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In order to design an intelligent assembly cushion with an adjustable pre-tightening force, a reentrant honeycomb structure was printed by additive manufacturing to realize the active and intelligent assembly process of filling gaps. The thermo-mechanical deformation experiments of the reentrant honeycomb structure were conducted at different pre-compressions, constrained displacements, and recovery temperatures. The recovery force and the force recovery ratio under semi-constrained conditions are explored emphatically. The results show that pre-compression, constrained displacement, and recovery temperature affect the recovery force and force recovery ratio under semi-constrained conditions. The recovery force and force recovery ratio increase with pre-compression, decrease with constrained displacement, and increase with recovery temperature below the glass transition temperature. Based on these results, the adjustability of the recovery force of a reentrant honeycomb cushion can be controlled by changing the thermo-mechanical deformation processes. Finally, the reentrant honeycomb cushion is applied to the mimetic assembly environment for corresponding testing, achieving the design of an active and intelligent assembly cushion with an adjustable pre-tightening force. [ABSTRACT FROM AUTHOR]

The combination of superelastic shape memory alloy fibers and ECC materials can form a new SMA fiber reinforced ECC composite material (SMAF-ECC) with good self-centering performance. In order to study the self-centering performance of the new composite material, 6 groups of pre-notch beam specimens were made for three-point bending cyclic loading tests, and the failure phenomenon, hysteresis curve, self-centering effect and influencing factors of the specimens were analyzed. The research results show that when the SMA fibers are effectively anchored in the ECC matrix, the SMA fibers can exert the superelastic properties to provide the ECC beams with recoverying force, and realize the crack self-closure and deflection self-recovery function for the beams, with the minimum residual crack width and deflection is only 0.9 mm and 1.3 mm respectively. Increasing fiber content can cause a small increase in the self-centering ability of the beams. However, only when the fiber diameter is appropriate, better self-centering effect can be achieved, but the difference caused by fiber diameter in the test was only 5%. SMA Fiber end forms have significant influence on self-centering performance. The knotted end beam can get a more than 70% self-centering ratio, while the straight end beams and bended end beams have no self-centering ability. The research results provide important reference for the research and application of this new self-centering materials and their structures. [ABSTRACT FROM AUTHOR]

Active disassembly (AD) is an emerging field of research in design for disassembly that enables a cost-effective nondestructive separation of product components. It is based on using active joints and fasteners that enables the self-disassembly of products without any direct contact between the product and the operator, where these joints and fasteners must be inserted in the product during its design and manufacturing phases. Generally, active joints and fasteners are made of smart materials such as shape memory alloys (SMAs), that can generate the necessary disassembly forces required to separate the different components of the product. Most of the exerted effort in this field of research was focused on separating products requiring small disassembly forces either in the electronic or automotive sectors. All these active disassembly applications were based on using shape memory alloy snap fits, clips, or wires that are characterized by their ability to generate small forces with large displacements. As, up to the authors knowledge, none of the exerted efforts were concerned with investigating the possibility of using the large disassembly forces that could be generated using shape memory alloy actuators in large force active disassembly applications. Consequently, the presented research aims to examine the possibility of applying active disassembly with products requiring large disassembly forces, having tapered surfaces and large mechanical structure. By presenting two case studies to validate the possibility of using active disassembly with large force applications, in addition to investigating the capability of using shape memory alloy actuators assembled either concentric or eccentric with the product structure. [ABSTRACT FROM AUTHOR]

Two‐way (reversible) chemically crosslinked semicrystalline shape memory polymers are synthesized using poly(ethylene‐co‐vinyl acetate) (PEVA) with benzoyl peroxide (BPO). The two‐way shape memory effect (2W‐SME) is achieved under both constant stress and stress‐free conditions. It is found that the stress‐free 2W‐SME can be achieved by the relationship between the initial prestretching strain (Rprestretch) and recovery strain (Rrec). Under the same prestretching stress, the stress‐free two‐way shape memory behavior can be controlled by variation of Rrec using a different setting temperature (Tset) in the recovery process. More importantly, the driving force and recovery force, as one of the key indicators for two‐way shape memory materials, are investigated, and they significantly change depending on the BPO content. The sample with high BPO content shows excellent high‐temperature creep resistant performance. A highly crosslinked structure can suppress viscous flow and provides sufficient force to allow the sample to recover its initial shape after crystal melting. Therefore, the PEVA/BPO samples are able to contract during heating. The presence of an oriented crystal structure with high applied stress that causes sample elongation during cooling is also investigated. These findings for PEVA/BPO two‐way shape memory polymers will contribute to their applications as soft actuators in various fields. [ABSTRACT FROM AUTHOR]

