Study On Vibration Characteristics Of Shape Memory Alloy Composite Structure

As a new intelligent material, shape memory alloy has be used widely in many fields such as civil engineering, control engineering, medical treatment engineering, energy mechanism engineering due to its special shape memory effect, superelasticity, excellent physical and chemical properties and biocompatibility. Shape memory alloy can act as sensors and driver, and it has obvious advantages on the vibration control. So it has great theoretical significance and engineering application prospect for the damping of the structure vibration of shape memory alloy.Firstly, the special nature of the shape memory alloy was analyzed and the research progress in structural vibration damping of shape memory alloy was summed up at length in this thesis. The constitutive models of the shape memory alloy were summarized. Then the constitutive model applied in this thesis was elaborated.To investigate the basic properties of phase transition temperature of the shape memory alloy wire, differential thermal analysis test was conducted by DSC. With a high power microscope, the crystal structure of the shape memory alloy wire was observed. And a series of tensile tests of the SMA wire were carried out. The phase transition characteristic at different temperatures of an alloy wire was received by tensile test inside incubator. Then the phase transition recovery stress was tested on the stretched alloy wire by heating. Through the cyclic tensile test of shape memory alloy, it was obtained that there was residual strainε_r for each time, and a fitting function curve of the residual strainε_r( in connection with stretching cycles and temperature) was given.In order to introduce the special constitutive relations into the finite element method software, the UMAT subroutine in ABAQUS was programmed. Because it is required to provide Jacobian matrix each step by the stress update algorithm, the constitutive model of the tensor form was discredited. The Jacobian matrix of the strain on the stress and the strain on the temperature were derived, and the matrix expression of tensor variables in UMAT was deduced. The SMA tensile test, combined with ABAQUS simulation, verified the correctness of compiled subroutine UMAT. The impact on the structural dynamic characteristics was discussed by the thermal excitation for the composite beam model containing SMA wire (with pre-strain). Calculation result showed that the effect of heating the SMA wire with pre-strain on the structure of natural frequency was obvious and the influence curve of frequency by different diameter SMA wire was achieved.The restored strain formula of the pre-strain SMA wire was derived, and the calculation model of lamination containing SMA wire was established. Then the influence factors on the vibration characteristics were discussed. With the increase of pre-strain, the frequencies of each order were significantly improved. The increase extent in fundamental frequency which was most critical to the structural vibration damping characteristics was particularly evident. SMA wires of different inbuilt angles had significant effects on the increase of the frequency and the structure mode of vibration. In modelⅠ90°, the increase in frequency was more compared with other cases, which should be paid more attention in the engineering application. And the change in elastic modulus under other factors could be ignored.