Study on Crack Initiation in Low-stress Cropping Process Based on Acoustic Emission

Abstract

In the current low-stress cropping technology, crack initiation at the tip of bar V-shaped notch is unstable, the crack initiation time cannot be obtained, and the initial loading force is difficult to determine accurately. Aiming at this problem, the acoustic emission technology is proposed and applied to the crack initiation in this paper. A low-stress cropping experiment system based on acoustic emission is established, and acoustic emission signals containing the crack initiation of the V-shaped notch tip are acquired based on the system. The acoustic emission signal of the crack initiation is described by the multi-feature parameter correlation analysis method, the signal is further processed by Kurtosis coefficient and the crack initiation time of 45 steel bar with V-shaped notch depth of 2.5mm is obtained quantitatively, about 24s. Based on the characteristics of acoustic emission signals in the low-stress cropping process, the concept of ratio T of Intensity to Absolute Energy is proposed, which is regarded as the criterion at the crack initiation stage for the low-stress cropping. The research finding shows that when the value of ratio of Intensity to Absolute Energy is between 1 and 10, this stage corresponds to the initiation stage of cracks. The low-stress cropping experimental results also further prove that the crack initiation can be judged by means of AE signal.