| This dissertation describes the application of thermodynamic concepts to crack propagation problems. The scope of the investigation is the application of thermodynamic concepts to three of the traditional subject areas in the field of fracture mechanics: fatigue crack propagation, slow-stable crack propagation and fracture plane orientation under mixed load loading. While each of these subject areas has received a great deal of study in recent years, there have apparently been no attempts to consider all three together in a general thermodynamic context. In the present work a unified theory of crack propagation thermodynamics is used to illustrate the relationship between these three traditionally separate areas of fracture mechanics.A single general thermodynamic energy balance is used to describe each crack propagation phenomenon considered. The general energy balance is first used to derive a fatigue crack propagation rate equation which is quite similar to equations proposed by several other authors in recent years. Application of the energy balance to slow-stable crack propagation yields several new results, including an R-curve expression derived directly from the general energy balance. The general thermodynamic energy balance also yields a new crack plane orientation criterion, dubbed the "Maximal Dissipation Rate Criterion." This criterion is applied to the problem of determining fracture plane orientation in nickel base superalloy single crystal fatigue crack propagation specimens. |
