Acoustic Emission Testing of Early Generation of Defects in CFRP Samples under Static and Thermal Loading

Abstract

Static tests of the samples of Torayca T700, T800 carbon fiber reinforced plastics consisting of nine monolayers with $$\left[ { \pm 45{\text{/}}90{\text{/}}{{0}_{3}}{\text{/}}90{\text{/}} \pm 45} \right]$$ stacking and geometric dimensions $$600 \times 100 \times 0.9$$ mm and $$500 \times 100 \times 1.4$$ mm were carried out. In the process of static and thermal loading, defects were monitored by the acoustic emission (AE) method. Two samples were statically loaded and simultaneously exposed to temperature $$T = 100$$ °C. Six samples were statically loaded at temperature $$T = 20$$ °C. The sources of AE signals corresponding to sample material destruction were localized in real time. For these signals, thin polished sections were prepared from location zones in the sample, and the fractography of the CFRP material was carried out. The analysis of the recorded AE information has been carried out. The main informative parameters of the AE signals localized in the working area of the samples are considered. Using cluster analysis by digital waveform, three types of clusters are identified for the AE signals. For the first type of clusters, the frequency of AE signals exceeded 175 kHz, and a relatively high level of the MARSE energy parameter was noted. In clusters of the second type, AE signals recorded under static loading and sample heating had lower MARSE values and a median frequency not exceeding 170 kHz. When testing samples with no heating, the median frequency did not exceed 140 kHz. The third type of clusters was formed by AE signals with the frequency not exceeding 400 kHz. Such clusters were typical only for samples tested at temperature $$T = 20$$ °C.