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.

Multiscale Toughening Mechanisms in Biological Materials and Bioinspired Designs

“…It was concluded that in both ambient dry and hydrated conditions, the fracture toughness increases significantly as the crack propagates (Figure e). This can be explained by the extrinsic toughening mechanism shown in Figure f, where the initial cracks which are perpendicular to the tubules are deflected by 90°, and start propagating along the tubules . Crack deflection by the tubular structures is caused by the weak interfaces between the cell lamellae, which is similar to that observed in bone osteons.…”

“…Baleen is a keratinized tissue with a relative low degree of mineralization (around ≈1–4 wt%). It was found that these microstructured tubules inside the baleen contributed to the fracture toughness of the whole structure in the direction perpendicular to the tubules . Figure d shows a schematic of the tubular structure, in which keratinized cells are indicated in both tubule and intertubular areas.…”

“…By introducing the nano‐ to microscale lamellar and interfaces in Al 2 O 3 /PMMA composites, the fracture toughness of the material increased from ≈2 MPa m 1/2 in a homogenous Al 2 O 3 /PMMA composite to 15–30 MPa m 1/2 in the structure with lamellae and interfaces 12a. In another work, Wang et al showed the toughness ( J integral, kJ m −2 ) of whale baleen increased from ≈1.5 kJ m −2 in longitudinal direction to ≈18 kJ m −2 in transverse direction because of the crack deflection by tubules occurred in transverse direction at the microscale . Although the quantification of contributions of different toughening mechanisms are in different biological systems, it is safe to conclude that the toughening mechanisms at different length scales all have the potential to increase the toughness by an order of magnitude.…”

Arapaima Fish Scale: One of the Toughest Flexible Biological Materials

“…2 The same applies to biological materials that are subjected to extreme loads. [3][4][5][6][7][8][9] The dermal armor of fish is a splendid example where the toughness is essential. [10][11][12][13][14][15][16][17] Arapaima gigas are a large Amazonian fish (weighing up to 150 kgf) living primarily in seasonal lakes infested with ferocious piranhas.…”

Recent Progress in 3D Printing of Bioinspired Structures

“…This implies that the hybrid design approach provides an alternative to the hierarchical design approach in improving mechanical performance. In Figure 2D, the hierarchical structures inspired by baleen were studied by using advanced multimaterial 3D-printed models (Wang et al, 2018). The simulation results show that the incorporation of the stiff "mineral" component (Model IV) leads to the largest increase in rate stiffening and strengthening.…”