Transformation and Plasticity of Shape Memory Alloy Structures: Constitutive Modeling and Finite Element Implementation

Journal of Intelligent Material Systems and Structures

2023

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Shape memory alloys (SMAs)—if trained properly—can induce two-way shape memory effect which is applicable in actuator design using SMAs. In this study, a three-dimensional phenomenological model is proposed for SMAs within the framework of irreversible thermodynamics in order to predict the training process under cyclic loading and the induced two-way shape memory effect. In this regard, transformation and permanent strains are considered as internal variables and Helmholtz free energy function is introduced using several material parameters accounting for elastic, transformation and permanent deformation mechanisms. In order to demonstrate the capabilities of the proposed model, we first compare the model results with several experimental results and prove that the current model fits well with various experiments under cyclic loading as well as two-way shape memory effect. In addition, the capabilities of the present model in predicting the two-way shape memory effect, degradation effects, evolution rate, stabilization of permanent strain as well as multiaxial loading have been carefully examined through parametric studies. It is concluded that the present model is able to predict the training process from the initial cycles to stabilization and two-way effect for different materials and conditions.

Section: Numerical Solutionmentioning

confidence: 99%

Constitutive modeling for the training process of two-way shape memory effect under thermal cyclic loading

Hakimi

Journal of Intelligent Material Systems and Structures

2023

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“…R is the radius of the phase change surface in this relation. Using this model and its numerical algorithm, the UMAT subroutine in ABAQUS software (Ashrafi, 2020) can be used to study the effects of SMA with different pre-strains in various structures.…”

Section: Constitutive Equationsmentioning

confidence: 99%

Self-healing performance of a microcapsule-based structure reinforced with pre-strained shape memory alloy wires: 3-D FEM/XFEM modeling

Taheri-Boroujeni

Journal of Intelligent Material Systems and Structures

2023

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Combination of microcapsules and shape memory alloys (SMAs) is one of the promising self-healing mechanisms. Although there are several parameters which affect the performance of such structures, limited studies are performed on this combined healing mechanism. In this work, we study the performance of such a composite structure using a 3-D finite element and extended finite element model consisting of matrix, glass microcapsule, healing agent, and Ni-Ti SMA wire. After examining the results, the effect of shape memory alloy wires on increasing the maximum fracture stress was observed. Moreover, the effect of radius of shape memory alloy wires, initial crack location, thickness ratio and volume fraction of microcapsules, and interface strength on ultimate fracture stress are investigated. Also, as a key parameter in self-healing performance, the crack opening distance decreased from 5 to 0.008 μm using 0.5% volume fraction of shape memory wires without pre-strain. In the case that the wires have a pre-strain of 1%, this value reaches almost zero and a compressive stress is induced between fracture surfaces which can enhance the healing process and adherence of healing agent.

“…In this paper, in order to simulate the pseudoelastic and plastic behavior of SMA sheets, we utilize the constitutive model developed by 7,29 which also considers the difference between elasticity of austenite and martensite phases.…”

Section: Modelingmentioning

confidence: 99%

Stress concentration in shape memory alloy sheets with circular cavities: Effects of transformation, saturation, and plasticity

Hosseini

The Journal of Strain Analysis for Engineering Design

2022

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The analysis of stress concentration in geometrically heterogeneous smart structures is of great importance. In this study, by utilizing a recent constitutive model which considered both transformation and plasticity of shape memory alloys (SMAs), the stress concentration factor (SCF) in plates with circular cavities is investigated and the effect of phase transformation, saturation, and plasticity which may occur locally is studied. The results show that the conversion of the austenitic phase to the martensite leads to a reduction in SCF. After saturation of phase transformation at the stress concentration point, the SCF increases until the entire sheet enters the martensite phase. In the example under study, the SCF reaches 5.8 which is greatly higher than the elastic SCF. By entering the plastic region locally, the SCF reduces. Also, the modeling of sheets with more than one cavity has been done. It is concluded that extra hole, as a stress relief method, has a stronger effect on decreasing maximum stress concentration of shape memory alloys (considering transformation and plasticity) compared to purely elastic stress concentration studies.