Health monitoring of Ceramic Matrix Composites from waveform-based analysis of Acoustic Emission

Abstract

Abstract. Ceramic Matrix Composites (CMCs) are anticipated for use in the hot section of aircraft engines. Their implementation requires the understanding of the various damage modes that are involved and their relation to life expectancy. Acoustic Emission (AE) has been shown to be an efficient technique for monitoring damage evolution in CMCs. However, only a waveform-based analysis of AE can offer the possibility to validate and precisely examine the recorded AE data with a view to damage localization and identification. The present work fully integrates wave initiation, propagation and acquisition in the analysis of Acoustic Emission waveforms recorded at various sensors, therefore providing more reliable information to assess the relation between Acoustic Emission and damage modes. The procedure allows selecting AE events originating from damage, accurate determination of their location as well as the characterization of effects of propagation on the recorded waveforms. This approach was developed using AE data recorded during tensile tests on carbon/carbon composites. It was then applied to meltinfiltrated SiC/SiC composites.

Damage Determination in Ceramic Composites Subject to Tensile Fatigue Using Acoustic Emission

“…The average energy per event was derived from the average energy on the outer sensors (#1 and #2). The outer sensors are used for energy because the attenuation of high frequency waveforms in these composites has been found to be very high for high frequency events and minimal for low frequency events [26]. In reality, there is little difference between taking the average energy from all three sensors or just the outer two for cumulative AE energy since the cumulative AE energy relationship is dominated by high energy low frequency events.…”

“…Figure 8 shows the waveform and Fast Fourier Transform (FFT) for the same events as Figure 6 except for the middle sensor 3. It has been shown that higher frequencies do not transmit over longer distances effectively in these types of composites [26], so the sensor closest to the source (middle) was used for frequency analysis. The waveform/FFT of the two events for the frequency centroid (FC) is also shown in Figure 9.…”

Volumetric assessment of fatigue damage in a SiCf/SiC ceramic matrix composite via in situ X-ray computed tomography

“…It is relatively straightforward to obtain a range of quantifiable measurements from AE analysis, but currently it is not understood to the degree that the presence and severity of individual or collective damage modes can be accurately identified from this technique alone. While there is significant research in the area of AE damage characterisation in composite materials [6,[8][9][10][11], it is necessary to validate these results via visual interpretation of the corresponding XCT, SEM or destructive fractography imaging. This paper investigates a method of visualising and quantifying 3-D damage accumulation during progressive fatigue cycles, using digital volume files obtained via in situ XCT.…”