Crack nucleation (and growth) can be characterized under static load (or cyclic loads) in the presence of an environment. Chemically assisted cracking is occurs when stresses to nucleate (or propagate cracks) are much lower fracture of a material in an inert (like in vacuum) environment where a material is free from the damaging chemical environment. Similarly, embrittlement occurs if chemically active elements are dispersed internally as in internal hydrogen, metalloids and other embrittling elements. The materials where such embrittlement phenomena occurs are also divergent: pure metals, alloys, and ceramics or glasses. Since materials are used in applications involve various chemical environments under load, the importance of understanding the role of environment in material performance need not be stressed. In fact, there are many analyses in the past highlighting the divergent behaviors in each of the systems and environments emphasizing the specialties specific to a given material/environment system. In addition, many efforts have been made in the past to arrive at some unifying principles governing the embrittlement phenomena. An inescapable conclusion reached on this topic by many is that the behavior is very “complex”. Hence, recognizing the complexity of material/environment behavior, we focus our attention, mainly on metallic systems, in extracting some similarities to arrive at some generic principles involved. The ultimate goal of this effort is to arrive at some self-consistent scheme for incorporating “chemical effects” into a life prediction model for components in service
