Hardness TestingMechanics Material LabSeyed Alavi Panther ID: 2630064 Date: 04/10/2010 Monday Section

Table of ContentsIntroduction ............................................................................................................................... 3 Hardness Testing Methods .................................................................................................... 4 Rockwell Hardness Test ......................................................................................................... 4 Brinell Hardness Test.............................................................................................................. 5 Vickers Hardness Test ............................................................................................................ 6 Observations: ............................................................................................................................. 7 Data and Results ....................................................................................................................... 8 Discussion ................................................................................................................................ 11 Conclusion and Recommendation ................................................................................... 12

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IntroductionHardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting. Hardness is not an intrinsic material property dictated by precise definitions in terms of fundamental units of mass, length and time. A hardness property value is the result of a defined measurement procedure. Hardness of materials has probably long been assessed by resistance to scratching or cutting. An example would be material B scratches material C, but not material A. Alternatively, material A scratches material B slightly and scratches material C heavily. Relative hardness of minerals can be assessed by reference to the Mohs Scale that ranks the ability of materials to resist scratching by another material. Similar methods of relative hardness assessment are still commonly used today. An example is the file test where a file tempered to a desired hardness is rubbed on the test material surface. If the file slides without biting or marking the surface, the test material would be considered harder than the file. If the file bites or marks the surface, the test material would be considered softer than the file. The usual method to achieve a hardness value is to measure the depth or area of an indentation left by an indenter of a specific shape, with a specific force applied for a specific time. There are three principal standard test methods for expressing the relationship between hardness and the size of the impression, these being Brinell, Vickers, and Rockwell. For practical and calibration reasons, each of these methods is divided into a range of scales, defined by a combination of applied load and indenter geometry.

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Hardness Testing Methods-Rockwell Hardness Test -Rockwell Superficial Hardness Test -Brinell Hardness Test -Vickers Hardness Test -Microhardness Test -Mohs Hardness Test -Scleroscope and other hardness testing methods

Rockwell Hardness TestThe Rockwell hardness test method consists of indenting the test material with a diamond cone or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load F0 (Fig. 1A). When equilibrium has been reached, an indicating device, which follows the movements of the indenter and so responds to changes in depth of penetration of the indenter, is set to a datum position. While the preliminary minor load is still applied an additional major load is applied with resulting increase in penetration (Fig. 1B). When equilibrium has again been reach, the additional major load is removed but the preliminary minor load is still maintained. Removal of the additional major load allows a partial recovery, so reducing the depth of penetration (Fig. 1C). The permanent increase in depth of penetration, resulting from the application and removal of the additional major load is used to calculate the Rockwell hardness number.

HR = E - e

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Figure 1

Brinell Hardness TestThe Brinell hardness test method consists of indenting the test material with a 10 mm diameter hardened steel or carbide ball subjected to a load of 3000 kg. For softer materials the load can be reduced to 1500 kg or 500 kg to avoid excessive indentation. The full load is normally applied for 10 to 15 seconds in the case of iron and steel and for at least 30 seconds in the case of other metals. The diameter of the indentation left in the test material is measured with a low powered microscope. The Brinell harness number is calculated by dividing the load applied by the surface area of the indentation.

Figure 2

Where, BHN= the Brinell hardness number F= the imposed load in Kg D= the diameter of the spherical indenter in mm d = diameter of the resulting indenter impression in mm

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Vickers Hardness TestThe Vickers hardness test method consists of indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1 to 100 kgf. The full load is normally applied for 10 to 15 seconds. The two diagonals of the indentation left in the surface of the material after removal of the load are measured using a microscope and their average calculated. The area of the sloping surface of the indentation is calculated. The Vickers hardness is the quotient obtained by dividing the kgf load by the square mm area of indentation

Figure 3

F= Load in kgf d = Arithmetic mean of the two diagonals, d1 and d2 in mm HV = Vickers hardness

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Observations:The equipment, which was used in this experiment, was found out very sensitive to vibration. Sensitivity of this equipment gives it a valid reason of being precise because its on such a small scale, which reaches to a microscopic scale. The specimen has to place under microscope in order to observe its surface. The indent made by this equipment is not visible by the naked eye therefore a microscope was build within the equipment. The shape of the indent into material looked like a pyramid. The color and grains of each testing sample were varied. For instance, the steel sample had tight close together grains. Aluminum on the other hand had much softer, loosen grains wasnt as packed together as steel. The computer software calculated the hardness value based on the two diameters of the pyramid deformation shape.

