Experimental Research On The Acoustic Emission Characteristics Of 15CrMoR Welding Cold Cracking

Welding cold cracking is one of the common welding defects in welding process. It is so difficult to detect and prevent it because of the delay characteristic. Security hidden danger appears during the use of welding structures and equipment, as well. Welding cold cracking is related to the metallurgy and mechanical factors of welding process, so there is a direct relationship between the cold crack shape and condition. Therefore, it is of great significance to ensure the welding quality and safety of engineering structure analyzing the influence factors and micromorphology to understand the mechanism of cold crack formation and propagation and then formulating the cold crack monitoring and prediction methods.In the paper, acoustic emission(AE) testing technique was used to monitor the natural cooling process after welding for the inclined y-shaped groove butt welding specimens in order to study the formation mechanism of welding cold cracking. AE entire characteristic is obtained based on the comprehensive analysis of the fracture images and AE evolution rules of different specimens in which there was cold cracking appearing or not. The characteristic is determined that the energy and activity in the microcrack gathering phase are highest during the process of cold cracking formation. The attenuation laws of energy and amplitude of AE signals are discovered in the welding process. The mechanism of crack initiation and propagation is revealed according to these laws. Meanwhile, the law is gained by the comparison of the specimen of the different thickness and restraint welding lengths that cold cracking sensitivity, signal intensity and activity raises with the thickness and restraint welding lengths increasing. AE source location method was used to identify the crack initiation signal. The result shows that cold cracking is generated at the end of the weld seam and then grows to the beginning along the seam. Numerical simulation was applied to analyze the residual stress with ANSYS and the simulation result verifies the AE laws then. Finally, the waveform and spectrum characteristics of the typical AE signal was acquired with continuous wavelet transform and higher order spectrum. The initiation signal can be distinguished from other signals detected in the whole crack formation process.