Papers by Keyword: SMA

Abstract: The welding of shape-memory alloys is a challenge due to the fact that there are numerous compositions and because the properties are greatly influenced by the temperature. Of the multitude of shape-memory alloy systems, the most popular and widely used is the Ni-Ti system. Pulsed laser welding is a solution used for joining NiTi shape-memory alloys, having the advantage of localized heating and the possibility to adjust the welding parameters to obtain optimal properties. NiTi wires were welded using a 500W pulsed laser equipment by varying the current intensity. Thus, laser melted spots were made on a NiTi wire, changing only the value of current intensity in 20A increments in the range of 100-200A. The results analyzed by scanning electron microscopy showed, as expected, that as the current intensity increased, the spot size and the heat affected zone (HAZ) increased for each spot. Differential scanning calorimetry revealed that the martensitic transformation is still present in all samples, but with a decrease in peaks related to the phase transformation, as well as an increase of the temperature (8-12 °C), compared to the base material.

Abstract: Embedding smart materials in the composite to enhance mechanical strength have become a research hotspot owing to their unique properties. The present research also focus on novel way to fabricate composite by embedding Shape Memory Alloy (SMA) wire and montmorillonite (MMT) nanoclay by varying clay concentration (0-7 wt.%). The extent of dispersion of nanoclay in epoxy resin was studied using Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD). Fabricated samples were examined for tensile, flexural and impact characteristics. Scanning Electron Microscopy (SEM) was used to study the adhesion, delamination and damage occurred within the composite due to tensile loading. Results shows that the tensile strength, flexural strength and impact energy of SMA/MMT/glass/epoxy composite was improved by 23%, 21% and 57% respectively, when it was compared with composite with glass/epoxy composite.

Abstract: Deep cryogenic treatment (DCT) is industrially applied to improve the wear resistance characteristics of tool steels. However, on non-ferrous metals, the knowledge about the obtained characteristics after DCT is limited. The purpose of this work was to investigate how DCT affects the properties and the behavior of the Cu-14Al-4Ni alloy treated at different times and after thermomechanical cycling was performed. In the present investigation, there was performed a comparative experimental analysis of the transformation temperatures, microhardness and shape recovery capacity of the alloy obtained by smelting, treated by DCT and thermomechanically cycled. The DCT provided the stabilization of the martensitic phase β'₁ and, consequently, the stabilization of the phase transformation temperatures and the shape recovery capacity of the shape memory effect of the alloy, increasing the alloy life.

Abstract: Finite strain elastoplastic J₂-flow equations are established toward the purpose of automatically, accurately simulating pseudo-elastic effects of SMAs. The uniaxial responses derived from these equations in each loading-unloading cycle exactly produce a closed stress-strain curve of any given shape. Then, any given test data for pseudo-elastic hysteresis loops of SMAs may be accurately fitted by means of a new technique for combining linear spline functions into a unified, smooth interpolating function, in a sense with no need to identify any unknown parameters.

Abstract: High damping capacity materials present an increased interest in many applications were vibration and noise reduction is absolutely necessary. Metallic materials with a high internal friction (IF) are becoming valuable because of them usual mechanical properties that fulfill the damping capacity in applications. Some of the shape memory alloys present a huge damping capacity during the solid state transformation (M↔A) based on the re-orientation and accommodation of the material structure. Iron based shape memory alloy present the best advantages for industrial application as dumpers in different areas. Beside civil construction domain these materials can cover also applications in automotive industry as shock impact absorbers for low velocities as protection for engine parts and also for noise reduction. By these means in this article we analyze FeMnSi+Al alloy with a new chemical composition obtained through classical melting method in Ar controlled atmosphere.

Abstract: Recycling asphalt pavement creates a cycle of reusing materials that optimizes the use of natural resources. Reclaimed asphalt pavement (RAP) is a useful alternative to virgin materials because it reduces the need to use virgin aggregate. This paper is concerned with the current issue of using RAP in Stone Mastic Asphalt (SMA). SMA is a wearing course, which is especially stable and durable. It describes the effects of application of rejuvenators on properties of asphalt binders. These rejuvenation additives restore the physical and chemical properties of aged binders. In addition, the aged asphalt binder with rejuvenators applied was subjected to a short-term laboratory aging using the RTFOT (Rolling Thin Film Oven Test). To assess the binder properties, both the standard empirical tests and more advanced functional tests (dynamic shear rheometer and bending beam rheometer) have been performed. Last part of the paper provides an evaluation of the individual rejuvenation additives. Based on the results it can be concluded that a positive change in properties of aged asphalt binder obtained from a modified RAP (from SMA) after applying all the rejuvenators has been proven. The effect of the rejuvenators during the manufacturing process and laying has been verified.

Abstract: This paper proposes one of the possible techniques for interacting for shape memory alloy (SMA) actuator based tactile display, which can act as demonstrator devices. This work is focused on developing a model of a pair of antagonistic high strain SMA tension actuators with independent control of force and displacement. The technology employed utilizes two Flexinol 100 micron heat actuated wires of Titanium-Nickel (NiTi) shape-memory alloy which contract when heated under pre-stress and produces up to 5% strain recovery. This phenomenon, which provides a unique mechanism for actuation, is associated with the unique interaction between the martensite and austenite crystal structures of the SMA. Physical measurements of the behaviour of the actuator elements were performed using a laser displacement sensor to verify the fidelity of response to software commands, and to measure step response to pulse-width modulated (PWM) current control at different frequencies and duty cycles. Results yielded high accuracy across a wide range of frequencies and duty cycles, proving the SMA actuation technique has potential to present and convey useful tactile information of surface deformation for virtual environment applications.

Abstract: This paper conducted an experiment to research flexural property of SMA unbounded prestressed box beam ,which applied the Shape Memory Alloy (SMA) at martensite state as externally prestressing tendons, and then through heating the SMA bars fully anchored on the beam with cracks by electrifying motivation, drove SMA to produce the “recovery stress” because of transformation, to study the effects of this stress on the deflection and crack width of concrete box-beam on work ,to study the recovery ability of SMA bars ,and to provide basis for the application of the SMA bars to bridge strengthening.

Abstract: As a new type of smart material, shape memory alloy (SMA) is widely used in the aerospace, biomedicine, civil engineering and so on due to its unique mechanical and physical properties such like the shape memory effect, pseudoelasticity and good biological compatibility. This paper investigates the numerical simulation and application of the SMA component: A SMA strip, which has been pre-curved in the room temperature and is expected to extend upon heating and shorten on cooling along the curve. According to the investigation of the thermal respond of the SMA strip component, it can be seen that the temperature of the phase transformation can increase with the initial transformation strains and the process of the phase transformation in the boundary is more complex due to the complicated stress state.

Abstract: The gradation curve of SMA asphalt mixture directly affect the performance of road. Before the optimization gradation of asphalt mixture material, the primary material of asphalt mixture gradation curve must be determined in the plan. Through the orthogonal experiment method, the full collision combination of three levels and three key factors of asphalt mixture effect, that will be taken into account. Through the 9 groups of grading curve experiment, the expected results of 27 groups in the general experiment will be achieved. Comparative analysis of advantages and disadvantages with the properties of the mixture road 9 group grading curve corresponding, can get the recommended gradation curve range. Comparing with the normal grading curve primary method, through the orthogonal experiment method in primary SMA asphalt mixture curve can reduce the testing time, reduce material’s artificial waste and environmental pollution.