Ni-Ti SMA bars behaviour under compression

Abstract

[EN] SMA (Shape Memory Alloys) is a type of material suitable for using in civil engineering as concrete reinforcement because of their shape memory effect or superelasticity and their high ductility and damping capacity. However, Ni-Ti alloys Young modulus could be 3 or 4 times lower than steel (200 GPa) depending on the composition and thermal treatment, which can cause the instability of compressed bars. The main objective of this work is to provide a modified constitutive model of SMA bars, particularized for Ni-Ti bars, that considers instability in compression. The inclusion of this effect in the constitutive equation allows for simulating Ni-Ti bars under compression in a simple way as if they were perfectly straight bars. To achieve this, six 12-mm diameter SMA bars made of Ni-Ti were tested under compression. The mechanical slendernesses of the six Ni-Ti samples were: 28.33, 38, 48, 66, 82 and 108.33. Thirty steel specimens were tested beforehand to validate the experimental setup and to calibrate the subsequent Abaqus finite element model. This model aims to conduct a parametric study to validate the proposed constitutive model of Ni-Ti bars, including instability in compression.