Search

This paper analyzes the influence of three different shape memory alloy (SMA) wires (i.e., Ni-Ti, Cu-Al-Ni, and Cu-Zn wires) for mitigating model cable vibration. Shape memory alloy (SMA) wires because of their superelasticity or shape memory properties can promise to be one of the effective damping materials in suppressing stay cable oscillations. The investigation explores through experimental works, the capabilities of three Ni-Ti, Cu-Al-Ni, and Cu-Zn SMA wires by estimating the vibration amplitude suppression of the model stay cable. The effective location of the SMA wires on the model cable for vibration suppression was estimated in free as well as forced vibration cases. To impart free and forced vibration, respectively, in the cable, a transducer-based hammer and exciter were used. An accelerometer and data acquisition system was used to record and acquire vibration data. It is also very appropriate to ascertain which wire among one of the three SMA wires performs well. It is found that the Ni-Ti SMA wire has a better performance in vibration suppression as compared to Cu-Al-Ni and Cu-Zn wires. It is also established that the attachment of the SMA wire at the mid-length of the cable gives better vibration suppression for the first mode. [ABSTRACT FROM AUTHOR]

Modular robots can adapt to different production needs and working conditions. However, the complexity of structures and the choice of driving modes limit the development of modularization. In this paper, a robot joint module with a universal joint configuration driven by shape memory alloy (SMA) wires is proposed, which has 2-DOFs. For lightweight, the main body of the module is made of polylactic acid materials. SMA wires are used as the actuator due to the advantages of large output displacement, high mass-to-energy ratio, and low activation voltage. Adopting antagonistically arranged SMA wires and bias springs combination method increases the recovery speed and driving angles. A locking device is creatively proposed to avoid the influence of self-biasing spring compression. The detailed kinematic model of the module is established. A proportional integral differential controller is used to precisely control module movements, and the attitude angle sensor is used as the monitoring device. Through the maximum rotation angles and trajectory tracking movement experiments, the module is tested comprehensively, and the results show that the module has good movement characteristics and control precision. In addition, analyzing the tracking performance of the module in the time domain shows that the module has a relatively fast tracking speed. This module is beneficial to the research of configurations, actuators, and controls of modular robots. [ABSTRACT FROM AUTHOR]

The phase transformation of thermal shape memory alloys (SMAs) can be described by surfaces in a temperature-stress-strain space. A novel experimental technique for the thermomechanical characterization of thin SMA wires allows to scan these surfaces with high resolution. Each experimental run uses a sequence of experimental conditions to traverse the phase transformation surfaces on a different path from "full martensite" to "full austenite" and vice versa. At all times, stress and strain are kept within the limits specified for the use of the SMA wire in actuators. The wire is heated externally through a silicon oil bath, which ensures a controlled and homogeneous temperature of the specimen. The experimental setup is designed to minimize the impact of the large oil temperature variations on measurement results. Experimental results are shown for both mechanical contraction and electrical resistance, each of which forms consistent surfaces for the phase transformation. Measurements for external heating in the oil bath are compared to electrical heating in air. [ABSTRACT FROM AUTHOR]

Many studies have been performed on composite patches as reinforcement of cracked metal sheets. However, in most previous research, composite patches without prestressing have been used to repair cracks. In the present study, a novel method for repairing cracked aluminum sheets is proposed by using polymer composite patches with embedded prestressed Nitinol shape memory alloy (Ni-Ti SMA) wires. Elastic-plastic finite element analysis of an aluminum plate, with a central crack in the pure mode I and the mixed-mode I/II fracture, repaired with SMA wires reinforced composite patch (SMA-CP) was performed. The peel stress on the adhesive layer between the composite patch and the aluminum plate was calculated to evaluate the performance and efficiency of the repair. The effect of the prestress of the embedded Ni-Ti SMA wires on the efficiency of the composite patch was examined. The results show that embedding prestressed SMA wires in the composite patch reduces the stiffness ratio of the patch. Also, the value of the J -integral and the size of the plastic area compared to the patch without SMA wires were decreased. [ABSTRACT FROM AUTHOR]

