Stable crack growth in NiTi shape memory alloys: 3D finite element modeling and experimental validation

Abstract

Crack growth in shape memory alloys under mode-I isothermal loading is simulated using finite element analysis. The experimental data refers to a compact tension (CT) experiment on nearequiatomic nickel-titanium (NiTi). The constitutive model used is calibrated from uniaxial experiments on the same material system. The simulation is run in a three-dimensional CT specimen modeled in Abaqus finite element suite using the virtual crack closure technique and an experimentally determined fracture toughness value. The numerical results provide a quantitative description of the observed stable crack growth in terms of load-displacement curve, deformation distribution, and size and shape of the stress-induced transformation zone close to the crack tip.

Notes on the experimental measurement of fracture toughness of shape memory alloys

“…The experimentally observed fracture of SMA specimens during phase transformation induced by cooling under a constant external mechanical loading (Haghgouyan, Jape, et al, 2019;Illiopoulos et al, 2017), which from an energetic point of view may seem to be in disagreement with the general view of dissipative processes resulting in an enhancement of fracture toughness, is characteristic of SMAs and should be attributed to phase transformation from austenite to martensite interacting with the stress and strain fields near the notches/cracks. As explained on the basis of finite element simulations and analytical arguments (Baxevanis et al, 2016), the increase in driving force for crack growth during cooling is due to transformation occurring in regions in front of the crack tip.…”

“…In contrast to most conventional structural materials, SMAs' fracture may be also thermomechanically assisted. According to recent experimental investigations (Haghgouyan, Jape, et al, 2019;Illiopoulos et al, 2017), SMAs may fracture during cooling under a constant external mechanical loading; this loading path is an idealization of typical loading paths that utilize these alloys as actuators. the fracture toughness dependence on temperature is piecewise constant, below and above M d (for nominal temperatures above M d , the austenite phase is stable and the deformation response of the SMA is similar to that of a conventional metal, with plastic deformation (via slip) occurring when the stress reaches the yield stress of austenite), with the fracture toughness above M d , that is, the fracture toughness of austenite, being considerably higher.…”

Phase field simulations on the rate‐ and grain‐size‐dependent crack propagation of polycrystalline NiTi shape memory alloy

“…To enhance computational efficiency, the dimension of the established simulation cell is much smaller than those of NiTi SMA specimen used in the experiments. 52,53 The number of grains in the systems with different GSs is greater than 30, therefore, it can reflect the mechanical response of NiTi SMA. 33,45 The two-dimensional systems are shown in Figure 2A-C (denoted as GS-15, GS-60, and GS-100, respectively).…”

Simulations of Magnetic Field Variations Around Rectangular Defects of Ferromagnetic Materials

“…One of the most used tools for these purposes is computer simulations, which can predict behavior in materials when subjected to certain conditions or damage. Some of the commercial software that performs this type of work are ANSYS or LS-DYNA, recently used in the simulation of faults in mechanisms [12][13]. Other types of analysis choose to predict the propagation of cracks in materials through complex mathematical models, which are supported by the use of specialized software such as MATLAB.…”