| During350million years evolution, the biological materials have excellentmechanical properties, and provide the inspiration for scientists to design newmaterials. They have been a learning object of material bionics. The biologicalmaterials are complex composite materials which have gradient andmultifunctional characteristics. They assembled by the common component, butthey have excellent mechanical properties. Many of them constituted by brittlecomponent(usually minerals) and toughness component(organic). However, thebionic about biological materials can not simply imitate and copy, because thebiological materials in nature are not only provide superior performance, but alsocan satisfy the needs of the specific biological constraints. We explore therelationship between the features and functions of the biological materials underthe case of the physical constraints and biological constraints, that is to say theresearch for biological materials properties and their functional integrationcharacteristics is the foundation to biomimetic materials.Mechanical properties are very important for the functionality of biologicalmaterials. Nano-mechanical analysis in recent years as a new technology hasproved to be an effective tool for those which are difficult to measure themechanical properties using traditional methods, as well as the complex andmulti-scale biological systems. The study of the natural biological materialsmechanical properties gradually transition from the macro scale to the micro-andnano-scale, and the performance of the materials on the nano-scale is significantlydifferent from the performance on the macro or even micro-scale.In this paper, the main research objects are three biological gradient materials,horn, dung beetle elytra and abalone shell. First, the samples preparation should becarried out. The horn, dung beetle elytra and abalone shell are cut on horizontal andvertical directions using precision cutting machine, and placed in a mixture of4:1ratio of the epoxy resin and curing agent. Preparation process includes roughpolishing and fine polishing. Loading rate and holding time are obtained by experiments. Due to the creepphenomenon, we need to consider the impact of holding time and loading rate onthe elastic modulus and hardness values during nano-mechanical testing. Hornsamples holding time is20s, and the loading rate is500μN/s. Dung beetle elytrasamples holding time is10s, and the loading rate is300μN/s. Abalone shellsamples holding time is10s, and the loading rate is750μN/s.Discuss the variation of the quasi-static nano-mechanical properties of thelayered composite structure. The test of nano-mechanical properties on thetransverse and longitudinal directions results show that the elastic modulus andhardness of the three materials have a significant upward trend from the inner tothe outer layer. The outer layer elastic modulus and hardness of horn are1.54timesand2.49times higher than the inner layer’s respectively in the transverse direction,and the outer layer elastic modulus and hardness are1.56times and2.21times thanthe inner layer’s respectively in the longitudinal direction. Compared with theelastic modulus and hardness values in both transverse and longitudinal directions,the variety trend of the elastic modulus in the longitudinal direction is slightlylarger than that in the transverse direction, but the variety trend of hardness ontransverse direction is greater than the longitudinal direction. The outer layer elasticmodulus and hardness of dung beetle elytra are4.99times and8.33times than theinner layer’s respectively in the transverse direction, and the outer layer elasticmodulus and hardness are5.11times and14times than the inner layer’srespectively in the longitudinal direction. Compared with the elastic modulus andhardness values in both transverse and longitudinal directions, the variety trend ofthe elastic modulus in the longitudinal direction is slightly larger than that in thetransverse direction, but the variety trend of hardness in the transverse direction isgreater than that in the longitudinal direction. The outer layer elastic modulus andhardness of abalone shell are1.37times and2.44times than the inner layer’srespectively in the transverse direction, and the outer layer elastic modulus andhardness are1.71times and2.73times than the inner layer’s respectively in thelongitudinal direction. Compared with the elastic modulus and hardness values inboth transverse and longitudinal directions, the variety trend of the elastic modulusand hardness in the longitudinal direction is slightly larger than that in thetransverse direction.Comparative analysis on nano-mechanical properties of three biologicalmaterials, the results show that the mechanical characteristics of the three biological materials are based on their material composition, structurecharacteristics, living environment and different functions.Explore the relationships between the loss modulus and storage modulus andfrequency in the dynamic nano-mechanical properties of three biological materials.The results show that the loss modulus is more sensitive to frequency than thestorage modulus to. Fit to the curve of dynamic storage modulus and loss modulusversus frequency.Viscoelastic properties of three biological materials are researched. Analysison the relaxation properties of three biological materials, and establish Fung-Kelvinmodel. Through fitting the curve, establish the differential constitutive equation. Itis important to design the bionic composite materials or coatings which haveexcellent mechanical properties.Finally, extract optimized model of three biological materials, then investigatethe mechanical behavior under uniform load and concentrated load.This paper has researched several lightweight and high strength gradientbiological materials. It supplied the foundation to design of the bionic gradientmaterials. However, this research is only a beginning, and biological gradientmaterials need further exploration. The biological gradient materials as theimportant area in the bionic study, many valuable characteristics are not awareness.The conclusions from this dissertation have some effects in biology and ecologyand will brings forward to bio-inspired idea for bionic engineering... |
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