The Application Of Acoustic Emission In The Detection Of Mechanical Structure Defects

Surface contact fatigue is one of the most common failures of rolling element bearings, which seriously infect the operation of the entire device. Therefore, condition monitoring and fault diagnosis of rolling element bearings is important for engineers. Commonly used detection methods, such as vibration signal analysis, oil analysis, temperature diagnostic analysis and so on could not diagnose the early failure of rolling element bearing effectively.Crane is widely used as one of the eight special equipment. As the quantity is huge, the structure is complex, lead to the increasing of crane accident. Conventional NDT methods for cranes both time-consuming, and requires cranes to stop the operation, which is the most important that they could not detect the faint defect which would lead to major accident in the structure of the key position. Therefor there is an urgent need to find an effective method to detect the defects, further, to achieve source positioning of the defects source. While acoustic emission is extremely sensitive to active defects, which could achieve integrity and dynamic detection for crane.In this paper, health rolling element bearings and cane girder are studied by theoretical and experimental by acoustic emission technology. It focus on the effectiveness of the acoustic emission in detecting early faint defect of both rolling element bearing and crane girder. There four main parts of this article:1) Characteristic parameters and information entropy are used here to analysis the acoustic emission signal of the rolling element bearings. Acoustic emission signal and vibration signal are comparative analysis by kurtosis, RMS, peak and information entropy. The conclusion is that the acoustic emission signal’s tendency of both characteristic parameters and information entropy could better reflect the current fatigue defects in the rolling element bearings.2) The result indicated that fault characteristic frequency in acoustic emission is more obviously than that in vibration signal in compared with enveloped spectrum analysis of acoustic emission signal and spectrum analysis of vibration signal. It also demonstrates that acoustic emission has a higher noise ratio than vibration signal, and it is more effective in fault diagnosis and condition monitoring.3) Screen the characteristic acoustic emission signal of the fatigue cracks initiation and expansion by carefully comparing the acoustic emission signal of crane girder which was collected in the period of the experiment with the definition of burst acoustic emission signal and some relevant characteristic parameters, by which a proper threshold condition is settled.4) The experiment result indicates that acoustic emission could monitor the whole process that the initiation and propagation of fatigue cracks of the crane girder by the method of feature analysis of acoustic emission, such as kurtosis, RMS, peak, crest factor and energy. Source location of the acoustic emission is also attempted here, and the sourcing accuracy is not very good.