This study aims to the understanding of the impact of uncertainties related to constitutive model parameters on the cyclic response of CuAlBe Shape Memory Alloy (SMA) strands, and to define an adequate methodology for constructing the strands, thereby reducing uncertainty in their behavior. Employing a Bayesian framework and utilizing experimental data from tensile tests, the prior knowledge of mechanical properties at the wire level is updated. Various scenarios are explored, including model parameter updating for wires tested at different strain levels and from the same and different heat treatment batches. The updated model parameters are then used in a strand model, considering two scenarios: the strand is constructed from pieces cut from a single wire, post-heat treatment; or from pieces cut from wires from different heat treatment batches. The study concludes proposing a practical methodology to define test conditions for CuAlBe SMA wires and guidelines for the utilization of experimental data to predict bounds in the cyclic response of CuAlBe SMA strands. • Formulates robust tuning of constitutive relationships for CuAlBe SMA wires. • Proposes a Bayesian framework based on cyclic response of CuAlBe SMA wires. • Experimental data from different strain levels and heat treatment batches are used. • Uncertainties in wires are propagated to strands. • A practical methodology is proposed to predict bounds in the strand's cyclic response. [ABSTRACT FROM AUTHOR]

In this paper, crushing length, deformations and energy absorption of thin walled square and rectangular composite tubes which are reinforced with Aluminium and SMA wires and without wire have been investigated under a quasi-static lateral load, both experimentally and numerically. To experimental study, square and rectangular composite tubes have been fabricated with SMA wire, Aluminium wire and without wire. To validate the results, a finite element model is constructed and analysed under the same conditions by using FEM27 and LS-DYNA software packages for composite tubes with Aluminium wire and without wire. The numerical results are in a good agreement with the experimental data. The results show that section geometry and the types of reinforcement wires have a considerable effect on the energy absorption. Rectangular cross-section samples with SMA wires have the most energy absorption capacity.

Refrigeration is responsible of twenty percent of the worldwide energy consumption and the majority of the systems are based on vapor compression. In the scientific community, elastocaloric refrigeration, belonging to solid-state refrigeration technologies, is increasingly attracting interest, as a valid alternative to vapour compression. It is based on the latent heat generated as a consequence of the austenitemartensite transformation phase, a phenomenon shown by Shape Memory Alloys (SMA) as a consequence of cycles of stress/unstress under adiabatic conditions. The main SMA property is the capability of keeping memory of the initial form and being able to recover it after the remotion of the uniaxial stress (unloading). The elastocaloric effect can be exploited in a regenerative thermodynamic cycle called Active elastocaloric regenerative refrigeration cycle (AeR). The paper reports the data coming out though a numerical analysis by modelling a single bunch of elastocaloric wires crossed by air. The heat transfer and the energy performances have been investigated under a wide set of conditions: different geometrical parameters of the wires and many air flow speed. [ABSTRACT FROM AUTHOR]

Due to their unique hysteretic energy dissipation capacity, shape memory alloy (SMA) wires are particularly interesting for the development of new-type of intelligent vibration control systems for structures. However, in structural control, most of the vibrations occur in high strain rate regimes, which interfere the release of self-generated heat and thus influence the hysteretic dissipation. This paper proposes a strain rate dependent formulation of the latent heat evolution and aims to improve the accuracy of existing macroscopic modeling approaches developed for SMA wires particularly for the dynamic load cases. The proposed formulation is determined phenomenologically and implemented in a continuum thermomechanical framework based constitutive SMA wire model without impairing the simplicity and robustness of the solution process. The proposed formulation is validated by cyclic tensile tests conducted on SMA wires. Results show that the calculations using the formulation can predict the wire response more accurately than the strain rate independent formulation. For the simulation of multistory frame structures incorporating multiple SMA wires, the governing equations are driven. Shaking table tests are conducted on a 3-story frame structure under harmonic and seismic excitation. The responses of the structure are successfully replicated using the strain rate dependent latent heat formulation. [ABSTRACT FROM AUTHOR]

In this paper, crushing length, deformations and energy absorption of thin walled square and rectangular composite tubes which are reinforced with Aluminium and SMA wires and without wire have been investigated under a quasi-static lateral load, both experimentally and numerically. To experimental study, square and rectangular composite tubes have been fabricated with SMA wire, Aluminium wire and without wire. To validate the results, a finite element model is constructed and analysed under the same conditions by using FEM27 and LS-DYNA software packages for composite tubes with Aluminium wire and without wire. The numerical results are in a good agreement with the experimental data. The results show that section geometry and the types of reinforcement wires have a considerable effect on the energy absorption. Rectangular cross-section samples with SMA wires have the most energy absorption capacity. [ABSTRACT FROM AUTHOR]