• This paper presents theoretical and numerical analyses for nonlinear vibrations of the shape memory alloy hybrid composite beam actuated by pre-stretched shape memory alloy fibers with tension-bending coupling effects. • During the nonlinear vibration, the low frequency of the transverse vibration is captured in the spectrum diagram of the longitudinal vibration of the SMAHC beam, which is characterized as one of high frequency. • In the event of nonlinear vibration, both the amplitude and frequency of the transverse vibration elevate with the increase of the temperature or the eccentric distance of the SMA fibers. • The double and triple fundamental frequencies of transverse vibration are also excited in the nonlinear vibration. • The findings from this study provide a theoretical basis for evaluating the safety and stability of smart composite structures. Theoretical and numerical analyses for nonlinear vibrations of the shape memory alloy hybrid composite(SMAHC) beam actuated by the pre-stretched shape memory alloy(SMA) fibers with tension-bending coupling effect are presented in this paper. Under the sudden action of thermal temperature, a recovery force and moment are caused in the SMAHC beam due to the phase transition in the SMA fibers, exciting the nonlinear vibration of the SMAHC beam. The one-dimensional Brison constitutive model was adopted to express the influence of the phase transition temperature, initial volume fraction of martensite, and pre-strain on the phase transition in the shape memory alloy. On this basis, the constitutive law of the SMAHC beam is built by considering the tension-bending coupling effect and the phase transition in the SMAHC beam. The equation of motion for nonlinear vibration of the SMAHC beam with geometric nonlinearity and material nonlinearity is derived from the Hamilton principle and is discretized into matrix form using the Galerkin method. According to the algorithm of the NewMark-β method, numerical solutions are computed by developing Matlab program and are compared with the results from ABAQUS analysis. It shows that the frequencies and amplitudes of the theoretical calculations are very consistent with those obtained from ABAQUS analysis. In addition, both the theoretical study and ABAQUS simulation indicates that the high frequency for longitudinal vibration is not observed in the spectrum diagram of transverse vibration, while the low frequencies for transverse vibration are captured in the longitudinal vibration. With the established Matlab program, parametric study is carried out to investigate the effect of the temperature and the location of the SMA fibers on the vibration responses of the SMAHC beam. The results from this study indicate that the transverse vibration of SMAHC beams is characterized as one of low frequency, while the longitudinal vibration has the characteristics of high frequency. Especially in the case of nonlinear vibration, not only the vibration of high frequency but also the vibration of low frequency observed in the transverse vibration will occur in the longitudinal direction of the SMAHC beam. Furthermore, the double and triple fundamental frequencies of the transverse vibration are excited in the nonlinear vibration of the SMAHC beam. The results of this paper can provide a theoretical basis for the evaluation of the safety and stability of smart composite structures. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) are a new class of materials in which their shapes can be changed over time. Despite their lightness and ease of fabrication, SMPs have very low recovery forces and are therefore inefficient when high loads are applied. To improve the mechanical properties of polymeric materials, glass fiber (GF) is commonly used as a reinforcement. The purpose of this study was to demonstrate a four-dimensional (4D) printing process using material extrusion additive manufacturing on both polylactic acid (PLA) and thermoplastic polyurethane (TPU). The goal was to improve the recovery forces in SMPs. GF roving was fed continuously into the nozzle of a three-dimensional (3D) printer to fabricate composite specimens. Also, multi-layer PLA/TPU specimens were printed. There was a measurement of shape fixity, shape recovery, and force recovery ratios. A multi-objective function analysis was performed to determine the optimum material based on recovery force priority in this study. In terms of recovery force, GF showed a superior effect. For composite specimens, shape fixity and recovery ratios decreased and increased, respectively. According to the result of optimization, PLA with 6.62 % GF proved to be the best material. PLA's recovery force has been improved by annealing heat treatment. Furthermore, cyclic experiments up to three cycles were conducted to evaluate the performance of the optimum material. [ABSTRACT FROM AUTHOR]

Abstract Four-dimensionally (4D) printed origami structures have great potential for applications in actuators and reconfigurable devices by taking the advantages of 3D printing technology and shape memory polymers. This study focuses on the shape recovery progression of 4D printed laminated Miura-origami tessellations and tubes under compressive load-induced unfolding and folding. Recovery forces of the specimens are characterized by dynamic mechanical analysis (DMA) experiments. The shape recovery behavior and recovery force are significantly influenced by the shape recovery temperature and loading pattern. The high shape recovery capability of the specimens are signified by the shape recovery ratio of over 94% and volume changes of up to 289%. Lastly, the actuator application of a 4D printed laminated Miura-origami structure has been demonstrated. [ABSTRACT FROM AUTHOR]

