Showing papers by "Marc A. Meyers published in 2019"

Hyperelastic phase-field fracture mechanics modeling of the toughening induced by Bouligand structures in natural materials

Abstract: Bouligand structures are widely observed in natural materials; elasmoid fish scales and the exoskeleton of arthropods, such as lobsters, crabs, mantis shrimp and insects, are prime examples. In fish scales, such as those of the Arapaima gigas, the tough inner core beneath the harder surface of the scale displays a Bouligand structure comprising a layered arrangement of collagen fibrils with an orthogonal or twisted staircase (or plywood) architecture. A much rarer variation of this structure, the double-twisted Bouligand structure, has been discovered in the primitive elasmoid scales of the coelacanth fish; this architecture is quite distinct from “modern” elasmoid fish scales yet provides extraordinary resistance to deformation and fracture. Here we examine the toughening mechanisms created by the double-twisted Bouligand structure in comparison to those generated by the more common single Bouligand structures. Specifically, we have developed an orientation-dependent, hyperelastic, phase-field fracture mechanics method to computationally examine the relative fracture toughness of elasmoid fish scales comprising single vs. double-twisted Bouligand structures of fibrils. The model demonstrates the critical role played by the extra inter-bundle fibrils found in coelacanth fish scales in enhancing the toughness of Bouligand-type structures. Synthesis and fracture tests of 3-D printed Bouligand-type materials are presented to support the modeling and complement our understanding of the fracture mechanisms in Bouligand-type structures.

Lessons from the Ocean: Whale Baleen Fracture Resistance.

Abstract: Whale baleen is a keratin-based biological material; it provides life-long (40-100 years) filter-feeding for baleen whales in place of teeth. This study reveals new aspects of the contribution of the baleen's hierarchical structure to its fracture toughness and connects it to the unique performance requirements, which require anisotropy of fracture resistance. Baleen plates are subjected to competing external effects of hydration and varying loading rates and demonstrate a high fracture toughness in transverse loading, which is the most important direction in the filtering function; in the longitudinal direction, the toughness is much lower since delamination and controlled flexure are expected and desirable. The compressive strength is also established and results support the fracture toughness measurements: it is also highly anisotropic, and exhibits a ductile-to-brittle transition with increasing strain rate in the dry condition, which is absent in the hydrated condition, conferring impact resistance to the baleen. Using 3D-printing prototypes that replicate the three principal structural features of the baleen plate (hollow medulla, mineralized tubules, and sandwich-tubular structure) are created, and the role of its structure in determining its mechanical behavior is demonstrated. These findings suggest new bioinspired engineering materials.

Arapaima Fish Scale: One of the Toughest Flexible Biological Materials

Abstract: Summary For fish scales to provide protection from predators without severely compromising mobility, they must be lightweight, flexible, and tough. The arapaima fish scale is a superb example of this, enabling its survival in piranha-infested lakes of the Amazon. These elasmoid scales comprise two layers: a laminate composite of parallel collagen fibrils arranged in a Bouligand-like pattern and a highly mineralized surface layer that prevents initial penetration damage. Here, we measure its J-integral fracture toughness and find that the crack-growth toughness is ∼100–200 kJ⋅m−2, representing a very high fracture resistance for a natural material. This toughness results from multiple deformation mechanisms acting in concert in the twisted plywood structure of the scale, involving the collagenous lamellae at varying orientations retarding crack advance through stretching, reorientation, delamination and shear, and fracture. The toughness values obtained for the arapaima scales indicate that they are among the toughest of nature's flexible biological materials.

External Field Assisted Freeze Casting

Abstract: Freeze casting under external fields (magnetic, electric, or acoustic) produces porous materials having local, regional, and global microstructural order in specific directions. In freeze casting, porosity is typically formed by the directional solidification of a liquid colloidal suspension. Adding external fields to the process allows for structured nucleation of ice and manipulation of particles during solidification. External control over the distribution of particles is governed by a competition of forces between constitutional supercooling and electromagnetism or acoustic radiation. Here, we review studies that apply external fields to create porous ceramics with different microstructural patterns, gradients, and anisotropic alignments. The resulting materials possess distinct gradient, core–shell, ring, helical, or long-range alignment and enhanced anisotropic mechanical properties.

Scaling of bird wings and feathers for efficient flight

Abstract: Aves are an incredibly diverse class of animals, ranging greatly in size and thriving in a wide variety of environments. Here, we explore the scaling trends of bird wings in connection with their flight performance. The tensile strength of avian bone is hypothesized to be a limiting factor in scaling the humerus with mass, which is corroborated by its experimentally determined allometric scaling trend. We provide a mechanics analysis that explains the scaling allometry of the wing humerus length, LH, with body weight W, LH ∝ W0.44. Lastly, wing feathers are demonstrated to generally scale isometrically with bird mass, with the exception of the spacing between barbules, which falls within the same range for birds of all masses. Our findings provide insight into the “design” of birds and may be translatable to more efficient bird-inspired aircraft structures.

