Maastricht, The Netherlands — INNOVATEST, a leading designer and manufacturer of precision hardness testers, motorized stages, and relatedhardness testing equipment, has just launched the new XXL iSmart Motorized Stage. It’s suitable for automated hardness testing in large-scale operations and works wonderfully well with INNOVATEST’s hardness testers.
INNOVATEST manufactures testers specific to the Vickers, Rockwell, Brinell, and Knoop hardness testing methods. They also have universal testers that enterprises and laboratories can use to conduct Vickers, Rockwell, Brinell, and Knoop testing with a single machine.
Read about the four standard hardness testing methods below.
1. Vickers Hardness Test
The Vickers hardness test is a static, optical hardness testing method that evaluates a material’s resistance to plastic deformation. It employs a diamond indenter in the shape of an equilateral pyramid with a 136° face angle, pressed onto the material at a specified load. The resulting indentation is measured under magnification, and the hardness is calculated from this optical measurement.
Results are expressed as:
a hardness value of 1 to 3,000;
- HV, indicating the testing method used – in this case, Vickers hardness;
- the test load, expressed in kilogram-force; and
- the duration of force application, i.e., the dwell time, expressed in seconds
A Vickers result of 780HV30/30 means the material has a Vickers hardness value of 780 when tested with a 30-kg load applied for 30 seconds.
A Vickers hardness tester is suitable for testing the hardness of metals. In fact, one of its primary advantages is its universal applicability. It also uses only one indenter instead of a combination of ball and loads, such as what the Brinell tester uses.
That said, Vickers testing requires extensive and high-quality surface preparation. For microhardness, the surface must be polished. For macrohardness, it must be finely ground. The sample should be firmly clamped, and the test environment must be free of shocks and vibrations to avoid distorting optical readings.
2. Rockwell Hardness Test
The Rockwell hardness test is a static depth-difference method standardised under ISO 6508 and ASTM E18. It is widely used to measure the hardness of metallic materials, and to some extent, plastics. It determines hardness by measuring the permanent penetration depth left by an indenter under a defined test load. Indenters vary depending on the method and include a diamond cone (120°) or a carbide ball.
The test begins with a minor preload, followed by a major load, and then a return to the minor load. The result is shown directly on the tester andexpressed as a numerical value, HR (for Rockwell method), and the scale used, such as:
- 60 HRC: A hardness score of 60 using the regular Rockwell method; a main load of 150 kgf applied using a standard diamond cone indenter
- 60 HR45TW: A hardness score of 60 using the superficial Rockwell method; a main load of 30 kgf applied using a 1/16” carbide tungsten ball indenter
The superficial Rockwell (super Rockwell) method is used when a more surface-sensitive hardness measurement scale is required. It uses lighter test loads: a preload test force of 3 kgf and main test forces between 15 and 45 kgf. The lighter test forces make super Rockwell suitable for testing the hardness of thin components and samples with coatings and layers.
Unlike Vickers, Rockwell provides a direct measurement of indentation depth and does not require an optical evaluation of indentation. Thus, Rockwell testing is fast and cost-effective as it does not require surface polishing for sample preparation.
However, the testing environment must be clean because Rockwell testing is sensitive to surface contamination. Equipment must also be checked for indenter wear, as a worn-out indenter can lead to inaccurate readings.
3. Brinell Hardness Test
The Brinell hardness test is a static, optical hardness testing method standardised under ISO 6506 and ASTM E10. It is primarily used in the macro and low-load ranges and is especially suited for testing coarse-grained or inhomogeneous materials such as castings and forgings.
ABrinell hardness tester uses a spherical tungsten carbide ball indenter with a diameter of 1, 2.5, 5, or 10 mm. This is pressed onto the sample material with a defined test force and for a set duration. The diameter of the indentation is optically measured and used to calculate the hardness value.
Here’s an example of a Brinell hardness test result: 210 HBW 5/250/30. This says the material has a hardness score of 210 when tested with the Brinell hardness method (indicated by the HBW) using a tungsten carbide ball 5 millimetres in diameter and a 250 kgf test load applied for 30 seconds.
Note: If the Brinell hardness has a dwell time of 10 to 15 seconds, the example result above will omit the 30 at the end (the dwell time figure).
The Brinell hardness test is flexible because of the many possible ball-size and test-load combinations. It’s great for testing rough surfaces and soft, and heterogeneous materials. The large indentation size also makes optical evaluation easier than Vickers.
However, Brinell cannot be used for significantly thin materials and may not be very reliable with extremely hard samples.
4. Knoop Hardness Test
The Knoop hardness test is a static, optical testing method standardized under ISO 4545 and ASTM E92/E384. With test loads from 1 gf to 2 kgf, it is designed formicro and low-load applications, particularly for testing thin layers and brittle materials (e.g., glass and ceramic).
The test uses a diamond pyramid indenter with a rhombic base, featuring a longitudinal angle of 172.5° and a transverse angle of 130°. The Knoop indentation is elongated and shallow, which is why it’s ideal for very thin samples and surfaces where deeper indentations might cause cracking.
A Knoop hardness value is expressed as a numerical score, followed by HK for Knoop hardness, the test load in kgf, and the dwell time. An example result is 850 HK120, which is 850 Knoop hardness with a test load of 120 kgf. Dwell time is not included in this case because it falls within the standard 10 to 15 seconds.
Knoop’s advantage lies in its suitability for measuring hardness in thin layers and brittle materials. It causes minimal surface damage and provides high resolution at low loads. However, it must be used with polished surfaces.
INNOVATEST for Precise Hardness Testing
You can rely on INNOVATEST hardness testers to provide precise and accurate hardness measurements.
Check out their Vickers, Rockwell, and Brinell hardness testers. Knoop hardness testing can be done with one of their Vickers machines. You can also get one of the INNOVATEST universal hardness testers if testing method versatility is a priority.
