Ni-Ti SMA bars behaviour under compression

Abstract

SMA (Shape Memory Alloys) is a type of material suitable for using in civil engineering as concrete rein-47 forcement because of their shape memory effect or superelasticity and their high ductility and damping 48 capacity. However, Ni-Ti alloys Young modulus could be 3 or 4 times lower than steel (200 GPa) depend-49 ing on the composition and thermal treatment, which can cause the instability of compressed bars. The 50 main objective of this work is to provide a modified constitutive model of SMA bars, particularized for Ni-51 Ti bars, that considers instability in compression. The inclusion of this effect in the constitutive equation 52 allows for simulating Ni-Ti bars under compression in a simple way as if they were perfectly straight bars. 53 To achieve this, six 12-mm diameter SMA bars made of Ni-Ti were tested under compression. The 54

Buckling of steel and Ni-Ti reinforcements in very high performance concrete (VHPC) elements

“…Finally, the bar reached a second instability point and the supported load decreased due to second-order effects. Pereiro-Barceló and Bonet [4] tested 12 mm-diameter bars and also found two instability points in the least slender specimens. They proposed a method to modify the constitutive equation under compression of SMA bars to consider buckling according to on an analytical procedure and experimental results.…”

“…This behaviour is caused because the reinforcement area increases when the bar is compressed due to the Poisson effect. In order to take this difference into account in behaviour, and in order to keep considering the same area in tension and compression from the engineering point of view, Dodd and Restrepo-Posada [49] proposed the following expressions to transform the constitutive relation under tension (r À e) to compression ðr 00 À e 00 Þ: Bonet [4] analysed inelastic buckling behaviour of these bars outside concrete with various slenderness ratios.…”

“…Compressed reinforcements buckling can reduce the expected ductility, which is why several research works on this matter are currently being conducted [1][2][3][4]. Accordingly, design codes limit tie spacing [5][6][7][8].…”

Safety Issues in Buckling of Steel Structures by Improving Accuracy of Historical Methods

“…The finite element model was validated with experimental results on circular columns in previous research [45]. The same boundary conditions, applied loads, imposed displacements, material type, and element type were employed.…”

Finite Element Method Analysis of Effect of Thickness of Tape-shaped Ti–Ni Shape Memory Alloy on Post-buckling Behavior

“…(8) Pereiro-Barceló and Bonet proposed a new analytical model of the buckling/post-buckling behavior of Ni-Ti SMA bars. (9) These studies found that Ti-Ni SMA memorized to a straight shape shows negative or quasizero stiffness during post-buckling deformation. Since the deformation of SMA elements can be recovered during the unloading process by superelastic behavior, the negative or quasizero stiffness characteristic can be used repeatedly.…”