Advances in Measurement of strength of materials using a portable hardness tester

For over a century hardness
testing Instruments have been used to measure the strength of metallic
materials and hardness of their surface finish. The original machines were
bench mounted and measured strength by applying a given force to a probe and
making an indentation which causes plastic deformation. The material hardness
is determined by measuring either the depth or width of the indentation. Different
shaped indenters and different methods of measuring the size of the Indent are
required for different materials. These machines were not suitable for fixed
structures or very large or very small and thin items. This resulted in the
development of less accurate portable instruments using different methods of
measurement. The two common methods were the dynamic Leeb method, used for
large items, where a spring loaded probe impacts the surface and its bounce
back distance is measured. The second method was the ultrasonic contact
impedance method, where different forces are used for different materials, used
for small items and for the thin surface finish on an item. The latest digital
technology has allowed a European manufacturer to offer a device of extreme
accuracy that uses both a Leeb and an ultrasonic contact impedance probe and
tests according to either US or European standards. This instrument is also
unique as it has a camera to record the position of the probe on the item and
any identifying number on the test item. The instrument can also provide a
digital readout of hardness and statistics on the tests. The instrument is also able to detect and
reject inaccurate Leeb readings. All the information from the tests can be
stored in the instrument and later downloaded to a PC.

The accuracy and calibration of
this instrument can be checked in the same way as for bench testers by
performing hardness tests on a range of certified test blocks of known

This instrument gives the user
many of the features previously only available on sophisticated bench mount
testers at a price similar to much simpler portable instruments.

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