Acoustic emission characteristics in eccentric rotary cropping process of stainless steel tube

The eccentric rotary cropping is a precise cropping technology based on low-cycle fatigue fracture of metal bars and tubes with stress concentration. This paper applied acoustic emission technology to monitor the crack initiation, propagation, and final fracture of stainless steel 304 tubes during the full cycle of cropping process. Experiments were carried out on a self-made eccentric rotary cropping machine which could apply periodic displacement load to the stainless steel tubes with variable loading frequency. As a technics parameter, the loading frequency has an important influence on the cropping efficiency and the fracture cross-section quality of tube. The traditional parameters, frequency spectrum, and time–frequency characteristics of acoustic emission waveforms were presented to study the relationship between acoustic emission activity and fracture process. It has been concluded that the acoustic emission parameters, particularly the kurtosis, have a good applicability to represent the crack status of fatigue fracture and provide guidance for the cropping process control.