A Semi-Empirical Model for Fracture Energy Evaluation of a Ni2MnGa Magnetic Shape Memory Alloy
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Ni 2 MnGa magnetic shape memory alloys (MSMAs) experience the shape memory effect due to magnetic field-induced or mechanical stress-induced microstructure reorientation. Crack nucleation and growth in Ni2MnGa is impacted by the alloy's evolving twin microstructure under magneto-mechanical loading conditions, eventually hampering its function in applications. This study reports on the evaluation of the fracture energy of a Ni2MnGa alloy under various magneto-mechanical loading conditions. The fracture energy of the alloy was evaluated through Vickers microindentation experiments that allowed the investigation of crack nucleation and growth under various magneto-mechanical loading conditions. The length of the cracks and the dimensions of the microindentation impressions were used to develop a semi-empirical relationship that predicts the fracture energy of the alloy as a function of magneto-mechanical loading conditions. The results confirm that the magnetic field (particularly the transversely applied magnetic field) facilitates crack growth, decreasing the fracture energy, while axial compressive stress impedes crack growth, increasing the fracture energy of the alloy. The proposed empirical relationship for the evaluation of fracture energy helps identify the magneto-mechanical loading conditions that are least conducive to fracture initiation and growth in MSMAs.
