Sharif Digital Repository

Magnetic Shape Memory Alloys (MSMAs) are a category of active materials which can be excited by magnetic field. These alloys have been used in sensor and actuator applications recently. MSMAs posses special properties such as large magnetic field-induced strains (up to %10) and high actuation frequency (about 1kHz), while ordinary Shape Memory Alloys can’t act in frequencies above 5Hz due to the time involved with heat transformation. In this thesis, MSMAs are modeled by means of incremental modelling which is a useful method in analysis of nonlinear behaviour of materials. Furthermore, stress-strain curve of MSMA is approximated using an analytical expression whose parameters can simply be... 

Shape memory alloys (SMAs) are metallic materials that have unique properties, including shape memory effects, superelastic effects, and high damping characteristics. Recovery of large deformation and capability of energy dissipation during mechanical loading-unloading cycles are special properties of superelastic effect of shape memory alloys. Due to these distinctive macroscopic behaviors, not present in most traditional materials, SMAs are the basis for innovative applications like devices for protecting buildings from structural vibrations. This paper presents a numerical investigation aimed at evaluating the improvements achievable through devices for passive seismic protection of... 

Various types of passive energy dissipating systems have been introduced for controlling the seismic response of structures during the last few decades. A number of these control devices have been practically implemented in different structures all over the world. Shape Memory Alloy (SMA) is among those passive control systems that have attracted a large attention due to its innate features, i.e., recovering the induced residual strains upon unloading (superelastic effect) or by heating (shape memory effect).This study investigates the seismic behavior of a set of steel structural models with different number of stories and eccentricities equipped with a type of fixed SMA connections. In the... 

Shape memory alloys (SMAs) are a type of smart materials which have unique features known as pseudo-elasticity, one-way and two-way shape memory eects. The interest in the mechanical behavior of SMAs is rapidly growing with the increasing number of potential industrial applications. The origin of SMA material features is a reversible thermo-elastic martensitic phase transformation between a high symmetry, austenitic phase and a low symmetry, martensitic phase. In most applications, SMAs experience general non-proportional thermo-mechanical loads. Thus, according to experimental observations, the so-called variant reorientation should be considered in the constitutive model development.... 

NiTi is known as a most important material for manufacturing implants and other medical devises duo to its shape memory and super elasticity properties, high energy damping and high corrosion resistance.In this project the possibility of producing nano structured NiTi implant with high porosity was investigated. For reaching to nano scale mechanical alloying process was done on Ti and Ni powder as row materials. Mechanical alloying process and the possibility of reaching nano structure or amorphous phase was investigated. Space holder technic was used for reaching a porous structure. Sintering process was planned in a way to inhibit grain growth as much as possible. The samples sintered in... 

Abstract Wire rope isolators are certain types of isolators that due to simplicity of structure and low maintenance costs are taken into consideration in various industries.A variety of different geometries and different features are provided so far that each have their own advantages and disadvantages. The main point is that in all cases they have large-scales. Therefore the usage of them in micro applications is not practical.Shape memory alloys are a class of materials with specific properties such as superelasticity and have inherent hysteresis. It is expected to achieve smaller dimensions suitable for use in micro-applications if they are used in the manufacturing of wire rope... 

Application of Shape Memory Alloys (SMAs) as a means for vibration suppression of structural systems has extensively been explored in recent years. Recovering the applied residual strain upon unloading (super-elasticity) or by heating (shape memory effect) at different temperature ranges are two inherent features of SMA materials that have gained most attention. In this work, the seismic behavior of a proposed beam-column semi-rigid end-plate connection that has been equipped with both steel and SMA studs in austenite phase is investigated. A number of 3-D steel MRF structural models with 6,9 and 12 number of stories are considered. These structural models are subjected to bi-directional... 

In this research to solve the problems related to titanium implants, a new type of dental implant was designed and fabricated by using shape memory and pseudoelasticity properties of porous nitinol alloys. The elastic modulus of this implant (equal to 0.8 GPa) is similar to the cancellous jaw bone (equal to 0.3-1 GPa) which causes a normal distribution of stress and prevents bone resorption. The current approach is use of radius variation to facilitate implant surgery. These radial changes are created by using one way shape memory effect. First, the implant enters the jaw cavity by decreasing the radius and after reaching the body temperature and restoring the initial shape, the radius of...