Mimicking key features of the scale The Ganoid Scales of Atractosteus spatula: Potential for Bioinspired Flexible Armor Vincent R. Sherman 1* , Wen Yang 2 , Marc A. Meyers 1 1 University of California San Diego, 2 ETH Zurich, * [email protected] Objective To produce a bioinspired flexible armor which incorporates key features of the alligator gar scale. Materials Conclusions • The alligator gar scale has unique features which allow for movement and protection including a unique scale overlapping pattern and crack deflecting tubules throughout. • Studying and replicating these features may lead to the production of more effective armors. • A simplified geometry based on an alligator gar scale is designed, produced, and shown to be capable of conforming to curvature. References W. Yang et al., Structure and fracture resistance of alligator gar (Atractosteus spatula) armored fish scales. Acta Biomater 9, 5876 (Apr, 2013). W. Yang et al., Natural Flexible Dermal Armor. Adv Mater 25, 31 (Jan, 2013). We gratefully acknowledge partial financial support from a Multi-University Research Initiative through the Air Force Office of Scientific Research (AFOSR- FA9550-15-1-0009). Dianne Ulery generously provided scales which were used for testing. Type I scales are collected from the deceased Atractosteus spatula. Scale Structure Design for Toughness 100 m (b) Under various conditions, different mechanisms contribute to the toughening of the scales. (a) In a wet state, water molecules act as plasticizers and post-yield plasticity allows for large energy absorbance. But in a dry state, hydrogen bonds form directly between collagen molecules, thus limiting plasticity. To compensate, tubules (b, c) create stress concentrations and cause significant crack deflection shown in (d). This crack deflection increases the toughness, K J , for the dry samples so that it is both wet and dry samples are of similar toughness. (e) 3 point bending tests of samples with a ganoine layer and a boney layer reveal that when the ganoine is in compression, the maximum flexural stress and strain nearly double with respect to when it is in tension. (f) Observation of the fracture shows that cracks which initiate in the brittle ganoine propagate into the bone causing premature failure. In a lifelike situation such as a predatorial attack, the ganoine is in compression; this corresponds to the ideal loading situation of the scale. Design for Flexibility Scales with high stiffness require the specialized geometry in order to allow the fish to swim. In order to maintain flexibility, the gar scales overlap in such a way that they can rotate across the surface of adjacent scales. This allows for movement, in spite of a large amount of scale overlap. A microCT scan is dissected to show two cross sections. ρ 1 is the radius of curvature on both sides of the cross-section made by the yellow dashed line and ρ 2 is from the cross-section marked by the red dashed line. Ρ 1 matches to both sides of the cross-section, while ρ 2 matches once the contributions of a third overlapping scale are considered. The key feature which allows for flexibility and efficiency of the scale is the matching curvatures on either side of the scale. In (a), a simplified version of this design was produced where the curvature on all sides of the scale is equal, and the scale is symmetric across the long direction of the rhombus. These synthetic scales are able to bend and stretch in all directions while maintaining protective coverage, as shown in (b). (c) shows an ABS printed version of the model scale conforming to a curve. Toughness and strength are also key. Similar to the actual scale, a tougher inner layer will make up the body of the scale, while a hard outer layer will contribute to strength and penetration resistance. ρ 2 ρ 1 Introduction The alligator gar (A. spatula) is covered with a configuration of bony scales that have an enamel- like surface layer. The scales form a tridimensional pattern in which neighboring scales overlap in such a manner that ensures flexibility. The mechanical properties, structure, and geometry are correlated and a magnified array of idealized, identical tiles is produced. Dry Wet (a) (c) (d) Cross sections with radii of curvature marked Configuration of multiple overlapping scales which enables flexibility (e) (f) Ganoine Bone Crack Propagation 3 Point Bending Ganoine in compression Ganoine in tension Cross sections with matching radii of curvature Configuration of multiple overlapping scales which enables flexibility Surface reconstruction of the alligator gar scale Model of synthetic scale (a) (b) (c) The alligator gar scale (a) consists of a yellowish boney base layer and a hard white enamel like ganoine layer (a- c). Small tubes, or tubules run from the interior to exterior surface of the scale (d). X Y Z (d) 500 m ganoine bone ganoine bone 500 m (a) Tensile stress (MPa)
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Mimicking key features of the scale
The Ganoid Scales of Atractosteus spatula:Potential for Bioinspired Flexible Armor
Vincent R. Sherman1*, Wen Yang2, Marc A. Meyers1
1 University of California San Diego, 2 ETH Zurich, *[email protected]
Objective
To produce a bioinspired flexible armor whichincorporates key features of the alligator gar scale.
