# Leeb Hardness Testing to ISO 16859, ASTM A965

Determination of the hardness of metallic materials according to Leeb is defined in the ISO 16859 and ASTM A956 standards. In this dynamic test method, the ratio of rebound velocity to impact velocity of a moving impactor is used to determine the hardness.

## Leeb hardness test classification to ISO 16859, ASTM A965

The Leeb hardness test is a dynamic test method and has the following characteristics:

• It is one of the standardized methods (ISO 16859, ASTM A956).
• Depending on the method, the impact velocity is between 1.4-3.0 m/s.
• It is a rebound test method, which means that in order to determine the hardness value of a test piece, the velocity of an impactor is measured before and after the impact. The ratio of rebound velocity to the impact velocity is the measure of the dynamic Leeb hardness of the test specimen.
• Impactor shape and material: tungsten carbide cobalt, ceramic or diamond, ball-shaped indenter with different radii.

## Leeb hardness test procedure

In the Leeb hardness test method to ISO 16859, an impact device accelerates an impactor with spring force. The velocity of the impactor is divided into three phases:

• 1.Approach phase , in which spring force accelerates the impactor onto the test surface.
• 2.Impact phase , in which the impactor and the specimen are in direct contact. The specimen is elastically and plastically deformed and the impactor comes to a complete stop. The rebound of the impactor is generated through the elastic recovery of the impactor and the specimen.
• 3.Rebound phase in which the impactor is re-accelerated with the remaining energy from the impact phase.

## Calculation of the Leeb hardness

The velocities are measured contact-free by means of an induced voltage. This induction voltage is generated by a moving magnet in a defined coil in the impact device. The induced voltage signal is recorded electronically and the peak values, the point of the impact phase and the point of the rebound phase, are used to calculate the Leeb hardness, also see illustration above. The ratio of rebound velocity vr to impact velocity vi, multiplied by a factor of 1000, gives the Leeb hardness (see formula).

## Leeb hardness test methods

The individual Leeb test methods are differentiated in terms of:

• The material and shape of the indenter of the impact device
• The impact velocities

More specific information on the differences between the individual methods can be found in the table below.

 Method Kinetic impact energy [mJ] Impact velocity [m/s] Rebound velocity [m/s] Maximum distance between indenter ball and test surface [mm] Mass of impactor [g] Spherical radius [mm] Indenter material Applications HLD 11.5 2.05 0.615 – 1.8245 2.00 5.45 1.5 WC-Co 300 – 890 HLD HLS 11.4 2.05 0.82 – 1.886 2.00 5.40 1.5 C 400 – 920 HLS HLE 11.5 2.05 0.615 – 1.886 2.00 5.45 1.5 PCD 300 – 920 HLE HLDL 11.95 1.82 1.1092 – 1.729 2.00 7.25 1.39 WC-Co 560 – 950 HLDL HLD+15 11.2 1.7 0.561 – 1.513 2.00 7.75 1.5 WC-Co 330 – 890 HLD+15 HLC 3.0 1.4 0.49 – 1.344 2.00 3.1 1.5 WC-Co 350 – 960 HLC HLG 90.0 3.0 0.9 – 2.25 3.0 20.0 2.5 WC-Co 300 – 750 HLG

## How is the Leeb hardness value read and represented?

The Leeb test hardness value consist of three components:

• A numerical hardness value
• The two capital letters HL, for Hardness according to Leeb
• The designation of the Leeb scale that defines the impact device and associated parameters

Example of how to represent and read a hardness value: 780 HL D

 780 Hardness value HL According to Leeb D Leeb method with spherical impact body of tungsten carbide cobalt with a radius of 1.5 mm and a weight of 5.45 g

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