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Lab Report 03

Materials Engineering

Experiment No. 02 ROCKWELL HARDNESS TEST OF A GIVEN SAMPLE

Introduction: Hardness of a material is generally defined as resistance to the permanent deformation such as indentation, wear, abrasion and scratch under static and dynamic load. Hardness is a property of a material by which it offers resistance to scratch or indentation.

Theory: The hardness test is a mechanical test for material properties which are used in engineering design, analysis of structures and material development. The hardness test is performed to determine the suitability of a material for a given application. Rockwell hardness test is developed by the Wilson instrument co U.S.A in 1920. This test is an indentation test used for smaller specimens and harder material. This hardness test is preferred because it is simple, easy and relatively nondestructive.

Objective: Determine the Rockwell hardness number of a given specimen using Rockwell hardness testing machine.

Principle: A standard minor load (based on type of material) is applied first to fixed the position of indenter on the surface where indentation has to be made than standard major load is applied to make the 1|Page

Lab Report 03

Materials Engineering

indentation through a standard indenter (diamond indenter) for a standard duration of time. The hardness number is directly obtained from the dial gauge in this test.

Specification: Rockwell hardness tester gives the direct reading of a hardness number on a dial provided with the machine. Specifications are as follows:  Ability to determine the hardness up to 100 RHN.  Maximum application of load 150 Kg.  Minimum application of load 10 Kg.  Method of load application, lever type.  Least measuring hardness number 1 RHN.

Test Specimen: A selected specimen should have a thickness three times higher than the depth of indentation to avoid the deformation to be extended to the opposite surface of a specimen.

Materials and Equipments:  Rockwell hardness testing machine.  Diamond cone indenter.  Specimens (Mild steel).

Figure 1: Rockwell Hardness Tester https://1.bp.blogspot.com/aIFJLQCoAc/WIDJob9t0MI/AAAAAAAAAXk/F8_qXkdBLrQ6mZJowiZ8rnwEhzlBcNJkwCLcB/s1600/rockwell_equipment_line_diagram.jpg

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Lab Report 03

Materials Engineering

Precautions:  Before test, the surface has to be clean from dust.  Test specimen should have a smooth and flat surface.  The position of a specimen should be fixed by applying minor load, if a specimen misplace it will damage the diamond indenter.

Procedure: 1. Keep the lever at position “A” which is unloading position. 2. Select a suitable indenter and weights based on type of the material. 3. Place the specimen on the testing table anvil. 4. Turn the hand wheel to raise the testing table anvil until it makes contact with indenter and continue turning till the small pointer reaches the spot at “4” this is automatic zero setting dial gauge. 5. The minor load of 10Kg is apply to a specimen to fix the position. 6. Turn the lever position “A” to “B”, from unloading to loading position. So that the total major load of 150 Kg will act. 7. When the longer pointer of the dial gauge reaches steady position, take back the lever to the unloading position “A”. 8. Note down the reading on the dial indicator by notifying the (black graduation) large pointer. 9. Turn back the hand wheel to lower the testing table anvil and remove the testing specimen. 10. Similarly, repeat the above steps for different trials and materials.

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Materials Engineering

Observation: Sr. Specime No n . 1.

Mild Steel

Indenter Type

Load Applied

Diamond Minor = 10Kg Major = 150Kg Cone

Rockwell Rockwel Hardness l Scale Number C scale

73 HRC

Result: Rockwell hardness number of a given specimen is: Mild Steel = 73HRC

Conclusion: For hard materials, diamond cone indenter with C scale (black graduation) is used applying major load up to 150Kg. For soft materials, ball (1/16) indenter with B scale (brown graduation) is used applying major load up to 100Kg.

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