Materials
Conclusions
• The alligator gar scale has unique features whichallow for movement and protection including aunique scale overlapping pattern and crackdeflecting tubules throughout.
• Studying and replicating these features may leadto the production of more effective armors.
• A simplified geometry based on an alligator garscale is designed, produced, and shown to becapable of conforming to curvature.
ReferencesW. Yang et al., Structure and fracture resistance of alligator gar (Atractosteus
spatula) armored fish scales. Acta Biomater 9, 5876 (Apr, 2013).W. Yang et al., Natural Flexible Dermal Armor. Adv Mater 25, 31 (Jan, 2013).
We gratefully acknowledge partial financial support from a Multi-UniversityResearch Initiative through the Air Force Office of Scientific Research (AFOSR-FA9550-15-1-0009). Dianne Ulery generously provided scales which were usedfor testing.
Type I scales are collected from the deceasedAtractosteus spatula.
Scale Structure
Design for Toughness
100 m
(b)
Under various conditions, different mechanisms contribute to the toughening of the scales. (a) In awet state, water molecules act as plasticizers and post-yield plasticity allows for large energyabsorbance. But in a dry state, hydrogen bonds form directly between collagen molecules, thuslimiting plasticity. To compensate, tubules (b, c) create stress concentrations and cause significantcrack deflection shown in (d). This crack deflection increases the toughness, KJ, for the dry samples sothat it is both wet and dry samples are of similar toughness. (e) 3 point bending tests of samples witha ganoine layer and a boney layer reveal that when the ganoine is in compression, the maximumflexural stress and strain nearly double with respect to when it is in tension. (f) Observation of thefracture shows that cracks which initiate in the brittle ganoine propagate into the bone causingpremature failure. In a lifelike situation such as a predatorial attack, the ganoine is in compression;this corresponds to the ideal loading situation of the scale.
Design for Flexibility
Scales with high stiffness require the specialized geometry in order to allow the fish to swim. In order tomaintain flexibility, the gar scales overlap in such a way that they can rotate across the surface of adjacentscales. This allows for movement, in spite of a large amount of scale overlap. A microCT scan is dissectedto show two cross sections. ρ1 is the radius of curvature on both sides of the cross-section made by theyellow dashed line and ρ2 is from the cross-section marked by the red dashed line. Ρ1 matches to bothsides of the cross-section, while ρ2 matches once the contributions of a third overlapping scale areconsidered.
The key feature which allows for flexibility andefficiency of the scale is the matching curvatures oneither side of the scale. In (a), a simplified version ofthis design was produced where the curvature on allsides of the scale is equal, and the scale is symmetricacross the long direction of the rhombus. Thesesynthetic scales are able to bend and stretch in alldirections while maintaining protective coverage, asshown in (b). (c) shows an ABS printed version of themodel scale conforming to a curve.
Toughness and strength are also key. Similar to theactual scale, a tougher inner layer will make up thebody of the scale, while a hard outer layer willcontribute to strength and penetration resistance.
ρ2
ρ1
Introduction
The alligator gar (A. spatula) is covered with aconfiguration of bony scales that have an enamel-like surface layer. The scales form a tridimensionalpattern in which neighboring scales overlap insuch a manner that ensures flexibility. Themechanical properties, structure, and geometryare correlated and a magnified array of idealized,identical tiles is produced.
Dry
Wet
(a)(c)
(d)
Cross sections with radii of curvature marked
Configuration of multiple overlapping scales which enables flexibility
(e)
(f)
Ganoine
Bone
Crack Propagation
3 Point Bending
Ganoine in compression
Ganoine in tension
Cross sections with matching radii of curvature
Configuration of multiple overlapping scales which
enables flexibility
Surface reconstruction of the alligator gar scale
Model of synthetic scale
(a)
(b) (c)
The alligator gar scale (a) consists of a yellowish boneybase layer and a hard white enamel like ganoine layer (a-c). Small tubes, or tubules run from the interior toexterior surface of the scale (d).
X
Y
Z
(d)
500 m
ganoine
bone
ganoine
bone
500 m
(a)
Ten
sile
str
ess
(M
Pa)
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