For several common electroplated materials: Ni, Cu, Au and Al, which one has strongest fatigue strength? We know the mechanical properties of thin films are different with their bulk counterparts due to the so called "size effect", and material properties depends largely on the microstructure and processing technique. But is there some mateiral laws or guidelines for designers to choose the "best material" as for fatigue resistant? Yield limit? ultimate tensile strength? or elongation? How could one compare material candidates without doing time-consuming test?