind turbines blades, with aluminum foam, polymeric foam and the proposed auxetic material is carried out. The numerical results demonstrate that the use of auxetic microstructures results in improved dynamic response of the system in comparison to conventional materials.
Dome-Shape Auxetic Cellular Metamaterials: Manufacturing, Modeling, and Testing
Frontiers in Materials
We present in this work the manufacturing, modeling, and testing of dome-shaped cellular structures with auxetic (negative Poisson's ratio) behavior. The auxetic configurations allow the creation of structures with synclastic (i.e., dome-shaped) curvatures, and this feature is used to evaluate the performance of cellular metamaterials under quasi-static indentation conditions. We consider here different cellular geometries (re-entrant, arrow-head, tri-chiral, hexagonal) and the implications of their manufacturing using 3D printing techniques with PLA material. The dome-shaped configurations are modeled using full-scale non-linear quasi-static and explicit dynamic FE models that represent both the geometry and approximate constitutive models of the PLA filament material derived from tensile tests on dogbone specimens. The cellular metamaterials samples are subjected to indentation tests, with maps of strains obtained through DIC measurements. The correlation between experimental and numerical simulations is good, and shows the peculiar indentation behavior of these cellular structures. We also perform a comparative analysis by simulation of the force/displacement, strain and fracture history during quasi-static loading, and discuss the performance of the different cellular topologies for these dome-shape metamaterial designs.
Advanced Engineering Materials, 2021
The advancements in additive manufacturing (AM) technology make the fabrication of complex architected materials and structures at multiple length scales possible to explore a new family of metamaterial. A metamaterial is an artificially engineered material to have a property not found in conventional materials. [1] Historically, the term "metamaterials" were limited to electromagnetism field, but, recently, it has been extended to photonic, phononic, and mechanical systems to design architected engineered materials that exhibit properties not usually found in conventional materials. [2] Mechanical metamaterials refer to a sort of metamaterials that designed artificial structural materials with counterintuitive mechanical properties derived from their tailored internal microstructure rather than the composition of base material. [3] The unusual properties include negative Poisson's ratio, negative modulus of elasticity, and negative compressibility. [4,5] Examples of mechanical metamaterials include acoustic metamaterials, auxetic materials, pentamode metamaterials, and micropolar metamaterials. The concept of metamaterials combined with AM opens new design avenues for the fabrication of complex microstructures over a wide range of length scales. [6-8] Auxetic mechanical metamaterials are recognized by a negative Poisson's ratio; i.e., materials will contract (expand) in the transverse direction when compressed uniaxially (stretched). Auxetic mechanical metamaterials are of interest because of their enhanced mechanical properties, such as increased indentation resistance, [9] shear modulus, [10] and fracture toughness. [11] They have a great potential in engineering applications, such as cellular materials with superior damping and acoustic properties, [12] piezoelectric metamaterials, [13] piezocomposites, [14] auxetic fasteners, [15] bioprostheses, [16] tissue engineering, [17] and mechanically tunable, elastically reversible, and transformable topological mechanical metamaterials. [18,19] The negative Poisson's ratio of auxetic material depends on the topology of auxetic building blocks and scaleindependent. [20,21] Several natural materials exhibit negative Poisson's ratio, such as silicates, [22] cubic elemental metals, [23] zeolites, [24] natural layered ceramics, [25] and monolithic ferroelectric polycrystalline ceramics. [26] Love [27] was the first to report the negative Poisson's ratio of naturally occurring cubic crystals of
2016-Controlled Unusual Stiffness of Mechanical Metamaterials.pdf
Mechanical metamaterials that are engineered with sub-unit structures present unusual mechanical properties depending on the loading direction. Although they show promise, their practical utility has so far been somewhat limited because, to the best of our knowledge, no study about the potential of mechanical metamaterials made from sophisticatedly tailored sub-unit structures has been made. Here, we present a mechanical metamaterial whose mechanical properties can be systematically designed without changing its chemical composition or weight. We study the mechanical properties of triply periodic bicontinuous structures whose detailed sub-unit structure can be precisely fabricated using various sub-micron fabrication methods. Simulation results show that the effective wave velocity of the structures along with different directions can be designed to introduce the anisotropy of stiffness by changing a volume fraction and aspect ratio. The ratio of Young's modulus to shear modulus can be increased by up to at least 100, which is a 3500% increase over that of isotropic material (2.8, acrylonitrile butadiene styrene). Furthermore, Poisson's ratio of the constituent material changes the ratio while Young's modulus does not influence it. This study presents the promising potential of mechanical metamaterials for versatile industrial and biomedical applications.