Indent depth is the depth from the surface of the sample to the indenter tip or indentation depth of the indenter. The maximum depth is the total displacement of the material and the indenter at maximum load which includes the plastic and elastic deformation. Contact depth can be calculated by:-
Where' hc' is the contact depth of deformed surface and it is the function of young's modulus E, Poisson ratio, and yield strength Y, 'h' is the indentation depth of original surface and 'hp' is the pile up height if it is positive or sink in depth if it is negative. The ratio hc / h is greater than one in the case of surface pile ups and less than one in the case of surface sinks in. Material possessing high elasticity will undergo sink in whereas material possessing plastic zone will undergo pile up. To measure contact indentation depth, pile up and sink in should be taken into account.
In this experiment a nanoindenter tip of known geometry is projected into the selected location on the material surface of the material to be tested. The load is continuously increased till a designated maximum value, after which we partially unload the material until desired depth is attained. Next holding segment is introduced to allow the material to relax before unloading. The process is repeated many times and position of the indenter tip and the surface is monitored with a differential transformer. The indent depth can be calculated as mentioned in the introduction.