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Journal of Physical Studies 5(3/4), 369–377 (2001)
DOI: https://doi.org/10.30970/jps.05.369 PHASE TRANSITION DETERMINED BY ULTRASOUND IN SHAPE MEMORY MATERIALSS. Stoimenov
Institute of Physics, Faculty of Natural Sciences and Mathematics |
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In principle, the shape memory effect is associated with thermoelastic martensitic transformation and reverse transformation. The unique feature of this shape memory materials is the formation of the high mechanical force due the thermal excitation. This specific thermal behaviour is most interesting for examination, from aspects of thermoelasticity. Shape memory refers to the ability of certain materials to ‟remember” the shape, even after rather severe deformations: once deformed at a low temperature (in their martensitic phase), these materials will stay deformed until heated, whereupon they will spontaneously return to their original, pre-deformation shape. The basis for the memory effects is that the materials can easily transform to and from martensite and reverse transformation. The incoming of thermal energy in the temperature region of the transformation changes the feature of elasticity. For this reason the value of the velocities and attenuation of ultrasound are changed. Using relationships from the theory of elasticity and values of the density and velocities of ultrasound it is possible to obtain the values of the elastic moduli ($E, K, G$) and Poisson's ratio $ν $. In this case it is possible to obtain complete information about the elastic, i. e. thermo-elastic state.
PACS number(s): 81.40.Jj, 81.70.Dw