جستجوی مقالات مرتبط با کلیدواژه « Shape memory alloy » در نشریات گروه « مواد و متالورژی »

Self-healing materials can be used as one of the types of smart materials in recovering and repairing equipment and preventing breakdown and fracture of tools. There are several ways to increase the efficiency and repeatability of the self-healing process, one of which is to combine self-healing microcapsules with shape memory alloys. Although several laboratory studies have been performed in this field, this method has not been given the attention it deserves. In this study, an attempt has been made to evaluate the performance of this compound using the finite element simulation method. For this purpose, used glass microcapsule and Ni-Ti SMA within the concrete matrix. After examining the results, the effect of shape memory alloy wires on increasing the maximum fracture stress was quite obvious. By adding two shape memory wires, the fracture tension has increased from 1.93 MPa to 2.08 MPa. Also, the most important effect is to close the crack opening distance in such a way that using two shape memory wires, the distance of the crack opening has decreased from 5 μm to 0.008 μm. Then, the effect of radius of memory alloy wires and thickness ratio and volume fraction of microcapsules on ultimate fracture stress and self-healing performance was investigated. Finally, the effect of interface strength on microcapsule fracture and ultimate fracture stress is evaluated.

The main of this paper is to determine the tensile properties of natural flexible composites. In order to fabricate the composites, the cotton fibers and the latex were used as the reinforcement and matrix, respectively. At the first step, the latex samples were manufactured and tested under tensile loading. In the next step, using the cotton fiber the latex was reinforced and then tested under tensile loading. In addition, the NiTi shape memory alloy (SMA) wire was used to improve the tensile properties of the pure latex and the cotton/latex laminated composites. Therefore, one, two or three NiTi wires were used in the pure latex and cotton/epoxy composites samples. The results of experimental study displayed that in the presence of cotton fiber, the ultimate tensile strength of pure latex was increased from 0.93 to 13.51 MPa. Moreover, it was observed that due to adding one, two or three NiTi wires, the ultimate strength of the pure latex was enhanced almost 70, 500 and 800%, respectively. However, the ultimate tensile strength of the cotton/epoxy laminated composites in the presence of one, two and three NiTi wires was increased almost 2, 20 and 40%, respectively. In addition, comparison of the current research results with the other researchers’ investigations manifests that the cotton/epoxy composites reinforced by NiTi wire, the tensile strength of this flexible material is greater than the tensile strength of natural and artificial leathers.

In this research, the impact behavior of trapezoidal corrugated core sandwich panel reinforced with SMA wires, has been investigated experimentally and numerically. Composite specimens were made to perform tensile, compression and shear tests, and the requisite properties were acquired from the tests. Then, sandwich structures with aluminum corrugated core and 4-layer glass/epoxy composites face-sheets were made using the hand-layup technique. In order to reinforce the composite face-sheets, SMA wires were used in two models: 3 SMA wires without pre strain, 3 SMA wires with 3% pre-strain and 3 SMA wires with 6% pre-strain. The test was performed using a gas gun. To validate and compare the results, the numerical models of the specimens were prepared in LS-Dyna, considering the experimental testing conditions. The results, including ballistic limited velocity and the absorbed energy of the structure were compared and validated by the experimental solutions. The aim of this study was to investigate the effect of adding shape memory alloy wire to reinforce the face-sheets and the effect of pre strain on the ballistic behavior of the sandwich structure. The results shows that presence of the SMA wires and applying pre-strain, leads to increasing energy absorption. Comparing to the wireless sample, the absorbed energy increased about 10%, 22% and 30% in the 3-wires sample without pre-strain, 3-wires sample with 3% pre-strain and 3-wires sample with 6% pre-strain, respectively.

