Papers by Author: Ai Kah Soh

Abstract: In-situ characterization of the mechanical behavior of geckos spatula has been carried out in detail using multi-mode AFM system. Combining successful application of a novel AFM mode, i.e. Harmonix microscopy, the more detail elastic properties of spatula is brought to light. The results obtained show the variation of the mechanical properties on the hierarchical level of a seta, even for the different locations, pad and stalk of the spatula. A model, which has been validated using the existing experimental data and phenomena as well as theoretical predictions for geckos adhesion, crawling and self-cleaning of spatulae, is proposed in this paper. Through contrast of adhesive and craw ability of the gecko on the surfaces with different surface roughness, and measurement of the surface adhesive behaviors of Teflon, the most effective adhesion of the gecko is more dependent on the intrinsic properties of the surface which is adhered.

Abstract: In-situ characterization of the mechanical behavior of geckos spatula has been carried out in detail using multi-mode AFM system. Combining successful application of a novel AFM mode, i.e. Harmonix microscopy, the more detail elastic properties of spatula is brought to light. The results obtained show the variation of the mechanical properties on the hierarchical level of a seta, even for the different locations, pad and stalk of the spatula. A model, which has been validated using the existing experimental data and phenomena as well as theoretical predictions for geckos adhesion, crawling and self-cleaning of spatulae, is proposed in this paper. Through contrast of adhesive and craw ability of the gecko on the surfaces with different surface roughness, and measurement of the surface adhesive behaviors of Teflon, the most effective adhesion of the gecko is more dependent on the intrinsic properties of the surface which is adhered.

Abstract: The present study focuses on investigation of the adhesive phenomenon of gecko with viscoelasticity using the finite element method. By simplifying a single spatulae as a flat-ended cylinder in contact with a rigid substrate, a model is devised to study the critical radius under which the stress becomes uniform for the adhesive structure. Furthermore, viscoelasticity is taken into consideration in the simulation model instead of elasticity. The critical cylinder radii determined are in agreement with theoretical calculations and experimental data.

Abstract: A novel method for characterizing a high actuating capability light-weight actuator is described and analyzed. The actuator comprises a truss core and smart face-sheets which result in bending. The deformation of this beam actuator is obtained by changing voltage inside face-sheets made from smart material. Materials selections are discussed for practice, and then optimization is designed to ascertain minimum weight or maximum achievable displacement subject to two types of constrains. Results show the composite trusses have higher stiffness and strength than metal trusses. Comparisons with two corrugated core actuators, the truss-core design has better actuating capability at specified weight.

Abstract: Micromagnetic simulation was carried out to investigate the behavior of ferromagnetic materials at a very small length scale, at which the materials usually exhibit different properties compared with those of the corresponding bulk materials. By solving the time and spatial dependent Landau-Lifshitz-Gilbert (LLG) equation in reciprocal space using fast Fourier transformation (FFT) technique, the equilibrium magnetization state was, thus, achieved. The hysteresis loops were also simulated, from which the relation of coercivity and characteristic length was established. Besides, the effect of external stress on coercivity was also taken into consideration. The results showed that at such length scales the external stress strongly affected the magnetic behavior of ferromagnetic materials.

Abstract: The propagation of shear horizontal (SH) wave is studied in a tri-material composed of a piezomagnetic layer and two semi-infinite piezoelectric half-spaces. These materials are hexagonal (6mm) crystals. A dispersion relation is exactly derived. The numerical results show the existence of the SH wave and its dispersion characteristics. These may be useful for the applications of piezoelectric-piezomagnetic media in the microwave technology.

Abstract: The fatigue behavior of piezoelectric ceramics PZT-5 subjected to three-point bending was investigated under a cyclic electric load coupled with a constant mechanical load. The direction of poling was perpendicular to that of the mechanical load. The fatigue life curves under high and low electric loading were compared. Non-linear relationship was observed between dS/dN and E/Ec.

Abstract: This paper deals with a Mode III interfacial edge crack in a magnetoelectroelastic bimaterial subjected to line singularities such as an out-of-plane line force, a line electric charge, a line magnetic charge and a straight screw dislocation. The surfaces (including crack surfaces) of the bimateral are assumed to be electrically open and magnetically closed. The closed-form analytical solution to the problem is obtained by employing the complex variable approach in conjunction with the conformal mapping technique. The intensity factors of stress, electric displacement and magnetic induction are given explicitly. The obtained results can be used as the Green's function to solve more complicated problems.

Abstract: A screw dislocation interacting with a semi-infinite interfacial crack in two dissimilar piezoelectric layers is studied. The complex variable method and the conformal mapping technique are employed to obtain the solution of the problem. The stress and electric displacement intensity factors are given explicitly. We find that the stress and electric displacement intensity factors depend on the effective electro-elastic material constants. Numerical example shows that the influence of piezoelectric effect on the crack tip shielding is significant.