Carbon fiber reinforced smart laminates based on nitinol microactuators: numerical modelling and empirical correlations

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 the main limits for a large use of these smart structures in the aerospace industry are still technological aspects (like passive and active invasivity) and especially the lack of useful numerical tools for design. The research line is devoted to overcame those issues. This paper shows numerical modelling approaches adopted for the constitutive laws implementation in commercial codes.

Two different techniques have been selected. The first one is based on the thermomechanical model proposed by Turner, the other one follows the thermodynamic macromechanical constitutive law developed by Lagoudas. Turner models the actuator shape memory effect on the host material considering a temperature dependent Young Modulus function and defining an Effective Thermal Expansion Coefficient. Instead, Lagoudas models the martensitic transformation using a more complex formulation that requires high computational efforts and dedicated routines not yet implemented in commercial codes.

The implementation of these models depends on the definition of some parameters (2 for Turner and 17 for mono-dimensional Lagoudas). The paper presents the test campaign carried out for the definition of these parameters (related to NiTiNOL wires) and the numerical-experimental correlation for both the models.