The Digital Vickers Hardness Tester: How It Works and Why It Matters
Representative Infinita Engineering Visual explaining the four-step workflow for Digital Vickers Hardness Tester.What Is Vickers Hardness Testing?
ASTM E92 is the Standard Test Method for Vickers Hardness and Knoop Hardness of Metallic Materials, covering the standard and low force range (200 gf to 120 kgf). A digital Vickers hardness tester automates load application and often includes optical measurement software to reduce operator variability in reading the indentation.
Test Principle
A square-based diamond pyramid indenter, with an included angle of 136 degrees between opposite faces, is pressed into the material surface under a defined test force and held for a specified dwell time (typically 10-15 seconds). After the indenter is withdrawn, the two diagonals of the resulting indentation are measured optically, and hardness (HV) is calculated from the applied force divided by the surface area of the indentation.
Test Procedure
- Prepare a flat, polished test surface free of scratches or contamination that could distort the optical reading
- Select an appropriate test force based on expected hardness and material thickness
- Apply the indenter under the selected load for the specified dwell time
- Retract the indenter and measure both diagonals of the indentation
- Calculate HV from the average diagonal length and applied force (digital testers typically automate this calculation)
- Repeat at multiple locations per the minimum spacing requirements between indentations
Notes on Precision
The Vickers indenter generally produces a consistent hardness number across test forces for homogeneous materials, except at very low forces (below 25 gf) or for indentation diagonals under approximately 25 microns, where ASTM E384 (microindentation) applies instead. Because a single reading may not represent bulk hardness in heterogeneous materials, multiple indentations are standard practice.
Also Read – Polymer Hardness Testing: Common Uses, Methods & Scale Selection
Industry Specifications Referencing ASTM E92
- ASTM E384: microindentation hardness (loads below 200 gf)
- ASTM E140: hardness conversion tables relating Vickers, Brinell, Rockwell, and other scales
- ISO 6507: international equivalent Vickers hardness standard
Conclusion
Vickers testing is prized for measuring the full hardness spectrum — from very soft metals to hardened tool steels — with a single indenter type, at the cost of requiring a well-prepared surface and slower per-test cycle times than Rockwell testing. Digital testers narrow the gap by reducing measurement subjectivity in reading the indentation.
How does the Vickers hardness test work? A controlled force is applied through a square-based diamond pyramid indenter. After removing the force, the two diagonals of the indentation are measured and used to calculate hardness.
What test forces are covered by ASTM E92? ASTM E92 covers Vickers test forces ranging from 1 gf to 120 kgf. For microindentation testing at forces of 1 kgf or below, ASTM E384 provides additional guidance.
How should the specimen surface be prepared? The test surface should be smooth, clean and free from scale, coatings or excessive grinding damage. Proper polishing is especially important when testing small indentations or thin surface layers.
Why are both indentation diagonals measured? Measuring both diagonals helps identify distorted or uneven impressions. Their average is normally used to calculate hardness, provided the indentation meets the required acceptance criteria.
What are the advantages of a digital tester? Digital systems can automatically detect indentation edges, calculate hardness and store test results. This reduces manual calculation time and helps limit variation caused by visual measurement.
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