Other test procedures

Leeb test

Back to overview

General

The 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 impact body is used to determine the hardness.

Classification of the Leeb Test

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

  • It is one of the standardised procedures (ISO 16859, ASTM A956).
  • The impact velocity lies between 1.4 and 3.0 m/s, depending on the method.
  • It is a rebound test method, i.e. the velocity of an impact body before and after the impact is measured to determine the hardness of a test specimen. The ratio of the impact velocity to the rebound velocity is the measure of the dynamic Leeb hardness of a test specimen.
  • Shape and material of the impact body: Tungsten carbide cobalt, ceramic or diamond, ball-shaped indenter with different radii.

 

Test Procedure

In the Leeb hardness test conducted according to ISO 16859, an impact device accelerates an impact body using spring force. The velocity of the impact body is broken down into three phases:

  1. Approach phase, during which the impact body is accelerated towards the test surface by means of the spring force.
  2. Impact phase, during which the impact body and the specimen are in direct contact. The specimen is thereby elastically and plastically deformed and the impact body is brought to a complete standstill. The elastic spring-back of impact body and specimen causes the impact body to rebound.
  3. Rebound phase, during which the impact body is again accelerated out of the impact phase with the remaining energy.

The velocities are measured contact-free by means of an induced voltage, 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, see also figure below. The ratio of rebound velocity vr to impact velocity vi, multiplied by a factor of 1000, gives the Leeb hardness (see formula).

Phases of the Leeb test

Legend:

A            Peak value of approach phase

B            Peak value of rebound phase

t             Time

U            Voltage

Methods

The individual methods are distinguished from each other by:

  • Material and shape of the indenter of the impact unit;
  • The impact velocities.

The specific differences between the individual methods can be seen in the following table.

Test method

Kinetic impact energy

[mJ]

Impact velocity

[m/s]

Rebound velocity

[m/s]

Maximum distance between indenter ball and test surface

[mm]

Mass of impact body

[g]

Spherical radius

[mm]

Material of indenter

Application range

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 hardness value read and represented?

The Leeb test hardness value consists of three components:

  1. A numerical hardness value;
  2. The two capital letters “HL”, standing for "Hardness according to Leeb";
  3. The designation of the Leeb scale that defines the impact device and the 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.