The Knoop method is a static microhardness testing technique developed as an alternative to the Vickers method. Knoop hardness testing is especially useful for evaluating brittle materials, thin films, and surface coatings, where precision and minimal indentation are essential. Rather than manufacturing separate Knoop hardness testers, GNEHM integrates Knoop testing functionality directly into the Vickers machines, combining two microhardness methods in one efficient solution.
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The Knoop hardness test method is a microhardness testing method that uses a narrow, elongated diamond-shaped indenter to measure surface hardness. Unlike the Vickers method, which creates a symmetrical square-shaped impression, the Knoop method produces an asymmetrical, shallow indentation, making it especially suitable for testing thin coatings and delicate materials.
The indenter features a rhomboid-based geometry with a longitudinal edge angle of 172.5° and a transverse angle of 130°, enabling high measurement sensitivity and minimal specimen deformation.
Knoop hardness testing is particularly suited for:
The Knoop hardness test follows a standardised step-by-step procedure to ensure precise and reproducible measurements, especially on small or delicate samples. The typical Knoop hardness test procedure includes the following steps:
The Knoop method supports test loads from as low as 1 gf up to 2 kgf. Typical values include 25 gf, 50 gf and 100 gf, depending on the application and material. These low loads allow for precise measurements on thin films, coatings, and other delicate materials without damaging the surface.
Whether in R&D environments, metallurgical labs, or quality control departments, the Knoop method is a reliable choice for fine-scale hardness evaluation. The most important benefits are:
Please note that the Knoop method is less suitable for bulk or rough-surfaced materials, as it requires highly polished samples and precise optical measurement conditions. For testing larger or coarser specimens, methods such as Brinell or Rockwell may be more appropriate.
While both methods fall under microhardness testing, there are distinct differences between the Vickers and Knoop tests:
Knoop testing is particularly beneficial for materials with directional properties (anisotropy), as the elongated shape of the indent reveals differences along material axes.
Whether you’re analysing metallographic samples, electronics, or fine surface coatings, our testing machines provide reliable support for both Vickers and Knoop testing methods, thanks to intelligent force control and adaptable software. All GNEHM Vickers hardness testers are designed to support Knoop testing, using the appropriate diamond indenter and load settings. Our systems feature:
Our industrial Knoop-compatible testers are ideal for production labs, research institutes and quality control teams. Looking to buy a Knoop hardness tester?
Explore our hardness testing machines, request a quote or book a product demo today.
At GNEHM testing, we combine decades of experience in hardness testing with Swiss precision engineering. Our hardness testing machines are modular, intuitive, and engineered for both Vickers and Knoop testing, eliminating the need for two separate systems.
Our team of hardness testing specialists is here to help you configure the right microhardness testing setup for your application. Whether you’re looking to buy a Knoop hardness tester, explore industrial testing solutions or simply request a quote, we offer expert guidance and tailored advice.
Contact us now for a quote, demo or personal technical consultation.
Not sure if the Knoop method is right for you? Check out our Vickers, Brinell or Rockwell testers to compare available methods.
The Knoop test uses an asymmetrical, elongated diamond indenter and is ideal for very thin materials or coatings. The Vickers test, in contrast, uses a symmetrical, square-shaped diamond and is more versatile for general-purpose microhardness testing.
A small load is applied through a narrow diamond indenter, leaving an elongated impression. The length of this indent is then optically measured to calculate hardness.
HK = 14.229 × F / L², where F is the force (gf) and L is the long diagonal (mm) of the indent.
The Knoop method is ideal for evaluating surface hardness on very thin materials, coatings, and brittle components, particularly when minimal indentation depth and high measurement resolution are required. It’s commonly used in R&D, microelectronics, biomedical devices, and coating analysis.
The Knoop indenter is made of diamond, selected for its extreme hardness and ability to produce consistent, precise impressions in a wide range of materials.
It has a pyramidal shape with a rhomboid base, featuring a longitudinal angle of 172.5° and a transverse angle of 130°. This geometry results in an elongated, shallow indentation with a length-to-width ratio of approximately 7:1, ideal for detecting hardness gradients in thin coatings and microstructures.
Common loads include 25 gf, 50 gf, and 100 gf, though the Knoop method supports a wide range from 1 gf up to 2 kgf, depending on the application.
The Knoop hardness test is defined in international standards such as ASTM E384, ISO 4545, and ASTM E92.
The Knoop test offers high measurement sensitivity and resolution, especially on small features. However, accuracy depends on proper surface preparation, lighting conditions, and operator technique.
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