Introducing the constitutive behavior of shape memory alloys into adaptive engineering structures

The variety of special mechanical properties of shape memory alloys (SMAs), including large recoverable strains and pseudoelasticity has made design engineers highly curious on how to apply these materials beneficially in their engineering structures. Tools required to partially satisfy this curiosity are certainly analytical approaches and mechanical models, which allow one to obtain a more realistic feeling of possible rewards to be expected when using SMAs. One of the major inputs required for studying the mechanical behaviour of structures is the constitutive material behaviour generally expressed in terms of stresses and strains. This paper starts from an analytical description of the constitutive behaviour of the SMAs, which will then be applied to a cantilever beam being activated by a SMA actuator. Taking full advantage of the SMA's actuation potential in terms of its maximum recoverable strain often leads to a situation where the assumption of linearized deformation is not valid anymore. Large deformations (nonlinear theory) will therefore be considered. Based on this model a variety of effects are studied such as active deformation, stress relaxation and stability.