Crack In Stress

Thin Solid Films 392 Ž2001. 65 74

Finite element modeling of the stresses, fracture and delamination during the indentation of hard elastic films on elastic plastic soft substrates
R.M. Souzaa,U , G.G.W. Mustoe b , J.J. Moore c
a

Surface Phenomena Laboratory, Department of Mechanical Engineering, Polytechnic School, Uni¨ ersity of Sao Paulo, A¨ . Prof. Mello ˜ Moraes 2231, Sao Paulo, SP05508-900, Brazil b Di¨ ision of Engineering, Colorado School of Mines, Golden, CO 80401, USA c Ad¨ anced Coatings and Surface Engineering Laboratory (ACSEL), Colorado School of Mines, Golden, CO 80401, USA Received 3 May 2000; received in revised form 22 March 2001; accepted 22 March 2001

Abstract In this work, the mechanical behavior of hard films on soft substrates was studied based on thefinite element analysis of an indentation with normal forces. As an attempt to reproduce situations found in practice, defects were considered during the preparation of the finite element mesh, both in the film and at the interface. A sequence of steps was considered during the loading sequence applied in the models. Initially, the deposition Žintrinsic . and thermal Žextrinsic . stresses wereintroduced to account for all residual stresses present in thin films deposited by processes such as sputtering. Later, a normal load of 50 N was applied on the pre-stressed system. The effects of a crack that propagated along the filmrsubstrate interface was studied directly, by calculating the normal and shear stresses that develop at the film surface and the filmrsubstrate interface, and indirectly, bylooking at the behavior of cracks located at the film surface and propagating perpendicular to the interface. The results indicated that the suppression of the constraint imposed by the interface resulted in a decrease in the stresses in the film. However, the crack at the interface apparently did not interact with the stresses responsible for the array of circular cracks usually observed at thecontact edge of the indentation of coated systems with soft substrates. 2001 Elsevier Science B.V. All rights reserved.
Keywords: Adhesion; Stress; Triboblogy

1. Introduction The deposition of coatings is a widespread technology for improving the behavior of parts subjected to wear. These methods are particularly important in the case of soft substrates, such as aluminum, which are known for theirpoor tribological properties w1x. In recent years, several processes were developed to deposit thin films on a substrate, each one associated with a series of process parameters that can significantly affect the characteristics of the film w2x. ThereU

Corresponding author. This paper was presented at ICMCTF 2000, San Diego, Califor-

nia.

fore, the number of possibilities to be tested for agiven application is not restricted to the choice of the coating and its dimensions, but involves the selection of other factors, such as the process and its parameters. Since this number of possibilities is elevated, methods were developed to give insights into the wear behavior of coated systems without the need for long-term tests. Some of these methods refer to the use of analytical w3,4x orfinite element analyses w5 8x to evaluate the contact stresses originated when the system is subjected to the normal andror tangential loads characteristic of many situations involving wear. In previous works w9 11x, the authors presented a sequence of finite element analyses studying the contact stresses developed during the normal indentation of systems with an elastic plastic aluminum substrate0040-6090r01r$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 0 - 6 0 9 0 Ž 0 1 . 0 0 9 5 9 - 2

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R.M. Souza et al. r Thin Solid Films 392 (2001) 65 74

coated with an elastic wear-resistant film. In those works, the authors improved the correlation between the simulations and the situations found in practice by considering that: Ži. the film was...