Papers by Keyword: Pencil Lead Breaks PLBs

Abstract: Some initial studies for an AE characterisation of damage in composites are presented in this paper. A PAC AE PCI-2 based system and four PAC WD AE broadband sensors are used. Pencil lead breaks (PLB) were used to introduce a source of elastic waves. An initial validation of the system based on PLB on an aluminium plate showed that there was a large difference in sensitivity of the four nominally identical sensors. It is shown that the AE parameters are so strongly related to the sensitivity of the sensors that they tend to describe the AE system more than the actual sources. To characterise damage in composite materials alternative AE parameters are required that are not dependent on the sensitivity of the sensors. In the paper, it is shown that the frequency spectra of the sources have relatively little variability with respect to the sensor. A frequency-based approach that examines the spectrum of each source is proposed in the paper. The procedure is demonstrated using PLBs on a CFRP plate and it is demonstrated that the approach can indicate the position of the source in relation to orientation of the fibres and the plate edge.

Abstract: Acoustic emission (AE) practitioners routinely use surface pencil lead breaks (monopoles) to observe expected AE signal characteristics. In contrast, stress-generated AE sources are almost universally composed of dipoles. Thus, understanding the primary differences between the signals generated by these two different source classes is of key importance. This research had the goal of analyzing and contrasting the AE signals generated by monopole and dipole sources. A finite-element-modeled database of AE signals provided an ideal means to study these two source types. The AE signals represented the top-surface out-of-plane displacement versus time from point sources inside an aluminum plate 4.7 mm thick. In addition, monopole sources both on the plate top surface and the edge surface were included in the database. The AE signals were obtained from both in-plane and out-of-plane monopole and dipole sources. Results were analyzed with both a 100 to 300 kHz bandpass filter and a 40 kHz high-pass filter. The wide-plate specimen domain effectively eliminated edge reflections from interfering with the direct signal arrivals.