Ultrasonic Contact Impedance Hardness Testing

Ultrasonic contact impedance hardness testing uses the dynamic coupling of a mechanical resonator and the surface being tested to measure the frequency shift that occurs upon application of test force. This is then converted into Rockwell, Brinell or Vickers hardness values.

This type of testing is ideally suited for applications such as incoming goods inspection, production control and maintenance on integrated components.

Non-destructive testing

The UCI method is non-destructive, meaning that it does not leave a mark or indentation on the surface of the test specimen. This is important for a number of reasons, including production efficiency. Detecting hardness defects during manufacturing can save thousands of dollars and avoid product or structural failure later.

UCI tests are also quick. A typical measurement takes less than 2 seconds. This speed opens up a wide range of applications, such as weld inspection and metal coating quality control in tight spaces. It can also be used on difficult-to-reach surfaces such as thin-walled parts, bearings and tooth flanks.

UCI uses a diamond indenter at the end of a vibrating rod to penetrate the test surface, similar to a Vickers microhardness tester, but instead of optical evaluation of the depth of the indent, the probe measures a frequency shift in the vibration of the indenter. This information can be converted into Leeb, Rockwell C, Brinell and Vickers hardness values.

Calibration

A lot of metal testing tasks cannot be solved easily or at all with conventional Leeb or other portable hardness testers. Qualitest offers portable UCI devices implementing the method of ultrasonic contact impedance in accordance with ASTM A1038. These devices allow you to make comparative hardness measurements with high accuracy, efficiency and portability. These devices are used for testing small forgings, cast materials, welds, heat-affected zones, ion-nitride stamping dies and molds, forms, presses, thin-walled parts as well as bearings and tooth flanks.

The probe of the portable UCI device consists of a vibration bar with a 136-degree diamond at the end. The vibration of the bar causes an oscillation in the frequency range which is measured with a microphone attached to the instrument. This allows you to determine the hardness of the material at the point of contact without damaging the surface of the test object. You can then convert the results into other hardness scales.

Convenience

UCI is ideal for use in weld and heat-affected zones, complex shape products, gear teeth, ion-nitrided stamping dies and molds, as well as thin-walled structures and parts. It creates a microscopic indentation, which is barely discernible to the naked eye, and it can be easily compared with results from other hardness testing methods.

This nondestructive method also gives a more accurate picture of the material’s overall hardness than traditional rockwell, Brinell and Vickers tests. Unlike these other procedures, which produce a physical indentation, the UCI method produces a digital change in vibrational frequency that can be converted to an equivalent hardness value on another scale.

The new generation of NOVOTEST Lab UCI wireless hardness testers provides users with the best possible combination of convenience and high accuracy. It features a built-in camera that allows for a picture to be taken of the tested object and marked with a hardness value, making it easy to store the data. It is also waterproof and frost-resistant to allow for use in any climatic zone on the planet, and a large LCD display for direct reading of measurement results.

Safety

Using the UCI method a diamond indenter attached to a resonating rod is moved over the surface of the material. When the resonating rod penetrates into the material, a frequency shift is measured and can be related to the depth of penetration. The UCI hardness tester NOVOTEST T-U3 detects this indentation digitally and evaluates it. The result is displayed as a microhardness value on the screen.

The measurement is completely non-destructive. The frequency change df is converted to the hardness HV value in a calibration process by means of known values for the modulus of elasticity E (or hardness) and a conversion formula.

This is especially advantageous when it comes to testing parts that cannot be easily dismantled, such as gear teeth or special-shape metal fasteners. It is also ideal for testing surfaces that are difficult to access or require a very small test force, such as the thin walls of metal sheets. The UCI method can even be used to measure the surface hardness of surface-hardened layers.