Mechanical analysis of the scratch test on elastic and perfectly plastic materials with the three-dimensional finite element modeling

Scratch test provides a convenient mean to study mechanical properties of t hin coatings. The mechanical analysis of this test is very intricate, espec ially for polymers, for which a large elastic part accompanies the plastic deformation. Most existing models describe the ploughing of a rigid plastic body by a rigid indenter. This paper describes a numerical study of the be havior of elastic-plastic materials during a scratch test. Simulations have been performed with a three-dimensional finite element code, the indenter is a cone of semi-angle 70.3 degrees and the contact is frictionless. The s cratched material is elastic and perfectly plastic, with a constant how str ess aa. For small Young's modulus, a sinking-in under load and an elastic r ecovery at the rear face of the indenter have been observed. In order to ta ke into account this elastic recovery, we have suggested a new model of the apparent coefficient of friction. For high Young's modulus, the deformatio n is mainly plastic, the behavior was close to the behavior of a metal, fro ntal and lateral pile-up pads have been observed. The scratch hardness and the shape ratio have been compared with results obtained in normal indentat ion under the same conditions: geometry under load is similar, but the defo rmation level is higher for scratch than for indentation. We have found a g ood agreement for the shape ratio between our numerical results and scratch experiments performed by other authors with a Berkovich pyramid on elastic -plastic materials. (C) 2001 Elsevier Science B.V. All rights reserved.