Leeb rebound hardness test
Encyclopedia
The Leeb rebound hardness test is one of the four most used method for testing metal
hardness. This portable method is mainly used for testing sufficiently large workpieces (mainly above 1 kg).
Traditional hardness measurements, e.g. according to Rockwell
, Vickers
and Brinell
, are stationary, i.e. fixed workstations are set up in segregated testing areas or laboratories of plants. Most of the times, these methods are used selectively in destructive tests. Samples are cut off from selected parts and measured in the laboratory. From the individual results, statistical conclusions are drawn for the entire batch. The portability of Leeb testers can sometimes help to achieve higher testing rates without destruction of samples (test is considered as non-destructive), which in turn simplifies processes and saves costs.
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.
When using the dynamic Leeb principle, the hardness value is derived from the energy loss of a defined impact body after impacting on a metal sample, similarly to the Shore
scleroscope
. The Leeb quotient (vi,vr)is taken as 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.When using a magnetic impact body, the velocities can 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.
While in the 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 / 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.
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.
Leeb hardness results in HL are often converted to the traditional hardness scales HRC, HB and HV mainly for convention reasons between supplier and customer.
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
hardness. This portable method is mainly used for testing sufficiently large workpieces (mainly above 1 kg).
History
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 to “Leeb rebound” due to the wide circulation of the “Equotip” product.Traditional hardness measurements, e.g. according to Rockwell
Rockwell scale
The Rockwell scale is a hardness scale based on the indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. There are different scales, denoted by a single...
, Vickers
Vickers hardness test
The Vickers hardness test was developed in 1924 by Smith and Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the...
and Brinell
Brinell scale
The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science....
, are stationary, i.e. fixed workstations are set up in segregated testing areas or laboratories of plants. Most of the times, these methods are used selectively in destructive tests. Samples are cut off from selected parts and measured in the laboratory. From the individual results, statistical conclusions are drawn for the entire batch. The portability of Leeb testers can sometimes help to achieve higher testing rates without destruction of samples (test is considered as non-destructive), which in turn simplifies processes and saves costs.
Method
The traditional methods are based on well-defined physical indentation hardnessIndentation hardness
Indentation hardness tests are used to determine the hardness of a material to deformation. Several such tests exist, wherein the examined material is indented until an impression is formed; these tests can be performed on a macroscopic or microscopic scale....
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.
When using the dynamic Leeb principle, the hardness value is derived from the energy loss of a defined impact body after impacting on a metal sample, similarly to the Shore
Shore durometer
Durometer is one of several measures of the hardness of a material. Hardness may be defined as a material's resistance to permanent indentation. The durometer scale was defined by Albert F. Shore, who developed a measurement device called a durometer in the 1920s. The term durometer is often used...
scleroscope
Scleroscope
A scleroscope is a device used to measure rebound hardness. It consists of a diamond-tipped hammer dropped from a fixed height. The device was invented in the early 1900s...
. The Leeb quotient (vi,vr)is taken as 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.When using a magnetic impact body, the velocities can 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.
While in the 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 / 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.
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
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.
Leeb hardness results in HL are often converted to the traditional hardness scales HRC, HB and HV mainly for convention reasons between supplier and customer.
Standards
- German standard:
- DINDinDIN or Din or din can have several meanings:* A din is a loud noise.* Dīn, an Arabic term meaning "religion" or "way of life".* Din is one of the ten aspects of the Ein Sof in Kabbalah ....
50156 “Metallic materials – Leeb hardness test” - DGZfP Guideline “Mobile Härteprüfung“
- VDIVerein Deutscher IngenieureVerein Deutscher Ingenieure is an organization of 139,000 engineers and natural scientists.Established in 1856, the VDI is today the largest engineering association in Western Europe....
/VDE Guideline 2616 Part 1 “Hardness testing of metallic materials”
- DIN
- American standard:
- ASTM A956 “Standard Test Method for Leeb Hardness Testing of Steel Products”
External links
- http://www.equotip.com/the-leeb-principle.html?L=0%2F