Abstract The electrical resistance Cu film on flexible substrate was investigated in cyclic bending deformation. The electrical resistance of 1 µm thick Cu film on flexible substrate increased up to 120 % after 500,000 cycles in 1.1 % tensile bending strain. Crack and extrusion were observed due to the fatigue damage of metal film. Low bending strain did not cause any damage on metal film but higher bending strain resulted in severe electrical and mechanical damage. Thinner film showed higher fatigue resistance because of the better mechanical property of thin film. Cu film with NiCr under-layer showed poorer fatigue resistance in tensile bending mode. Ni capping layer did not improve the fatigue resistance of Cu film, but Al capping layer suppressed crack formation and lowered electrical resistance change. The NiCr under layer, Ni capping layer, and Al capping layer effect on electrical resistance change of Cu film was compared with Cu only sample.

Abstract The debugging-time for polycrystalline MEMS structural layers is the aim of this paper. A description of the fatigue phenomenon for elementary structure in the case of microactuators is presented. It is obtained by combining elementary in situ test benches of varying dimensions and cyclic actuation; in the same way, the debugging-time is determined according to the design and the structural material. Test benches have been developed allowing performance of bending fatigue tests of polycrystalline structural layers, describing the fatigue phenomenon and obtaining a constant debugging-time for a same polycrystalline layer, whatever the excitation frequency and the beams length.

Abstract This article deals with an investigation to determine the root cause of the differences noted in the fatigue test data of main rotor spindle assembly retaining rods fabricated from three different materials. The US Army Research Laboratory - Materials Directorate (ARL) subjected the failed tie rods to visual examination and light optical microscopy and then performed dimensional verification and measured the respective surface roughness of the rods in an effort to identify any discrepancies. Next, mechanical testing (hardness, fatigue, and tensile) was performed, followed by metallography, and chemical analysis. Finally, the ARL performed laboratory heat treatments at the required aging temperature. The results suggested that the difference in performance could not be directly linked to chemical composition, dimensional intolerance, surface roughness or any metallographic variance and that the likely explanation for the difference observed in the mechanical performance of materials lies within a variation of the heat treatment.