ORAL/POSTER REFERENCE: ICF100602OR DOUBLE COHESIVE ZONE MODEL AND PREDICTION FOR MICRO-SCRATCH TEST ALONG SOLID SURFACE M. Zhao1, Y. Wei1,2 and J. W. Hutchinson2 1LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080, China 2Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA ABSTRACT A new double cohesive zone model describing the failure of ductile film in the micro-scratching test is presented in this paper. The failure behavior and adhesion work in the micro-scratch test is simulated and predicted based on the model. In the present analyses, the thin film is treated as the elastic-plastic material, and substrate is elastic material, and three-dimensional elastic-plastic finite element method is adopted. In order to simplify the analyses, the total problem will be divided into two sub-problems. One problem is that elastic-plastic large bend deformation of scratched film is considered, and an analytical solution can be obtained. Another problem is that the thin film is delaminated plastically along the interface with the elastic substrate, for which a special three-dimensional finite element method is used. The parameter relations of the horizontal driving force for the scratch test with the separation strength of thin film/substrate interface and the material shear strength, as well as the material parameters are developed. As an example of the application, the prediction result is applied to a scratch test for the Pt/NiO material system given in the literature, and both results are fairly agreement with each other. KEYWORDS Micro-scratch test, driving force, double cohesive zone model. INTRODUCTION The micro-scratch test is an important approach for determining the interfacial strength, toughness and adhesion properties for the thin film or coating layer on the substrate interface [1]. Its principle can be described as follows: On the material or specimen surface along the vertical direction an indentation force is exerted and indenter tip penetrates inside the material, then the indenter is moved in the horizontal and vertical directions simultaneously according to a fixed proportion. When the indenter tip moves near the film/substrate interface, a region of the thin film or coating layer near the indenter tip will be delaminated along the interface. Through measuring driving forces, the scratch depth, and the failure geometry, one will obtain the material or interface adhesion properties. According to usual experimental observations, there are two main kinds of failure characters in the scratch tests [1-5] depending on the material property of thin film or coating, whether ductile or brittle. One kind of failure character can be described as that for the ductile film case, a delaminated film strap is formed before the end of the scratch test and the delaminated film will be curved into a circular shape. The geometry of the delaminated area is fan shaped. Another failure character is that when film is brittle. A damage zone is formed near the indenter tip, inside which the film will be pressed to break into many small pieces and also delaminated from the substrate. In the present research, our attention will be focused on the metal film/ceramic substrate case. The ductile failure character will be simulated and analyzed in detail. On the research of the material surface properties and adhesion work and strength of thin film or coating
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