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Measuring material strength with portable hardness testers

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article image The new portable hardness tester equips users with greater capabilities

Hardness testing instruments have been in use for more than a century to measure the strength of metallic materials and hardness of their surface finish.

The earlier models of these machines were bench mounted and measured strength by applying a given force to a probe and making an indentation to cause plastic deformation. The material hardness was determined by measuring the depth or width of the indentation. However, different materials required different shaped indenters and different methods of measuring the size of the indent. Additionally, these machines were not suitable for fixed structures or very large or very small and thin items, resulting in the development of less accurate portable instruments using different methods of measurement.

The two common methods for this application include the dynamic Leeb method, used for large items, where a spring loaded probe impacts the surface and its bounce back distance is measured; and the ultrasonic contact impedance method, where different forces are used for different materials, as well as for small items and for the thin surface finish on an item.

Advances in digital technology have led to the development of an instrument by a European manufacturer that not only offers extreme accuracy using both Leeb and ultrasonic contact impedance methods but also tests to either US or European standards.

Key features and advantages of the new instrument include a camera to record the position of the probe on the item and any identifying number on the test item; digital readouts of hardness and statistics provided on the tests; ability to detect and reject inaccurate Leeb readings; and facility to store all the information from the tests in the instrument for downloading later to a PC.

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

Available from Hylec Controls , the new portable hardness testers equip users with greater capabilities, previously only available on sophisticated bench mount testers, at a price similar to much simpler portable instruments.

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