Active control of delaminations in smart composite structures

Delaminations are one of the most commonly observed defects in laminated composite structures. Presence of delaminations significantly degrade the performance of a structure. Under certain loading conditions, these delaminations may grow and the growth of such delaminations may eventually lead to catastrophic failures. In this thesis, control of growth of delaminations is studied using the concepts of smart structures.; As a first step, a detailed dynamic model of a delaminated beam, is studied. Effects of the delamination on dynamic characteristics such as natural frequencies, mode shapes and dynamic response under various loading conditions are studied. It is observed that the presence of delaminations not only affect the natural frequencies but also significantly alter the mode shapes when compared with the natural frequencies and mode shapes of a perfect beam. Later, this dynamic model has been improved to study the effects of shear deformation and rotary inertia on dynamic characteristics. Elements based on first order and third order shear deformation theories that include rotary inertia effects are developed to study the dynamics of the delaminated beam. It is observed from these studies, that shear deformation effects are quite significant for small delamination sizes.; Observed changes in the dynamic behavior of the delaminated beam and the perfect beam are used to detect the size and the location of the delamination. Ibrahim time domain identification technique that uses the free response data is used for identifying natural frequencies and mode shapes. From the identified natural frequencies and mode shapes, it is concluded that changes in dynamic responses of delaminated beams can be used for the detection of the size and the location of a delamination.; As a next step, growth of this identified delamination is controlled by using active control techniques. Since growth of delamination is due to high interlaminar stresses, an active control scheme that reduces the high interlaminar stresses is proposed to control the growth of delamination. Fracture mechanics based total energy release rate criterion is used to characterize the growth of delamination.; Robustness aspects in the design of active control schemes are discussed for a smart structure. A robust controller that reduces vibrations even when the sensors are partially debonded is designed. {dollar}mu{dollar} synthesis is used for the design of robust controllers.