A review of past applications has shown the direct-current electric potential (d-c EP) technique has been applied successfully to fatigue, high-temperature creep, stress-corrosion cracking, dynamic crack growth, stable ductile crack growth under monotonic loading, etc. The work presented herein shows that the d-c EP versus crack-mouth opening displacement record can be used to determine crack initiation under monotonic or sustained loading. This data recording technique differentiates plasticity effects on the electric potential from crack growth, hence, also allowing for a single specimen J_1c method.

For studying the fracture behavior in piping or pressure vessels under monotonic or sustained loading, the d-c EP crack-mouth opening technique for defining crack initiation has been found successful. Several examples for through-wall and surface circumferential cracks are illustrated, as well as axial surface cracks. For surface cracks with aspect ratios less than 0.15 it was found also that the d-c EP signal could be used to monitor the entire shape of the surface flaw.