what is Brinell hardness test ? How to perform in the lab?

BRINELL  HARDNESS TEST:  -Hardness of  a  material is generally defined as Resistance  to the  permanent  indentation under static and  dynamic load. 

When a material is required to  use  under direct static or dynamic loads, only indentation hardness test will be useful to find out resistance to indentation. 

In Brinell hardness test, a steel ball of diameter (D) is forced under a load (F) on to  a surface of test specimen. Mean diameter (d) of indentation is measured after the  removal of the load (F). 

Title:  Brinell hardness test. 

 Aim:  To determine the hardness of the given specimen using Brinell hardness test. Specimen and specimen Brinell hardness tester (fig.2) Aluminum specimen  Ball indenter.

Precautions :1.  Thickness of  the specimen  should not be less than  8  times the depth of  indentation to avoid the deformation to be extended to the opposite surface of  a specimen.  

2.  Indentation  should  not be made  nearer  to the  edge of a  specimen  to  avoid  unnecessary concentration of stresses. In such case distance from the edge to  the  center of  indentation  should  be  greater  than 2.5 times diameter of  indentation.

 3.  Rapid rate of applying load should be avoided. Load applied on the ball may rise a little because of its sudden action. Also rapidly applied load will restrict  plastic flow of a material, which produces effect on size of indentation.

 4.  Surface of the specimen is well polished, free from oxide scale and any foreign  material.

 Theory:   Hardness of  a  material is generally defined as Resistance  to the  permanent  indentation under static and  dynamic load. When a material is required to  use  under direct static or dynamic loads, only indentation hardness test will be useful to find out resistance to indentation. In Brinell hardness test, a steel ball of diameter (D) is forced under a load (F) on to  a surface of test specimen. Mean diameter (d) of indentation is measured after the  removal of the load (F). Observation 1.  Take  average of  five  values  of  indentation  of  each specimen. Obtain  the hardness number from equation (!).  2.  Compare Brinell and Rockwell hardness tests obtained.

 Procedure:   1.Load  to  be  applied  for hardness test  should  be  selected  according  to  the expected hardness of the material.  However test load shall be kept equal to 30  times the square of the diameter of the ball (diameter in mm)

 F=30.D 2  

Where ball diameter, generally taken as 10 mm. 

 For guidelines hardness range for standard loads given below

2.Apply the load for  a minimum  of  15 seconds to  30 seconds. [if  ferrous metals are to be tested time applied will be 15 seconds and for softer metal 30  seconds] .

3.Remove the load and measure the diameter of indentation nearest to 0.02 mm using microscope (projected image)

  4.Calculate Brinell hardness number (HB). As per IS: 1500.

  5.Brinell hardness number

where D is the diameter of ball indenter and d is the diameter of indentation.  Hardness numbers normally obtained for  different  materials are given below  (under 3000 kg and 10 mm diameter ball used)

Note:  Brinell test is not recommended for then materials having HB over 630.  It is necessary to mention ball size and load with the hardness test when standard  size of ball and load are not used. Because indentation done by different size of  ball and  load  on  different  materials are not geometrically similar.  Ball also undergoes deformation when load is applied. Material response to the load is not same all the time. 

 6.Brinell hardness numbers can be obtained from tables 1 to 5 given in IS: 1500,  knowing diameter of   indentation, diameter of the ball and load applied.

Result;  The Brinell hardness number of the specimen is ­­­­­­­.........

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