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The Vickers Hardness Number (VHN) is a measurement used to determine the hardness of materials, especially metals and alloys. It is calculated based on the size of an indentation made by a diamond-shaped indenter under a specific load. This article provides a clear, step-by-step guide to calculating the VHN, along with practical examples.
Understanding the Vickers Hardness Test
The Vickers test involves pressing a diamond pyramid-shaped indenter into the material surface with a known load. The size of the resulting indentation is measured to determine the material’s hardness. The VHN is calculated using a standardized formula that relates the load and the indentation’s surface area.
Step-by-step Calculation Procedure
Follow these steps to calculate the Vickers Hardness Number:
- Measure the length of the diagonal of the indentation (d) in millimeters.
- Calculate the surface area of the indentation using the formula: Area = 0.1887 × d².
- Use the standard formula for VHN: VHN = (2 × F) / (d²), where F is the applied load in kilograms-force (kgf).
- Adjust the formula to include the surface area: VHN = (1.854 × F) / (d²).
Practical Example
Suppose a load of 0.5 kgf is applied, and the measured diagonal of the indentation is 0.02 mm. The calculation proceeds as follows:
Calculate the surface area: Area = 0.1887 × (0.02)² = 0.00007548 mm².
Calculate VHN: VHN = (1.854 × 0.5) / (0.02)² = (0.927) / 0.0004 = 2317.5.
Additional Tips
Ensure accurate measurement of the indentation diagonal for precise results. Use a microscope or a high-magnification lens to measure the diagonal length. Repeat the test multiple times for consistency.