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Bio-inspired Study on Microstructure and Static Mechanical Properties of Pincers

Author: WuZhiWei
Tutor: ZhouFei
School: Nanjing University of Aeronautics and Astronautics
Course: Mechanical Design and Theory
Keywords: crustacean pincers exoskeleton microstructures twisted plywood mechanical properties bio-inspired design
CLC: Q811
Type: Master's thesis
Year: 2009
Downloads: 33
Quote: 3
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Abstract


The microstructure and static mechanical properties of lobster and crab’s pincers were studied. The XRD analysis results indicated that the mineral phase consist of mainly calcium carbonate for lobster and crab’s pincers. There are three states of change: evaporation of water and protein decomposition、the decomposition of chitin and calcium carbonate decomposition according to DSC analysis which reflect the thermal properties of biological materials. There are many concave hollows and stings on the surface of pincers, which exhibited no-smooth surface. The exoskeleton consisted of twisted plywood which are arranged in chitin-protein fibers rotated from one plane to another by 180o about its normal direction. The exocuticle is denser than the endocuticle. Exoskeleton deproteinated and decalcified indicate the distribution of carbonate calcium and the porous structure, which affect the mechanical properties of pincers. The exoskeleton are analysis by EDS which indicate the gradient in the calcium content between exocuticle and endocuticle. Density porous structure and the gradient in the calcium content impact the mechanical property of the pincers.The hardness and elastic modulus are higher near the tip of pincers by nano-indentation measurement. The mean hardness freshwater lobster’s pincer is smallest (0.27±0.02GPa), the mean hardness of freshwater crab is 0.33±0.06GPa. The mean hardness of sea lobster and sea crab’s pincer are0.37±0.06GPa and 0.51±0.44GPa separately. The abrupt transition for the hardness and elastic modulus between the exocuticle and endocuticle was observed. The mean hardness of endocuticle and exocuticle of freshwater crab’s pincer are 0.55±0.22GPa and 0.97±GPa separately, and mean modulus of which are 16.28±4.37GPa and 26.60±2.90GPa separately. This indicated that the composite was anisotropic. The samples dried and thermal treatment are also measured via microindentation testing which reveal the mechanical properties affected by water and temperature. The tensile strength of fresh sample were higher than those of dry samples during tensile testing.According to the present works, the composite materials model reinforced by fiber was proposed and analysis by finite element analysis. Twisted fibers models have better anti-compressive and anti-torsional properties, especially twisted fibers are arrayed 30o. Composite material models with different basic body and fiber are analyzed by FEA also. The research works can provide bio-inspired information for the design of light composite structure and materials.

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