Effect of the grain boundary on the fatigue crack growth for aluminum bi-crystals

Grain boundaries (GBs) are relevant as structural barriers for deformations in nano-crystalline materials and their resistance against fatigue crack propagation. The overall behavior of the material's structure is the result of a complex confluence of multiple grains with a variety of relative orientations and their interaction with other structural defects. The effect of the grain boundary on cracked grains is an important factor in order to establish the mechanical behavior of nano-materials under static and dynamic loading conditions. For studying the effect of the grain boundary on the mechanical behavior of nano-crystalline solids a single boundary is placed as a defect that separates two miss-oriented crystals with a relative tilt or twist angle. The purpose of this study is to analyze the effect of the GB and the relative tilt and twist angles on the crack propagation under increasing cyclic loading of cracked FCC bi-crystals. Molecular dynamics simulations at room temperature of fatigue crack growth tests were performed to characterize the retardation effect of different grain miss-orientations on fatigue crack propagation. Al by-cristals with an initial edge crack and different miss-orientattion angles are simutalted, in the present research, under increasing cyclic loading condition. As a general trend high twist angles showed a greater effect on the resistance to crack propagation under single and compound grain miss-orientation.