In this research similar joining of NiTi shape memory alloy was studied. For this purpose, NiTi alloy in the form of wires with circular cross section possessing martensitic phase structure at room temperature was used. By utilizing Nd:YAG pulsed laser welding method followed by optimizing its technical parameters, a defectless joint in terms of appearance and metallurgical properties was obtained. In the next step, the effect of various pulsed laser duration time on properties of the obtained similar joint of NiTi was investigated. Moreover, the resultant microstructures were studied using optical microscope (OP) and Scanning Electron Microscope (SEM) equipped with chemical analysis of EDS. Furthermore, the samples prepared under different pulsed laser duration time conditions were characterized by using tensile and micro-hardness tests. Investigating the results of the performed evaluations revealed that higher levels of heat input has resulted in grain growth, dissolution of precipitations as well as reduction in hardness and ultimate tensile strength of the samples in the joint zone.

In this study, boron containing Cu-12wt%Al-4wt%Ni shape memory alloy was prepared by mechanical alloying, pressing and rolling. In this regard, 20 and 40 hour-milled powder was compacted and changed to the bulk alloy by cold pressing, sintering, rolling, heat treatment and quenching. Phase structure, micro-structure, micro-hardness, and transformation temperatures of the prepared samples were studied. It was found that increasing the milling time from 20 to 40 hours led to the rise of the starting temperature of martensite transformation (Ms) from 254 to 264°C. Also, the results showed that adding 0.5 wt.% B decreased the Ms temperature to 211°C and enhanced the micro-hardness from 154 (for the sample without B) to 193 vickers. These alternations were attributed to the fine structure caused by Boron rich precipitations. Moreover, two martenistic transformations with different structures were formed due to the non-homogeneity of the Al concentration in the matrix, which appeared in the form of two different transformation temperatures (Ms) in the Differential Scanning Calorimetry curves.

This research is on the energy absorption level in a metal-fiber laminate reinforced with a ‎shape-memory-alloy under low velocity impact. The parameters of the study are fiber angle, level of pre-strain and ‎position of memory wires in a GLARE reinforced with two memory-wires. In addition, a 200-J Charpy-Impact device was used to exert the impact‏. Taguchi method was used in designing of the experiments for this research and the investigated specimens were constructed based on L16 ‎orthogonal array. During the usage of array, parameters of "fiber angel" and the "pre-strain level of shape-memory wires" were ‎tested in four levels as well as the parameter related to the location of shape-memory-wires, tested in two levels. The scrutinized ‎GLAREs were constructed of 16layers containing 3layers of aluminum.‎ The analysis of variance was performed on extracted data to investigate the effect of changes in parameters on the energy absorption level ‎of laminate. It was found that the changes in following parameters of pre-strain of shape-memory wires, fiber's angel and ‎the location of these wires in laminate, have the influence of 39.12%, 32.13%, 4.56% , respectively, on the energy absorption level of ‎laminate. The variance analysis also proved that changes in energy absorption have confidence level of 92.1%, 90.6% and 71% ‎respectively with the changes in aforementioned parameters.

Nitinol shame memory alloy is very useful in manufacturing of medical implants and stents. Thermal oxidation and TiN coating are of common Nitinol surface modification processes and in return Fenton's oxidation using Fenton reagent is a new approach in modifying the surface of Nitinol for medical applications. To study the effects of this novel process, experimental tests including oxide surface characterization, investigation of corrosion behavior and biocompatibility of the created oxide surfaces in simulated body fluids were performed. Parameters such as temperature and duration of oxidation process were studied. Based on the results, the optimized conditions considering temperature and process duration were determined. Accordingly, Fenton's oxidation process at 65 oC for 24 hours can create an oxide surface without any cracks which produces desirable biocompatibility and corrosion resistance and helps to improve its in vivo performance.

