| Acoustic emission testing (AET) is a dynamic passive nondestructive evaluation (NDE) technique. We can estimate the nature and mechanism of the damage, using a special method according to the characteristics of the complicated AE signals come from the damage. And then the structure health monitoring technique using acoustic emission technique could be realized.AE sensor is an important device for acquiring damage information, and the analysis processing of the AE signal is the key of damage identification in AET. In this paper, based on the introduction of the characteriscics of AE signals, the sensing characteristics of the 1-1 orthotropic piezoelectric composite materials AE sensors were studied, and the response rule of the sensor to signals was found. Based on the rule, the damage position (simulated by the lead break) coule be located exactly using distributed orthotropic AE sensors through a unique method.For the existences of many spurious signals and the difficulties of AE signals' feature extraction, Hilbert-Huang transform (HHT) appears resently years was introduced to analysis AE signals. In this article, we illustrated the basic theory, characterics and the improve methods of HHT systermly, and used Matlab sofrware realize the computational process of HHT.The analysis results of several real AE signals show that: HHT is a powerful nonlinearity and non-stationary signal processing method; The Intrinsic Mode Functions are very helpful to study the mechanism of signals' production; Compared to the Gabor spectrum, Hilbert spectrum could reflect the transient property more clearly. By HHT analysis, the critical states of prestressed concrete beams are found. There are many marked characterics during the failure process of the prestressed concrete specimens. Thus, we can find the important portent that the cracks are unstable.These conclusions result from the experiments carried out in the laboratory, and they might need some deeper reasoning and improvement, if it is applied to the engineering practice. |
