Mean stress effect on mechanical fatigue of MEMS under alternate loads

The mechanical fatigue behavior of gold components for MEMS applications is analyzed; an experimental procedure to measure the lifetime of components under alternate loads with different mean stress conditions is presented. Dedicated devices were designed and built able to produce alternate loading on the embedded specimens; the electrostatic actuation is used as driving force. Gold microbeams are tested under tensile variable load with different levels of the mean and alternate stress. FEM models are used to estimate the stress level produced in the material under the variable actuation conditions. Experimental results are analysed to investigate the effects of different mean stress levels on the time to failure under mechanical fatigue; the fatigue results are represented using a Goodman-Smith diagram able to combine the amount of mean and alternate stress.