Dr Xinyao Zhu

This study presents an investigation on the behavior of adhesive contact between a rigid sphere and an elastic film which is either perfectly bonded (Case I) or in frictionless contact (Case II) with a rigid substrate. By using linear fracture mechanics, we formulate an convenient semi-analytical approach to develop relations between the applied force, penetration depth and contact radius. Finite element analysis (FEA) is used to verify the relationships. Our results reveal that the interfacial boundary conditions between the film and substrate have distinct effects on the adhesive contact behavior between the sphere and the film. The aim of the present study is to provide an instructive inspiration for controlling adhesion strength of the thin film subject to adhesive contact.

The present study explores the effect of surface tension on adhesive contact behavior where the adhesion is interpreted by long-range intermolecular forces. The adhesive contact is analyzed using the equivalent system of a rigid sphere and an elastic half space covered by a membrane with surface tension. The longrange intermolecular forces are modelled with the Lennard-Jones (L-J) potential law. The current adhesive contact issue can be represented by a nonlinear integral equation, which can be solved by Newton-Raphson method. In contrast to previous studies which consider intermolecular forces as short-range, the present study reveals more details of the features of adhesive contact with surface tension, in terms of jump instabilities, pull-off forces, pressure distribution within the contact area, etc. The transition of the pull-off force is not only consistent with previous studies, but also presents some new interesting characteristics in the current situation.

In this study, atomic force microscopy (AFM) is used to investigate the alterations of the poropelastic properties of hepatocellular carcinoma (SMMC-7721) cells treated with fullerenol. The SMMC-7721 cells were subject to AFM-based creep tests and a corresponding poroelastic indentation model was used to determine the poroelastic parameters by curve fitting. Comparative analyses indicated that the both permeability and diffusion of fullerenol-treated cells increased significantly while their elastic modulus decreased by a small amount. From the change trend of the determined parameter, we verified the corresponding alternations of cytoskeleton (mainly filaments actin), which was reported by the previous study using confocal imaging method. Our investigation on SMMC-7721 cell reveals that the porpelastic properties could provide a better understanding how the cancer cells are affected by fullerenol or potentially other drugs which could find possible applications in drug efficacy test, cancer diagnosis and secure therapies.

Based on the surface elasticity theory, we investigate the effect of surface tension on miniaturized contact problems of an elastic graded half-plane under plane strain and axisymmetric situations. The Fourier sine and cosine transform method is used to derive the solution for the problem under uniform pressure. The results show some interesting features in the distribution of surface elastic fields, which are different from their homogeneous counterparts. The surface Green?s functions of the nonhomogeneous half-plane are finally obtained which are verified using finite element method. The outcome of this study provides us not only as a potential method for precise nanoindentation-based analysis of elastic graded materials, but also as the investigations of surface effect-induced failure in nanomaterials and nano-devices.

This present study reconsiders the effect of surface tension on the behavior of adhesive contact between a rigid sphere and an elastic half-plane, in which the adhesive interactions are supposed to follow the Dugdale laws. The adhesive contact issue is transformed into two inter coupled non-linear integral equations which are governed by two parameters: » (Maugis adhesion parameter) and S (elastocapillary number). By means of iteration method, numeric results are obtained. Analogous to the traditional Maugis-Dugdale (M-D) model, the results provide transition of the pull-off force between JKR and DMT type contact models through the Maugis adhesion parameter » with a fixed parameter S. On the other hand, with a fixed adhesion parameter », we also present the transitions of the pull-off force between four extreme models, named M-D, JKR, Bradley models and Young?Dupre equation, through adjustment of the parameter S. Finally, we find the uniformity and discontinuity of the pressure distribution are affected by the combination of three factors: applied load P, adhesion parameter » and elastocapillary number S.