The purpose of this study is controlling the forced vibration of a layered composite cantilever plate embedded with shape memory alloys wires using classical and fuzzy controllers. The governing equations of motion of the composite plate including shape memory alloy wires are calculated using the classical laminated plate theory and the Hamilton principle. The Liang formula is also used to model the thermo-mechanical behavior of the shape memory alloys wire actuators. Then, the free vibration solution for the layered composite plate is calculated using semi-analytical Rayleigh-Ritz method and then is compared with experimental method. Comparison between the obtained natural frequencies of the composite plate and those of published experimental results confirms the accuracy of the purposed modeling and solution. Finally, three controlling system are designed to reduce the amplitude of vibrational displacement of the structure against forced vibrational excitations including PID controller, Fuzzy controller and PID-Fuzzy controller. Finally, the genetic algorithm is used to optimize the gain coefficients of the classic controller and the rules and parameters of the fuzzy controller to reduce the vibrational displacement amplitude of the plate. The obtained results show that the all designed controllers can reduce the steady-state vibrational displacement amplitude of the plate significantly, but the PID-Fuzzy controller has the best performance.

In this research Cu-12wt%Al-4wt%Ni shape memory alloy powder with and without addition of boron as alloying element was produced by using mechanical alloying method. Bulk samples were produced from the powder by press-sinter and subsequently rolling-heat treatment processes. The density and the amount of porosity of the samples were measured, subsequently. The effect of milling time on phase changes in produced powder, size of crystallites and lattice strain was also investigated. Results showed that after 20h of milling with rotating speed of 250 rpm and ball to powder mass ratio of 20:1, peaks of pure elements disappear and solid solution with FCC structure and lattice parameter close to that of copper forms. Morphology of milled powder and microstructure of bulk samples were studied by optical microscope and scanning electro-microscope. It was observed that adding boron lead to decrease in the size of particles after milling. Results showed that the density of samples after press-sinter processes decreases. However, the final density increased after rolling-heat treatment processes. It was also shown that adding boron to the powder mixture results in more homogenous distribution of porosities after rolling-heat treatment processes.

Shape Memory Alloys (SMAs) are a type of Shape Memory Materials (SMMs) which can recover large deformation and return to their primary shape by rising temperature. In this study, numerical simulation of thermo mechanical behavior of composites reinforced with shape memory alloys under static uniaxial loading was conducted. By inserting SMA wires inside the host composite the macro mechanical behavior of hybrid composite changed to a bilinear curve which is due to the phase transformation of SMA wires and nonlinear behavior of host composite. Simulated results are compared with available data in the literature. Validated model is used to evaluate the effect of various parameters as, wires pre-strain, temperature, interface conditions between SMA wires and Epoxy matrix on hybrid composite behavior. Also a theoretical method was developed to calculate the compressive and tensile strain induced in host composites and wires, after releasing of SMA wires. According to the results obtained, considering weak interface between SMAs wires and matrix improved simulation results rather than perfect bonding assumption. Pre-strained SMA wires would cause initial compressive stress in the host composite and its value will increased by increasing service temperature, however, it will increased interface separation of SMA and host materials, too. Therefore, in design of Shape memory alloys hybrid composites, optimum amount of applied pre-strain on SMA wires and working temperature should be selected.

In the present paper, nonlinear dynamic analysis of low-velocity impact of rectangular composite plates reinforced by SMA strips is investigated and the effects of the instant phase changes and the local and istatantaneous non-uniform distribution of transformation of the austenite to martensite phases and vice versa is considered, for the first time, implementing a written user defined material subroutine code in the ABAQUS/EXPLICIT finite element analysis code. In contrast to the available models which have used the approximate plate theories, a 3D finite element simulation is utilized for extracting the impact responses based on the elasticity theory. Finally, effects of different parameters such as the in-plane preloads, eccentricity, and indenter energy on the impact responses of the hybrid composite plate are investigated. The simulation results indicate that the SMA can absorb a remarkable portion of the stored impact-induced strain energy due to the superelastic and hysteretic natures of the SMA material, which results in increasing impact strength of the composite plate and decreasing the damage caused due to the impact. Moreover, results show that in the cases of the eccentric impact and presence of the tensile preloads, the contact force increases due to the less movability of the impacted point of the plate; a fact that may lead to higher damages.