AFM and SEM observation on mechanism of fatigue crack growth in an Fe-Si single crystal

Fatigue crack growth tests are carried out on sheets of an Fe-3.2% Si single crystal with a cry stallographic orientation appropriate for striation formation. The behaviour of slip near a crack tip during the loading and unloading parts of a fatigue cycle is observed using an Atomic Force Microscope and a Scanning Electron Microscope. The fracture surfaces are also analysed with an AFM and an SEM. The mechanism of fatigue crack growth is discussed based on the observations, and a fundamental kinematic model for fatigue crack growth is proposed. The model gives a reasonable explanation for both the crack and striation formation.