Biomedical Engineering Reference
In-Depth Information
Continuous recording of both force components as functions of indenter penetration and path enables
one to determine not only the coefficient of friction, but also the onset of irreversible processes in
the material, demonstrated by discontinuities or other changes in the force-depth curves. Moreover,
the characteristic points on these curves can be assigned to the corresponding places on the scratch
trace on the sample, which can then be studied in detail using an electron microscope or atomic force
microscope (AFM). Scratch tests are also very important in the development of special coatings, as
they can reveal the instant of coating fracture or delamination
[22]
.
Scratch tests have been used in industry for a long time, but gradually they become common also
in dental research; see, e.g., Refs
[44-46]
.
17.8
DEVICES FOR NANOINDENTATION
Various commercial devices are available for nanoindentation measurements in dentistry. They usu-
ally consist of a frame, which carries the measuring head and enables its positioning over a small
table with the sample. The measuring head carries the indenter and electromagnetic, electrostatic,
or piezoelectric actuators and sensors for its movement and loading. A videomicroscope enables the
observation of specimen surface and imprints and facilitates the indenter positioning. The device is
usually placed in a cabinet, protecting against temperature variations. This is very important with
regard to the extreme sensitivity of displacement sensors. Some devices enable coupling with AFM.
Still there are no small lightweight devices for nanoindentation measurements on teeth
in situ
, i.e., in
mouth, but the development is in progress also in this direction.
Nanoindenters can work over a very wide range of loads (from μN to hundreds of mN) and dis-
placements (from nm to hundreds of μm), depending on the range used. A part of the equipment is
software, serving for the control of indenter load and displacement and for gathering the load-depth-
time data and their processing. A test sequence (number of indents, indenter positions, loads, load
rates, test duration, etc.) can be programmed in advance. Usually the software yields the values of
common quantities, such as hardness and elastic modulus, and also all basic data (load-depth-time)
in a text file, so that the user can process them according to his/her special needs.
The devices differ in parameters and price. As they have been continuously improved, no particu-
lar data will be given here; the reader is referred to the web-pages of individual manufacturers given
below. The short list contains only those mentioned in the literature most often, and does not mean
advertising—the arrangement is alphabetical. Some other devices could be found via web search.
There are also special manufacturers of indenters and other accessories; the nanoindenter providers
can help with their choice.
Manufacturers and names of some nanoindentation devices
Agilent
Technologies, Inc:
http://www.agilent.com/ind/nano
Nano Indenter (various types; some enable also scratch testing)
CSM Instruments
SA:
http://www.csm-instruments.com
Nanoindentation testers (NHT, UNHT, TTX), scratch testers, tribometers
Hysitron
, Inc:
http://www.hysitron.com
Triboindenter, Picoindenter, Triboscope, etc.
