Research On Acoustic Emission Characteristics Of Crane Girder Fatigue Crack

The girder is the major part of the bridge crane. The girder has huge volume, works in bad environment and endures long-term high load, so the girder usually cracks. The research shows that 80% of the crane serious accidents are caused by the girders’ fatigue fracture, so the nondestructive testing of girders is an important method to ensure the safe operation of the crane. Acoustic emission is passive detection and sensitive to active defects, so it is a useful method for the crack detection of the crane’s girder. The acoustic emission technology is proposed recently and still in the research stage. This paper researches the characteristics of the crane girder’s acoustic emission signal through the bridge crane girder fatigue test and Q235 specimens fatigue tensile test.The paper is supported by the National Science-technology Support Plan Projects "light weight design technology and application of general bridge crane". This paper’s main work and achievements are as follows:1. During the acoustic emission signal monitoring of crane girder, we also collect the environmental noise, electrostatic noise, grid noise, friction noise and impact noise. This paper analyzes these five typical noises’ waveform characteristics and the main range of acoustic emission characteristics parameters.2. We collect the entire acoustic emission signal during the whole crane girder’s fatigue test. The data we collected can verify that the acoustic emission technique can effectively detect the initiation and propagation of the girder’s fatigue crack. The influence of the acoustic emission modal and the dispersion phenomenon of Lamb wave to the velocity of acoustic emission is analyzed in this paper, and the attenuation coefficient and velocity distribution of acoustic emission wave of the girder were determined through the test.3. We found that the acoustic emission parameters including event counts, amplitude, ring count and energy are changed and phased. This paper proposes that the propagation of the crane girder’s crack can be divided into three phases by the activity of the acoustic emission. The three phases are the energy release phase of inherent defects and residual stress, the ecological competition phase of active defects and the initiation and the propagation phases of girder fatigue crack. The main types and characteristic parameters ranges of acoustic emission signal in all phases are also analyzed in this paper.4. In Q235 material specimens fatigue tensile test, we found that the characteristic parameters of acoustic emission signal are similar with the crane girder fatigue test. We analysis the acoustic emission waveforms and characteristic parameters in the two fatigue test, and verify the development law of the Crane girder fatigue crack.