Ultrasonic Contact Impedance

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The Ultrasonic Contact Impedance Method ( UCI method for short ) is a hardness testing method . Since the technology can be built compactly, hardness testers with this technology are suitable for mobile hardness testing. The procedure is standardized according to DIN 50159 and ASTM A1038.


A rod is excited to vibrate lengthways at a frequency (approx. 70 kHz). There is a Vickers diamond at one end . This is pressed into the material to be tested . A defined load is applied via a spring. If the Vickers diamond penetrates into the sample, it comes to damping of this oscillation . This is associated with a change in the resonance frequency. This can easily be measured.

The damping of the rod and thus the frequency change to be measured depends on the size of the contact area between diamond and sample and thus on the hardness of the sample with a constant test load.

Furthermore, the frequency change is influenced by the modulus of elasticity of the tested material. The hardness of the material is calculated from the known test load, the measured frequency change and the stored calibration values ​​for taking the modulus of elasticity into account.


The advantages of the UCI process are the ease with which it can be automated and the good reproducibility of the hardness values, since the entire contact area is included in the measurement. Devices with this method are also very suitable for mobile hardness testing, as they can be built small and light and calibration (e.g. on the base material of the sample) is quick. The measurement of the frequency changes is free from the subjective judgment of the individual user.


Individual evidence

  1. ^ Standard Test Method for Portable Hardness Testing Hardness by the Ultrasonic Contact Impedance Method. ASTM International, accessed July 30, 2015 .
  2. Hardness test - The UCI method. BAQ GmbH, 2014, accessed on July 30, 2015 (German).
  3. Hardness Testing FAQ. GE Measurement & Control, 2015, accessed July 30, 2015 .
  4. The UCI hardness test method - NewSonic. Retrieved October 17, 2017 .