Rockwell Hardness Test for Rebar: Evaluating Material Strength

Rockwell Hardness Test 

Objective and Significance

To determine the hardness of rebar, which is a measure of its resistance to deformation, scratching, or indentation. This helps in understanding the material’s strength and wear resistance.

• Hardness is an important property that affects the rebar’s ability to resist mechanical wear and deformation during handling, fabrication, and service.
• Understanding the hardness of rebar ensures that it meets the required specifications and can perform adequately in its intended application.
• Hardness testing provides a quick and relatively simple method to evaluate the quality and consistency of rebar materials.

Aim

To measure the hardness of rebar using standardised testing methods, such as the Rockwell, Brinell, or Vickers hardness tests.

Apparatus

1. Hardness Testing Machine: Depending on the chosen method, this could be:
   • Rockwell hardness tester
   • Brinell hardness tester
   • Vickers hardness tester
2. Indenter: A specific type of indenter for each test method:
   • Rockwell: Diamond cone or steel ball
   • Brinell: Hard steel or carbide ball (typically 10 mm in diameter)
   • Vickers: Diamond pyramid
3. Loading Mechanism: To apply a specific force on the indenter.
4. Microscope: For measuring the indentation size (especially for Brinell and Vickers tests).
5. Calibration Block: A reference block with a known hardness value for machine calibration.
6. Sample Preparation Tools: Cutting tools, sandpaper, and polishing equipment to prepare a smooth and clean surface on the rebar sample.

Procedure

1. Sample Preparation:
   • Cut a piece of rebar to a suitable length (typically 10-15 cm).
   • Grind and polish the surface of the rebar sample to obtain a smooth and clean testing area.
2. Machine Calibration:
   • Calibrate the hardness testing machine using the calibration block to ensure accurate results.
3. Testing Procedure (varies slightly depending on the method):
   • Select the appropriate indenter (diamond cone or steel ball) and load based on the hardness scale being used (e.g., HRC, HRB).
   • Place the rebar sample on the testing platform.
   • Apply a preliminary minor load to the indenter to create a small indentation.
   • Apply the major load to the indenter and maintain it for a specified dwell time.
   • Remove the major load while maintaining the minor load, and measure the depth of the indentation.
   • Read the Rockwell hardness value directly from the machine’s dial or display.

Result

1. Hardness Value:
   • Rockwell Hardness Number (HR) for Rockwell test