An Experimental Approach for Delayed Stress Corrosion

Abstract

Failures of structural and mechanical components have long been attributed to environmentally assisted cracking (EAC). The umbrella of EAC encompasses several phenomena, including stress corrosion cracking (SCC), corrosion fatigue (CF), hydrogen embrittlement (HE) and liquid metal embrittlement (LME). The latter, LME, has resulted in the failure of components in petrochemical and aeronautical industries, among others. The effects are detrimental, with crack tip velocities on the order of centimeters per second and failures occurring rapidly. Previous research has provided numerous underlying microstructural failure mechanisms aimed at identifying the true failure mode. Conflicting experimental data has extended the debate over the true mechanism promoting renewed interest in novel experimental regimes. Utilizing fracture mechanics specimens, the solid-liquid Al-Hg couple was analyzed to extend or reject current theories. Through the implementation of an original environmental chamber capable of testing notched and pre-cracked components in corrosive environments, C(T) specimens were subjected to experiments submersed in liquid mercury. Upon the application of an initially applied stress intensity factor (under load-control), incubation periods preceding failure were observed. Crack initiation and propagation were observed to occur along the starter notch, as well as other regions on the specimen. Results provided evidence that additional factors, such as a critical load or critical microstructural orientation, were factors in crack initiation and propagation. In the quest to observe the influence of these additional factors, a variation of the experimental setup was implemented and initial tests have begun.