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 thin coatings. The mechanical analysis of this test is very intricate, especially 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 behavior 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° and the contact is frictionless. The scratched material is elastic and perfectly plastic, with a constant flow stress σ0. For small Young’s modulus, a sinking-in under load and an elastic recovery at the rear face of the indenter have been observed. In order to take into account this elastic recovery, we have suggested a new model of the apparent coefficient of friction. For high Young’s modulus, the deformation is mainly plastic, the behavior was close to the behavior of a metal, frontal and lateral pile-up pads have been observed. The scratch hardness and the shape ratio have been compared with results obtained in normal indentation under the same conditions: geometry under load is similar, but the deformation level is higher for scratch than for indentation. We have found a good agreement for the shape ratio between our numerical results and scratch experiments performed by other authors with a Berkovich pyramid on elastic–plastic materials.