Modeling of Magnetomechanical Actuators in Laminated Structures

A magnetomechanical plate model (MMPM) has been developed to predict the elastic and magnetostrictive strains and mechanical stress in laminated structures with magnetostrictive and non-magnetic layers under the simultaneous effect of quasi-static mechanical stress and magnetic field. This model was obtained by combining an energy-based statistical magnetomechanical model with the classical laminated plate theory. The magnetomechanical plate model was used to study a unimorph structure having a magnetostrictive iron-gallium (Galfenol) patch attached to different non-magnetic substrates. The actuation response from the patch was obtained for in-plane axial magnetic field acting on the unimorph. The MMPM was used to predict the normalized tip displacement due to induced-strain actuation in a unimorph cantilever beam and the results were compared with existing modeling techniques. The model was used to study the effect of tensile and compressive axial pre-loads on the actuation response of the structure. A study was also performed to understand the effect of total thickness of the structure, the ratio of the active/passive layer thickness and the effect of the mechanical properties of different substrate materials on the actuator performance. A non-dimensional parameter STi (percentage strain transfer) was introduced to explain the behavior of the actuator in extension and bending dominated regimes and a critical thickness ratio (t(rc)) was defined to demarcate these two regimes. The results demonstrate that the model captures the non-linearity in the magnetomechanical process and the different structural couplings.