TITLEHardness testing of metallic material.OBJECTIVEDetermine the hardness of metallic materials by using the Rockwell scale.INTRODUCTIONHardness is the amount of resistance towards deformation. The value of hardness could be found using the Rockwell hardness test which is one type of hardness testing method and known as indentation hardness testing, where an indentation hardness tester with a diamond (Engineers Edge, n.d.) indenter or tungsten carbide ball indenter is forced into a material, and the depth of the indentation is measured to determine the hardness of the material.THEORYThere are many methods to find the hardness (amount of resistance towards deformation), and one of the methods is the indentation hardness testing. Depending on the method, the units and the scales of hardness changes. By using the Rockwell hardness test, the load is applied gradually, and the area of the indentation is measured. Rockwell us used industrially because it is quick, and the convenient. Rockwell alone has 15 different scales, according to the hardness of the material being tested (Carmichael and Krikorian, n.d.). In this lab, Rockwell scales C is used with a diamond indenter.The hardness of any material is an arbitrary number derived from the net increase in depth of indention as the force on an indenter is increased from a specific value. This test is done under a constant temperature due to reason that the properties of the material changes with the temperature.

Figure 1: Indentation tester

MATERIALS AND APPARATUS Indentation tester Specimen (medium carbon steel) Indenter [Diamond (120, 0.2 tip radius )]

Figure 2: Rockwell Diamond Indenter

PROCEDURE Before the experiment, the specimen was taken and made sure it was clean from foreign matter. The required indenter (Diamond (120, 0.2 tip radius)) was fixed to the machine for this specific test. Then the support for the specimen was selected (in this case a flat surface was selected) Then it was made sure that the crank was in the unload position. The correct load was selected by rotating the load wheel in the indentation tester. The large pointer in the dial face was adjusted to zero. The preminilary load was applied by rotating the hand wheel until the specimen which was placed on the anvil, touched the tip of the indenter. Then it was continued to rotate till required number of revolution of the larger pointer, till the position of the smaller pointer reached the red dot. Then the machine was let to rest for 0.1 4 s Then the major load was applied by moving the crank to the load position very slowly, and then let to rest for 2-6s. The load was then released slowly by moving the crank to the unload position and the reading on the scale was recorded. This test was repeated several times to get the average value. The minor load is removed by lowering the anvil.

CALCULATION

HRC calculation: Hardness of medium carbon steel on either sidesAverage Value60.375

Average Value==72.75

RESULTSThe hardness test for the medium carbon was repeated six times and the average were taken, and the results are shown in table 1.Table 1: Results of hardness testing of Medium carbon steel

HRC Test Results

Sample1st Value2nd Values3rd Values4th ValueAverage value

Medium carbon Steel60.5

60.56060.560.375

Medium carbon Steel7274.56876.572.75

CONCLUSIONOverall, it was found that the indentation testing, compared to other testing methods such as scratch hardness testing, gives a specific value of hardness, and it is much quicker and much more efficient. Using this test, only a comparison could be made, but cannot gain any further properties of material, and specifically, in this lab, since only one material (Medium Carbon Steel) was tested (Hardness: HRC 60.375 to HRC 752.75), this cannot be compared to any other materials. (n.d.)

REFERENCES

[Online], Available: http://www.asminternational.org/documents/10192/3467819/06671g-ch.pdf/edc484d2-0cdc-43bb-a15e-c2ffdd8c940c [16 August 2014].Carmichael, and Krikorian, A., [Online], Available: http://engin.swarthmore.edu/~rcarmic1/E59HardnessLab.pdf [15 August 2014].Engineers Edge, [Online], Available: http://engineersedge.com/material_science/hardness.htm [16 August 2014].

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