Study Of Aet Ndt Of Crane Ream

The aim of this subject is to discover the feasibility of crane beam' AET NDT and the characteristic of AE signal, which has never been reported in literature until today. The technique way adopted in this subject is shown as following block diagram.First, conventional NDT (UT & MT) is carried out determining whether there are existing crack in the beam. If there are no existing cracks, a crack is made artificially in suitable location as the point to be tested; secondly, the crane beam is loaded by hydro-pluses tired-test machine, during the cycle of loading AE signal is monitored. At last, I analyze the AE signal obtained and assess the critical degree of the crack.Main equipments used in the test are: CTS-23 ultrasonic tester, CDX-III magnetic powder detester, Spartan AT-24 channel AE monitor (US), hydro-pluses tired-test machine, YT-18 static resistance strain measurers.Main parameters of the crane beam are: max load 7.1t,material 16Mn, Span10000mm,width 255mm, and height 500mm.For example, take 7.1x1.1=7.8t.as the max test load. Two loading cycle has been carried out. In the first loading cycle at velocity 2.5t/min by 5 steps (5t, 6.25t, 7.0t, 7.5t, 7.8t), load is persisted constantly at leak step 5 min or 10min (at step 7.8t), then unloading to 0t,In the second cycle, loading progress at velocity 2.5t/min by 4 steps (5t, 6.25t, 7.0t, 7.5t), the others are same the as the first cycle. AE signals are picked simultaneously with loading.There are two transducer arrays being arranged around the crack, i.e. linear array (No:7,5,1,2,6& 8 transducer) and triangle arraySound created by breaking off an HB0.5mm pencil core (Japan) is used to calibrate the transducer array.Decay measurement reveal that signal decay varies as the distance from transducer to sound source change. When the distance is less than 1m signal energy decay sharply, when the distance is l-3m it keep constant nearly, when the distance is 3-5m, it does not decay but amplifies. This fact indicates that the propagation mechanism of AE signal in the crane bean is very complex.Conventional NDT indicate that there are no existing cracks in the crane beam, under this condition when loading the beam to max test load, no AE signal can be detected. After the artificial crack is made, numerous AE signal emitted during loading process.Location calculation revealed that all AE sources locate at the crack top, it proves that AET is feasible for NDT of crane beam. It cans accurately locate the crack in the beam. According to assessment criteria recommended by relative authority, all AE sources discovered are high intense active source.As the loading increases count of hit and AE energy increases markedly. This proves that safety assessment of crane beam by AET is fully creditable. It can accurately evaluate the critical degree of crack and the safety reliability of the crane beam.Main parameters of AE signal detected are:Amplitude >70dB, energy count 65535-27, hit count ( ring down count ) 0-65355, rise time 0-671 us, duration 43704-919656 u s.These parameters vary in large range. Except hit count, other parameters, such as amplitude energy count; frequency response, etc. are depending obviously on the characteristic of the monitor apparatus and location of the transducer. In author's opinion, the critical evaluation criteria of AE source should base on hit counts.The principle of nervous network mode discrimination of AE signal is introduced in this paper briefly. Inputting AE signal to BP nervous network carries out mode discrimination. Complex data form, low signal -noise ratio, bad data repetitiveness, uncertain environment are the inherent characteristic of AE signal, so it is difficult to obtain numerous topic training data. Therefore, after training with a signal set topic data, carrying out mode discrimination by testing relative error may be a better method.This subject applies AET to safety assessment of crane beam first, so extend the application area of AET.