Four-dimensional (4D) printing of multi-directionally reinforced preforms has tremendous potential for the development of next generation functional composites by using the capabilities of 3D printing technology, 3D textile preform design, and polymer shape memory behavior. This work demonstrates the shape memory behavior and recovery force of 4D printed circular braided tube preforms and their silicone elastomer matrix composites. The preforms were printed by fused deposition modeling using the shape memory polymer (SMP), polylactic acid (PLA). The effects of braiding angle, tube wall thickness, and shape recovery temperature on the shape memory behavior of 4D printed tube preforms and their silicone elastomer matrix composites have been characterized. Measurements of shape recovery forces of the preform and composite were conducted using dynamic mechanical analysis (DMA). The braided microstructural parameters and shape recovery temperature have a significant effect on the preform shape memory behavior. The introduction of the silicone elastomer matrix greatly enhances the shape recovery force, shape recovery ratio, as well as radial compressive failure load of the 4D printed preform/silicone elastomer matrix composite. Building on these results, a potential application for 4D printed textile functional composites is presented. [ABSTRACT FROM AUTHOR]

In this work, a numerical model of a SMA plate reflecting the tension/compression asymmetry of axial stress under pure bending was developed and verified experimentally. To achieve the goal, ABAQUS user-material (UMAT) based on the Brinson model with modified martensite transformation kinetics was proposed with the Drucker–Prager yield criterion to realize the tension/compression symmetry of SMA. To demonstrate the performance of the proposed model, we conducted several predictions on the recovery bending moment with temperature variation with diverse thicknesses under various strain conditions. These results were compared with pure bending test results obtained by a test device that can simulate a pure bending state for maximum 4% axial strain with uniform deformation curvature. [ABSTRACT FROM AUTHOR]

In this paper, an analytical study on thermal, mechanical, and thermomechanical buckling and post-buckling of symmetric laminated composite plates reinforced with shape memory alloy (SMA) fibers are presented. The closed-form solution used in this study is developed based on the FSDT incorporated with the Von-Karman non-linear strains. The effect of SMA fibers is captured by adding a tensile recovery, stress term that determined using 1-D simplified Brinson’s model, in the constitutive equations of the SMA composite plate. Galerkin technique is implemented for solving the nonlinear partial differential equations of motion to obtain buckling load and post-buckling path. The influence of several parameters such as SMA activation temperature, SMA fiber volume fraction, SMA pre-strain, biaxial ratio, etc., are studied in this work. Due to the generation of recovery force, significant improvement in buckling load is attained by increasing each of the SMA fiber volume fraction, activation temperature or SMA pre-strain. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMP) are a class of stimuli-responsive materials which can change shape upon activation. The objective of this study is to optimize the actuation (or shape recovery) properties of the biocompatible thermoplastic polyurethane (TPU)/polylactic acid (PLA) shape memory polymer (SMP) blend by altering the blend composition and programming temperature. A comprehensive characterization of the shape memory, morphological, and actuation properties of TPU/PLA blends was carried out on 80/20, 65/35, and 50/50 TPU/PLA blends and neat TPU. Three programming temperatures were utilized: 25 °C (room temperature), 37 °C (body temperature), and 70 °C (above the glass transition temperature). The transition temperature ( T trans ) range was characterized by recovering the samples between 30 °C and 100 °C, at 10 °C intervals. The results showed that the shape fixity ratio ( R f ) increased significantly with increasing PLA composition and programming temperature, and the shape recovery ratio ( R r ) was not dependent on the programming temperature. The T trans increased with increasing programming temperature, and its range decreased with increasing PLA composition. The highest shape recovery force was observed in the 80/20 and 65/35 TPU/PLA blends programmed at 70 °C, reaching up to 0.6 N/cm. These samples were able to lift a 50 g weight during the shape recovery process. The actuation forces of the TPU/PLA blends in this study is an order of magnitude higher compared to the currently available biocompatible SMPs. Therefore, these SMP blends can be further developed into actuators for biomedical applications such as artificial muscles. [ABSTRACT FROM AUTHOR]

The thermostatic valve was equipped with the spring made of CuAiNi shape memory alloy as the pari for sensing and controlling the temperature. For the forming process, the CuAlNi wire was transformed into a SM A spring, whose phase-transition temperature and recovery force were tested. The experimental results of the thermostatic valve show that, with the temperature of in- water ranging from 50°C to 70°C, the temperatures of the out-let water at different spool positions are 38. 50°C and 38. 75°C respectively, and that the thermostatic valve is reliable in controlling the temperature with the margin of error being 1.50°C. [ABSTRACT FROM AUTHOR]

