CMOS MEMS devices, fabricated from up to 13 layers of materials to create independent conducting paths, are subject to incremental fracture at high stress and to charging effects. This paper expands on preliminary reserach, which has revealed several stages of change in CMOS MEMS physical properties as they are exposed to resonant motion. Cracks are the first induced inside the stiffest lasyers, often silicon dioxide, in laterally resonant test structures with cyclic stress of 620 Mpa. Prior to cracking, the aluminum top layer of the structure can also deform, which affects the electrical integrity of the conductor. Measured frequency reponses of folded-flexure resonators demonstrate a nonlinear Duffling effect, producing mushroom-shaped resonant peak. Cyclic stress of 70 Mpa at the maximal stress points was insufficient to induce significant mechanical fracture in foled flexure resonators after 5 billion cycles, however an onset of change in stiffness was detected. Devices with a fixed dc actuation voltage experienced a change in electrostatic force attributed to charge accumulation in polymer and oxide layers. The force decayed with an approximate one-hour time constant while resonant frequency and quality factor remained constant.