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Highly-stretchable 3D-architected Mechanical Metamaterials

View Article: PubMed Central - PubMed

ABSTRACT

Soft materials featuring both 3D free-form architectures and high stretchability are highly desirable for a number of engineering applications ranging from cushion modulators, soft robots to stretchable electronics; however, both the manufacturing and fundamental mechanics are largely elusive. Here, we overcome the manufacturing difficulties and report a class of mechanical metamaterials that not only features 3D free-form lattice architectures but also poses ultrahigh reversible stretchability (strain > 414%), 4 times higher than that of the existing counterparts with the similar complexity of 3D architectures. The microarchitected metamaterials, made of highly stretchable elastomers, are realized through an additive manufacturing technique, projection microstereolithography, and its postprocessing. With the fabricated metamaterials, we reveal their exotic mechanical behaviors: Under large-strain tension, their moduli follow a linear scaling relationship with their densities regardless of architecture types, in sharp contrast to the architecture-dependent modulus power-law of the existing engineering materials; under large-strain compression, they present tunable negative-stiffness that enables ultrahigh energy absorption efficiencies. To harness their extraordinary stretchability and microstructures, we demonstrate that the metamaterials open a number of application avenues in lightweight and flexible structure connectors, ultraefficient dampers, 3D meshed rehabilitation structures and stretchable electronics with designed 3D anisotropic conductivity.

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Mechanical behaviors of elastomer lattices under large-strain tensions.(A) Sequential images to show a Kelvin elastomer lattice under increasing uniaxial tensile strains. The arrow indicates the reversibility of the stretching. Scar bar denotes 4 mm. (B) Nominal stresses of Kelvin and Octet elastomer lattices in functions of tensile strains. The experimentally measured curves (“Exp”) are fitted to the Arruda-Boyce model with μ = 6 kPa and λm = 2.8 for Kelvin, and μ = 10.1 kPa and λm = 2.3 for Octet. (C) Nominal stresses of Kelvin elastomer lattices with varied beam diameters in functions of tensile strains. The fitted shear moduli are 4.2 kPa (0.5 mm), 6 kPa (0.7 mm) and 10 kPa (0.9 mm), respectively. (D) Relative shear moduli of Kelvin and Octet elastomer lattices in functions of relative densities. The finite-element-analysis (“FEA”) simulated relationships are μ/μ0 ≈ 0.57 ρ/ρ0 (Kelvin) and μ/μ0 ≈ 0.49 ρ/ρ0 (Octet). The dash line in (D) indicates the slope for scaling relationship μ/μ0 ∝ ρ/ρ0. (E) The maximum reversible tensile strains of Octet, Kagome, Octahedron, Kelvin and Dodecahedron elastomer lattices, and elastomer foams. The error bars denote the standard deviation among at least 3 data points.
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f3: Mechanical behaviors of elastomer lattices under large-strain tensions.(A) Sequential images to show a Kelvin elastomer lattice under increasing uniaxial tensile strains. The arrow indicates the reversibility of the stretching. Scar bar denotes 4 mm. (B) Nominal stresses of Kelvin and Octet elastomer lattices in functions of tensile strains. The experimentally measured curves (“Exp”) are fitted to the Arruda-Boyce model with μ = 6 kPa and λm = 2.8 for Kelvin, and μ = 10.1 kPa and λm = 2.3 for Octet. (C) Nominal stresses of Kelvin elastomer lattices with varied beam diameters in functions of tensile strains. The fitted shear moduli are 4.2 kPa (0.5 mm), 6 kPa (0.7 mm) and 10 kPa (0.9 mm), respectively. (D) Relative shear moduli of Kelvin and Octet elastomer lattices in functions of relative densities. The finite-element-analysis (“FEA”) simulated relationships are μ/μ0 ≈ 0.57 ρ/ρ0 (Kelvin) and μ/μ0 ≈ 0.49 ρ/ρ0 (Octet). The dash line in (D) indicates the slope for scaling relationship μ/μ0 ∝ ρ/ρ0. (E) The maximum reversible tensile strains of Octet, Kagome, Octahedron, Kelvin and Dodecahedron elastomer lattices, and elastomer foams. The error bars denote the standard deviation among at least 3 data points.

Mentions: Compared to reported architected materials with 3D complex architectures (not including foams with stochastic architectures), our elastomer lattices pose the highest reversible stretchability and compressibility (Fig. 2). The fabricated elastomer-lattice metamaterials can be reversibly stretched over 414% strain (Fig. 3A) and compressed over 98% strain (Supplementary Fig. 5). However, the solid or hollow micro/nano lattices (including rigid plastics, metals and ceramics) fabricated by projection microstereolithography252634, waveguide polymerization27 and two-photon lithography2428293031 generally can only be reversibly compressed or stretched up to ~15% strain before yielding or fracture. Elastomer lattices fabricated with the commercially-available photoresins (usually thermoplastic elastomer) via stereolithography can only be reversibly compressed to ~50% and stretched to ~80%538. Elastomer nanolattices fabricated by an inverse processes of photolithography can be reversibly compressed to ~70% and stretched to ~225%10; however, they are limited to selective architectures that are determined by the waveguide etching pathways. As a result, the reversible stretchability of the elastomer metamaterials presented in the current paper (414% strain) is more than four times larger than that of lattice structures in similar level of architecture complexity (e.g., stereolithography of commercial thermoplastic elastomer). In addition to the outstanding deformability, our elastomer metamaterials are also very lightweight: Compared to the elastomer solids with density ~1000 kg/m3 (shown as the dash lines in Fig. 2), the density of our elastomer lattices are only 6–50% of their bulk, in a comparable range of those of the microlattices fabricated by the existing additive manufacturing techniques (Fig. 2)25262734.


