ASTM A956 Leeb Hardness Testing of Steel Products

Scope:

The Leeb hardness test, ASTM A956, is a dynamic or rebound method that determines the Leeb hardness by comparing the rebound velocity to the impact velocity of a tungsten carbide ball or a diamond-tipped impact body. This portable approach is mostly used for determining whether or not a workpiece is sufficiently large. It calculates the restitution coefficient. The Leeb hardness of steel, cast steel, and cast iron is determined by ASTM A956, and the results are indicative of strength and depend on the heat treatment of the material examined.

Test Procedure:

During the ASTM A956 Leeb hardness test, an impact body is propelled to the specified velocity towards a test surface from which it rebounds. The impact body has a spherically shaped tip made out of tungsten carbide, silicon nitride or diamond. The impact and rebound velocities are measured when the impact body is approximately 0.039 inches [1 mm] from the test surface. This is accomplished utilizing a permanent magnet mounted in the impact body which, during the test, moves through a coil in the impact device and induces an electric voltage on both the impact and rebound movements. The quotient of these measured voltage values derived from the impact and rebound velocities, multiplied by the factor of 1000 produces a number that constitutes the Leeb hardness value. 

 Specimen size:

For ASTM A956, the test pieces with curved surfaces, may be tested on their convex or concave surfaces provided the radius of curvature of the test specimens is not less than 1.181 inches (30 mm) for impact devices.

Data:

Leeb hardness is reported in SI unit or Inch-pound and is considered as a standard separately. Leeb Hardness for ASTM A956 is calculated as : 

L= (Rebound Velocity / Impact Velocity) x 1000

Conclusion:

The hardness of a moving body is determined using the ASTM A956 Leeb Hardness testing method, which uses the ratio of rebound velocity to impact velocity. It’s a nondestructive testing technique.