The rotational joint plays a vital role in the industrial and civil areas, which is typically utilized to achieve the relative rotation between the adjacent parts. Generally, structuring a conventional rotational joint involves the bulk actuators (e.g., motor and hydraulic cylinders) and complex structures, bringing difficulty for miniaturing the dimension. In this paper, a class of novel rotational mechanisms, which were constructed by the combination of compliant mechanisms (e.g., cartwheel pivot and multileaf pivot) and intelligent actuator (e.g., shape memory alloy (SMA) wire and spring), was proposed to reduce the complexity of the conventional rotational joints. As the case study, a novel SMA wire-driven flexural rotational mechanism (SDFRM), which is constructed by the cartwheel pivot and SMA wire, was developed to demonstrate the feasibility of combining the compliant mechanism and smart actuator. After establishing the static model of the cartwheel pivot and the thermal effect model of the SMA wire, the overall model of SDFRM was developed for the comprehensive performance analysis and the control system design. After that, the model validation and experiments were performed with the proposed prototype and control system. It can be seen from the experimental results that the proposed model can be validated within the error of 3.8%. In addition, the performance study on SDFRM indicates that the prototyped SDFRM system can track the given trajectories within the error of 0.2 mm in the workspace. As a result, the proposed concept was demonstrated as an effective way to reduce the dimension and weight of the conventional rotational joint.

The properties and the shape memory effect depend, among other things, on chemical composition, as well as the method of shape memory alloy (SMA) production. One of the manufacturing methods that leads to the amorphous/nanocrystalline SMA is high-energy ball milling combined with annealing. Using this technique, an SMA memory alloy, with the nominal chemical composition of Ni25Ti50Cu25, was produced from commercial elemental powders (purity −99.7%). The structure and morphology were characterized (at the various stages of its production) by the use of X-ray diffraction, as well as electron microscopy (both scanning and transmission). Choosing the appropriate grinding time made it possible to produce an NiTiCu alloy with a different crystallite size. Its average size changed from 6.5 nm (after 50 h) to about 2 nm (100 h). Increasing the grinding time up to 140 h resulted in the formation of areas that showed the B19 martensite and the Ti2(Ni,Cu) phase with the average crystallite size of about 6 nm (as milled). After crystallization, the average size increased to 11 nm.

Prandtl–Ishlinskii (PI) model has an excellent compromise to characterize an asymmetric saturated hysteresis behavior of shape-memory-alloy (SMA)-driven systems, but it cannot consider thermomechanical relations between components of SMA-driven systems. On the other hand, constitutive models are composed of these relations, but their precision needs to be improved. In this paper, PI model is proposed to boost constitutive models in two cases. In the first case, PI model is used to characterize martensite volume fraction (MVF) called hybrid model. In the second case, the model is applied as a regulator in the output of a constitutive model called PI-based output (PIO) regulator. Due to simplicity and ability of Liang–Rogers (LR) model in transformation phases, it is considered as an MVF in the original constitutive model. The performance of both proposed models is compared with the original LR-based constitutive model. Unknown parameters of all three models are identified using genetic algorithm in MATLAB Toolbox. The performance of the three models is investigated at three different frequencies of \[\frac{{2\pi }}{8}\], \[\frac{{2\pi }}{{15}}\], and \[\frac{{2\pi }}{{30}}\] Hz because the excitation frequency changes the hysteresis behavior. Results show that the proposed hybrid model keeps the precision of the original constitutive model at different frequencies. In addition, the proposed PIO model shows the best performance to predict hysteresis behavior at different frequencies.

This paper focus on the mechanical and martensitic transformation behaviors of axially functionally graded shape memory alloy (AFG SMA) beams. It is taken into consideration that material properties, such as austenitic elastic modulus, martensitic elastic modulus, critical transformation stresses and maximum transformation strain vary continuously along the longitudinal direction. According to the simplified linear SMA constitutive equations and Bernoulli-Euler beam theory, the formulations of stress, strain, martensitic volume fraction and governing equations of the deflection, height and length of transformed layers are derived. Employing the Galerkin’s weighted residual method, the governing differential equation of the deflection is solved. As an example, the bending behaviors of an AFG SMA cantilever beam subjected to an end concentrated load are numerically analyzed using the developed model. Results show that the mechanical and martensitic transformation behaviors of the AFG SMA beam are complex after the martensitic transformation of SMA occurs. The influences of FG parameter on the mechanical behaviors and geometrical shape of transformed regions are obvious, and should be considered in the design and analysis of AFG SMA beams in the related regions.

