Pattern switching in two and three-dimensional soft solids

Willshaw, Stephen; Mullin, T.

doi:10.1039/c1sm06765f

Cited by 25 publications

(20 citation statements)

References 15 publications

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“…In most of the examples mentioned above, elastic instabilities are exploited to trigger a pattern switch by a broken rotational symmetry, mostly governed by Euler buckling. In these works instabilities are induced by an applied compressive load . This observation naturally leads to the question of whether one can either benefit from other mechanical instability mechanisms for metamaterial design or extend current concepts to other loading conditions.…”

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confidence: 99%

Snapping Mechanical Metamaterials under Tension

2015

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We present a monolithic mechanical metamaterial comprising a periodic arrangement of snapping units with tunable tensile behavior. Under tension, the metamaterial undergoes a large extension caused by sequential snap-through instabilities, and exhibits a pattern switch from an undeformed wavy-shape to a diamond configuration. By means of experiments performed on 3D printed prototypes, numerical simulations and theoretical modeling, we demonstrate how the snapping architecture can be tuned to generate a range of nonlinear mechanical responses including monotonic, S-shaped, plateau and non-monotonic snap-through behavior. This work contributes to the development of design strategies that allow programming nonlinear mechanical responses in solids.Mechanical metamaterials are man-made materials, usually fashioned from repeating unit cells which are engineered to achieve extreme mechanical properties, often beyond those found in most natural materials.[1] They gain their unusual, sometimes extraordinary, mechanicalproperties from their underlying architecture, rather than the composition of their constituents. Metamaterials exhibit interesting mechanical properties, such as negative Poisson's ratio, [2,3] negative incremental stiffness, [4] negative compressibility [5] and unusual dynamic behavior for wave propagation. [6] As Ron Resch (artist and applied geometrist) points out in his statement "the environment responds by collapsing quite often", [7] instabilities can be exploited to design advanced materials with innovative properties. [8] Recently, harnessing elastic instabilities played a central role in the rational design of novel 2D [9][10][11][12][13][14] and 3D [15][16][17] mechanical metamaterials with either significantly enhanced mechanical properties or equipped with new functionalities, e.g. programmable shape transformations. [14] In most of the examples mentioned above, elastic instabilities are exploited to trigger a pattern switch by a broken rotational symmetry, mostly governed by Euler buckling. In these works instabilities are induced by an applied compressive load. [16] This observation naturally leads to the question of whether one can either benefit from other mechanical instability mechanisms for metamaterial design or extend current concepts to other loading conditions. In this work, we exploit mechanical instabilities triggered by snap-through buckling to create a metamaterial which experiences a pseudo pattern switch in tension and exhibits a programmable mechanical response. Our design is inspired by a monolithic bistable mechanism, [18] i.e. two curved parallel beams that are centrally-clamped as schematized in Figure 1a. A normal force applied in the middle of the double-beam mechanism can prompt it to snap through to its second stable state ( Figure 1a, dashed lines). We release clamped conditions at both ends to create a repeatable unit cell (Figure 1b), composed of two centrally connected cosine-shaped slender segments, which can be tessellated in plane to form a periodic ar...

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Snapping Mechanical Metamaterials under Tension

2015

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“…Recently, we and others have explored buckling instabilities of soft membranes with periodic hole arrays, where the bending of the interpore ligaments triggers homogeneous and reversible pattern transformations . The transformation occurs at a broad range of length scales ranging from submicron to centimeter scale, and offers a unique mechanism to induce significant change of the physical properties of the metamaterials, including photonic and phononic bandgaps, mechanical properties (e.g., negative Poisson's ratio), and symmetry breaking arising from simultaneous alterations of lattice symmetry, pore size and shape, and volume filling fraction.…”

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Directing the Deformation Paths of Soft Metamaterials with Prescribed Asymmetric Units

Cho

Choi

et al. 2015

Advanced Materials

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“…Early investigations were primarily concerned with the prevention of buckling, but much recent work has focused on harnessing the effect 6 with novel applications in soft robotics 7 , and nature inspired photonics [8][9][10] . Lattice structures formed by perforated elastomers have attracted a great deal of recent attention [11][12][13][14][15] , in part because despite being geometrically simple they exhibit non-trivial buckling modes. Moreover, the reported effects are length-scale independent, suggesting the same instabilities could control optical solitons 16 at the microscale as well as potentially diverting damaging earthquake vibrations 17 over kilometre scales.…”

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confidence: 99%

Buckling of a holey column

2016

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We report the results from a combined experimental and numerical investigation of buckling in a novel variant of an elastic column under axial load. We find that including a regular line of centred holes in the column can prevent conventional, global, lateral buckling. Instead, the local microstructure introduced by the holes allows the column to buckle in an entirely different, internal, mode in which the holes are compressed in alternate directions, but the column maintains the lateral reflection symmetry about its centreline. The internal buckling mode can be accommodated within a smaller external space than the global one; and it is the preferred buckling mode over an intermediate range of column lengths for sufficiently large holes. For very short or sufficiently long columns a modification of the classical, global, lateral buckling is dominant.

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Pattern switching in two and three-dimensional soft solids

Cited by 25 publications

References 15 publications

Snapping Mechanical Metamaterials under Tension

Snapping Mechanical Metamaterials under Tension

Directing the Deformation Paths of Soft Metamaterials with Prescribed Asymmetric Units

Buckling of a holey column

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