| Durability and reliability are important objectives in the design of mechanical structures for vibration environments. Traditionally, these objectives have been achieved using passive design strategies involving the modification of design geometry, the use of stronger materials, and viscoelastic damping materials. Recent advances in piezoceramic materials and structural control theory suggest the use of an additional design tool for the pursuit of durable structures; active stress and damage control. That is, actuators and sensors may be distributed on a structure in such a way that control is exercised over the state of stress, strain, and the accumulation of structural damage.;In this research, an investigation into fatigue control of beam structures using surface mounted piezoceramics is performed, consisting of both modeling and hardware testing. Both classical and finite element dynamic modeling techniques are applied to generate modal based closed loop state space models. A test bed is designed and built for life testing active beams. Control system hardware and performance measurement techniques are developed. Vibration damage suppression is demonstrated in a design employing an active beam with modal rate feedback control and lead zirconate titanate (PZT) actuators. The life of this design example is extended by two orders of magnitude in resonant dwell testing.;A thermally based pre-stress procedure is presented for enhancing the durability of PZT actuators. In this process, actuators are placed in a compressive stress state by elevated temperature bonding to materials with higher coefficients of thermal expansion. Subtle negative effects of pre-stress on actuation strength are observed and measured.;Actuator mount fatigue is evident in the life test data, suggesting the presence of electrical and mechanical fatigue effects in PZT. The results show that piezoceramics may be limited but viable fatigue control actuators in some applications. |
