Modelling of acousto-plastic effect in TiNi alloy

An acousto-plastic effect expressed in a drastic flow stress change under ultrasonic vibrations was simulated for the TiNi alloy in the range of martensitic transformation temperatures. The structure-analytical theory of strength was used for the computer simulation. It was assumed that the main factors of the ultrasound effect on the flow stress are a temperature increase and an oscillating stress of the ultrasound wave. Diagrams of the quasistatic deformation of a TiNi specimen at different temperatures corresponding to the martensitic, austenitic and two-phase states were calculated. The temperature is taken to change linearly: abruptly rise after vibration start and smoothly fall after vibration finish. It was found that the temperature change may lead either to the rise or to the drop of the flow stress depending on the material structure state. An oscillating stress applied during the quasistatic deformation leads to material softening during loading and to the rise of the stress during unloading. At joint action of oscillating stress and temperature variation in the course of the quasistatic deformation one can observe both material softening and a complicated flow stress evolution: a decrease of the stress followed by its rise. All results are consistent with the available experimental data on the action of ultrasound on TiNi shape memory alloys.