Measurement of residual stresses in a plate using bulging test and a dynamic technique: application to electroplated nickel coatings

The development of new metallic actuators fabricated by LIGA technique depe nds on the mechanical characterization of electroplated coatings. Particula r attention must be devoted to residual stresses in order to lower the degr adation of the microsystems performances. The aim of this paper is the inve stigation of residual stresses in electroplated nickel plates clamped on si licon substrates using two methods based on optical measurements. The bulgi ng test is a steady-state technique, which gives the in-plane stresses pres ent in a plate as well as the Young's modulus of the material. As a complem entary experiment, we have analyzed these stresses using a dynamic techniqu e. The purpose of this method is to generate via a piezoelectric actuator s tationary waves inside the plates. The frequencies of the different modes d epend on the geometry of the plate and are strongly modified by in-plane st resses. The values obtained by these two techniques are compared to a previ ous work devoted to the X-ray analysis of the residual stresses on the same samples. (C) 2000 Elsevier Science S.A. All rights reserved.