In-situ Monitoring of Active Crack in Steel Structure Using Acoustic Emission Technique

The paper introduces a non-destructive testing (NDT) method-Acoustic Emission (AE) technique to detect active crack in steel structure of large lifting machinery used in hydropower stations. A test apparatus has been established, in which a beam with seeded cracks was loaded using a press machine. AE signals were collected during the test. Due to the complexity of the AE signals, Empirical Mode Decomposition (EMD) has been exploited to decompose them. The results have demonstrated that the frequency feature band is low in the crack initiation. With the crack growth, the frequency feature band becomes higher. The total frequency range of the crack propagation is 25 KHz-160 KHz. The research work has laid a theoretical foundation to application of the AE technology for safety evaluation of steel structures in lifting machinery. It also demonstrates that AE technique is an effective method for in-situ monitoring of the steel structures.