This work presents a novel five-fingered soft hand prototype actuated by Shape Memory Alloy (SMA) wires. The use of thin (100 μm diameter) SMA wire actuators, in conjunction with an entirely 3D printed hand skeleton, guarantees an overall lightweight and flexible structure capable of silent motion. To enable high forces with sufficiently high actuation speed at each fingertip, bundles of welded actuated SMA wires are used. In order to increase the compliance of each finger, flexible joints from superelastic SMA wires are inserted between each phalanx. The resulting system is a versatile hand prototype having intrinsically elastic fingers, which is capable to grasp several types of objects with a considerable force. The paper starts with the description of the finger hand design, along with practical considerations for the optimal placement of the superelastic SMA in the soft joint. The maximum achievable displacement of each finger phalanx is measured together with the phalanxes dynamic responsiveness at different power stimuli. Several force measurement are also realized at each finger phalanx. The versatility of the prototype is finally demonstrated by presenting several possible hand configurations while handling objects with different sizes and shapes.

To meet the needs of present-day robotics, a family of gripping flexible fingers has been designed. Each of them consists of a number of independent and flexible modules that can be assembled in different configurations. Each module consists of a body with a flexible central rod and three longitudinally positioned shape memory alloy (SMA) wires. When heated by the Joule effect, one to two SMA wires shorten, allowing the module to bend. The return to undeformed conditions is achieved in calm air and is guaranteed by the elastic bias force exerted by the central rod. This article presents the basic concept of the module and a simple mathematical model for the design of the device. Experimental tests were carried out on three prototypes with bodies made of different materials. The results of these tests confirm the need to reduce the antagonistic action of the inactive SMA wires and led to the realization of a fourth prototype equipped with an additional SMA wire-driven locking/unlocking device for these wires. The preliminary results of this last prototype are encouraging.

The availability of engineering strength data on shape memory alloys (SMAs) under cyclic thermal activation (functional fatigue) is central to the rational design of smart actuators based on these materials. Test results on SMAs under functional fatigue are scarce in the technical literature and the few data available are mainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased by elastic springs or by another SMA element, their stress state is far from constant in operation. The mismatch between actual working conditions and laboratory arrangements leads to suboptimal designs and undermines the prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality. Four test procedures are planned, covering most of the typical situations occurring in practice: constant-stress, constant-strain, constant-stress with limited maximum strain and linear stress-strain variation with limited maximum strain. The paper describes the experimental apparatus specifically designed to implement the four loading conditions and presents fatigue results obtained from commercial NiTi wires tested under all those protocols.

Until recently, shape memory alloys (SMAs) were predominantly developed for applications in the biomedical and engineering industry, and only a limited number of applications in textiles are known. The biomedical success of these materials is due to their unusual properties, which make them superior to conventional materials. Among many SMAs, NiTi alloy is considered to be the best because of its superb characteristics. This studyin vitroaimed to design a medical textile material that could be used around internal organs to support in case of inability of peristaltic motion. NİTİ alloys were embedded in textile structure to simulate the peristaltic motion. Three types of knit prototypes were produced and controlled by electronic system. Their structures and behaviors simulating smooth muscles were assessed and compared. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are thermally activated and show a strong thermomechanical coupling (i.e. the relationship between strain, stress and temperature). SMA wires are commonly used to develop SMA-based actuators. The most important characteristics of SMA wires is their capability to exert linear forces with strokes up to 8% of their original length. This make SMAs an attractive smart material for actuation purposes. However, the main weakness of SMAs is their limitation on actuation bandwidth. This limitation comes from the rate at which the SMA wires are able to heat up and cool down, releasing heat energy to the surroundings. This paper focuses on the effects that different heating and cooling rates have on the SMA wire’s working rate that can be attained. An SMA wire has been experimentally tested under different conditions of heating, cooling and applied load to find the influence of these parameters on the contraction and cooling times of an SMA wire and, therefore, on its attainable frequency. In addition, a model for SMAs has been implemented in a finite element analysis software and the experiments have also been simulated, which has been used to corroborate the conclusions drawn from the experiments. [ABSTRACT FROM AUTHOR]

