Analysis of the practical force accuracy of electromagnet-based nanoindenters

Two important factors that influence the force accuracy of the electromagnet-based nanoindenters but have not yet attracted much attention are analyzed, and a more reasonable way to estimate the force accuracy is presented in this paper. MTS Nano Indenter®, with the characteristics of a coil suspended in a uniform magnetic field by two sets of springs acting as an actuator and force measuring unit, is used as an example. One of the two factors is the uniformity of the magnetic field. The other is the stiffness of the supporting spring. Consequently, the practical force accuracy varies considerably from test to test because it firmly depends on the working position of the coil and the displacement stroke. A reasonable estimated accuracy value is of the order of 100 μN for typical indentation tests with a 102 nm indentation depth or a 100 mN test force.