Friction monitored scratch adhesion testing

During a scratch adhesion test, the plot of the frictional force against the normal applied load on the diamond can indicate different types of failure: small oscillations in the measured friction correspond to chipping, bigger variations show the presence of flaking. The first contact of the diamond with the substrate, total failure, is marked by an inflection point in the measured frictional force. A mathematical method is given to approximate the curve and determine the critical load where the derivative d(frictional force)/d(load) is maximum.