Experimental methods for the characterization of fatigue in microstructures

Abstract

The mechanical fatigue behavior of gold microbeams is analyzed. Dedicated devices have been designed and built able to produce alternate loading on gold specimens; the electrostatic actuation is used as driving force. Gold beams are tested under both bending and tensile alternate loadings. Results were used to plot S-N curves and fatigue Goodman-Smith diagram in order to estimate the fatigue limit of the material in presence of mean and alternate stress conditions. The surface topography evolution is studied and failure modes are discussed.

Fatigue fracture mechanics in gold-based MEMS notched specimens: experimental and numerical study

“…Furthermore, the variation of the vertical displacement measured during the fatigue test is attributed to the variation in the device stiffness due to the crack growth at the notch. This is quite reasonable for three reasons: (1) the central specimen is the most stressed component of the microstructure, as also demonstrated by FEM analysis; (2) the notch acts as a stress raiser, fostering crack nucleation [42,47]; (3) the plates and flexural beams are less affected by damage, as also confirmed by SEM analyses and by results from previous works [32,33].…”

“…Loading strategy Goals References Gold Electrostatic actuation Fatigue characterization of microbeam through pull-in monitoring [28][29][30][31][32] Gold Electrostatic actuation Effect of mean stress on fatigue of microbeam [33]…”

“…It is important to point out that the fabrication process is designed to limit the onset of residual stress, as explained in detail in previous authors' works [45,46,52]. The design of the test microstructure is addressed to correlate the degradation of the specimen stiffness due to cycling to the variation in the device deflection, as previously reported in [32,33,47]. The kinematic scheme of the test microstructure is shown in figure 2.…”

“…Different attempts to obtain Wöhler curves of micromechanical samples were made [28][29][30][31][32][33][34][35][36], on the other hand, few works applying Paris' law to characterize fatigue fracture process in MEMS devices exist in the literature [20,[37][38][39].…”

“…A test microstructure is specifically designed and built to characterize the fatigue fracture in gold-based MEMS notched specimen with on-chip testing. The design of the test microstructure, as well as its fabrication process and the advantages over other designs proposed in the literature, are extensively reported in authors' previous works [32,33,[45][46][47], thus just a brief description is given below for the sake of clarity.…”