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Homogenization of Porous Shape Memory Alloys Using Monte Carlo Technique
M. Heidary, S.h. Hoseini, Sh. Faroughi,
Volume 19, Issue 8 (8-2019)
Abstract
In this paper, the superelastic response of porous shape memory alloys (SMAs) containing spherical pore shape with pore volume fraction between 5% and 40% has been considered. Using digital images processing, the distribution of pores in 2D images of porous NiTi SMA has been extracted. In this method, the 3D distribution of pores has been appraised with the Monte Carlo method and 3D porous SMA models have been established. To investigate the superelastic behavior of shape memory alloys, the Lagoudas’s phenomenological model was used, in which a phase transformation function was used. To homogenize the porous SMAs, the Young’s modulus and the phase transformation function have been assumed to be a function of the pore volume fraction. Based on the proposed constitutive model a numerical procedure was proposed and executed by the commercial finite element code ABAQUS with developing a user material subroutine. The numerical results show that the Young’s modulus and the phase transformation function are the approximately linear function of the pore volume fraction; furthermore, these results demonstrate the accuracy of the proposed homogenization method to predict the superelastic behavior of porous SMAs.

Matrix Reinforcement Coefficients Models for Fracture Investigation of Orthotropic Materials
H. Manafi Farid, M. Fakoor,
Volume 19, Issue 11 (11-2019)
Abstract

In this paper, the new theory has been3 proposed to investigate the fracture behavior of cracked composite materials. Conforming to this theory, crack is created and distributes in the isotropic matrix. Therefore, contrary to the previous theories related to fracture mechanics of these types of material, which assumes that crack growth occurs in anisotropic homogenous material, the new theory assumes that crack growth occurs in the isotropic matrix, which is affected by fibers in the composite structure of the material. In this approach, fibers are considered as isotropic matrix reinforcements and the reinforcement effects are defined as coefficients in stress state of the isotropic matrix. The coefficients are called reinforcement factors and derived via three different approaches to study the arbitrary crack in 2D materials. Quantifying the reinforcing effects of fibers are conducted when tension across and along fibers and shear loadings exerted on the body. The three methods demonstrate that the reinforcement factors depend on elastic properties, crack growth location and the crack and fiber orientations. However, the method, derived from the micro-mechanic approach, displays their dependence on the fiber volum ratio. Comparing the results of these cofficients with the existing fracture theories illustrates the efficiency and ability of the reinforcement factors in investigation and explanation of the fracture behavior of orthotropic materials.In this paper, the new theory has been3 proposed to investigate the fracture behavior of cracked composite materials. Conforming to this theory, crack is created and distributes in the isotropic matrix. Therefore, contrary to the previous theories related to fracture mechanics of these types of material, which assumes that crack growth occurs in anisotropic homogenous material, the new theory assumes that crack growth occurs in the isotropic matrix, which is affected by fibers in the composite structure of the material. In this approach, fibers are considered as isotropic matrix reinforcements and the reinforcement effects are defined as coefficients in stress state of the isotropic matrix. The coefficients are called reinforcement factors and derived via three different approaches to study the arbitrary crack in 2D materials. Quantifying the reinforcing effects of fibers are conducted when tension across and along fibers and shear loadings exerted on the body. The three methods demonstrate that the reinforcement factors depend on elastic properties, crack growth location and the crack and fiber orientations. However, the method, derived from the micro-mechanic approach, displays their dependence on the fiber volum ratio. Comparing the results of these cofficients with the existing fracture theories illustrates the efficiency and ability of the reinforcement factors in investigation and explanation of the fracture behavior of orthotropic materials.


Thermoelastic Time-Dependent Creep Analysis of a Rotating Thick-Walled Cylinder Made of Magneto-Electro-Elastic Materials
M. Saadatfar,
Volume 19, Issue 11 (11-2019)
Abstract
An analytical solution for the problem of time-dependent stress redistribution of a piezomagnetic rotating hollow cylinder subjected to an axisymmetric thermo-magneto-electro-mechanical loading is derived for the condition of plane strain. A differential equation containing creep strains is found using the constitutive equations, equilibrium equation and solving heat equation in plate strain. In the first step, eliminating creep strains in the differential equation, an analytical solution for the differential equation is obtained. Then, by adding creep strains and assuming constant thermal conditions, the creep stress rates and electric and magnetic potential are obtained using solving a differential equation. Lastly, the history of stresses, radial displacement, magnetic potential, and electric potential during the time can be obtained using an iterative method. In the numerical examples, the effects of time passing on the structure behavior and the effective parameters such as thermal boundary condition, angular velocity, and electromagnetic boundary condition were investigated comprehensively.

Multi-Mode Bulk Magnetostrictive Actuator for Precision Positioning system
Saeed Ansari, Mohammad Reza Karafi,
Volume 24, Issue 9 (8-2024)
Abstract
This paper presents an innovative bulk magnetostrictive actuator made of a 2V-Permendur alloy rod, capable of functioning across multiple deformation modes—longitudinal, torsional, and flexural. In longitudinal mode, displacement is produced by the Joule effect, where a magnetic field applied along the rod’s axis, generated by a surrounding coaxial coil, induces deformation along its length. Torsional mode activation follows the Wiedemann effect, wherein an electric current passed directly through the rod produces a circumferential magnetic field that twists the material. Additionally, flexural deformation is achieved by a special designed magnetic core that directs a magnetic field to the rod’s surface, producing bending movements along the rod’s length. The actuator operates using controlled DC magnetic fields. Experimental results demonstrated outstanding performance, with maximum displacements reaching 12 microns in longitudinal mode, 7 microns in flexural mode, and 0.15 degrees in torsional mode. Such multi-functional performance highlights the actuator’s potential in precision positioning systems, with particular suitability for advanced microscopy, optical instrumentation, and other fields requiring sub-micrometer positioning accuracy.
 
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