The effect of Berkovich tip orientations on friction coefficient in nanoscratch testing of metals

In this paper, an analytical model is established to calculate both the ploughing and adhesive friction coefficients of metals in a scratch test with the Berkovich indenters at different tip orientations. Using the finite element analysis of nanoscratch test, the patterns of material flow lines around the indenter at different tip orientations are extracted. The adhesive friction coefficient is predicted based on the average angle of material flow lines along each side of the contact surface. When the scratch direction is between the edge-forward and side-forward orientations, the material pile-up in front of the indenter becomes unbalanced between the area of two sides of the contact surface and it highly affects the ploughing friction coefficient.