Modified method developed for contact-induced adhesion in indentation
- PDF / 1,218,470 Bytes
- 8 Pages / 584.957 x 782.986 pts Page_size
- 117 Downloads / 241 Views
Jen Fin Lina) Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan, Republic of China; Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 701, Taiwan, Republic of China; and Institute of Nanotechnology and Microsystems Engineering, National Cheng Kung University Tainan 701, Taiwan, Republic of China (Received 12 December 2008; accepted 23 January 2009)
A modified method for contact-induced adhesion on the elastic deformation contact between a rigid spherical indenter and a polydimethylsiloxane (PDMS) specimen is proposed in the present study. Adhesion due to van der Waals interactions was found to be minimal during loading processes. During the unloading process, the experimental load-displacement data revealed two-stage phenomena. The successive advancing contacts between the specimen and the indenter were considered to induce interfacial adhesion and resulted in elastic tension outside the Hertzian contact radius. A real-coded genetic algorithm (RGA) was applied to evaluate how adhesion energy varied with penetration depth.
I. INTRODUCTION
Indentation provides an effective technique for measuring microscale and nanoscale mechanical properties.1–3 However, indentation has been reported as being invalid for measuring the mechanical properties of soft materials (elastic modulus below 5 MPa).4,5 The interpretation of measured load-displacement profiles is complex due to surface interactions between the tip and the surface as well as nonlinear deformation characteristics. The decrease in indenter and specimen dimensions correlates with the decrease in indentation force and the increased influence of the contact adhesion.6,7 Several models for characterizing contacts with adhesion have been established in the contact mechanics community.8–11 For materials with low modulus, high surface energy, and indented by a tip with a large curvature radius, the Johnson-Kendall-Roberts (JKR) model8 is more conventionally appropriate. Based on the Hertzian contact theory,12 the JKR model was derived for frictionless contact between two elastic solid spheres. In the JKR model, the air gap exterior of the contact region is treated as an external crack; therefore, there is infinite tensile traction and the deformed profile meets the flat surface as a sharp corner at the contact edge. In reality, of course the stress is not infinite, nor is the corner perfectly sharp, and the adhesion forces outside the area of contact are not taken into account. However, in the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0196 J. Mater. Res., Vol. 24, No. 5, May 2009
http://journals.cambridge.org
Downloaded: 16 Mar 2015
Derjaguin-Muller-Toporov (DMT) approximation, the adhesion forces are taken into account, but the profile is assumed to be Hertzian, as if the adhesion forces could not deform the surfaces.9 The DMT model applies to long-range surface forces (i.e., high elastic modulus, low adhesion, and small tip radius sys
Data Loading...