The shape memory properties of Ni–Al alloy are investigated using molecular dynamics simulation. The phase transformation behaviors for various Ni composition ratios are studied under quasistatic cooling and heating process. Various loadings, i.e., uniaxial, shear, and biaxial, are applied on a 68% Ni–Al alloy till plasticity takes place. The atomic configurations are inspected and analyzed using a common neighbor parameter. The shape recovery capability of the plastically deformed alloy is examined after heating above the phase transformation temperature. It is found that there would be shape recovery if the twinning plane reorientation or moving was the major yielding mechanism. For those loadings in which stacking faults or dislocations nucleate, the deformed model would not restore to its original shape after heating and the corresponding maximum shear stress is noticeably higher. There is no direct dependence between the yield strain and the shape recovery capability. Our findings could provide a possible explanation for the functional fatigue of the polycrystalline shape memory alloy.

Shape memory alloys (SMAs) are unique class of smart materials with excellent physical, mechanical and biomedical properties, which have wide applications in several fields such as aerospace, robotics, biomedical, and dental etc. These alloys are well known for exhibiting shape memory effect (SME) and pseudoelasticity (PE), it is a well-established fact that they are required to be processed into functioning parts. The conventional machining affects the internal properties of shape memory alloys and hence, it is reported that nonconventional machining techniques are more suitable. Wire electro discharge machining (WEDM) is one of the nonconventional machining processes for machining complicated shapes without hampering the internal properties of such type of materials. In the present experimental investigation, wire electro discharge machining of Ti50Ni40Co10 shape memory alloy (SMA) has been carried out and machining performances such as surface roughness (SR), and material removal rate (MRR) have been evaluated. Experimental results exposed that pulse on time, pulse off time and servo voltages are most influential process parameters on the responses. The machined surface has been characterised with respect to microstructure, microhardness, and phases formed.

A theoretical model for the Functionally Graded Shape Memory Alloy (FG-SMA) cylinders subjected to internal pressure is investigated. The gradient properties in this work are embodied in the Young’s modulus and Poisson’s ratio gradient through the thickness of the cylinder. The critical transformation stresses and maximum formation strain are all assumed to be constant. Combining the elasticity and exponential function of the Young’s modulus and Poisson’s ratio with the different gradient parameters, the elastic stress distributions and displacement distributions for the FG-SMA cylinder under the internal pressure are obtained, respectively. To get the theoretical solution, the Tresca yield function and the ideal elastic–plastic constitutive model are selected for the shape memory alloy to illustrate the phase transformation. The relationships between the internal pressure and total strain at the internal radius with different gradient parameters are then given, and the results show that the total strains are greatly influenced by the different parameters.

In the paper, the influence of shape memory alloy (SMA) by varying the parameters such as volume fraction, orientation, and temperature on the hybrid-SMA composite laminate subjected to low-velocity impact is studied. A theoretical model for the composite laminated plate bonded with SMA reinforced layers is presented. The constitutive relation of the SMA layer is obtained by using the method of micromechanics. The governing relations obtained can be used for theoretical predications of thermomechanical properties of SMA plies in this paper. The analytical expressions for the hybrid SMA composite plate are derived based on Tanaka's constitutive equation and linear phase transformation kinetics presented by Liang and Rogers.

The laminated plate theory, first-order shear deformation theory and minimal potential energy principle is utilized to solve the governing equations of the hybrid composite plate and calculate the absorbed energies including tensile, shear and bending.

An orthogonal array and analysis of variance is employed to investigate the influence of the mentioned parameters on the energy absorption of the hybrid laminated plate. The results showed that the effects of the phase transformation temperature are more significant than the effects of the volume fraction and orientation of SMA on structural energy absorption.

This review article deals with the current state-of-art research and developments in the field of elasto-caloric effect as applicable for solid-state refrigeration devices. Furthermore, the current challenges and future prospects in the field of elasto-caloric refrigeration technology have also been discussed.

