Sharif Digital Repository

Shape memory alloys (SMA) exhibit a number of features which are not easily explained by equilibrium thermodynamics, including hysteresis in the phase transformation and ‘‘reverse’’ shape memory in the high symmetry phase. Processing can change these features: repeated cycling can ‘‘train’’ the reverse shape memory effect, while changing the amount of hysteresis and other functional properties. These effects are likely to be due to formations of localised defects and these can be studied by atomistic methods. Here we present a molecular dynamics simulation study of such behaviour employing a two-dimensional, binary Lennard–Jones model. Our atomistic model exhibits a symmetry breaking,... 

This thesis aims to introduce a numerical method for investigating the appropriate arrangement of visco-pseudo-elastic dampers applicable to shell and plate structures under large deformation. These passive dampers are considered as viscoelastic layers and discrete shape memory alloy (SMA) wires in which this combination improves their overall efficiency and reduces their drawbacks. Also, the main advantages of these dampers are discussed during some illustrative problems. The current finite element formulation is based on an incremental updated Lagrangian (UL) approach along with the Newmark's integration technique. In the layerwise shell element, the Mindlin-Reissner theory is adopted in... 

The use of shape memory alloys (SMAs) has been seriously considered in earthquake engineering due to their unique capabilities, such as the ability to tolerate cyclic deformations, recentering, and dissipating energy. Consequently, the effect of hybrid connections (SMA and steel based beam-column connection) in asymmetric structures is investigated in this research.A 4 story steel special moment resisting frame with 0%, 10%, and 20% eccentricities have been considered to find out the performance of a novel beam-column connection in reducing the seismic response of structures such as maximum drift ratio and residual displacement. In order to find out this issue first, the symmetric model has... 

Bio-based shape memory polymers with fast-response have high potential for use in medical applications. In this study, biocompatible and biodegradable nanocomposites based on shape memory polyurethane acrylates (SMPUA)/cellulose nanocrystals (CNC), were synthesized by in-situ polymerization. CNC is a natural and renewable nanoparticle that has been considered for medical applications due to its excellent mechanical and biological properties and surface chemistry. At the first phase of this study, in order to synthesize UV-curable shape memory polyurethane acrylate, polycaprolactone diol (PCL-Diol), hexamethylene diisocyanate (HDI) and hydroxyethyl methacrylate (HEMA) were used as an reactive... 

The current research focuses on preparing conductive hydrogels with combined shape memory and actuating under the effect of external stimuli. Two studies were conducted in which hydrogels simultaneously showed shape memory and actuating behaviors. The magnetic carrageenan-based double network hydrogels were prepared in the first part. The presence of magnetic nanoparticles not only strengthened the mechanical properties, but also induced shape memory properties under a magnetic field. These hydrogels had good electrical conductivity and showed successful performance as strain sensors. The hydrogels performed well in simple and complex shape memory experiments in response to the temperature....