A combined experimental and numerical analysis of fracture and crack growth in SMAs is presented. Crack extension is investigated under mode-I, isothermal, monotonic, mechanical loading in near-equiatomic nickel- titanium (NiTi) SMA compact tension (CT) specimens. Stable crack growth is observed and the associated J-R curve is evaluated along with the crack initiation toughness. Finite element analysis (FEA) with an energetics based fracture toughness criterion is also carried out and crack is assumed to extend when crack-tip energy release rate reaches the material specific critical value. Fracture toughening behavior is observed during crack growth and is mainly associated with the energy dissipated by the progressively occurring phase transformation close to the moving crack tip. A comparison between the experimental and numerical results is presented.
Numerical analysis of static cracks in a plane strain center-cracked infinite medium shape memory alloy (SMA) panel subjected to cyclic thermal variations and a constant mechanical load is conducted using the finite element method. In solid-state SMA actuators, permanent changes in the material's microstructure in the form of dislocations are caused during cyclic thermomechanical loading, leading to macroscopic irreversible strains, known as transformation induced plastic (TRIP) strains. The influence of these accumulated TRIP strains on mechanical fields close to the crack tip is investigated in the present paper. Virtual crack growth technique (VCCT) in ABAQUS FEA suite is employed to calculate the crack tip energy release rate and crack is assumed to be stationary (or static) so that the crack tip energy release rate never reaches the material specific critical value. Increase in the crack tip energy release rate is observed during cooling and its relationship with accumulation of TRIP due to cyclic transformation is studied.
A finite element analysis of crack growth is carried out in an in nite center-cracked shape memory alloy plate subjected to thermal variations under plane strain mode I constant applied loading. Crack is assumed to propagate when the energy release rate reaches a material specific critical value. The virtual crack growth technique is employed to calculate the energy release rate, which was shown to increase an order of magnitude at constant applied loading as a result of phase transformation induced by thermal variations.<sup>1</sup> A fracture toughening is observed associated with the energy dissipated by the transformed material in the wake of the growing crack and its sensitivity over key thermomechanical parameters is presented.