The rational design of smart actuators based on shape memory alloys requires reliable strength data from the thermo-mechanical cycling of the material (functional fatigue). Functional tests results do not abound in the technical literature and the few data available are mostly limited to the condition of constant applied stress, which is hardly achieved in operation. The disagreement between actual working conditions and laboratory conditions leads to suboptimal designs and undermines the prediction of the life of the actuator. To bridge the gap between experiment and reality, this paper envisions four cyclic tests spanning the range of loadings which can occur in practice: constant-stress, constant-strain, constant-stress with limited maximum strain and linear stress–strain cycle. Commercial NiTi wires (0.15 mm diameter) are tested under constant-stress, constant-strain and constant stress with limited maximum strain conditions using a custom machine and the disclosed results are critically discussed. [ABSTRACT FROM AUTHOR]

The availability of engineering strength data on shape memory alloys (SMAs) under cyclic thermal activation (thermomechanical fatigue) is central to the rational design of smart actuators based on these materials. Test results on SMAs under thermomechanical fatigue are scarce in the technical literature, and even the few data that are available are mainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased by elastic springs or by antagonist SMA elements, their stress states are far from being constant in operation. The mismatch between actual working conditions and laboratory settings leads to suboptimal designs and undermines the prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality by completing an experimental campaign involving four fatigue test conditions, which cover most of the typical situations occurring in practice: constant stress, constant-strain, constant stress with limited maximum strain, and linear stress-strain variation with limited maximum strain. The results from the first three test settings, recovered from the previously published works, are critically reviewed and compared with the outcome of the newly performed tests under the fourth arrangement (linear stress-strain variation). General design recommendations emerging from the experimental data are put forward for engineering use. [ABSTRACT FROM AUTHOR]

In this paper, free vibration response of a hybrid composite plate was studied. Effects of some geometrical, physical and material parameters on response of the composite plates embedded with shape memory alloy (SMA) wires were investigated, which have not been reported in the literature thus far. Some of these parameters included important factors affecting free vibration response of the smart hybrid composite plates. The SMA wires were embedded within the layers of the composite laminate. First-order shear deformation theory (FSDT) was utilized to obtain the governing equations of hybrid composite plates. Transverse shear and rotary inertia effects of the plate were taken into consideration. For simply- supported boundary conditions, systematic closed form solutions were obtained by Navier's technique. It was established that dynamic behavior of the smart hybrid composite plate depended on various parameters such as volume fraction, temperature dependent recovery stress and tensile pre-strain of SMA wires and aspect ratio of the laminated hybrid plate. [ABSTRACT FROM AUTHOR]

The availability of engineering strength data on shape memory alloys (SMAs) under cyclic thermal activation (functional fatigue) is central to the rational design of smart actuators based on these materials. Test results on SMAs under functional fatigue are scarce in the technical literature and the few data available are mainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased by elastic springs or by another SMA element, their stress state is far from constant in operation. The mismatch between actual working conditions and laboratory arrangements leads to suboptimal designs and undermines the prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality. Four test procedures are planned, covering most of the typical situations occurring in practice: constant-stress, constant-strain, constant-stress with limited maximum strain and linear stress-strain variation with limited maximum strain. The paper describes the experimental apparatus specifically designed to implement the four loading conditions and presents fatigue results obtained from commercial NiTi wires tested under all those protocols. [ABSTRACT FROM AUTHOR]

Abstract: Shape memory alloys (SMAs) are increasingly used for the construction of simple solid-state actuators characterized by outstanding power density. The rational design of these actuators requires reliable data on the fatigue strength of the alloy under cyclic thermal activation (functional fatigue). The technical literature shows scanty test results for SMAs under functional fatigue. Furthermore, the few data available are mainly limited to the condition of constant stress applied to the material. Sincethe SMA elements used within actuators are normally biased by conventional springs or by another SMA element, their stress condition is far from constant in operation. The disagreement between actual working conditions and laboratory conditions leadsto suboptimal designs and undermines the prediction of the life of the actuator. This paper aims at bridging the gap between experiment and reality. Four characteristic test conditions are envisioned, covering most of the actual situations occurring inpractice: constant-stress, constant-strain, constant-stress with controlled maximum strain and cyclic-stress with controlled maximum strain. The paper presents the experimental apparatus specifically designed to implement the four test conditions. Fatigue results on a commercial NiTi wire (0.15 mm diameter) tested under constant-stress and constant-strain loading are also presented and discussed. [Copyright &y& Elsevier]

