The mechanical and fatigue characteristics of superelastic NiTi thin plates in the large strain area were obtained by tensile and pulsating 4-point bending tests to establish the design guidelines for the ferromagnetic shape memory alloy (FSMA) composite actuator and its fatigue life. The stress-strain curves of NiTi thin plates were found to be strain rate dependent. The finite element analysis (FEA) result using the stress-strain curve measured by tensile test is in good agreement with the experimental results of the 4-point bending tests. The relationship between the maximum bending strain and the number of cycles to failure in pulsating 4-point bending fatigue tests was obtained as well as an analysis of the fatigue fracture surfaces of NiTi thin plates.
This paper is aimed at to discuss two cases of active composites, (i) ferromagnetic shape memory alloy composites, and (ii) piezoelectric ceramic-shape memory alloy composites. Here we discuss the merits of designing such active composites, for use as possible actuator materials. To optimize the nano-/micro-structures of such composites, we developed analytical models based on Eshelby type modeling. Based on the modeling study; a few cases of optimized active composites are suggested.
A hydrid composite comprised of shape memory alloy (SMA) fibers with piezoelectric ceramic is designed to transform
thermomechanical energy into electrical energy that can be stored or used to power other devices. SMA fiber, after its
shape is memorized and prestrained at martensitic phase, extends to its original length upon heating to austenitic finish
temperature. The compressive residual stress of the composite is induced at austenitic phase, and then by cooling to
martensitic finish temperature, SMA will shrink and the residual stress will reduce. By direct effect of the piezoelectric
matrix material the mechanical energy which was induced by temperature change can be converted to electrical energy.
1-D and 3-D models for the energy harvesting mechanism of the composite have been proposed. Eshelby formulation
with Mori-Tanaka mean field theory modification is used to determine the effective thermo-electro-mechanical
properties of the composite. Attention is focused on the constrained recovery behavior of SMA phase in this study.
Electrical model is examined and the electrical energy stored in the piezoelectric matrix as a result of stress fluctuation is
estimated. Numerical example is given that illustrate the ability of the composite to convert the thermomechanical
energy into electrical energy.
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