ABSTRACTThe main objective of this experiment is to have the students to experience Rockwell Hardness test machine firsthand, and how to use this equipment to determine a materials hardness. Two specimens are used for this experiment, wherein the first specimen is subjected into the Rockwell Hardness testing machine. Then the specimen is subjected into a given load, which is in the form of a diamond cone. After the indentation is made, the empirical hardness number is then gathered from a dial gage. The above process is then repeated for the second specimen. The data gathered is used to evaluate the hardness of the two specimens. INTRODUCTIONHardness can be defined as resistance to penetration, resistance to abrasion, resistance to scratching, or resistance to cutting. These are related in that they all require plastic flow of the material. A variety of tests for hardness are in use, depending on which of the above situations is of most interest. Material properties, such as hardness can be altered to desired levels by various heat treatment procedures. In this experiment, the Rockwell Hardness Test shall be introduced to determine a materials hardness.

Procedure and data:

Table 1: Measured values Table 1: Experimental Results

Trial Steel Soft Treated

116.268

217.067

315.766

416.864

517.264

1. For each of the samples find the average values of hardness and then standard deviation?Table 2: Experimental Results

Trial Steel Soft Treated Steel

116.268

217.067

315.766

416.864

517.264

Average16.5865.8

Variance275.204332.2

Standard Deviation16.5865.8

Sample calculation (data from the Steel Soft specimen):

Same calculation had done for the treated steel; from the results of both materials we can see both standard deviation and average are the same for each specimen. On the other hand, variance was extremely different than both deviation and average for each specimen used.

2. Does the hardness which you found agree with the properties which may be found in a book?Yes, the empirical hardness values agree with the properties found in a reference book for materials3. Why cannot indentations be very close to one another?If those indentations were placed close to the edge of this sheet metal the Rockwell hardness number of the same metal will decrease consequently, thus getting an inaccurate reading.4. What is the effect if the surface is not horizontal and smooth?When the surface is not clean and not placed correctly, mistakes could occur when doing the experiment; more so, it will also provide inaccurate readings for the hardness number of the material. Unlike from the Brinell and Vickers Hardness Test, the Rockwell method suffers this effect greatly when the support anvil has many obstructions or if the surface is rough and unclean.5. Why should different indenter be used for different materials?The indenter should depend on how soft or hard the specimen or material is for the experiment. For example, soft materials require 1/16 inch to be tested. 6. What are the basic principles behind Rockwell Hardness Tests?The Rockwell hardness of the material is based on the difference in the depth of the indenter at two specific times during the testing cycle. The value of hardness is calculated using a formula that was derived to yield a number falling within an arbitrarily defined range of numbers known as a Rockwell hardness scale.7. For the values obtained from your samples; what can be said about the strength of the material? Is this correct with the published values of the given material?The results of both A2 soft steel and treated steel can see both standard deviation and average are the same.8. Generally when a hardness value is given, it is given in Rockwell C scale, why is this so?This means that the indenter and the material used for the experiment has a much more hardness than the materials specified for the HRB scale. Materials like steel, hard cast irons, case hardened steel belongs to the Rockwell C scale. But there are cases that the B and C scales for the Rockwell hardness test overlaps, such that readings below HRC 20 and above HRB 100 are generally considered unreliable.CONCLUSIONIn this experiment, the student concludes that the Rockwell hardness test experiment is accurate and is faster than most hardness tests. Also, the student learned more about a materials hardness and where this can be used in the field of engineering depending on the materials hardness scale.