Impactor velocity measurement system for dynamic hardness testers and calibration machines on Leeb scales

• Published in: Measurement : journal of the International Measurement Confederation 2021-03, Vol.173, p.108632, Article 108632
• Main Authors: Gogolinskii, K., Syasko, V., Umanskii, A., Kazieva, T., Gubskiy, K., Kuznetsov, A., Gluhov, R.
• Format: Article
• Language: English
• Subjects: Acceleration; Calibration; Dynamic hardness; Fiber optics; Hardness; Hardness calibration machine; Hardness testing; Heterodyning; Interferometry; Laser interferometer; Leeb scales; Measurement; Optical communication; Optical heterodyning; Permissible error; Velocimetry; Velocity; Velocity measurement
• ISSN: 0263-2241; 1873-412X
• DOI: 10.1016/j.measurement.2020.108632

•Velocity measuring system for Leeb hardness testers based on laser interferometer.•Achieved measurement uncertainty 0.2·10-3 m/s at time resolution of 190 µs.•Impact body velocity of 2.05 m/s meets the requirements of international standards. The article aims to solve the problem of measuring the impactor velocity for dynamic hardness testers according to the Leeb, as one of the key parameters to ensure the accuracy and reliability of hardness measurements by this method. The gravitational method of impactor acceleration, used in calibration machines, and spring acceleration, typical for hardness testers, have been studied. Various technical solutions for velocity calibration are analyzed. Accurate, easy to implement, compact and inexpensive device based on fiber optic and allows monitoring the dynamics of the object without the use of additional reflective elements is developed. This system suitable for calibration or verification of dynamic hardness testers and calibration machines. The system is based on a laser interferometer in which the direct optical heterodyning of Doppler signals (Photonic Doppler Velocimetry) is applied. The maximum permissible error of the system is determined by the requirements for the metrological characteristics of the Leeb hardness calibration machine and is 0.0025 m/s at a speed of ~2 m/s. The possibility to measure the impact body velocity with an error of 0.2·10-3 m/s is confirmed.