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Shape memory alloys (SMAs) belong to the class of smart materials and have been used in numerous applications. Solid phase transformations induced either by stress or temperature are behind the remarkable properties of SMAs that motivate the concept of innovative smart actuators for different purposes. The SMA element used in these actuators can assume different forms and a spring is an element usually employed for this aim. This contribution deals with the modeling, simulation and experimental analysis of SMA helical springs. Basically, a one-dimensional constitutive model is assumed to describe the SMA thermomechanical shear behavior and, afterwards, helical springs are modeled by considering a classical approach for linear-elastic springs. A numerical method based on the operator split technique is developed. SMA helical spring thermomechanical behavior is investigated through experimental tests performed with different thermomechanical loadings. Shape memory and pseudoelastic effects are treated. Numerical simulations show that the model results are in close agreement with those obtained by experimental tests, revealing that the proposed model captures the general thermomechanical behavior of SMA springs.

The thermomechanical behavior of shape memory alloys (SMAs) may be modeled either by microscopic or macroscopic point of view. Shape memory, pseudoelasticity and thermal expansion are phenomena related to the SMA behavior. Constitutive models consider phenomenological aspects of these phenomena. The present contribution considers a one-dimensional constitutive model with internal constraint to describe SMA behavior including the effect of plastic strains. The proposed theory contemplates four phases: three variants of martensite and an austenitic phase. Different material parameters for austenitic and martensitic phases are considered. Thermal expansion phenomenon and plastic effects are also contemplated. Hardening effect is represented by a combination of kinematic and isotropic behaviors. A plastic-phase transformation coupling is incorporated into the model. A numerical procedure is developed and numerical results show that the proposed model is capable to capture the general thermomechanical behavior of shape memory alloys.

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Smart materials have a growing technological importance due to their unique thermomechanical characteristics. Shape memory alloys belong to this class of materials being easy to manufacture, relatively lightweight, and able to produce high forces or displacements with low power consumption. These aspects could be exploited in different applications including vibration control. Nevertheless, literature presents only a few references concerning the experimental analysis of shape memory alloy dynamical systems. This contribution deals with the experimental analysis of shape memory alloy dynamical systems by considering an experimental apparatus consisted of low-friction cars free to move in a rail. A shaker that provides harmonic forcing excites the system. The vibration analysis reveals that shape memory alloy elements introduce complex behaviors to the system and that different thermomechanical loadings are of concern showing the main aspects of the shape memory alloy dynamical response. Special attention is dedicated to the analysis of vibration reduction that can be achieved by considering different approaches exploiting either temperature variations promoted by electric current changes or vibration absorber techniques. The results establish that adaptability due to temperature variations is defined by a competition between stiffness and hysteretic behavior changes.