Detection of Acoustic Emission (AE) from Zinc Emibrittlement Cracking During Welding Using Optical Fiber AE Monitoring System

We have developed an optical fiber acoustic emission (AE) monitoring system equipped with phase and polarization control systems. The phase control system has an integration-type feedback loop with a phase lead process that maintains the phase difference between the sensing and the reference beam at π/2 and compensates for environment noise in the frequency range of less than one hundred hertz. Additionally, we controlled the polarization of the sensing beam corresponding with the reference beam to keep the system highly sensitive. We applied the developed system to the detection of zinc embrittlement cracking in an AISI type 304 plate during a simulated welding process (melt-run) at elevated temperatures. We succeeded in detecting a significant amount of AE from the cracking during welding process.