Surface damage characteristics and identification based on acoustic emission in diamond point grinding carbon/carbon ceramic matrix composites

This study mainly investigated the effect of machining parameters on acoustic emission (AE) characteristics in grinding three-dimensional carbon/carbon ceramic matrix composites with superabrasive diamond grinding points. Signal processing techniques including fast Fourier transform (FFT) and short-time Fourier transform (SWFT) were applied to evaluate frequency features of AE signals. The RMS values were used as an indicator to detect grinding energy releasing characteristics. Results indicated that grinding speed and grinding depth were the main influencing factors on RMS values, while feed speed presented limited effects. The maximum undeformed chip thickness hmax and active grits number were two key factors affecting RMS variation of the AE signals, which corresponded to the intensity of single AE source and the number of total AE ones, respectively. The material removal mechanisms were studied via detailed SEM micrographs of machined surfaces, revealing that fiber fracture and debonding were the main material removal modes in point grinding carbon/carbon composites. The material removal mode can be possibly identified from the frequency of AE signal, as the band of 12-35 kHz mainly corresponded to fiber fracture, 35-70 kHz referred to debonding between the fiber and matrix, 70-90 kHz indicated the frictions, and the fourth band (90-120 kHz) was related to the matrix cracks.