Modeling of Cold Plastic Deformation of the Holes Made in Specimens of Shape-Memory Alloy
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MODELING OF COLD PLASTIC DEFORMATION OF THE HOLES MADE IN SPECIMENS OF SHAPE-MEMORY ALLOY P. V. Yasnii,1 O. V. Dyvdyk,1, 2 and V. P. Iasnii1
UDC 539.3
The process of cold plastic deformation of a hole in a plate made of shape-memory alloy is simulated by the finite-element method by setting the mechanical characteristics and the temperatures of the onset and termination of direct and reverse phase transformations. By using the ANSYS Workbench software, we determine the distribution of residual stresses in the plate in the vicinity of a functional hole. The highest normal compressive and tensile stresses are formed in the middle part of the plate and at a distance of 2–4 mm from the edge of the hole, respectively. Keywords: shape-memory effect, NiTi alloy, phase transformations, martensite, austenite, normal stresses, strengthening of the holes.
Introduction The development of contemporary engineering advances new elevated requirements to structural materials and their characteristics of strength and durability. The shape-memory alloys (SMA) [1–3] have good characteristics of durability, high strength, high damping ability, and high resistance to the action of corrosive media [4, 5], which explains their extensive application in various branches of engineering. At low temperatures, in the absence stresses, martensite stays in the twin phase. Under mechanical loads, it passes into the reorientation phase and changes its microstructure [6]. The distributions of residual stresses in structural elements with holes after their cold pressure treatment can be found by using analytic [7], numerical [8–10], and experimental methods [8, 11]. The main regularities of the influence of mandrelling tension (degree of cold expansion) and the diameter of the hole on the distribution of stresses in the vicinity of the hole and the durability of plates made of aluminum alloys under loading with constant amplitude were established in [10, 12, 13]. The holes can be strengthened as a result of cold plastic deformation performed by using various technological procedures: punching of the balls or mandrels of conic shape with calibrating sections [13–15] and the methods of split bush [16, 17] or barrier drafting. A method of cold hardening of the holes with the help of tools made of shape-memory alloys proves to be quite promising [18, 19]. In particular, we can mention an improved method of strengthening of the holes guaranteeing the formation of residual compressive stresses around the hole in the axial and radial directions [19] due to the application of tools with cylindrical collars made of shape-memory alloys. As usual, the shapememory effect is simulated by using the finite-element method (FEM) with the help of 3D thermomechanical models [20–22]. 1 2
I. Pulyui Ternopil National Technical University, Ternopil, Ukraine. Corresponding author; e-mail: [email protected].
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 56, No. 2, pp. 46–51, March–April, 2020. Original article submitted December 13, 2019. 188
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