Highly-stretchable 3D-architected Mechanical Metamaterials
Mechanical behaviors of elastomer lattices under large-strain tensions.(A) Sequential images to show a Kelvin elastomer lattice under increasing uniaxial tensile strains. The arrow indicates the reversibility of the stretching. Scar bar denotes 4 mm. (B) Nominal stresses of Kelvin and Octet elastomer lattices in functions of tensile strains. The experimentally measured curves (“Exp”) are fitted to the Arruda-Boyce model with μ = 6 kPa and λm = 2.8 for Kelvin, and μ = 10.1 kPa and λm = 2.3 for Octet. (C) Nominal stresses of Kelvin elastomer lattices with varied beam diameters in functions of tensile strains. The fitted shear moduli are 4.2 kPa (0.5 mm), 6 kPa (0.7 mm) and 10 kPa (0.9 mm), respectively. (D) Relative shear moduli of Kelvin and Octet elastomer lattices in functions of relative densities. The finite-element-analysis (“FEA”) simulated relationships are μ/μ0 ≈ 0.57 ρ/ρ0 (Kelvin) and μ/μ0 ≈ 0.49 ρ/ρ0 (Octet). The dash line in (D) indicates the slope for scaling relationship μ/μ0 ∝ ρ/ρ0. (E) The maximum reversible tensile strains of Octet, Kagome, Octahedron, Kelvin and Dodecahedron elastomer lattices, and elastomer foams. The error bars denote the standard deviation among at least 3 data points.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5035992&req=5

f3: Mechanical behaviors of elastomer lattices under large-strain tensions.(A) Sequential images to show a Kelvin elastomer lattice under increasing uniaxial tensile strains. The arrow indicates the reversibility of the stretching. Scar bar denotes 4 mm. (B) Nominal stresses of Kelvin and Octet elastomer lattices in functions of tensile strains. The experimentally measured curves (“Exp”) are fitted to the Arruda-Boyce model with μ = 6 kPa and λm = 2.8 for Kelvin, and μ = 10.1 kPa and λm = 2.3 for Octet. (C) Nominal stresses of Kelvin elastomer lattices with varied beam diameters in functions of tensile strains. The fitted shear moduli are 4.2 kPa (0.5 mm), 6 kPa (0.7 mm) and 10 kPa (0.9 mm), respectively. (D) Relative shear moduli of Kelvin and Octet elastomer lattices in functions of relative densities. The finite-element-analysis (“FEA”) simulated relationships are μ/μ0 ≈ 0.57 ρ/ρ0 (Kelvin) and μ/μ0 ≈ 0.49 ρ/ρ0 (Octet). The dash line in (D) indicates the slope for scaling relationship μ/μ0 ∝ ρ/ρ0. (E) The maximum reversible tensile strains of Octet, Kagome, Octahedron, Kelvin and Dodecahedron elastomer lattices, and elastomer foams. The error bars denote the standard deviation among at least 3 data points.
Mentions: Compared to reported architected materials with 3D complex architectures (not including foams with stochastic architectures), our elastomer lattices pose the highest reversible stretchability and compressibility (Fig. 2). The fabricated elastomer-lattice metamaterials can be reversibly stretched over 414% strain (Fig. 3A) and compressed over 98% strain (Supplementary Fig. 5). However, the solid or hollow micro/nano lattices (including rigid plastics, metals and ceramics) fabricated by projection microstereolithography252634, waveguide polymerization27 and two-photon lithography2428293031 generally can only be reversibly compressed or stretched up to ~15% strain before yielding or fracture. Elastomer lattices fabricated with the commercially-available photoresins (usually thermoplastic elastomer) via stereolithography can only be reversibly compressed to ~50% and stretched to ~80%538. Elastomer nanolattices fabricated by an inverse processes of photolithography can be reversibly compressed to ~70% and stretched to ~225%10; however, they are limited to selective architectures that are determined by the waveguide etching pathways. As a result, the reversible stretchability of the elastomer metamaterials presented in the current paper (414% strain) is more than four times larger than that of lattice structures in similar level of architecture complexity (e.g., stereolithography of commercial thermoplastic elastomer). In addition to the outstanding deformability, our elastomer metamaterials are also very lightweight: Compared to the elastomer solids with density ~1000 kg/m3 (shown as the dash lines in Fig. 2), the density of our elastomer lattices are only 6–50% of their bulk, in a comparable range of those of the microlattices fabricated by the existing additive manufacturing techniques (Fig. 2)25262734.

View Article: PubMed Central - PubMed

ABSTRACT

Soft materials featuring both 3D free-form architectures and high stretchability are highly desirable for a number of engineering applications ranging from cushion modulators, soft robots to stretchable electronics; however, both the manufacturing and fundamental mechanics are largely elusive. Here, we overcome the manufacturing difficulties and report a class of mechanical metamaterials that not only features 3D free-form lattice architectures but also poses ultrahigh reversible stretchability (strain > 414%), 4 times higher than that of the existing counterparts with the similar complexity of 3D architectures. The microarchitected metamaterials, made of highly stretchable elastomers, are realized through an additive manufacturing technique, projection microstereolithography, and its postprocessing. With the fabricated metamaterials, we reveal their exotic mechanical behaviors: Under large-strain tension, their moduli follow a linear scaling relationship with their densities regardless of architecture types, in sharp contrast to the architecture-dependent modulus power-law of the existing engineering materials; under large-strain compression, they present tunable negative-stiffness that enables ultrahigh energy absorption efficiencies. To harness their extraordinary stretchability and microstructures, we demonstrate that the metamaterials open a number of application avenues in lightweight and flexible structure connectors, ultraefficient dampers, 3D meshed rehabilitation structures and stretchable electronics with designed 3D anisotropic conductivity.

No MeSH data available.


Related in: MedlinePlus