The UCI method (Ultrasonic Contact Impedance), or modified Vickers method, was invented by Claus Kleesattel and has been in use in the metal-processing industry for more than 50 years. In the past, the preferred areas of application were generally heavy and/or unmovable parts where traditional, standardised testing methods could not be used, or only with great difficulty. However, the reliability, speed of application, excellent selectivity and simple operation of modern UCI hardness testing devices has ensured that they are being used for a great deal more than traditional hardness testing

The hardness testing devices consist of a measurement probe (manual measurement probe or motorised measurement probe), plus a testing device to assess, save and compare measured values. Tests can be carried out in all directions, in tight spaces and in the case of difficult to reach areas or challenging material geometries.

The measurement process

The manual measurement probe is positioned by hand during mobile hardness testing and is then pushed down onto the material. After 1 second (typically), the measured hardness values will be displayed digitally and saved. The automatic saving of the measurement series means that the operator can concentrate on the exact positioning of the probe and evaluate the results later at their leisure. The measuring of hardness at the individual measurement points takes place immediately once the test force has been reached, which will be indicated visually and acoustically by the device.

Using motorised measurement probes allows the operator to achieve even more precise results while applying lower test forces. Using this method, the probe is positioned and held in the hand. However, the test force is applied by the integrated motor
It is also possible to integrate automatic measurements into a production line for the purposes of quality assurance. This generally involves use of a manual measurement probe with special holder

On-site assessment using the SonoDur series

The measurement results can be analysed on location directly in the device. The measurement device also offers the option of colour-based differentiation and calculation of tolerance deviations (thresholds) and additionally features a whole range of statistical functions, including single-error correction.

It is also possible to reassess the data in accordance with EN ISO 18265, DIN 50150 and/or ASTM E140 for use with prevalent hardness scales such as Vickers, Brinell, Rockwell and Shore.

Measurements can also be automated for the production line

The SonoDur-R also enables the automation of measurements on a production line. A fully isolated, digital I/O interface makes it possible to directly control actuators. A measured value counter with statistical functions and a USB interface for transmitting measured values are also available.

The extensive customisation options, particularly the quality assurance functions for during production, make these devices the ideal way to complement traditional hardness testing procedures.

Advantages of testing hardness using the UCI method

  • Location-independent mobile measurements, also capable of functioning in all directions within tight spaces
  • Capable of taking measurements on large objects, in difficult test positions and challenging component geometries, such as at the base of gear teeth and similar.
  • Fast, reliable measurements (1 second is typical)
  • Hardness measuring can be easily automated
  • Small indentation size/depth - the process can be considered nondestructive
  • Highly reproducible results and lower sensitivity even in the case of unsymmetrical test indentations since the entire contact surface is included in hardness calculations
  • Easy to align and adjust in line with the intended testing application

A detailed look at the UCI hardness testing procedure

The UCI method (Ultrasonic Contact Impedance or modified Vickers procedure) – first put to use in 1965 under the name “SonoDur” - electronically evaluates each Vickers hardness test indentation in a fraction of a second and displays the results digitally.

As with traditional Vickers hardness testing, the material surface is exposed to the tip of an indenter with a defined geometry (= Vickers diamond) with a predetermined force.
However, unlike the traditional procedure, dynamic coupling impedance measurements are used to measure the hardness value under load. For this purpose, a mechanical resonator (vibrating rod) equipped with an indenter at its tip is excited to longitudinal vibrations of about 78kHz and forced into the test material. Through this coupling of materials, contact resistance arises beneath the Vickers diamond, thereby causing a dampening of vibration amplitude and a simultaneous increase in vibrational frequency in the characteristic manner. This frequency shift is exactly determined once a predetermined test force has been achieved and the Vickers hardness is derived immediately therefrom.

The resonating frequency of the vibrating rod increases as the test force (or contact surface) has more of an impact. If the test force is constant, the deviation of the vibration frequency (= differential frequency Δf) from stand-by frequency f0 in the air is therefore an indirect measure of a material’s hardness. However, differential frequency is also dependent on the elastic property (e-module, Poisson's ratio) of the resonator, indenter and test materials. Since these parameters are generally not known, the system must be calibrated for probes of a known hardness (= normal, reference plates). It will then be easy to calculate the hardness from the differential frequency, test force and calibration data.

Substrate properties

The surface must be prepared (sanded down) in accordance with the requirements of Standard DIN 50159/MC1 Guidelines of the DGZfP. UCI measurements can also be taken on challenging surfaces, such as dark backgrounds, which are outside the range of traditional Vickers testing methods.

Which applications are suitable for UCI hardness testing?

  • Incoming goods inspection, mix-up checks, production controls, maintenance of built-in components.
  • Complements the traditional types of hardness testing in the lab
  • Hardened surfaces, complex geometry, coatings
  • Thermal cutting edges and weld seams
  • For any situation where traditional hardness measuring techniques are not possible or useful (challenging surface properties) or where they would be too slow

Adopting mobile hardness testing using the UCI process

The wide array of application possibilities for the UCI method means that the user must prepare for performing tests accordingly. When doing so, it is of the utmost importance to check the functionality of the test equipment as well as ensure that the component properties and surface quality of the test material are suitable for the UCI method - a task which is often neglected when using other surface hardness test procedures. This can mean that expectations for the test results are not met and/or it is not possible to compare the results with those of other testing procedures.

Furthermore, performing a UCI hardness test, despite being fairly easy for the operator, requires a basic level of skills if the measurement probe is to be used manually. Due to this, it is always recommended to initially test the suitability of mobile hardness testing procedures in your operations to ensure your personnel receives the required training for proper hardness measuring. This is important because the operator is a fundamental part of the measuring apparatus and thus requires understanding of how to use a precision measuring tool.

Before purchase, new testing devices should generally be tested on a component to ensure it is the right application for the tool. NewSonic would be pleased to provide you with rental measuring devices and will also provide free advice on how to best resolve your measurement issue.

Advice on hardness testing and our UCI hardness testing devices

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Mobile UCI hardness testing device

Main application areas are inspection tasks on serial parts after heat treatment, after surface processing, weld inspection or for coat hardness measuring on gravure cylinders with highly selective low load motorized probes.

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SonoDur-R (Rack)

SonoDur-R (Rack)

19” desktop device for automated UCI hardness testing

SonoDur-R is a 19” desktop device for fully automated, 100% checks of mass-produced parts. The measurement system enables rapid process monitoring (at one-second intervals) of mix-up testing procedures.

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Manual measurement probes

Manual measurement probes

For reliable, hand-held hardness testing

Our manual measurement probes are available with test forces 10N, 50N and 100N. They are ideal for general, hand-held testing procedures in the fields of production and maintenance.

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Motorised measurement probes

Motorised measurement probes

Consistent application of force via an integrated motor

Our motorised measurement probes are available with test forces of 1N, 3N and 8.6N They are ideal for testing the hardness of delicate surfaces and enable an equal distribution of force at all times.

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