Abstract
In this investigation, an analysis system that enables the nanoscopic in situ imaging the environmentally induced damage such as a stress corrosion crack under a dynamic loading condition has been developed. The system consists of an atomic force microscope (AFM), a dynamic loading system, an x-y-x positioning stage, an environmental chamber, and their controllers. To reduce disturbing vibrations, the system is equipped with an environmental chamber, and their controllers. To reduce disturbing vibrations, the system is equipped with an isolator. A dynamic load can be applied to a sample by using an electromagnetic actuator, with various loading wave forms including sinusoidal, triangular, and other programmable ones, and with a maximum load capacity of ±100N. The nanoscopic in situ AFM observation can be done in a controlled gaseous environment or in an aqueous solution. By using the developed system, in situ nanoscopic AFM observation of a fatigue crack in dry air and an environmentally-induced crack under a sustained load (static stress corrosion crack), under a sustained load with a high-frequency varying load (cyclic stress corrosion cracking), was successfully performed in a high-strength stainless steel : the nanoscopic crack tips can be clearly visualized. The crack tips of the environmentally induced or stress corrosion cracks are sharp compared with a fatigue crack in dry air, with a larger scatter band. This resulted from structure sensitive crack growth of a stress corrosion crack and what the growth is sensitive to the hydrogen content at the crack tip.
