What Is Leeb Hardness
Source: https://en.wikipedia.org/wiki/Leeb_rebound_hardness_test
invented by Swiss company Proceq SA, The Leeb Rebound Hardness Test (LRHT) 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). [citation needed]
It measures the coefficient of restitution. It is a form of nondestructive testing.
History
The Equotip (later also called simultaneously the Leeb method) 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 that 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 the destruction of samples, which in turn simplifies processes and reduces costs.
Method
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, the hardness value is derived from the energy loss of a defined impact body after impacting on a metal sample, similar to the Shore stereoscope. 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 of 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 HLx (where x indicates the probe and impact body type: D, DC, DL, C, G, S, E).
While in traditional static tests, the test force is applied uniformly with increasing magnitude, dynamic testing methods apply an instantaneous load. A test takes a mere 2 seconds and, using the standard probe D leaves an indentation of just ~0.5 mm in diameter on steel or steel casting with a Leeb hardness of 600 HLD. By comparison, a Brinell indentation on the same material is ~3 mm (hardness value ~400 HBW 10/3000), with a standard-compliant measuring time of ~15 seconds plus the time for measuring the indentation.
Use a certain quality of impactor equipped with tungsten carbide ball heads to impact the surface of the specimen under a certain force, and then rebound. Due to different material hardness, the rebound speed after impact also varies. A permanent magnet material is installed on the impact device. When the impact body moves up and down, its peripheral coils induce electromagnetic signals proportional to the speed, which are then converted into Leeb hardness values through electronic circuits, with the symbol HL.
The Leeb hardness tester does not require a workbench, and its hardness sensor is as small as a pen, which can be operated directly by hand. Whether it is large, heavy workpieces or workpieces with complex geometric dimensions, it can be easily detected.
Another advantage of Leeb hardness is that it causes minimal surface damage to the product and can sometimes be used for non-destructive testing; The hardness testing of narrow spaces and special parts in various directions is unique.
Scales
Depending on the probe ("impact device") and indenter ("impact body") types that vary by geometry, size, weight, material, and spring force, diverse impact devices and hardness units are distinguished, e.g.:
Equotip impact device D with hardness unit HLD
Equotip impact device G with hardness unit HLG
Equotip impact device C with hardness unit HLC
Equotip impact device E with hardness unit HLE
Equotip impact device DL with hardness unit HLDL
Equotip impact device S with hardness unit HLS
Equotip impact device DC with hardness unit HLDC
Generally, impact device types are optimized for certain application fields. This is similar to using various indenter geometries and test loads in Rockwell (e.g. HRA, HRB, HRC), Brinell, and Vickers. Equotip hardness results in HLx are often converted to the traditional hardness scales HRC, HB, and HV mainly for conventional reasons between supplier and customer.[5][6]
Standards
German standards and specifications:
DIN 50156-1 "Metallic materials – Leeb hardness test - Part 1: Test Method"
DIN 50156-2 "Metallic materials - Leeb hardness test - Part 2: Verification and calibration of the testing devices"
DIN 50156-3 "Metallic materials - Leeb hardness test - Part 3: Calibration of reference blocks"
DGZfP Guideline "Mobile Härteprüfung"
VDI/VDE Guideline 2616 Part 1 "Hardness testing of metallic materials"
