In situ AFM imaging system for the environmentally induced damage under dynamic loads in a controlled environment

Abstract

The atomic force microscope (AFM) based system has been developed for in situ topographic imaging of the environmentally induce damage such as a stress corrosion crack under a dynamic loading condition. The system consists of an atomic force microscope (AFM), a mechanical testing machine, an X-Y-Z positioning stage, an environment chamber, and their controllers. To reduce disturbing vibration, the system is equipped with isolators. A dynamic load can be applied to a sample by using an electromagnetic actuator: it provides various loading waveforms including sinusoidal, triangular, and other arbitrary programmable ones, and has a maximum load capacity of ±100 N. Nanoscopic in situ AFM observation can be conducted in a controlled gaseous environment or in an aqueous solution. By using the developed system, in situ AFM observation of the following growing crack was successfully performed in a high-strength stainless steel: a fatigue crack in dry air and a stress corrosion crack under high-frequency vibratory stresses superimposed on a sustained load (dynamic stress corrosion cracking), and under a low-frequency varying load (cyclic stress corrosion cracking): the nanoscopic crack tips can be clearly visualized. The crack tip of the stress corrosion crack under dynamic loads is sharp compared with a fatigue crack in dry air, with a larger scatter of the crack tip opening displacement than those of the fatigue crack in dry air.