Vickers Hardness Testing: Method, Formula, and ASTM E384
Introduction to Vickers Hardness Test
The Vickers hardness test, developed in 1921 by Robert L. Smith and George E. Sandland of Vickers Ltd., provides an alternative to the Brinell hardness test with a simpler scale. While it can be used to test the hardness of metals and other hard materials, its main focus is on assessing the ability of softer materials, such as plastics, to withstand sustained stress.
The Vickers test utilizes its unit of hardness, known as the Diamond Pyramid Hardness (HV) or Vickers Pyramid Number (DPH). Unlike pressure units, HV should not be used as a substitute. The test involves applying a load onto a specially designed diamond indenter, creating an indentation on the material’s surface. However, for accurate results, the material must have a flat and polished surface.
The Vickers indenter, shaped like an inverted pyramid, ensures a well-defined indentation and is made of diamond due to its resilience to deformation. Once the calibrated tester is ready, the load is applied, causing the indenter to penetrate the material under the force of gravity. After a dwell time, the load is removed, and the indentation size is optically evaluated using a specific equation to determine the material’s hardness value.
Advantages of Vickers Hardness Test
Wide range of applications: Unlike the limited application of the Rockwell method, the Vickers test can be applied to various materials, including both soft and hard substances. It possesses one of the broadest hardness ranges among the different test methods.
Consistent indentation: The Vickers indenter’s universal shape facilitates quicker calibration, and diamonds ensure minimal deformation. Consequently, no correction factors for specific materials are required, leading to accurate results if the sample meets the test requirements.
Non-destructive: Apart from the visible indentation, the Vickers test does not cause significant damage to the material, allowing for reuse. This feature is advantageous for minimizing waste and optimizing test materials in a testing facility.
Different Models of Vickers Testers
Different models of Vickers testers are available, including analog, digital, and CCD optical analysis systems. The latest advancements in Vickers hardness testing systems focus on simplicity and automation, with features like automatic turret movement, motorized XYZ table, and built-in software for data analysis and reporting.
Certain consumables are necessary to conduct the Vickers hardness test, including the indenter (diamond pyramid), optical measuring instrument, hardness test blocks for calibration, and software assistance for accurate and automated measurement. While the initial investment for a Vickers hardness tester may be higher than for a Rockwell tester, the comprehensive package of essential consumables and accessories can streamline the purchasing process.
Despite some limitations, such as the need for surface preparation, longer test cycles, and higher costs, the Vickers hardness test remains a reliable method widely used in testing facilities and workshops. Selecting a reputable company that can provide suitable testers and accessories will ensure accurate and precise results for each testing cycle.
In conclusion, the Vickers hardness test is a versatile and trustworthy method for assessing material hardness. Understanding its principles and acquiring the appropriate equipment and instruments will enable precise testing and reliable results in various applications.
