Microfracture characterization through crack diagnosis at sharp notch of mart microsystem materials using the electrostatic comb test device

摘要

As the size of a mechanical structure used in smart microsystems such as sensors and actuators becomes susceptible to defects, the effect of such defects on structural strength has a vital importance. So, the electrostatically acturated test device is presented to avaluate microfracture properties through a microcrack diagnosis of micromaterials forming the mcrosystems for improvement of micromechanical reliability. The designed test device consists of comb drives for lading and a suspending beam for testing. The sharp notch is introduced to the suspending beam in the test device. On the basis of the electrostatic comb test device, a theoretical model to auantify the notch radius effect on fracture toughness is proposed by considering the elastic stress concentration factor. From the model, fracture toughness can be predicted by variations in stress intensity factors in terms of the notch effect without precrack formation. The test device is in its lateral resonance mode during repeated operation. The structural damage or microcrack initiation can be quantified from the shift in the resonance frequency that is related to the crack propagation in the test device. During electrostatic cyclic loading to the test device including the nothc, microcrack initiation can be simultaneously detected by variation in the resonance frequency. From the analytical model, a diagnosis of microcrack initiation at the notch tip in the microsystems and materials is quantified.