A Fast Cleavage Fracture in the Polythionic SCC of Type 304 Stainless Foil Revealed by the Lamb Wave Analyses and Direct Observation

Abstract

With the aim of visualizing the fast cleavage fracture suggested by the AE source simulation of bulk waves, both the microscopic video image and Lamb wave monitoring were attempted for a loaded type 304 foil in a polythionic acid solution. A laser ultrasonic system revealed that the Mode-I fracture in the foil emitted the Lamb wave with the largest amplitude in the direction of crack opening vector. PZT transducers used for SCC test of the thin foil SUS 304 monitored only the zero-th order anti-symmetric Lamb mode (Ao-Lamb) whose amplitude and velocity are dispersive depending on the fracture kinetics. Polythionic intergranular SCC of a sensitized Type 304 foil emitted a number of high frequency Ao-Lamb waves. Direct observation by a CCD video demonstrates the fast crack opening at the source location of the Lamb waves, The developed system, applicable to a thin foil, possesses a potential capability for visualizing the microscopic fracture mechanism of SCC, when both the time and frequency resolution of the system are improved.