Development of martensite transformation kinetics of NiTi shape memory alloys under compression

Abstract

Martensite transformation kinetics is the principal factor underlying the constitutive model of shape memory alloys (SMAs). Therefore, the transformation kinetics formulation is essential for predicting the thermo-mechanical behavior of SMAs. In this work, we show that previous models, including the Brinson model, which is the most widely used onedimensional phenomenological model, cannot describe the compressive thermo-mechanical behavior of SMAs due to the tension-compression asymmetry. In addition, a new transformation kinetics is derived which precisely predicts the compressive behavior of SMAs based on the following experimental results: (1) drastic variation exists during transformation, and the plastic deformation is not ignored in compression; (2) the plastic deformation increases in proportion to the volume fraction of detwinned martensite; and (3) the critical stress-temperature slopes largely increase and the slopes of the start and finish temperatures of each phase are not identical to each other. Finally, numerical calculations using the suggested transformation equation are conducted to verify its capability through a comparison with the compressive experimental results. According to the results, the suggested transformation kinetics can predict the thermo-mechanical behavior of SMAs more precisely under compression.

Cross-linked ethylene-vinyl acetate – poly(urethane) temperature-memory composite actuator

“…Moreover, the lower strain obtained in shape memory experiments can be compared to the maximum strain reported in the shape memory alloys, such as NiTi 6%-8%. 52,53…”

“…Moreover, the lower strain obtained in shape memory experiments can be compared to the maximum strain reported in the shape memory alloys, such as NiTi 6%-8%. 52,53 The effect of the cycling temperature is also presented in Figure 8. The cycles were conducted between 40 to 75 C for all the samples, and pre-heating treatments at lower temperatures (60 and 70 C) were performed to improve the fixing of the shifting shape.…”

Functional graded NiTi manufactured with powder bed fusion

“…The stress-strain curves with the phase proportions at testing temperature are shown in Fig. 8 and exhibit typical compression behavior associated with shape memory and superelasticity [32]. Higher energy densities ( ≥ 90 J/mm 3 ) lead to shape memory properties due to the elevated transformation temperature while testing at room temperature.…”

Simulation of Shape Memory Alloy (SMA)-Bias Spring Actuation for Self-Shaping Architecture: Investigation of Parametric Sensitivity

“…Mechanical modeling of SMA-bias coil spring actuation has been intensively explored in various aspects [18,20,21]. Based on previous work, a concise expression of the modeling to estimate stroke and output force during the initial stage of actuator design was developed.…”