Bioinspired composite segmented armour: Numerical simulations

Abstract: Nature has evolved ingenious armour designs, like the flexible carapaces of armadillo and boxfish consisting of hexagonal segments connected by collagen fibres, that serve as bioinspiration for modern ballistic armours. Here, Finite element modelling (FEM) used to analyze the effect of scale geometry and other impact parameters on the ballistic protection provided by a bioinspired segmented ceramic armour. For this purpose, the impact of cylindrical fragment simulating projectiles (FSPs) onto alumina-epoxy non-overlapping scaled plates was simulated. Scale geometrical parameters (size, thickness and shape) and impact conditions (FSP diameter, speed, location) are varied and the amount of damage produced in the ceramic tiles and the final residual velocity of the FSP after the impact are evaluated. It is found that segmentation drastically reduces the size of the damaged area without significantly reducing the ballistic protection in centred impact, provided the tile size is kept over a critical value. Such critical tile size (∼20 mm, inscribed diameter, for impacts at 650 m/s) is independent of the scale thickness, but decreases with projectile speed, although never below the diameter of the projectile. Off-centred impacts reduce the ballistic protection and increase the damaged area, but this can be minimized with an appropriate tile shape. In this sense and in agreement with the natural hexagonal tiles of the boxfish and armadillo, hexagonal scales are found to be optimal, exhibiting a variation of ballistic protection—measured as reduction of projectile speed—with impact location under 12%. Design guidelines for the fabrication of segmented protection systems are proposed in the light of these numerical results.

On the Nature of the Transparent Teeth of the Deep-Sea Dragonfish, Aristostomias scintillans

Abstract: Summary The dragonfish is a voracious predator of the deep sea with an arsenal of tools to hunt prey and remain concealed. In contrast to its dark pigmented skin, the dragonfish is equipped with transparent teeth. Here, we establish the structure, composition, and mechanical properties of the transparent teeth for the first time. We find the enamel-like layer to consist of nanocrystalline hydroxyapatite domains (∼20 nm grain size) embedded in an amorphous matrix, whereas in the dentin layer the nanocrystalline hydroxyapatite coats nanoscale collagen fibrils forming nanorods. This nanoscale structure is responsible for the much-reduced Rayleigh light scattering, which is further ensured by the sufficiently thin walls. Here, we suggest that the nanostructured design of the transparent dragonfish teeth enables predatory success as it makes its wide-open mouth armed with saber-like teeth effectively disappear, showing no contrast to the surrounding blackness of the fish nor the background darkness of the deep sea.

Arapaima Fish Scale: One of the Toughest Flexible Biological Materials

Abstract: In order for fish scales to provide protection from predators without significantly compromising mobility, they have to be lightweight, flexible and tough. The Arapaima fish scale is a superb example of these properties, which enable survival in piranha-infested seasonal lakes of the Amazon. These elasmoid scales are composed of two layers: a laminate composite of parallel collagen fibrils arranged in a Bouligand-like pattern, and a hard, highly mineralized surface layer that prevents initial penetration damage. We measure here the J-integral based fracture toughness of the scale and find that the crack-growth toughness as high as ~200 kJ⋅m-2, representing a very high fracture resistance for a flexible biological material. This toughness is primarily the result of multiple mechanisms of deformation acting in concert in the twisted plywood structure of the scale, involving the collagen lamellae at varying orientations controlling crack advance through stretching, rotation, delamination and shear, and finally fracture. These toughening mechanisms operate in sequence at the crack tip, retarding its advance in a most effective manner. The toughness values obtained for the Arapaima scales indicate that they are among the toughest of nature’s flexible biological materials.

Nonequilibrium Molecular Dynamics Simulations of Ejecta Formation in Helium-Implanted Copper

Abstract: Abstract The effect of He concentration and morphology on ejecta production is investigated via molecular dynamics simulations. Identical He concentrations are inserted into Cu single crystals as interstitial atoms or bubbles near a flat free surface. The resulting ejecta is quantified through total mass, cluster size, and velocity of ejected particles. The presence of He increases total ejected mass as compared to pure Cu; He bubbles produce 56% more mass than atomic He. This increase is attributed to non-planarities in the shock front and reflected pulse due to He bubbles, akin to ejecta resulting from traditional Richtmeyer–Meshkov instabilities.