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Title: Shape memory alloys : numerical simulation and optimal design of SMA actuators
Author: Han, L.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2006
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Shape memory alloys (SMAs) are particularly attractive as actuators in smart structures, due to their large actuation strain/stress, high power/weight ratio, single actuation mechanism and low noise etc. However, the lack of reliable predictive models and computational and design tools severely limits their applications. This thesis is concerned with the models appropriate for the numerical implementation, and the optimal design procedure of SMA actuators. To understand the thermomechanical characteristics of NiTi SMAs, a number of tests have been carried out, including iso-thermal tension tests under different constant temperatures, iso-thermal tension tests with different constant strain rates, iso-stress thermal cycling tests under different constant stresses, repeated iso-stress thermal cycling tests and repeated iso-thermal superelastic mechanical cycling tests. The stress-temperature phase diagrams for phase transformations are constructed. Under the framework of generalized plasticity with an internal-variable formalism, a three-dimensional phenomenological model is developed. Based on the stress-temperature phase diagram, the evolution equations of phase fractions are derived. The model reproduces the basic features of SMAs, such as the shape memory effect (SME) and superelasticity (SE), and can deal with incomplete phase transformations. Using return mapping algorithms, the incremental numerical formulation of the model is implemented into ABAQUS, through a user-defined material subroutine. Numerical examples and comparisons between the simulations and experiments have shown the capacity of the model and the feasibility of the subroutine. The design method of a typical bias SMA actuation unit is developed. The relationship of the actuation stress, strain and temperature is obtained by solving a coupled problem combining a thermomechanical constitutive model, heat conduction equations and the spring response. A novel lightweight SMA actuator integrating SMA actuation units into a truss structure is proposed, optimised and manufactured to demonstrate the possibility of SMA actuators in the application of smart structures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available