Functional Properties of Spherical Segments Made of Ti-Ni Alloy with Shape Memory Effect

Abstract

Abstract. The article is devoted to the investigation of changing behavior of force parameters developing in the material of spherical (buckled) segments at heating, depending on the temperature of overheat and presence of strain concentrators. It is shown that overheats of spherical segments relatively to the temperature of reverse martensitic transformations (A f influence considerably the impact force and reactive forces. Specifically, the spherical segments exposed to overheat at temperatures in a free state always snap back with a stroke against the obstacle and with development of reactive forces at heating. Overheat of the spherical segments in a fixed state decreased the force parameters, and at annealing (200 250 ), 1h the shape memory effect is suppressed completely. Influence of strain concentrators made up deliberately on the edges of the spherical segments depends on their length. It is shown that notches no more than 0,5 mm long do not influence the impact force and reactive force, while notches 1,0 mm long cause generation and development of nuclear cracks.

The Effect of Loss of Stability of an Arc-Plate Made of Ti-Ni Shape Memory Alloy

“…It was shown in [2,3] that form changing of an arc is unstable in case of hinge support. Transition from stable to unstable state of an arched strip occurs abruptly (with a clap), the same process is observed on spherical segments [4]. Kinetics of reactive forces in the material of the se objects, caused by a loss of stability, is quite similar.…”

“…The full-scale deflection value of the arched strip (H) was H = 2f 0 h, where f 0 -initial bending deflection (9 mm). Fig.4 shows the diagram of the bend of the arched strip as with the spherical segment [4] and presents a characteristic dependency between force F and bending parameter H. It is seen that the bending force of the arch to the centre of the curvature increases up to the upper critical value P u , after which the arch gives a clap (snap) from equilibrium position B to position C. After that the bending force increases again, reaching F max at a full-scale deflection value (H-h). The removal of the applied force results in minor decrease in H as a consequence of elastic strain display.…”