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Data and ResultsIn this experiment Steel, Aluminum and Brass were used as the experimental materials. The following table shows the magnitude of the force that was used in this experiment and also the time duration.Table 1

Vickers Hardness Test Applied load (N) 0.981 Time 5 Material 1 Steel Material 2 Aluminum Material 3 Brass

The following table shows the distances of the diameters of pyramid shape deformation in Steel. This value was used by computer software to determine the hardness value. The pyramid deformation shape is shown in the figure 4 and 5.Table 2

D1 ( mm) D2 ( mm) Hardness

1st test 44.34 44.14 94.8

Steel Sample 2nd test 3rd test 44.32 44.53 45.34 46.4 92.3 89.7

Average 44.397 45.293 92.267

Standard Deviation 0.116 1.131 2.550

Figure 4- Steel sample

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Figure 5- Steel Sample

The following table shows the distances of the diameters of pyramid shape deformation in Aluminum. This value was used by computer software to determine the hardness value. The pyramid deformation shape is shown in the figure 6.

Table 3

D1 ( mm) D2 ( mm) Hardness

1st test 65.05 67.67 71.4

Aluminum Sample 2nd test 3rd test 64.9 65.63 66.52 64.22 72.8 72.4

Average 65.193 66.137 72.200

Standard Deviation 0.386 1.757 0.721

Figure 6- Aluminum Sample

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The following table shows the distances of the diameters of pyramid shape deformation in Brass. This value was used by computer software to determine the hardness value. The pyramid deformation shape is shown in the figure 7.Table 4

D1 ( mm) D2 ( mm) Hardness

1st test 53.99 51.82 66.2

Brass Sample 2nd test 3rd test 55.98 54.91 51.75 50.91 67.4 66.2

Average 54.960 51.493 66.600

Standard Deviation 0.996 0.506 0.693

Figure 7- Brass Sample

Figure 8- Brass Sample

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DiscussionThe result of Vickers Harness test determines that Steel is the strongest material in all three tested materials with the average value of 93. The hardness value of Aluminum was determined 72.20 and finally Brass is the weakest material with the average value of 66.60. The indention made on each specimen was not shaped as a perfect diamond and this is likely due to the poor surface finish of each material. Each material was tested three times and the magnitude of hardness and the distances were obtained and recorded. The average value and the standard deviation were calculated based on the values were obtained from each trial. The parameters calculated by the machine included the length of each diagonal and the Vickers Hardness (HV) number. In order to compare the results obtained from the experiment, results were obtained for Steel, Aluminum and Brass.

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Conclusion and RecommendationIn conclusion, hardness testing has various different definitions as in can used in various different fields. The purpose for this experiment is to determine the hardness for a material in other words its ability to resist deformation. The test used for this experiment is called Vickers hardness test as it uses a square based pyramid in order to create indentations. These indentations are very small and require a microscope to view. The diamond indenter used has very specific dimensions that are intended to give ratios comparable to that of Brinell testing. Throughout this experiment we used different materials to see their deformation based on their property. To compare these materials for example Aluminum, which is a softer metal then steel, has a lower hardness Vickers number and Brass being softer than Aluminum but Steel prevails them both. The Vickers Hardness for the Aluminum was measured to be roughly 72.2, for Brass it was about 66.60, and for the Steel the hardness was approximately 93. To improve upon the accuracy of this experiment it is recommended ensuring a well-polished surface finish for each material. The surface finish effects the shape of the indent imposed by the diamond therefore, affecting the readings for each diagonal length. Also to make sure that when the indentation is being done, not to move the table since it could affect the process giving inaccurate results.

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