Application of thermal and acoustic emission to mechanical behaviour prediction on shape memory alloys (Ni-Ti)
Tensile tests were carried out at room temperature on a NiTi (49.8%) alloy with a Ms temperature of about 10ºC.
Two real-time supporting techniques, adiabatic thermal emission and acoustic emission, were employed:
Thermal emission allowed to follow local temperature variations in the material due to loading, while acoustic emission was able to detect the propagation of related stress wave. When the material is subjected to repeated loading and provided that test conditions remain the same, results from these two techniques could be compared and enhance the knowledge of material behaviour.
Difficulties lie nevertheless in the choice of experimental conditions suitable for a successful application of both techniques. Thermal emission in fact has to be performed during a quasi-adiabatic test, while acoustic emission has different requirements, needing a sufficient loading time to allow stresses distribution.
Beginning of dislocation movement was observed by thermal emission even at low (1 mm/min.) cross-head speed
Onset of acoustic emission activity corresponds to local temperature inversion