In this article, the response of rectangular smart hybrid composite plate subjected to low velocity impact is studied and the effect of some geometrical and material parameters on the response of the composite plate embedded with shape memory alloy (SMA) wires is investigated. The interaction between the impactor and the composite plate is considered in the impact analysis. The SMA wires are embedded within the layers of the composite laminate. The effect of the SMA wires on contact force history, deflection, in-plane strains and stresses of the structure was studied. The classical first-order shear deformation theory (FSDT) as well as the Fourier series method is utilized to solve the governing equations of the composite plate analytically. The interaction between the impactor and the plate is modeled with the help of two degrees-of-freedom system, consisting of springs-masses. The Choi's linearized Hertzian contact model is used in the impact analysis of the laminated hybrid composite plate. The simultaneous application of the FSDT, Fourier series method, springs-masses and Choi's linearized contact model helps to get a complete model and more accurate result and save computational time and effort for the analysis of the composite structures subjected to the transverse impact. The results indicated that some of the geometrical and material parameters like the volume fraction, the orientation and the through thickness location of the SMA wires, the longitudinal to transverse elastic modulus ratio of the plate and the material type of composite medium are some of the important factors affecting the impact process and the design of the structures. [ABSTRACT FROM AUTHOR]

In this paper the dynamic performance of a multi-layered composite plate with embedded shape memory alloy (SMA) wires has been investigated in terms of the changes in its relative fundamental natural frequency. A sensitivity analysis has been carried out on the influence of various geometrical parameters and material properties on the plate’s dynamic performance, as well as the influence of the form of boundary condition. The use of the active property tuning (APT) method and the active strain energy tuning (ASET) method has also been discussed within the paper. The finite element method has been used for the analysis, and a new element has been exploited for modelling multi-layered composite plates. It has been found that the dynamic performance of the multi-layered composite plate with embedded SMA wires strongly depends on the plate geometry and the form of boundary condition, however, the dynamics can be successfully controlled and influenced by an optimal selection of the geometrical parameters and material properties. [Copyright &y& Elsevier]

To meet the needs of present-day robotics, a family of gripping flexible fingers has been designed. Each of them consists of a number of independent and flexible modules that can be assembled in different configurations. Each module consists of a body with a flexible central rod and three longitudinally positioned shape memory alloy (SMA) wires. When heated by the Joule effect, one to two SMA wires shorten, allowing the module to bend. The return to undeformed conditions is achieved in calm air and is guaranteed by the elastic bias force exerted by the central rod. This article presents the basic concept of the module and a simple mathematical model for the design of the device. Experimental tests were carried out on three prototypes with bodies made of different materials. The results of these tests confirm the need to reduce the antagonistic action of the inactive SMA wires and led to the realization of a fourth prototype equipped with an additional SMA wire-driven locking/unlocking device for these wires. The preliminary results of this last prototype are encouraging. [ABSTRACT FROM AUTHOR]

In this paper, free vibration response of a hybrid composite plate was studied. Effects of some geometrical, physical and material parameters on response of the composite plates embedded with shape memory alloy (SMA) wires were investigated, which have not been reported in the literature thus far. Some of these parameters included important factors affecting free vibration response of the smart hybrid composite plates. The SMA wires were embedded within the layers of the composite laminate. First-order shear deformation theory (FSDT) was utilized to obtain the governing equations of hybrid composite plates. Transverse shear and rotary inertia effects of the plate were taken into consideration. For simply-supported boundary conditions, systematic closed form solutions were obtained by Navier's technique. It was established that dynamic behavior of the smart hybrid composite plate depended on various parameters such as volume fraction, temperature dependent recovery stress and tensile pre-strain of SMA wires and aspect ratio of the laminated hybrid plate.

Ahead of Print article withdrawn by publisher.