The feasibility of laboratory-synthesized polyurethane-based shape-memory polymer (SMPU) actuators has been investigated for possible application in medical pressure bandages where gradient pressure is required between the ankle and the knee for treatment of leg ulcers. In this study, using heat as the stimulant, SMPU strip actuators have been subjected to gradual and cyclic stresses; their recovery force, reproducibility and reusability have been monitored with respect to changes in temperature and circumference of a model leg, and the stress relaxation at various temperatures has been investigated. The findings suggest that SMPU actuators can be used for the development of the next generation of pressure bandages. [ABSTRACT FROM AUTHOR]

The SMC belt composed of two kinds of SMAs with different phase transformation temperatures and SMP, was fabricated and the three-way (reciprocating) movement and recovery force in bending actuation were investigated. The results obtained can be summarized as follows. 1) The three-way bending movement was achived during heating and cooling, based on the characteristics of the SMA tapes and the SMP tape. 2) The recovery force decreased at first and increased thereafter during heating and decreased during cooling. The recovery force was roughly estimated by the proposed model. 3) The development and application of multi-functional SMCs with simple structure for three-dimensional actuators are highly expected. [ABSTRACT FROM AUTHOR]

The behavior of smart concrete beams with embedded shape memory alloy (SMA) bundles is investigated in this study. Two beams measuring 1996 × 99 × 85 cm3, which will be integrated into a smart bridge in a freeway, are manufactured and examined. Each beam contains six trusses of SMA bundles used as actuators to achieve recovery force. The SMA bundles are connected with pre-stressing steel strands and separated from the concrete matrix, so that temperature interaction between SMA bundles and the matrix can be reduced to as low as possible. Some temperature sensors, reinforcement meters, and displacement sensors are used to monitor the active control effect of SMA bundles, all the data are acquired through a 16-channel dynamic data-acquisition system, and each beam is examined several times with different activating current intensity. Experimental results indicate that the recovery force induced by SMA bundles is significant and controllable, the deflection generated by the SMA bundles at the middle span of the beam is about 0.44 mm, and the capability of resisting overload of each beam is about 2.98 kN (average). A relationship between SMA temperature and activating/inactivating time is also formulated. The conclusion is that SMA can be used in civil engineering structures either from a technological or economic aspect. [ABSTRACT FROM AUTHOR]

A shape memory composite (SMC) belt with a TiNi-shape memory alloy (SMA) wire fiber and a polyurethane-shape memory polymer (SMP) sheet matrix is fabricated. The bending actuation characteristics of the belt are investigated by the thermomechanical tests. The results obtained are summarized as follows. (1) Residual deflection close to the maximum deflection is obtained by cooling under constant maximum deflection. The residual deflection disappears by heating under no load. Both the rate of shape fixity and the rate of shape recovery are close to 100%. (2) Recovery force appears by heating under constant residual deflection. The recovery force is 93-94% of the maximum force. The development of high functionality of SMC elements is expected by various combinations of SMAs and SMPs. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) possess inherent superior properties that make their applications in active disassembly an emerging and interesting field of research. This is because extremely large forces can be generated repeatedly using a small compact-sized element, such as an SMA actuator. To ensure the ability of the SMA actuator to generate a repeated large force or withstand repeated load, several factors should be considered. These include factors that affect the value of the generated recovery forces, such as the amount of strain used, activation temperature, activation time, and cross-sectional area of the SMA element. In general, the compressive strain can be considered as the most influential factor that affects the value of the generated recovery force. The present research investigates the possible use of the SMA actuator in large-force active disassembly applications. To the best of the authors' knowledge, all the studies conducted in this field are concerned with implementing active disassembly in applications requiring small disassembly forces. The present research was conducted in three phases. First, the behaviour of the SMA element upon exposure to different repetitive compressive strains was studied, and the generated recovery force and strain hardening induced in the material were considered to ensure the continuous generation of large recovery forces with the least amount of residual strain induced in the material. Second, the optimum value of the compressive strain required to generate the maximum force with the least amount of residual strain induced in the material was estimated. Third, a practical case study was presented to validate the possible implementation of SMA actuators in large force active disassembly applications. The study successfully estimated the optimum compressive strain value that generated the required recovery force to disassemble the conducted case study using active disassembly technique., (© 2020 Published by Elsevier Ltd.)