Delayed Fracture Of An Aluminum Alloy Subjected To Hg Lme

Structural components in a variety of industries are routinely subjected to static and cyclic loadings over an extended period of time; all while exposed to aggressive reactants in the environment. Of critical importance is the interaction between a material discontinuity and its environment. Environmentally assisted cracking (EAC) has been observed in chemical processing, piping and power generation industries to result in the rupture and failure of components. Notably, stress corrosion cracking (SCC) and liquid metal embrittlement (LME) have been extensively researched over the last century; however, there exists uncertainty in the microstructural failure mechanisms. Discrepancies are rooted in theories accounting for some liquid-solid couples but not others subjected to identical conditions. Recently, fracture mechanics experiments have revealed a life-dependency on the level of an initial static stress intensity of a cracked member. Unstable crack growth is observed above a threshold stress intensity value, KILME, or critical stress, σLME, below which rupture does not occur as quickly or at all. Experimental findings suggest that rupture can still occur at a lower stress intensity, provided a favorable microstructural orientation and/or critical stress is achieved that promotes crack initiation. Crack initiation processes are, therefore, the critical limiting factor in assessing the life of a component subjected to corrosive environments. An experimental study implemented Al7075-T651 notched tensile specimens in the study on delayed fracture of specimens subjected to liquid mercury at room temperature. Through varying loads and loading patterns, the stress and strain at the notch root can be evaluated and correlated with time to crack initiation. Life predictions can then be made based on the level of stress experienced in a structural component, even before the existence of a crack is detected. Copyright © 2011 by ASME