M. A. Khusainov, Yaroslav the Wise Novgorod State University, Velikiy Novgorod, Russia; A. B. Bondarev, Industrial center “MATEKS”, Moscow, Russia
Spherical segment from shape memory alloy, not fixed on edges, after a bending mirror in relation to an initial form, gives click through at heating up with a clap. The observable effect as have shown experiences, is caused by loss of stability of a segment owing to development of reactive stress on edges and in the center of a segment. Cycling a segment on a mode the bending in martensite « heating up to àustenite conditions, with realization of effect click through results in essential change of functional - mechanical properties of an alloy, in connection with accumulation of irreversible deformations at simultaneous occurrence and development of zones of plastic deformation - the potential centers of nucleation of microcracks.
It is shown, that fracture of spherical segments from an alloy of the set structure represents complex multiphasic process. The first stage, the longest, is characterized by nucleation of microcracks in places of the greatest concentration of tensile stress which arise, as a rule, at edges during a bending of a segment in màrtensite and in the center at the moment of loss of stability. At the second stage transition from absent-minded microcracks to formation of the main crack wedge-shaped type and to its extend with enough high speed to the center of a spherical segment is marked. Thus the cracks arising at edges, develop faster, than on a dome of a segment.The conclusion that artificial introduction of concentrates of stress (cuts) has allowed to construct the circuit of fracture of spherical segments of alloys "iNi with shape memory of the form is made.
Summary: The spherical segment or convex segment from an alloy " Ti, Ni" with effect of memory of the form, is formed of a round plate, by a deflection in concave sphere, a jamming and giving of memory of the form at 500°Ñ, 30 minutes. The convex segment deflected in martenseite condition smooth initial form at heating up loses stability and click through (with a clap) to originally set form. Now if on a way of return of the form to put opposed a solid, for example, a dynamometer, kick of the certain force is realized.
In the given work results of experimental researches of an intense condition and convex segments at stages of a deflection in martensite and heating up to austenite conditions are submitted. It is shown, that on edges of a segment generate the highest pressure of a stretching, than on its dome. For studying kinetics development of cracks concentrators of pressure at edges and a dome of segments, with the help of the electro-spark machine tool were entered. The data on change of principal parameters describing effect of a clap (force of kick and reaction efforts) are simultaneously resulted.
The received data, on development of reaction efforts in researched elements and its efficiency at thermo-mechanical cyclonage were used at shut-off valves.
