Diagnostics of welded joints failure while welding

The author has analyzed and found out the regimes and factors that arouse defect nucleation, starting from the level of crystal lattice and up to the micro cracks at different steps of welding, from heating of welded edges to crystallization of weld seam metal of austenic steel. Due to the methods of mathematical modeling, the genetic linkage of open positions with defects of higher structural range was established, and regimes of their further extension up to the appearance of micro cracks were determined. The author found out additional sources of defects formation, specified the mechanism of welding seam destruction while welding, and recommended an acoustic emission method of its diagnostic. Now it is possible to state the relation of the linear size of cracking arising on welding the cylindrical homogeneous-metal. Mathematical simulation of metal crystallization on welding and microstructural analysis give an insight into the fact that there begins crack nucleation in a weld root. The greater the length of a crack is, the smaller the width of the weld and the temperature of a near-welding zone are. On the other hand the smaller the width of a crack is, the greater the welding zone and the temperature of a near-welding zone are. Crack length decreases when preheating temperature of the welded edges grows. Experimentally, by means of acoustic emission (AE), one can study welding and obtain the amplitude distribution of AE signals from cracking against the background of the hindrance accompanying this process. The multichannel amplitude analyzer was used to measure the energetic parameters of AE spectrum of cracking on welding. The analyzer was used to obtain the amplitude distributions of AE signals from different constituents of welding and defect-formation as the industrial noises, electromagnet hindrance, motion of welded head, ignition and burning of arc, melting and crystallization of the joint weld, cracking. It was determined that AE signals obtained on melting, crystallization and defect formation may be separated by the amplitude criterion. From the other hand, separation of AE signals obtained on crack nucleation is performed by AE pulses number, in the range of each channel of the analyzer. The conditions were found making impossible cracking.