PSI - Issue 54

Claudia Barile et al. / Procedia Structural Integrity 54 (2024) 225–232 C. Barile et al. / Structural Integrity Procedia 00 (2023) 000–000

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NDE tool, however, it is not as e ffi cient as the signal-based analysis. The signal-based analysis is time-consuming and cost-intensive in monitoring large structures. Researchers tried to bridge the gap between these two types of analysis by introducing some new parameters such as entropy, complexity etc [Burud and Kishen (2021), Barile et al. (2023)]. Time of Arrival (ToA) is one of the most e ffi cient and robust parameters in the analysis of stress waves / acoustic waves. Several researchers, over the years, have introduced di ff erent techniques for estimating the ToA of the AE signals. While most of them function e ffi ciently, they all share a common limitation: their e ffi ciency depends on the Signal-to-Noise ratio (SNR) of the acquired signal. None of the available techniques are applicable for signals with lowSNR. In this research work, a novel approach, which is based on the popular Akaike Information Criterion (AIC) is introduced to estimate the ToA of the AE signals. Its e ffi ciency is tested by characterizing the damage evolution stages of syntactic foam test specimens under tensile loading. The ToA of the AE signals generated from the static tensile test are estimated and used for analysis.

2. Methods

2.1. Estimation of Time of Arrival

The novel procedure proposed to estimate the ToA of the AE signal is schematically presented in Figure 1. First, the signal must be converted to its characteristic form in order to overcome the limitations regarding the SNR of the signals. Several researchers have proposed di ff erent methods such as the envelope of the signal, absolute level or RMS of the signal as their characteristic form [Siracusano et al. (2016), Sedlak et al. (2008)]. In this work, a characteristic function based on Allen’s function is proposed. Consider an AE signal X of length N as shown in Equation (1).

Fig. 1. Schematic Representation of the Procedure for Estimating ToA

X = x 1 , x 2 , x 3 , ..., x N

(1)

The characteristic function of signal X is calculated using Equation (2). X ( n ) = | x ( n ) | + R | x ( n ) − x ( n − 1) | , R = 4 (2) x ( n ) is the signal datapoint at n and R = 4 is calculated based on trail-and-error method. Figure 2 shows the original signal and its characteristic form compared to the envelope and absolute level of the signal.