The Mechanical Properties Of Nanomaterials

As a new type of material, the nanocrysalline and nanocomposite material has drawn world-wide attention in recent years, twenty-first century is the century which nano technology is predominated. As a challenge subject, much work has been done concerning the abnormality, usefulness, wide application scope on mechanical and other areas of this attractive materials. Nanomaterials are received tremendous attention at present because of their unusual properties, such as higher strength, hardness and superplasticity, and special microstructure, ultra-fine grains in those materials gives rise to significant amount of interfaces and a substantial fraction of atoms located in grain boundary. The difference between nanomaterials and their coarse grain materials is that the former makes traditional ductile metal hard and strong and makes conventional ceramics deforming plastically. Some nanomaterials can serve the properties both of mechanics and function. This will influence the traditional mechanics dramatically. The purpose of this paper is mainly to examine the fabrication process and mechanical characteristic of nanocomposite material. The paper is divided into five parts concerning the two aspects respectively. Part I covers international general situation in this aspect, and point out the purpose, content, method and value of this study. Part II discusses the fabrication process of nanocomposite, two methods are used: one is powder metallurgy method, the other is mechanical alloying method. Also investigates the mechanical characteristic of nanocomposite based on the result of the experiment. Part III proposes a model of intra-granular particle residual stress strengthening, studied the strengthening mechanism of nanocomposites. Also estimates the residual stress of Al203-Cu nanocomposites. This model gives a good explanation of the variation of strength and fracture mode with the content of strengthening particles. Part IV stress distributions in nano-particle filled composite are considers by finite element method. The distribution of stress is illustrated when the interaction among the multi-particle is taken into account.Part V establisbes the reIationship on the grain size dependence of mechanicaIproperties of nanocrysalline material, e.g, on the Hall-Petcb relatiousbip of tbis newmaterials. As is wcll known, nanocrystalline materials usually show decreasedmicrobardness compared with the prediction frOm thc H-P relationship and even a negativeH-P slope. In order to clarify tbis problem, a mesoscopic dcscription on the yield stress ofnanocrystals was proposed by regarding the nanocrystals as a composite of crystallinematrix and incIusion of intercrystalline layers. This modeI explain the sizc cffect quite well.