2.materials properties lab hardness test

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IE 337: Materials and Manufacturing Processes Lab # 2

2 January 9, 2010

Hardness Test

Rockwell Hardness:

This hardness test uses a direct reading instrument based on the principle of differential depth

measurement. Initially a minor load is applied, and a zero datum position is established. The major

load is then applied for a specific period and removed, leaving the minor load applied. The resulting

Rockwell number represents the difference in depth from zero datum position as a result of theapplication of major load. The conical diamond (Brale) indenter is used mainly for testing hard

materials such as hardened steels and cemented carbides. Hardened steel ball indenters with

diameters 1/16, 1/8, 1/4, 1/2 in. are used for testing softer materials such as fully annealed steels,

softer grades of cast irons, and a wide variety of nonferrous metals.

Generally, in Rockwell testing, the minor load is 10 kgf, and the major load is 60, 100 or 150

kgf. The indenter used may be either a diamond cone (Brale) or steel ball, depending principally on

the characteristics of the material being tested. Common Rockwell hardness scales are provided in

Table 2.1.

Table 2.1. Common Rockwell hardness scales

Objective:

1. To understand the importance of hardness test in engineering.2. To learn how to use Rockwell hardness tester.3. To understand the different hardening mechanisms in different material systems and effect on

hardness values.

4. To understand the significance of Engineering Standards.Equipment and Materials:

1. Rockwell Hardness tester2. Material systems

a. Steel (Martensitic 440a vs. 440c )b.Aluminum alloy (6061-T6 vs. 6061-0)c.

Brass (Preannealed vs. Postannealed)

Experimental Procedure:

Three different material systems (6 samples) will be tested using Rockwell hardness tester.

The test parameters and conditions will be selected according to the materials. For each sample a total

of 3 measurements are required for statistical analysis. In order to obtain uniform and accurate

results, it is important that all tests have to be conducted under standard conditions.


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The American Standard for Testing and Materials (ASTM) has set up standard methods of

hardness tests, which are included in the reference.

a) Identify the material of each specimen used.

Proceed with the following steps:

b) Clean the surface of the specimen using an emery cloth, if needed.

c) Position the specimen under the indenter of the instrument.

d) Apply a specific load depending on the material and indenter.

e) The student will need to insert the correct tip and change the amount of load applied

for the Rockwell tests. (e.g. The Rockwell B scale uses a 1/16-inch diameter hard steel ball

and a 100-kg load. The C scale uses a conical diamond point and a 150-kg load.

g) Take other hardness measurements at different locations.

In all cases, be sure to write your observations in your notebook for each test. You need to include

these observations in your report.

Lab Deliverables:

1. Report the Rockwell hardness number for each test. Report the values for all tested specimensin a table format. One column should indicate the average values, and an adjacent column

should show the standard deviations of the results. (Include raw data)

2. Predict the tensile strength from the Rockwell hardness numbers for steel and brass specimensusing Figure 2.2.

3. Comment on the usability of the hardness experiment (specify few examples if possible).4. Discuss the comparisons of different material systems by comparing the hardness values

obtained. (e.g. compare within a group: Martensitic Steel 440a vs. 440c etc.)5. What is the limitation on the thickness of specimens for a hardness test? Explain. Calculate

the minimum thickness for a specimen for the Rockwell test.6. What are the limitations for distance from specimen edge to indentation and distance between

indentations? Explain why these limitations exist in both cases.

7. How would you measure the hardness of1a) Unmovable part of a large machine which is very heavy to transport

b) How do you differentiate between these pair of materials:

i. Martensitic vs. Austenitic Steel

ii. Steel vs. Al

iii. Brass vs. Al8. Use your observations from the lab to support your discussion.

References:

1. W.D. Callister, Jr., Materials science and Engineering an introduction, 6th2. M.P. Groover, Fundamentals of modern manufacturing, 3 edition (2003).rd3. Standards: edition, (2007).

1 Question 7: Dont think only from hardness perspective. Use lateral thinking. Carries extra credits.


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a. Conversion : ASTM E 140: 1956b. Rockwell: DIN50103, ASTM E l8-74, BS 4175: Part 1: 1967, TS 14O

Figure 2.2. Hardness and tensile strength co-relation.


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Hardness Test

Figure 2.3. Comparison of different hardness scales.

2.materials properties lab hardness test

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