Question

Projected area rather than surface area of the indentation is used in

• A. Brinell test
• B. Rockwell test
• C. Vickers test
• D. Meyer test

Hint:

Remember the key calculation basis for major hardness tests: Brinell & Vickers use surface area, Meyer uses projected area, and Rockwell uses depth.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Indentation hardness tests measure a material's resistance to localized plastic deformation. Most tests calculate a hardness number based on the applied load and the size of the resulting indentation. The key difference between some tests lies in how the indentation size is measured and used in the formula (surface area vs. projected area).

Step 2: Detailed Explanation:
Let's examine how each test calculates hardness:

• (A) Brinell test: Uses a spherical indenter. The hardness number (HBW) is calculated by dividing the applied load by the surface area of the curved indentation.

• (B) Rockwell test: This test is unique as it measures the depth of the indentation, not its area. The hardness number is an inverse function of the depth.

• (C) Vickers test: Uses a square-based diamond pyramid indenter. The Vickers hardness number (HV) is calculated by dividing the load by the surface area of the four triangular faces of the indentation.

• (D) Meyer test: Meyer hardness is defined as the applied load divided by the projected area of the indentation. The projected area is the area of the impression as seen from the direction of indentation (i.e., the area of the circle at the surface). The formula is \( H_M = \frac{4P}{\pi d^2} \), where P is the load and d is the diameter of the indentation.

Step 3: Final Answer:
The Meyer hardness test is the one that specifically uses the projected area of the indentation in its calculation.