On the friction behaviour in nanoscratch testing

In nanoscratch testing, it is generally observed that the lateral force does not linearly increase with the applied load. In other words, the apparent friction coefficient, defined as the ratio between the lateral force and the applied load, does not have a constant value. This one may be split into two components, the adhesion coefficient and the ploughing coefficient due to the surface deformation. In the present paper, simulations of the evolution of the ploughing friction coefficient estimated from the model of a conical indenter with a blunted spherical tip taking into account the elastic recovery is compared to the experimental values of the apparent friction coefficient. The comparison of simulations and experiments shows that the non-linear behaviour of the lateral force with the applied load may be mainly explained by the fact that the indenter is not perfectly sharp but has a rounded extremity.