Study of Mechanical Behaviour in Shape Memory Alloys Through Adiabatic Thermal Emission and Acoustic Emission Technique

Abstract

Tensile tests were carlied out on con~mercialty available NiTi alloys in order to study their mechamcal d~aracterirtics up to tlie onsct of thc superelasticity effect. Two realtimc supporting techniques, adiabatic thermal emission and acoustic emission, were employed. Thermal ekssion 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 m a i n the same, compared results from these two techniques could enhance the knowledge of material behavio~ir. A difficulty lies however in the choice of experimental conditions apt to 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 in particular a sufficient loading time to allow stresses distribution. Results are promising as a preliminary assessment and could prospectively provide a persuasive quality discrimination.

Martensite transformation bands studied in TiNi shape memory alloy by infrared and acoustic emission techniques

“…In the meantime, not so significant AE signals were recorded at the stage of the advanced transformation, being the final one of the SMA loading. It confirms that the strong AE signals are created by a sudden change in the material or process state, not by the same process, even if the process develops very fast [17][18][19][20][21]. Moreover, looking at Fig.…”

“…One of the reasons is that it is still difficult to explain the acoustic emission data in terms of the fundamental understanding of the phase transformation mechanisms, however, different approaches have been published, e.g. [17][18][19][20][21].…”

Suppression of acoustic emission during superelastic tensile cycling of polycrystalline Ni50.4Ti49.6

“…Near-equiatomic Ni-Ti polycrystalline alloys have been previously investigated using AE [45][46][47], but under a limited number of mechanical loading/unloading cycles, and without location of AE, which permits eliminating extrinsic contributions that arise near the grips of the mechanical testing machine. Dunand-Châtellet and Moumni assigned their total AE recorded during mechanical cycling to dislocation formation and microcracking [45], whereas Pieczyska et al assigned their total AE recorded during one single cycle to the B2-B19' transition [46], despite AE being detected before the plateau in the stress-strain curve that marks the occurrence of the martensitic transition [2,[48][49][50], suggesting that this AE could arise from the mechanical testing machine.…”