7.1 Determine the depth micrometer reading shown in FIGURE 7.1 - NSC Mechanical Technology Fitting and Machining - Question 7 - 2021 - Paper 1

1. Choose the Desired Load: Select the appropriate load for the test, usually specified for the material being tested.

2. Position the Test Indenter: Place the test indenter, normally a steel ball, in contact with the surface of the steel specimen by using the handwheel to apply pressure.

3. Apply the Load: Allow the load to be applied for approximately 15 to 30 seconds to let the indentation settle properly.

4. Measure the Indentation Diameter: After releasing the load, carefully measure the diameter of the indentation left by the indenter on the steel surface.

5. Calculate Hardness Value: Use the measured diameter and the applied load to calculate the Brinell hardness number (BHN) using the formula: $BHN = \frac{2P}{\pi D(D - \sqrt{D^2 - d^2})}$ where P is the load, D is the diameter of the indenter, and d is the indentation diameter.

6. Record the Hardness Value: Document the Brinell hardness number obtained from the measurement.

1. Yield Strength: The maximum stress that a material can withstand without permanent deformation.

2. Ultimate Tensile Strength (UTS): The maximum stress that a material can withstand while being stretched or pulled before necking occurs.

3. Elongation Percentage: The measure of how much a material can stretch or elongate before it breaks, expressed as a percentage of its original length.

The instrument in FIGURE 7.4 is a micrometer screw gauge.

The function of the micrometer screw gauge is to measure small dimensions with high accuracy, typically in the range of 0.01 mm.