牛鲨牙齿微观结构组成和摩擦磨损特性

为研究牛鲨咬合力大的原因,并以牛鲨牙齿为原型设计仿生刀具,以牛鲨上颌齿和下颌齿为研究对象,利用扫描电子显微镜观察牛鲨牙齿的微观结构,利用能谱仪测试牙齿的元素组成。采用微观摩擦磨损试验机进行摩擦磨损试验,考察了牛鲨上颌齿、下颌齿的摩擦学性能,通过激光共聚焦扫描显微镜测量磨损深度,利用扫描电子显微镜观察牛鲨牙齿的磨损形貌。试验表明:釉质层由条状纤维束形成致密的结构,本质层为多孔结构,孔径范围在3~20μm,这些孔洞呈不规则的排布;能谱仪测试结果中,牛鲨牙釉质比牙本质中Ca、F含量高,氟和钙的组合效应可以帮助其在生存环境下有更好的耐酸性和硬度。牛鲨上下颌齿牙釉质磨斑表面有片状磨屑剥落,且有大量的细小磨粒,上颌齿磨损体积约为1.72×10~7μm~3,主要是磨粒磨损;下颌齿出现明显裂纹,磨损体积约为2.11×10~7μm~3,比上颌齿的磨损体积大。上述结果为新型刀具的仿生设计提供理论依据。

Micro-structure composition and behavior of friction and wear for bull shark teeth

Natural biological materials generally have a perfect macro and micro compound structure.Animal's teeth,claws and bones have formed the optimized geometry with excellent mechanical properties after a long period of evolution,and have occupied an important position in the field of engineering bionics.Teeth are an integral part of the predation process of vertebrates,which use their teeth to break prey down into small pieces,and remove the inedible parts of the prey.Bull shark is an animal with great bite force,and its teeth structure is one of the main reasons for its bite force.Taking bull shark's maxillary and mandibular teeth as the research object,the microstructure of bull shark teeth was observed by using scanning electron microscope (SEM),the elementary composition of bull shark teeth was observed by using energy disperse spectroscopy (EDS),and the friction and wear behavior of the bull shark teeth was investigated systematically in this paper.The wear resistance of the bull shark teeth was estimated by a wear tester.Experimental results showed that enamel layer was a compact structure formed by strip fiber bundles,and the dentin was a porous structure,which holes were in the range of 3-20 μm with an irregular arrangement,and could improve the bonding strength.Compared with the dentin,the contents of calcium (Ca) and fluorine (F) in the bull shark teeth enamel were much higher,and these 2 types of elements could help teeth have better acid resistance and hardness.The surface roughness of the polished teeth sample,which contacted with Si3N4 ceramic ball,was small at first.Therefore,the enamel of bull shark's maxillary and mandibular teeth had a low initial friction coefficient.After a period of time,due to fatigue damage in the enamel surface and brittle cracking,the friction coefficient rapidly increased in the enamel material with the peeling of teeth.The friction coefficient of the 2 different samples changed with time and presented different trends.The friction coefficient of the maxillary teeth showed a rapid increase after 60 s,while the time for the mandibular teeth was 35 s.The flake wear debris peeled off in the surface of bull shark enamel,and the surface was attached to a lot of fine abrasive particles.The maxillary teeth wear volume was 1.72× 107μm3,and the wear debris peeling was mainly caused by fatigue wear;the mandibular teeth presented obvious cracking phenomenon,and the wear volume was 2.11 × 107μm3,higher than the maxillary teeth.The friction and wear experimental results showed that the abrasion resistance of maxillary teeth was better than that of mandibular teeth because the maxillary teeth are responsible for cutting their prey,but the mandibular teeth are only responsible for piercing prey in the process of long-term predation.This paper provides a reference for the design of a new type of cutlery and the experiment data and theoretical basis for the study of the tribology properties of animal teeth in the future by observing the microstructure and testing the friction properties.