Stiffness tailoring using prestress in adaptive composite structures

Adaptive aerostructures offer the potential of increasing both aerodynamic and structural efficiency compared to conventional aerospace technologies. However, there is frequently an awkward trade-off between designing for large deformations whilst being able to withstand external loads. Multistable laminates which derive their multistability via thermal expansion mismatches are of interest for adaptive structures due to their ability to demonstrate relatively high stiffness in multiple stable states whilst being able to undergo large deformations with reduced stiffness. In addition, actuators only need to work during transition between stable shapes. However, many practical problems have arisen with the application of these laminates when designing adaptive structures. Such problems include hygrothermal variability, a limited design space with regards to achievable shape change, and insufficient stiffness for many applications. Prestressing technologies offer solutions to all of these problems. This paper summarises recent developments concerning the various means by which prestress can be used for stiffness tailoring in adaptive structures. Example prestressed structures are given including camber and twist change morphing airfoils. The use of prestress for stiffness tailoring in the design of novel passive vibration isolators and adaptive air intakes is also discussed.