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Abstract
An FFT-based signal processing method for the micro-scratch test, proposed by Baba was compared with a conventional micro-scratching method to quantitatively evaluate the suitability of the technique. Original scratch signals from a micro-scratch system were first digitized by a 16-bit analog-to-digital converter with a sampling frequency of 44.1 kHz, which were fed into a personal computer. Then, the FFT-based method and the conventional method were used to process the signals according to their individual algorithms. The output results from the two methods were compared, showing that the FFT-based method effectively reduces unnecessary signals arising from the micro-scratching mechanism, and that the output level of the unnecessary signals for the FFT-based method is about 50% lower than that observed in the conventional method. The FFT-based method was implemented into a micro-scratch tester for actual application and critical loads of various thin films were measured using various measurement parameters. The results showed that the critical load increases with increasing stylus radius, or increasing thickness of the film, whereas it decreases with increasing frequency of forced vibration. It is also shown that the amplitude of the forced vibration has only little effect on the critical load.