Brinell Hardness Test - Computer Programming

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## Sunday, March 13, 2011

Aim : To find the Brinell Hardness number for the given metal specimen.

Equipments Required :
1. Brinell Hardness Testing Machine
2. Metal Specimens
3. Brinell Microscope.

Formulae:

Brinell Hardness Number ( BHN) = 2P / { p D [ D - Ö ( D 2 – d 2 ) ] }

Where,
P = Load applied in Kgf.
D = Diameter of the indenter in mm.
D = Diameter of the indentation in mm.

Description:

It consists of pressing a hardened steel ball into a test specimen. In this usually a steel ball of Diameter D under a load ‘P’ is forced in to the test piece and the mean diameter ‘d ’ of the indentation left in the surface after removal of load is measured. According to ASTM specifications a 10 mm diameter ball is used for the purpose. Lower loads are used for measuring hardness of soft materials and vice versa. The Brinell hardness is obtained by dividing the test load ‘P’ by curved surface area of indentation. This curved surface is assumed to be portion of the sphere of diameter ‘ D’.

Test Requirements:
1. Usual ball size is 10 mm  + 0.0045 mm. Some times 5 mm steel ball is also used. It shall be hardened and tempered with a hardness of at least 850 VPN. ( Vicker Pyramid Number) . It shall be polished and free from surface defects.
2. Specimen should be smooth and free from oxide film. Thickness of the piece to be tested shall not be less than 8 times from the depth of indentation.
3. Diameter of the indentation will be measured n two directions normal to each other with an accuracy of  + 0.25% of diameter of ball under microscope provided with cross tables and calibrated measuring screws.

Precautions:
1. Brinell test should be performed on smooth, flat specimens from which dirt and scale have been cleaned.
2. The test should not be made on specimens so thin that the impression shows  through the metal , nor  should impressions be made too close to the edge of the specimen.

Procedure:
1. Specimen is placed on the anvil. The hand wheel is rotated so that the specimen along with the anvil moves up and contact with the ball.
2. The desired load is applied mechanically ( by gear driven screw) and the ball presses into the specimen.
3. The diameter of the indentation made in the specimen by the pressed ball is measured by the use of a micrometer microscope, having transparent engraved scale in the field of view.
4. The indentation diameter is measured at two places at right angles to each other, and the average of two readings is taken.
5. The Brinell Hardness Number ( BHN) which is the pressure per unit surface area of the indentation is noted down.

Observation.

 Sl.No. Material Load in Kgf DiameterOf the Indenter in mm Diameter of the indentation in mm BrinellHardnessNumber(BHN) 1 2 3

Result:

Thus the Brinell Hardness of the Given Specimen are

1. Mild Steel = ------ BHN
2. EN 20      = ------- BHN.