Modeling of partial transformation cycles of SMAs with a modified hardening function

Abstract

A physical constitutive model is combined with a new function expression that describes the hardening behaviour of Shape Memory Alloys to enable the accurate and efficient prediction of partial transformations during cyclic thermo-mechanical loading. The reversal point memory and the associated memory wipe-out are successfully modeled for single partial transformation Smart Materials and Structures

Effect of shape memory alloys partial transformation on the response of morphing structures encompassing shape memory alloy wire actuators

“…The authors have recently extended the SMA constitutive material model of Lagoudas et al (2012) as extended by Hartl et al (2012), to adopt PT capabilities through a modified hardening function expression (Karakalas et al, 2019a). The modified constitutive model does not require any additional calibration parameters, as well as sophisticated memory tracking, thus showing significant computational advantages and has been experimentally validated for thermo-mechanical behavior of thin SMA wires (diameter of 1.00 mm) under constant mechanical load.…”

“…Karakalas et al (2019a) proposed a modification of the hardening function expression of the original model to account for PT as well as the formation of closed minor loops inside the branches of the major cycle. To achieve that, the authors replaced the value of MVF in equation (2) with two updated values: one for the forward transformation and one for the reverse transformation expression.…”

“…The truss element is adequate for the modeling of the wire SMA actuators considered in the following cases. The previously mentioned, extended constitutive thermo-mechanical model, which encompasses PT capabilities (Karakalas et al, 2019a) is implemented in a developed 1-D User MATerial (UMAT) subroutine (SIMULIA, 2014a). Fully coupled thermal-stress analysis is conducted meaning that there is two-way dependence and coupling in the equilibrium equations between the temperature and stress solution.…”

“…Furthermore, the unique behavior observed during incomplete phase transformation could potentially enhance the design and performance of a wide range of applications entailing SMA materials, such as robots (Rodrigue et al, 2017a), soft actuators (Rodrigue et al, 2017b; Yuan et al, 2018), active needles (Konh and Podder, 2017), morphing radiators (Walgren et al, 2018), and so on. Hence, the aim of the presented work is bifold: (1) to include a previously enhanced and experimentally validated constitutive model for PT into the modeling of SMA actuated adaptive structures (Karakalas et al, 2019a) and (2) to investigate and unravel the potential benefits from the effective modeling of PT on the performance of SMAs actuator configurations. Specifically, we focus our study on the effect of PT operation on the prediction of the target adaptive shape and trajectory, the actuation frequency, the alleviation of the developed actuator stresses, and the required temperature variation.…”

Hysteretic Behavior and Ultimate Energy Dissipation Capacity of Large Diameter Bars Made of Shape Memory Alloys under Seismic Loadings

“…This model uses multiple inelastic mechanisms to organize the exchange between the energy stored and energy dissipated during the deformation history. Karakalas et al [27] proposed a different approach that combines a physical constitutive model with an expression that describes the hardening behavior of SMA.…”