Measurement of residual stresses in a plate using bulging test and a dynamic technique: application to electroplated nickel coatings
Résumé
The development of new metallic actuators fabricated by LIGA technique depends on the mechanical characterization of electroplated coatings. Particular attention must be devoted to residual stresses in order to lower the degradation of the microsystems performances. The aim of this paper is the investigation of residual stresses in electroplated nickel plates clamped on silicon substrates using two methods based on optical measurements. The bulging test is a steady-state technique, which gives the in-plane stresses present in a plate as well as the Young's modulus of the material. As a complementary experiment, we have analyzed these stresses using a dynamic technique. The purpose of this method is to generate via a piezoelectric actuator stationary waves inside the plates. The frequencies of the different modes depend on the geometry of the plate and are strongly modified by in-plane stresses. The values obtained by these two techniques are compared to a previous work devoted to the X-ray analysis of the residual stresses on the same samples.