Tensile deformation and fracture characteristics of polyimide/montmorillonite nanocom-posite films are investigated to enhance the particular mechanical properties and understandthe effective factors in dominating the mechanical properties of nanocomposites, such as thenanolayer, matrix and nanolayer/matrix interface. How to contribute to the mechanical prop-erties of nanocomposite film is a very complex problem. In this paper, these factors are analyzedbased on the addition amount and fracture mechanics. The results indicate that the specimen at20 wt% MMT breaks prematurely with a fracture strength (σb = 78 MPa) much lower than that(σb = 128 MPa) at the 1 wt% MMT. However, the Young’s modulus (3.2 GPa) of the formeris higher than that (1.9 GPa) of the latter. Fractography also indicates that the brittle crackingformed in high content addition is the main cause of failure but microscopically ductile fracturemorphology still exists locally. And for the trace element addition, the smaller threading slippingveins are evenly distributed on the entire fracture section of these films. Therefore, these character-istics would presumably be associated with both the concentration effects of size of nanocompositesheets and the increasing deformation harmony in nanolayers.
One-dimensional nanostructured materials are often used as beams in many applications such as ultrahigh-frequency resonators and ultrasensitive sensors.Compared with usual macroscopic beams,nanobeams have much higher surface/volume ratios so that their surface energies may play a significant role.Besides,they often bear large deflections due to their typically large slenderness ratios and larger elastic ranges.There is,however,lack of a theory that takes into account of both the above two features owned by nanobeams.In this paper,we present such a theory and give applied examples to show that surface energy and large deflection may individually or jointly have notable effects.
Dujuan Zeng Quanshui Zheng 1(Department of Engineering Mechanics,Tsinghua University,Beijing 100084,China)