Solid-state refrigeration is of interest since it has the potential to be a light-weight and environmentally-friendly alternative for small scale cooling. Much research is currently being undertaken to develop solid-state cooling technologies which is primarily achieved by utilizing the significant caloric effect exhibited by particular classes of materials. A variety of caloric effects exist including: electro-caloric, magneto-caloric, baro-caloric, and elasto-caloric. Among these, the elasto-caloric effect has shown potential within the field of mechanical refrigeration with shape-memory alloys being potential materials for producing significant levels of elasto-caloric cooling. This article explains the elasto-caloric effect in shape memory alloys, polymers, and ferroelectric materials. Technical parameters associated with the elasto-caloric performance of these materials are discussed. A discussion regarding existing functional shortcomings and future prospects in the field of mechanical refrigeration is covered. Aspects related to the long term environmental impact of solid-state cooling technology are also discussed. This study is aimed at promoting the understanding and commercial investigation of the elasto-caloric effect in the field of solid state refrigeration.

This article aims to provide a fundamental understanding of the deformation mechanisms of NiTi shape memory alloy (SMA) during the wear process at different temperatures when different microstructures are present. Three temperature regimes were selected namely, T < Mf, As < T < Af, and T > Af, where fully martensitic, martensite co-existing with austenite, and fully austenitic microstructures were formed, respectively. When T < Mf, it was observed that the coefficient of friction had decreased initially and thereafter stabilized at a lower value with increasing wear cycles. More decrease was found when the temperature was near to As. Furthermore, when tested above Af, the coefficient of friction had decreased more significantly under higher load. Difference in the trend of coefficient of friction at different temperatures is originated from the different deformation mechanisms involved in the wear process, particularly the martensite detwinning process, the stress-induced phase transformation process, and the plastic deformation of martensite.

The influence of aging treatment on the shape memory effect and corrosion resistance of a newly developed Fe–Mn–Si–Cr–Ni-based alloy containing C, N, and V elements was investigated. Results showed that V(CN) and Cr23C6 particles, precipitated during aging, could improve the shape recovery ratio to 72%, compared with that of 21% for the solution treated sample, when the alloy was aged for 24 h. The corrosion behavior in 0.5 M H2SO4 solution was almost the same for all the samples, barring a slight difference in the passivation range. In addition, the passivation current and critical current required for the onset of passivation of the aged samples were almost triple that of the unaged. In 3.5% NaCl solution the corrosion behavior of all aged samples was that of general dissolution with localized attack (pitting), which can be attributed to the micro-cathodic effect of the V(CN) and Cr23C6 particles precipitated during aging. Although the best corrosion resistance in both H2SO4 and NaCl solutions was shown by the solution treated sample, 24 h-aged sample exhibited an improved corrosion resistance, ascribed to the improved chemical homogeneity of the austenite matrix due to long aging time (24 h).

Transformation behaviors of the technologically important polycrystalline Ti50.75Ni47.75Fe1.50 shape memory alloy were investigated using differential scanning calorimeter (DSC) and powder diffraction techniques. DSC revealed that there are two-stage (i.e., cubic→trigonal→monoclinic) martensitic phase transformations on cooling and a one-step transformation (monoclinic→cubic) on heating. In situ structural refinement of cubic→trigonal→monoclinic on cooling was carried out using the D1A high-resolution neutron powder diffractometer at the Institut Laue-Langevin Neutrons for Science in Grenoble, France. Results showed that the phases involved during the phase transition are consistent with the differential scanning calorimeter cooling curve, and the refined crystal structure parameters obtained from Rietveld refinements with the generalized spherical harmonic description agreed reasonably well with X-ray single-crystal data. Subsequently, a combined neutron and synchrotron structural refinement for each phase was conducted because the trial refinements initially using only the synchrotron data of trigonal phase yielded a false minimum with a somewhat high goodness-of-fit χ2. Results obtained from the combined neutron and synchrotron data of the cubic, trigonal, and monoclinic phases show that the same minimum goodness-of-fit indices were always obtained.

