Depth and Load Sensing Equipment

A schematic diagram of equipment that is often used in depth-sensing indentation is shown in Figure 1. It consists of a system of a vertical axis supported by springs to a cell. The indenter is at the end of the axis, as shown in Figure 1. The system is composed of a force actuator, normally an electromagnetic shaker actuator, and a sensor of depth that is generally a capacitance displacement gauge. Other systems that use electrical force applied by capacitance plates

Figure 1. Schematic of a nanoindenter showing the various equipment parts.

or piezoelectric actuators are also used in different equipment designs.

The force actuator normally is capable of applying forces as lower as 1 /N, and the displacement gauge sensor can give a depth resolution better then 0.1 nm. However, for measurements at depths lower than 20 nm, additional rigor and care are needed to obtain useful results. The maximum load used in this kind of equipment is normally about 500 mN. On the other hand, if better displacement and load resolutions are necessary, the maximum load is normally lower, and the depth resolution is increased for shallow penetration. An extensive description with details of different equipments used in nanoindentation, as well as their calibration processes, is presented by Bhushan [9].

Some nanoindentation machines allow the user to build an indentation pattern in a two-dimensional array by using a previous programming. These arrays can consist of a combination of a linear x and y pattern in order to form different two-dimensional geometrical figures like a square, a rectangular, or also triangular shapes. A typical example of an indentation shape produced by a Nanoindenter XPTM is shown in Figure 2. The distance between each indentation can also be programmed, and in the most general case, it is about 50 / m in order to avoid residual deformation

Figure 2. Typical two-dimensional indentation pattern obtained by a Nanoindenter XPTM machine. The distance between the indents is 50 /m.

generated by indentations. This resource permits an easy method to map the mechanical properties in a composite surface, for example. At low loads, the nanoindentation area is small. Then one indentation can be made inside a single grain. In this case, it is also possible to make several indentations, and after that, to make some chemical attack to reveal the grain boundaries. Finally, the indentation position inside or at the grain boundary of grain may be verified, and the different behavior analyzed.

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