Carbon fiber reinforced smart laminates based on NiTiNOL microactuators: embedding techniques and interface analysis

In the last few years the Composite Materials Lab. of the Aerospace Engineering Department (DIA) of Politecnico di Milano has activated a research line on development of Smart Structures and their applications. Among the sensors and actuators that can be embedded in the composite laminates, generally, the shape memory alloys ones are preferred when large displacements are required (i.e. morphing for wing profiles tuning, buckling control, etc.).

Up to now one of the main limits for a large use of these smart structures in the aerospace industry is the lack of useful numerical tools for design. Otherwise some technological aspects still need a more detailed investigation.

This paper shows how to deal with issues regarding embedding of both NiTiNOL wires and strips in a carbon fibre/epoxy laminates. A crucial aspect of those structures is related to the load transfer capabilities between the SMA actuators and the host material during their activation.

In order to characterize the real conditions interface, pull-out tests have been conducted on NiTiNOL embedded in composite fiber laminates. The results have been compared to standard experiments on pure epoxy resin blocks. The reason of this correlation is due to the major difference between the two resin systems involved and boundary conditions. Other aim considered in this work is related to the embedding technologies in itself that have to take into account problems like thermal and electrical compatibility between actuators and host material and passive/active invasivity. Simple smart laminates with several actuators have been manufactured, tested and deeply analysed.