Stiff bioinspired architectured beams bend Saint-Venant’s principle and generate large shape morphing

Yokota, Kenichiro; Barthelat, François

doi:10.1016/j.ijsolstr.2023.112270

Cited by 7 publications

(4 citation statements)

References 23 publications

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“…Proper morphing along the entire ray requires a fine balance between the stiffness of the hemitrichs and the stiffness of the core, which we approached for this study by using 17 rubber ligaments. How these ligaments are distributed in the core may also affect the morphed ray, and to capture these more subtle effects, we first measured the local curvature of the ray κ(s) at u 0 = 18.2 mm, and we then computed the first moment of curvature κ (1) [42,51]:…”

Section: Morphing Testmentioning

confidence: 99%

Gradients of properties increase the morphing and stiffening performance of bioinspired synthetic fin rays

Das,

Kunjam,

Ebeling

et al. 2024

Bioinspir. Biomim.

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State-of-the-art morphing materials are either very compliant to achieve large shape changes (flexible metamaterials, compliant mechanisms, hydrogels), or very stiff but with infinitesimal changes in shape that require large actuation forces (metallic or composite panels with piezoelectric actuation). Morphing efficiency and structural stiffness are therefore mutually exclusive properties in current engineering morphing materials, which limits the range of their applicability. Interestingly, natural fish fins do not contain muscles, yet they can morph to large amplitudes with minimal muscular actuation forces from the base while producing large hydrodynamic forces without collapsing. This sophisticated mechanical response has already inspired several synthetic fin rays with various applications. However, most “synthetic” fin rays have only considered uniform properties and structures along the rays while in natural fin rays, gradients of properties are prominent. In this study, we designed, modeled, fabricated and tested synthetic fin rays with bioinspired gradients of properties. The rays were composed of two hemitrichs made of a stiff polymer, joined by a much softer core region made of elastomeric ligaments. Using combinations of experiments and nonlinear mechanical models, we found that gradients in both the core region and hemitrichs can increase the morphing and stiffening response of individual rays. Introducing a positive gradient of ligament density in the core region (the density of ligament increases towards the tip of the ray) decreased the actuation force required for morphing and increased overall flexural stiffness. Introducing a gradient of property in the hemitrichs, by tapering them, produced morphing deformations that were distributed over long distances along the length of the ray. These new insights on the interplay between material architecture and properties in nonlinear regimes of deformation can improve the designs of morphing structures that combine high morphing efficiency and high stiffness from external forces, with potential applications in aerospace or robotics.

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Section: Morphing Testmentioning

confidence: 99%

Gradients of properties increase the morphing and stiffening performance of bioinspired synthetic fin rays

Das,

Kunjam,

Ebeling

et al. 2024

Bioinspir. Biomim.

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“…In a recent study on morphing lattice beams [ 56 ], we examined several possible metrics for flexural morphing, all based on curvature. The maximum curvature

and an average curvature

(the curvature averaged over the length of the ray) were first considered as morphing metrics, but these metrics are not adequate: cases where the deformations are concentrated near the base of the ray, forming a deformation ‘hinge’ represent poor morphing response but produce high values of these metrics (the very high curvature near the base of the ray biasing

and

towards high values).…”

Section: Finite Element Model and Design Explorationmentioning

confidence: 99%

“…The maximum curvature

and an average curvature

and

towards high values). A better metric is the first moment of curvature κ (1) given by [ 56 ]:…”

Section: Finite Element Model and Design Explorationmentioning

confidence: 99%

Stiff morphing composite beams inspired from fish fins

Das,

Kunjam,

Moling

et al. 2024

Interface Focus.

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Morphing materials are typically either very compliant to achieve large shape changes or very stiff but with small shape changes that require large actuation forces. Interestingly, fish fins overcome these limitations: fish fins do not contain muscles, yet they can change the shape of their fins with high precision and speed while producing large hydrodynamic forces without collapsing. Here, we present a ‘stiff’ morphing beam inspired from the individual rays in natural fish fins. These synthetic rays are made of acrylic (PMMA) outer beams (‘hemitrichs’) connected with rubber ligaments which are 3–4 orders of magnitude more compliant. Combinations of experiments and models of these synthetic rays show strong nonlinear geometrical effects: the ligaments are ‘mechanically invisible’ at small deformations, but they delay buckling and improve the stability of the ray at large deformations. We use the models and experiments to explore designs with variable ligament densities, and we generate design guidelines for optimum morphing shape (captured using the first moment of curvature), that capture the trade-offs between morphing compliance (ease of morphing the structure) and flexural stiffness. The design guidelines proposed here can help the development of stiff morphing bioinspired structures for a variety of applications in aerospace, biomedicine or robotics.

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“…While the morphing matter has demonstrated the potential to emulate the functionalities of living organisms and has made significant contributions across various engineering domains, attaining the ability for shape-morphing is not trivial [17,18] . The transformation from a two-dimensional (2D) flat sheet to intricate three-dimensional (3D) shapes requires a controlled manipulation of surface curvature [19][20][21] . Basic shape morphing forms (e.g., bending and rolling of flat sheets), which preserve the Gaussian curvature, can be achieved by leveraging the elasticity [22,23] and instabilities of materials and/or structures [24,25] , such as strain-mismatch in bilayers and buckling of slender beams [21] .…”

Section: Introductionmentioning

confidence: 99%

Morphing matter: from mechanical principles to robotic applications

Yang,

Zhou,

Zhao

et al. 2023

Soft Sci

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The adaptability of natural organisms in altering body shapes in response to the environment has inspired the development of artificial morphing matter. These materials encode the ability to transform their geometrical configurations in response to specific stimuli and have diverse applications in soft robotics, wearable electronics, and biomedical devices. However, achieving the morphing of intricate three-dimensional shapes from a two-dimensional flat state is challenging, as it requires manipulations of surface curvature in a controlled manner. In this review, we first summarize the mechanical principles extensively explored for realizing morphing matter, both at the material and structural levels. We then highlight its applications in the soft robotics field. Moreover, we offer insights into the open challenges and opportunities that this rapidly growing field faces. This review aims to inspire researchers to uncover innovative working principles and create multifunctional morphing matter for various engineering fields.

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Stiff bioinspired architectured beams bend Saint-Venant’s principle and generate large shape morphing

Cited by 7 publications

References 23 publications

Gradients of properties increase the morphing and stiffening performance of bioinspired synthetic fin rays

Gradients of properties increase the morphing and stiffening performance of bioinspired synthetic fin rays

Stiff morphing composite beams inspired from fish fins

Morphing matter: from mechanical principles to robotic applications

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