Development of a torsional theory for radially functionally graded porous shape memory alloy circular bars

2021 ◽  
pp. 1045389X2110530
Author(s):  
Nguyen Van Viet ◽  
Wael Zaki
Keyword(s):  
Shape Memory Alloy ◽  
Constitutive Model ◽  
Shape Memory ◽  
Fem Simulation ◽  
Phase Evolution ◽  
Functionally Graded ◽  
High Porosity ◽  
Porous Shape Memory Alloy ◽  
Circular Bar ◽  
Good Agreement

This work develops a novel torsional theory for a radially functionally graded (FG) porous shape memory alloy (SMA) circular bar. Prior to the theoretical development, the effective three-dimensional (3D) phenomenological constitutive model for SMAs with high porosity is proposed. To help derive successfully the theory, the pure shear-driven material parameters in the effective model are expressed in the cubic polynomial. Subsequently, the torsional theory for radially FG porous SMA circular bar is derived considering the evolution of effective phase evolution in the bar. This phase evolution consideration guarantees the accuracy of the developed theory. Indeed, the soundness of effective constitutive model is confirmed by 3D finite element method (FEM) simulation of porous SMA structure in Abaqus using the well-established ZM’s model for dense SMAs. Specifically, the simulating results in terms of the shear stress-shear strain response obtained from two prediction methods considering a variation of SMA volume fraction and temperature are in good agreement. Furthermore, accuracy of torsional theory is validated by 3D FEM simulation using the 3D effective constitutive model with a good agreement observed. It is found that the superelasticity of the bar can be enhanced by increasing the gradient index and decreasing the temperature and wall thickness.

An Analysis of Phase Transformations for Porous Shape Memory Alloy Considering Hydrostatic Stress

2011 ◽  
Vol 675-677 ◽  
pp. 1151-1154
Author(s):  
Bing Fei Liu ◽  
Guan Suo Dui ◽  
Yu Ping Zhu
Keyword(s):  
Shape Memory Alloy ◽  
Spherical Shell ◽  
Shape Memory ◽  
Volume Fraction ◽  
Hydrostatic Stress ◽  
Constant Thickness ◽  
Composite Sphere ◽  
Porous Shape Memory Alloy ◽  
Applied Stresses ◽  
Good Agreement

According to micromechanics, consider the porous shape memory alloy (SMA) as a composite-sphere model. Isolate a constant thickness spherical shell which is composed of SMA, and is traction free on its inner surface and subjected to the uniform hydrostatic pressure and the deviatoric stress on its external surface. Then, a constitutive model for porous SMA considering hydrostatic stress is proposed by elasticity solution. The stress distribution of the spherical shell was calculated. Corresponding to different applied stresses, the spherical shell is divided into different regions of pure austenite, pure martenite, and austenite/martensite mixture under isothermal circumstances. The martensite volume fraction is then obtained. The predicted results have been compared with the obtained experimental data by Zhao and Sia Nemat-Nasser. It shows that the modeling results are in good agreement with the experiments and the initial phase transition point for porous SMA is lower than the dense SMA.

On size-dependent bending behaviors of shape memory alloy microbeams via nonlocal strain gradient theory

2021 ◽  
pp. 1045389X2098699
Author(s):  
Bo Zhou ◽  
Zetian Kang ◽  
Xiao Ma ◽  
Shifeng Xue
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Functionally Graded ◽  
Strain Gradient Theory ◽  
Gradient Theory ◽  
Size Dependent ◽  
Material Length Scale Parameter ◽  
Material Length Scale ◽  
Material Length ◽  
Nonlocal Strain Gradient

This paper focuses on the size-dependent behaviors of functionally graded shape memory alloy (FG-SMA) microbeams based on the Bernoulli-Euler beam theory. It is taken into consideration that material properties, such as austenitic elastic modulus, martensitic elastic modulus and critical transformation stresses vary continuously along the longitudinal direction. According to the simplified linear shape memory alloy (SMA) constitutive equations and nonlocal strain gradient theory, the mechanical model was established via the principle of virtual work. Employing the Galerkin method, the governing differential equations were numerically solved. The functionally graded effect, nonlocal effect and size effect of the mechanical behaviors of the FG-SMA microbeam were numerically simulated and discussed. Results indicate that the mechanical behaviors of FG-SMA microbeams are distinctly size-dependent only when the ratio of material length scale parameter to the microbeam height is small enough. Both the increments of material nonlocal parameter and ratio of material length-scale parameter to the microbeam height all make the FG-SMA microbeam become softer. However, the stiffness increases with the increment of FG parameter. The FG parameter plays an important role in controlling the transverse deformation of the FG-SMA microbeam. This work can provide a theoretical basis for the design and application of FG-SMA microstructures.

A constitutive model for Fe-based shape memory alloy considering martensitic transformation and plastic sliding coupling: Application to a finite element structural analysis

2012 ◽  
Vol 23 (10) ◽  
pp. 1143-1160 ◽  
Author(s):  
Walid Khalil ◽  
Alain Mikolajczak ◽  
Céline Bouby ◽  
Tarak Ben Zineb
Keyword(s):  
Finite Element ◽  
Phase Transformation ◽  
Structural Analysis ◽  
Shape Memory Alloy ◽  
Constitutive Model ◽  
Shape Memory ◽  
Internal Variables ◽  
Thermomechanical Loading ◽  
Proposed Model ◽  
Numerical Tool

In this article, we propose a finite element numerical tool adapted to a Fe-based shape memory alloy structural analysis, based on a developed constitutive model that describes the effect of phase transformation, plastic sliding, and their interactions on the thermomechanical behavior. This model was derived from an assumed expression of the Gibbs free energy taking into account nonlinear interaction quantities related to inter- and intragranular incompatibilities as well as mechanical and chemical quantities. Two scalar internal variables were considered to describe the phase transformation and plastic sliding effects. The hysteretic and specific behavior patterns of Fe-based shape memory alloy during reverse transformation were studied by assuming a dissipation expression. The proposed model effectively describes the complex thermomechanical loading paths. The numerical tool derived from the implicit resolution of the nonlinear partial derivative constitutive equations was implemented into the Abaqus® finite element code via the User MATerial (UMAT) subroutine. After tests to verify the model for homogeneous and heterogeneous thermomechanical loadings, an example of Fe-based shape memory alloy application was studied, which corresponds to a tightening system made up of fishplates for crane rails. The results we obtained were compared to experimental ones.

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