Bulk metallic glasses are a new type of advanced materials. They are characterized by their topologically disordered
atomic structures. The lack of long-range translational symmetry in the atomic arrangement in bulk metallic glasses
contributes to a range of unique and outstanding mechanical properties. For example, the yield strength of metallic
glasses can be as large as twice that of corresponding crystalline alloys. However, the major issue to hinder metallic
glasses application is the apparent brittleness. Unlike crystalline alloys, metallic glasses show abrupt failure with zero
macroscopic plasticity. Various methods are being investigated in material engineering to improve the plasticity of bulk
metallic glasses. The most recent progress is to develop shape memory bulk metallic glass composites, a combination of
metallic glass and shape memory alloy. The large stress-induced transformation strain in shape memory alloy leads to the
increase in the plasticity of the new composite material. The stress-strain behaviour of shape memory bulk metallic glass
composites was investigated in this paper by using the finite element method. A unit cell model, which includes shape
memory alloy phase and metallic glass phase, under uniaxial tension were numerically simulated. The effects of phase
volume fraction, transformation stress and strain on the stress-strain behaviour of this new composite material were
examined in this research.
The fatigue failure of a super-elastic NiTi alloy was observed by uniaxial stress-controlled cyclic tests. During the cyclic
loading a hysteresis loop with a varied but stabilized size after certain cycles was obtained, which is similar to plastic
shakedown. The material exhibits unique brittle fracture with a large transformation strain. The fatigue life of the
material greatly depends on the applied peak nominal stress, the nominal stress amplitude and the mean nominal stress. A
relation between the dissipation energy at the stabilized stage of cyclic loading and the number of cycles at failure was
derived from the experimental results. Based on the obtained experimental results, a uniaxial fatigue failure model based
on the energy approach was proposed to predict the fatigue life. It was shown that the proposed model provides good
predictions to the uniaxial fatigue lives of super-elastic NiTi alloys with different types of cyclic stressing.
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