Leeb rebound hardness test
The Leeb rebound hardness test is one of the four most used methods for testing metal hardness. This portable method is mainly used for testing sufficiently large workpieces (mainly above 1 kg). It measures the coefficient of restitution.
The Leeb rebound hardness test method was developed in 1975 by Leeb and Brandestini at Proceq SA to provide a portable hardness test for metals. It was developed as an alternative to the unwieldy and sometimes intricate traditional hardness measuring equipment. The first Leeb rebound product on the market was named “Equotip”, a phrase which still is used synonymously with “Leeb rebound” due to the wide circulation of the “Equotip” product.
Traditional hardness measurements, e.g., those of Rockwell, Vickers, and Brinell, are stationary, requiring fixed workstations in segregated testing areas or laboratories. Most of the time, these methods are selective, involving destructive tests on samples. From individual results, these tests draw statistical conclusions for entire batches. The portability of Leeb testers can sometimes help to achieve higher testing rates without destruction of samples, which in turn simplifies processes and reduces cost.
The traditional methods are based on well-defined physical indentation hardness tests. Very hard indenters of defined geometries and sizes are continuously pressed into the material under a particular force. Deformation parameters, such as the indentation depth in the Rockwell method, are recorded to give measures of hardness.
According to the dynamic Leeb principle, hardness value is derived from the energy loss of a defined impact body after impacting on a metal sample, similar to the Shore scleroscope. The Leeb quotient (vi,vr) is taken as a measure of the energy loss by plastic deformation: the impact body rebounds faster from harder test samples than it does from softer ones, resulting in a greater value 1000×vr/vi. A magnetic impact body permits the velocity to be deduced from the voltage induced by the body as it moves through the measuring coil. The quotient 1000×vr/vi is quoted in the Leeb rebound hardness unit HL.
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