BACKGROUND
Hardness is the resistive property of a material which is induced by either mechanical indentation or abrasion to a localised plastic deformation.1 It is a relative property and depends on various characteristics, such as ductility, elastic stiffness, plasticity, toughness, viscosity etc. Hardness is determined by the amount of indentation on the material. Smaller the indentation, harder is the stuff and vice versa.2
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Robert L. Smith and George E. Sandland who studied at Vickers Ltd. developed an alternative to Brinell hardness in 1921 which was named as Vickers hardness. In the Vickers test, the entire calculation is independent of the size of the indenter which makes it easier to use than other hardness testing methods.
Determination of Hardness Strength of Materials by Vickers Testing Methods
This test method is also known as microhardness test methods and is mostly used for thin sections, a small part, or case depth work. This test is defined in ASTM E – 384 standard which specifies the process of making an indentation mark on a specimen using the range of light loads through a diamond indenter.3
A 136-degree square pyramid indenter is used in the process, and the sample is made highly polished so that the mark of indentation is easily visible. The square indenters have an advantage over round inters which is used in Brinell and Rockwell testing methods as square indentations are more comfortable to measure in comparison to round impressions which are obtained through a spherical or conical indenter.4
In general, light loads are applied which vary between 10 gm to 1 kgf, and in “macro Vickers”, the load usually very up to 30 kgf. This test can be implemented in almost any material including metals, ceramics or composites.
The main objective of this experiment is to determine the hardness strength of a material by Vickers testing methods.
REQUIREMENTS
Materials:
Vicker’s Hardness Testing Machine
Diamond cone indenter
Specimen
PROCEDURE
After cleaning the surface of the specimen, embed the indenter in the hardness tester and switch ON the power supply. Place the specimen on a worktable in such a way that its clean surface will face will face the indenter which is fastened on an anvil.
Now, press the load button so that the loading lever start moving upward until it finds a steady position. Now, gradually release the loading lever to bring it down. Calculate the major and minor readings for two opposite corners of the diagonal indentation. Now, repeat the entire process for a different set of materials and calculate their hardness.
CONCLUSION
The process of finding the hardness of a material through Vickers Hardness testing method is discussed. It is a characteristic property which is used to measure the depth of indentation.
REFERENCES
- George E. Dieter, “Metallurgy and Metallurgical Engineering Series,” in Mechanical Metallurgy, New York, TMH, 1961, pp. 47-82.
- N. C. Y.-L Shen, “On the correlation between hardness and tensile strength in particle reinforced metal matrix composites,” Journal of Elsevier, vol. 297, no. 1-2, pp. 35-48, 2000.
- H. Hoefler and R. Averback, “Grain growth in nanocrystalline TiO sub 2 and its relation to vickers hardness and fracture toughness,” Scripta Metallurgica; (United States); Journal , vol. 24, no. 12, pp. 21-32, 1990.
- M.M.Chaudhri, “Subsurface strain distribution around Vickers hardness indentations in annealed polycrystalline copper,” Acta Materialia, vol. 46, no. 9, pp. 3047-3056, 1998.
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