The effect of shape memory alloy (SMA) on the postbuckling behavior of rectangular cross-ply and angle-ply plates by varying the SMA fiber spacing was investigated using the Finite Element Method. The formulation of the location-dependent linear, nonlinear stiffness matrices due to non-homogeneous material properties and the temperature-dependent recovery stress stiffness matrix were derived. Numerical results show that the increase of SMA fiber volume fraction and prestrain may generate more recovery stress, and increase the stiffness of SMA reinforced composite laminate. Therefore, the postbuckling deflections of the plate may be decreased significantly. The buckling mode that plate will buckle into is dependent on the fiber orientation of the angle-ply laminates. When the SMA fibers are concentrated in the center of the plate, the postbuckling deflections of the plate will be decreased considerably.

In this paper, the dynamics and biomimetic control of an artificial finger joint actuated by two opposing one-way shape memory alloy (SMA) muscle wires that are configured in a double spring-biased agonist–antagonist fashion is presented. This actuation system, which was described in Part I, forms the basis for biomimetic tendon-driven flexion/extension and abduction/adduction of the artificial finger. The work presented in this paper centres on thermomechanical modelling of the SMA wire, including both major and minor hysteresis loops in the phase transformation model, and co-operative control strategy of the agonist–antagonist muscle pair using a pulse-width-modulated proportional-integral-derivation (PWM–PID) controller. Parametric analysis and identification are carried out based on both simulation and experimental results. The performance advantage of the proposed co-operative control is shown using the metacarpophalangeal joint of the artificial finger.

A prototype of a catheter which can move like a snake, incorporating distributed shape memory alloy actuators, is described. Since this active catheter has an instrumental navigation ability, minimally invasive diagnosis and interventional therapy will be possible. The outer diameter of the active catheter is 2.8 mm and it has many links fabricated by 3-dimensional silicon micromachining. The silicon batch process was used for the fabrication of the link to minimize assembly work. A new heating method (indirect heating) is suggested which is necessary when the JC chip is mounted on the link.

This paper discusses a novel design for a rotary differential NiTi shape memory alloy actuator, which incorporates a mobile heat sink. The new mechanism is described in detail, and its performance in a position control system is compared with that of the same actuator without heat sink. Experimental results are presented which show an improvement in actuator response time, as well as closed-loop bandwidth. The design of the mechanism gives enhanced performance, without the increased power consumption associated with fixed heat sinks.

In this paper, a new biomimetic tendon-driven actuation system for prosthetic and wearable robotic hand applications is presented. It is based on the combination of compliant tendon cables and one-way shape memory alloy (SMA) wires that form a set of agonist–antagonist artificial muscle pairs for the required flexion/extension or abduction/adduction of the finger joints. The performance of the proposed actuation system is demonstrated using a 4 degree-of-freedom (three active and one passive) artificial finger testbed, also developed based on a biomimetic design approach. A microcontroller-based pulse-width-modulated proportional-derivation (PWM-PD) feedback controller and a minimum jerk trajectory feedforward controller are implemented and tested in an ad hoc fashion to evaluate the performance of the finger system in emulating natural joint motions. Part II describes the dynamic modeling of the above nonlinear system, and the model-based controller design.

The work presented here concerns the design and manufacturing possibility of a polymodular autonomous microrobot moving like an earthworm. The study consists of the development of a new locomotion actuator based on shape memory alloys. This actuator is formed by a flexible frame forced in post-buckling by its assembly on a rigid skeleton cage. This mechanical structure, forming a knot in the microrobot chain, uses its two post-buckling equilibrium positions to achieve first the support and second the local lengthening enabling the movement of the microrobot. Initially, we present the technical solution designed for the locomotion actuator and the mechanical characterization of its malleable structure. Then, we present the instrumentation by educated SMA of a malleable structure and the capability of microrobot locomotion task in a vertical tube.

The Shape Memory Alloy (SMA) is a device which is lightweight and small in volume. The SMA can be used as the actuator of a micro-robot, but it is difficult to design a controller to handle the highly nonlinear properties of the SMA. In this paper, a Fuzzy Walking Pattern (FWP) is proposed to control a small biped robot, using an SMA as the actuator. In fact, the desired walking pattern of the small biped robot is used to construct the FWP. The proposed FWP can control the biped robot under the desired walking pattern, and handle the exceptional case when the biped robot is subject to disturbance. The proposed FWP not only solves the control problem of the SMA, but also provides a new method in controller design of the biped robot. In addition, a transputer network is designed to impelement the FWP. Experimental results demonstrate the functions of the FWP.