Ab initio simulation of electronic and mechanical properties of aluminium for fatigue early feature investigation

Fatigue crack initiation and propagation are the central issues for understanding fatigue behaviours, and early detection of fatigue will be useful in industry before cartographic events occur. It has been found that surface work function, Young's modulus and surface energy are inter-dependent with the occurrence of fatigue, and we compute these material properties using ab intio simulation for aluminium. We found that the highest work function represents stability of the surface with respect to fatigue, and that the closest-packed (111) face has the highest work function. Also, the work function with C impurities is higher than that without C impurities for all orientations of Al, indicating that C impurities can help to stabilise the surface. Surface work function is also found to be dependent on the surface roughness, and the dependence varies with Al orientations. In particular, the work functions of the closest-packed Al (111) and Al (100) decrease as roughness increases. However, for Al (110), the work function increases with roughness, and the different dependences on roughness require further study in order for work function to be used to detect the potential site of fatigue as well as the initiation of fatigue. Lower surface energy indicates a more stable surface from fatigue as most cracks initiate from the surface. Our calculation shows that Al surface energy decreases with the existence of Si impurities but increases slightly with that of Ca impurities, showing the importance of surface impurities in affecting fatigue early behaviours. It has been shown that Young's modulus decreases with fatigue cycles and when a low threshold is reached, cracks will be initiated. We find that the Young's modulus of Al (111) is the largest, indicating its robustness against fatigue as compare to other orientations.