Homogeneous and heterogeneous deformation mechanisms in an austenitic polycrystalline Ti–50.8 at.% Ni thin tube under tension. Investigation via temperature and strain fields measurements

Abstract

An initially austenitic polycrystalline Ti-50.8 at.% Ni thin-walled tube with small grain sizes has been deformed under tension in air at ambient temperature and moderate nominal axial strain rate. Temperature and strain fields were measured using visible-light and infrared digital cameras. In a first apparently elastic deformation stage, both strain and temperature fields are homogeneous and increase in tandem. This stage is followed by initiation, propagation and growth of localized helical bands inside which strain and temperature increases are markedly higher than in the surrounding regions. During the first apparently elastic stage of the unloading, both strain and temperature fields are homogeneous and decrease. The temperature and strain fields evolutions are then analysed in order to determine the deformation mechanisms (types and extents of phase transformations, variants (de)twinning, macroscopic banding) involved during the homogeneous and heterogeneous stages of deformation throughout the whole tube. The findings have significant implications for the understanding and modelling of superelastic behaviour of NiTi shape memory alloys.

Mechanical behavior and infrared imaging of ferromagnetic NiFeGaCo SMA single crystal subjected to subsequent compression cycles

“…Similarly to classical SMA, these alloys in most cases are characterized by a high-symmetry cubic structure in the high-temperature phase and a low-symmetry tetragonal structure in the low-temperature phase. An actuator using FSMA is rapid and can operate with 50-100 Hz frequency, whereas the frequency of TiNi SMA is 1 Hz only [1][2][3][4]. Thanks to these advantages, the FSMA are applied as elements of instruments demanding very fast operation.…”

“…Investigation of mechanical characteristics, the alloys related temperature changes and the manner of the transformation development is crucial for their applications, since the SMA are very sensitive to the temperature changes [5][6][7][8] occurring during the stress-induced martensitic transformation under various loadings have recently been studied in several research centers. For e.g., thermomechanical results of NiTi SMA subjected to simple shear are presented in [3], to tension in [4][5][6] and to compression in [7,8]. In [6], nucleation and development of the transformation pattern in TiNi SMA was studied by fast infrared camera.…”

Transition from many domain to single domain martensite morphology in small-scale shape memory alloys

“…At the millimeter scale, the nucleation and propagation of martensite has been studied by various in situ techniques such as optical microscopy (OM) [24][25][26][27][28], digital image correlation [29][30][31] and thermal observations with an infrared camera [32,33]. In large single crystals loaded uniaxially the evolution of martensite plates seems to be one of nucleation, growth (both perpendicular and parallel to the loading axis) and coalescence of plates [24,25].…”

Regularized InfraRed Image Correlation Applied to Laser-Induced Thermal Shocks

“…The use of IR cameras in the field of experimental mechanics is more and more common [1][2][3][4][5][6][7][8][9][10][11][12][13] in order to quantify the thermomechanical response of materials under load. Most of the time the sought information consists of the kinematic and temperature fields.…”

“…Most of the time the sought information consists of the kinematic and temperature fields. Both are induced by either the mechanical loading [1][2][3][4][5][6][7][8][9][11][12] or the applied thermal history [10,[13][14]. In the first case, temperature elevations are of few degrees Celsius, and accessing the thermomechanical response may provide a better understanding of localization and dissipative phenomena [1][2][3][4][5][6][7][8][9][11][12].…”