Non-linear analysis of thermomechanical bechaviour of a unidirectional composite with shape memory alloy fibers | Mekhanika | kompozitsionnykh | materialov i konstruktsii
> Volume 24 > №2 / 2018 / Pages: 221-241

Non-linear analysis of thermomechanical bechaviour of a unidirectional composite with shape memory alloy fibers

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Abstract:

N the framework of the modified model of nonlinear thermomechanical behavior of the shape memory alloy during phase and structural transformations, the processes of changing the stress-strain state of a unidirectional composite with an elastic matrix and fibers of titanium nickelide are described. Preliminary, with the help of the phenomena of direct strain accumulation or martensitic inelasticity, the fibers are given the initial tension phase-structural deformation. After this, the fibers in the martensitic phase state are combined with the matrix in order to ensure joint deformation of both components. With the subsequent heating of the fibers, in them an inverse thermoelastic martensitic phase transformation occurs, accompanied by a shape memory phenomenon. As a result, the entire composite experiences longitudinal compressive deformations, internal stresses appear in its elements (compressing in the matrix and stretching in the fibers). Upon subsequent cooling of the fibers, a direct thermoelastic martensitic phase transformation will occur in them under the action of internal tensile stresses. The fibers will elongate in the longitudinal direction, providing the process of deformation by stretching the entire composite. Using the approaches of micromechanics of composite materials, in a coupled statement, taking into account the variability of the Young’s modulus of titanium nickelide, the processes of changing the stress-strain state of such a composite as a whole and its components, changes in the phase composition of fibers were studied. Special attention is paid to the investigation of the possibility of implementing in this system a closed two-way shape memory effect (the phenomenon of repeatedly reversible shape memory) in which the internal stresses in the system disappear completely at the point of the direct thermoelastic phase transformation termination in the fibers. It is shown that this phenomenon can be described only in the framework of the shape memory alloys behavior model, taking into account, not only the process of martensitic meso-elements nucleation, but the process of their development under direct transformation, i.e. in the case of using systems of constitutive equations correctly describing the phenomenon of oriented transformation. It is shown that a closed two-way shape memory effect takes place at a certain value of the filament volume fraction, which is a decreasing function of a given initial deformation of filament.

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