Micromechanical Modeling of Multifunctional Composites

In the new generation of aircrafts in which the use of composite materials is ever increasing, smart composites reinforced with active fibers are expected to play a major role in monitoring health and performance of the airframe in addition to their load carrying capabilities. While advancements in material development, e.g. PZT filaments, bring the fabrication of structural components with multifunctionality closer to reality, reliable predictions of their behavior and performance are lacking. In particular, the modeling of damage progression on multiple lengthscales in structural composites is essential in modeling both sensing and/or actuation functionalities. Moreover, temperature changes affect the response of active constituents through changes in thermomechanical fields and/or changes in coupled functions, as for example in pyroelectric materials. These complexities invite a novel modeling approach of the problem. This paper represents a major departure from present approaches, which focus mainly on undamaged, unidirectionally reinforced multifunctional fibrous composites at ambient temperatures. The work presented models multifunctional composite materials and structures on multiscales considering piezoelectric and pyroelectric phenomena. In particular, fibrous laminates with a general layup are considered under membrane forces and bending moments in combination with temperature changes. The solution for the local fields and overall response is determined in terms of a transformation field analysis scheme in which the local stresses or strains that cannot be removed by mechanical unloading are treated as eigen fields applied in an otherwise elastic medium. In the current application, the latter represents an aggregate of unidirectional plies and their phases. The proposed modeling strategy is applied to fibrous laminates subjected to mechanical and/or thermal loads. While the modeling of damage follows the same strategy, it is discussed elsewhere.