Laboratory # 1 Material Hardness Testing
Althea Smith (Team Leader)
IEGR 309-001: Manufacturing Engineering
Dr. M. Salimian
Department of Industrial Engineering
Morgan State University
Introduction Christina Mayo
The purpose of this lab is to measure the hardness of the two unknown metals. Hardness is defined as 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. Relative hardness tests are limited in practical use and do not provide accurate numeric data or scales particularly for modern day metals and materials. The goal of this lab is to achieve the hardness value by measuring 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 two principal standard test methods used to express the relationship between hardness and the size of the impression, these being Rockwell and Vickers respectively.
Each test has both advantages and disadvantages and under some circumstances will give conflicting results indicating that the same characteristics of the material are not being measures by the two different tests. However, the two tests are used in these experiments to gain two different measurements.
Theory and Calculations - Althea Smith and Christina Mayo
The Rockwell hardness test method was used to do macrohardness testing. In this procedure the test material is indented with a diamond cone or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load. When equilibrium has been reached, an indicating device, which follows the movements of the indenter in order to respond to changes in the depth of penetration of the indenter, is set to a position. While the preliminary minor load is still applied, an additional major load is applied with resulting increase in penetration. 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. 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.
HRC (Diamond cone) = 100 500t
HRB (1/16 in diameter steel ball) = 130 -500t
t = depth of penetration of the indenter into the test material
All hardness numbers were calculated automatically by the machine (Buehler hardness tester).
Vickers hardness test
The second test was performed using the Vickers hardness test. This test was used for microhardness testing. The Vickers test consists of indenting the test material with a pyramid-shaped diamond indenter with a square base between opposite faces subjected to a load. 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 load by the square mm area of indentation. When the mean diagonal of the indentation has been determined the Vickers hardness may be calculated from the formula, but is more convenient to use conversion tables. In this test the values of the diagonals were measured manually and the Vickers hardness number was calculated by the machine (Buehler hardness tester) based on these values.
Several different load settings give practically identical hardness numbers on uniform material. This is much better than the arbitrary changing of scale with the other hardness testing methods. The advantages of the Vickers hardness test are that extremely accurate readings can be taken, and just one type of indenter is used for all types of metals and surface treatments. The Vickers machine is thoroughly adaptable and very precise for testing the softest and hardest of materials.
P = Applied Load
L = Diagonal length of the indenter
TRIALS Ernest Aseidu
ROCKWELL SCALE B 1/16 BALL 100 kgf
1. 52.6 HRB
2. 52.9 HRB
3. 52.6 HRB
4. 53.0 HRB
5. 53.0 HRB
1. Turn on machine.
2. Select penetrator (1/16 ball).
3. Select test force (100 kgf) and adjust knob.
4. Insert penetrator carefully guarding tip.
5. Tighten the penetrator.
6. Place workpiece squarely on the platform.
7. Gently raise platform to near penetrator.
8. When contact is initiated between the workpiece and the penetrator, gently raise the platform until the squares on the left side of the monitor reach the set square. at this point, release the platform knob and wait for the reading.
9. The finished screen displays the final result of the test. In this case the final reading of the metals hardness is 86.6 HRB.
10. Release the platform, clear and reset the screen, then repeat the steps until you have completed 5 trials.
BUEHLER MICROMET 2100 SERIES MICROHARDNESS TESTER
1. Turn on machine, select test force.
2. Place workpiece on platform.
3. Adjust platform to secure workpiece on platform. Use height adjustment knob on right of machine to raise workpiece up to the penetrator.
4. Select the penetrator by rotating the carousel until you hear a click.
5. Raise the platform gently until workpiece nears penetrator to a close proximity.
5a. Select the test-type on the monitor: hv or hk.
A view of the final indentation vertically and horizontally
TRIALS(HV 1000 gf)
1- HV 1.8
2- HV 2.1
3- HV 1.8
4- HV 1.8
5- HV 1.8
Analysis Thomas Bryant
Scale Penetrator Measurement
1 1/16 Ball 52.6 HRB
2 1/16 Ball 52.9 HRB
3 1/16 Ball 52.6 HRB
4 1/16 Ball 53.0 HRB
5 1/16 Ball 53.0 HRB
Range: 53.0-52.6= .4
Variance: 52.6+52.6+52.9+53.0+53.0= 64.1
4 = .17 = S^2
Scale Penetrator Measurement
1 Diamond 2.1 HV
2 Diamond 2.0 HV
3 Diamond 1.8 HV
4 Diamond 1.8 HV
5 Diamond 1.8 HV
Median: 1.8+1.8+1.8+2.0+2.1 = 1.9
Range: 2.1- 1.8= .3
Variance: 1.8+1.8+1.8+2.0+2.1= 9.5
5___ = .025 = S^2
Standard Dev.= .158
Conclusion Althea Smith
The aim of this lab was to familiarize the group with the practical aspect of hardness testing. This exercise not only demonstrated the use of the hardness testing machines, but emphasized the importance of using the correct scale for the testing of materials.
The lab instructions did not specifically instruct the team on which Rockwell scale should be used for the material. Because the material was unknown there was an element of trial and error in determining which scale was appropriate. The first test was done using the Rockwell C-scale which uses a pyramid-shaped diamond shaped indenter. The resulting hardness values were suspiciously low (3 5 HRC). As a result, the decision was made to change to the B-scale, which uses a 1/16th inch ball indenter. The values with the second indenter were more acceptable because they were within the lower mid-region of the B-scale.
The problems with the lab were mainly as a result of the learning curve. A better understanding of the theory of the procedure and the fact that the process is not cut and dried allowed the team to make the necessary adjustments.
The aim of this lab was definitely achieved. In addition to an appreciation for the theoretical and practical aspects of hardness testing, the group was able to deduce that the metal for the Rockwell test may be either nickel or pure iron, and the metal for the Vickers test may be lead.