Two-way Shape Memory Research Articles

A soft syntactic foam actuator with high recovery stress, actuation strain, and energy output

Novel syntactic foams were prepared by incorporating three types of glass microbubbles in a crosslinked cis poly(1,4-butadiene) (cPBD) matrix. The as-prepared semi-crystalline polymer-based syntactic foams displayed a clear two-way shape memory effect (2W-SME) with remarkable strain actuation of about 56% expansion when the temperature drops from 60 °C to − 40 °C, and about 40% contraction when the temperature rises from − 40 °C to 60 °C, comparable to most pure two-way shape memory polymers. Compared to the pure cPBD, which was actuated under 0.32 MPa tensile stress, the foams were actuated under a much larger external tensile stress of up to 1.6 MPa, signifying its superior actuation capability. The energy output is also much higher for the syntactic foam, up to 0.83 MJ/m3, compared to 0.28 MJ/m3 for the pure cPBD. Furthermore, it has a working temperature below zero Celsius and may be actuated at temperatures lower than most other available shape memory polymer foams. With a low density, decent mechanical properties, and great actuation capability, these syntactic foams can be adopted for applications such as artificial muscles, biomedical devices, soft robots, sealants, and aerospace structures, which can be potentially manufactured by 3D printing.

Mechanism of Behavior of Two-Way Shape Memory Polymer under Constant Strain Conditions

In this paper, we report detailed investigation of structural changes occurring in two-way shape memory polymers (2W-SMP) upon thermal cycling at constant strain conditions. We demonstrate that cooling of stretched chemically cross-linked polycaprolactone results first in a slow decrease of stress, the stress drops rapidly upon further cooling, and further cooling results in sharp increase of stress. In this paper, we investigated structural changes occurring in each of these three phases using in situ force measurements and XRD analysis (SAXS and WAXS). In the first phase, the stress decreases due to decrease of entropic factor in the elastic state. In the second phase, polymer chains start to crystallize in the stretched state as a result of the number of active springs producing stress decreasing. This results in the decrease of the stretching degree of other polymer chains, and finally, unstretched polymer chains crystallize that result in an increase of stress─the polymer simply tends to shrink.

Environmentally Responsive Intelligent Dynamic Water Collector.

Collecting water from fog flow is emerging as a promising solution to the water shortage problem. This work demonstrated a novel environmentally responsive water collector made from a self-prepared Janus polyvinyl alcohol sponge in combination with a two-way shape memory alloy spring, which transforms the traditional manner of static water collection into a dynamic one. The unidirectional water transport of the Janus structure together with the dynamic collection approach correspond to a 30.8% increase in the water-collection rate (WCR). The resultant WCR is up to 5.1 g/h, which ranks relatively high compared to similar studies. The light- and thermal-response capability, easy fabrication, and good cycling performance indicate that our devices could be utilized in a variety of applications. In this work, an efficient, intelligent adaptive, simple-preparation, precision-guided, and economical fog-collecting devices are recommended. Our work provides new insights on the design of high-efficient water collectors with practicability.

Converse two-way shape memory effect through a dynamic covalent network design

A unique thermally driven two-way shape memory polymer is reported through a dynamic covalent network design. Its actuation direction relative to the programming force is reflected as cooling-induced contraction and heating-induced elongation.

Functional properties of NiTi nanofilm/Kapton composite

The aim of the paper was to study the one-way and two-way shape memory effects in the NiTi nanofilm/Kapton composite. 500 nm film of the Ni50Ti50 alloy was deposited to Kapton by flash evaporation. After deposition, the NiTi layer was amorphous and the sample was held at a temperature of 350 - 400 °C for two hours in vacuum to crystallize the NiTi layer. As deposited sample as well as samples after heat treatment were bent around the mandrel with various diameters at room temperature and subjected to heating – cooling – heating through a temperature range of the martensitic transformations. It was shown that as-deposited sample did not demonstrate the recoverable stain variation. At the same time, the heat treated sample demonstrated the one-way shape memory effect on heating and a maximum recoverable strain was found to be 2 %. The two-way shape memory effect was not observed on further cooling and heating.

Achieving multimodal locomotion by a crosslinked poly(ethylene-co-vinyl acetate)-based two-way shape memory polymer

Locomotion is a critically important topic for soft actuators and robotics, however, the locomotion applications based on two-way shape memory polymers (SMPs) have not been well explored so far. In this work, a crosslinked poly(ethylene-co-vinyl acetate) (cPEVA)-based two-way SMP is synthesized using dicumyl peroxide (DCP) as the crosslinker. The influence of the DCP concentration on the mechanical properties and the two-way shape memory properties is systematically studied. A Venus flytrap-inspired soft actuator is made by cPEVA, and it is shown that the actuator can efficiently perform gripping movements, indicating that the resultant cPEVA SMP is capable of producing large output force and recovering from large deformations. This polymer is also utilized to make a self-rolling pentagon-shaped device. It is shown that the structure will efficiently roll on a hot surface, proving the applicability of the material in making sophisticated actuators. With introducing an energy barrier, jumping can be accomplished when the stored energy is fast released. Finite element simulations are also conducted to further understand the underlying mechanisms in the complex behavior of actuators based on cPEVA SMP. This work provides critical insights in designing smart materials with external stimulus responsive programmable function for soft actuator applications.

Effect of one family of Ti3Ni4 precipitates on shape memory effect, superelasticity and strength properties of the B2 phase in high-nickel [001]-oriented Ti-51.5 at.%Ni single crystals

In this study, we investigated the effect of the number of Ti3Ni4 particle variants (obtained via stress-free and stress-assisted aging at 823 K for 1 h) on the shape memory effect, superelasticity, and strength properties of the B2-phase in high-nickel [001]-oriented Ti-51.5 at.% Ni single crystals. Four crystallographically equivalent variants of lenticular Ti3Ni4 particle with the {111}B2 habit plane and a diameter of 250–300 nm were obtained via stress-free aging. Aged under an applied compressive stress of 150 MPa along the <111> direction, single crystals contain predominantly one variant of Ti3Ni4 particle, forming plane-parallel plates with lengths from 1 to 5 μm. The oriented arrangement of semi-coherent Ti3Ni4 particles leads to the formation of long-range stress fields, an increase of 23 K in the martensitic transformation (MT) starting temperature Ms, the induction of a two-way shape memory effect, and a decrease of 200 MPa in the stress required to obtain the maximum reversible strain (1.5–1.7%) during cooling/heating cycles compared to stress-free aged single crystals. The number of variants of Ti3Ni4 particle determines the mechanism of the formation of B19′-martensite and the strength properties of the B2-phase (1600 MPa in stress-assisted aged crystals and 2100 MPa in stress-free aged crystals).

The Effect of Subsequent Stress-Induced Martensite Aging on the Viscoelastic Properties of Aged NiTiHf Polycrystals

This study investigated the effect of stress-induced martensite aging under tensile and compressive stresses on the functional and viscoelastic properties in Ni50.3Ti32.2Hf17.5 polycrystals containing dispersed H-phase particles up to 70 nm in size obtained by preliminary austenite aging at 873 K for 3 h. It was found that stress-induced martensite aging at 428 K for 12 h results in the appearance of a two-way shape memory effect of −0.5% in compression and +1.8% in tension. Moreover, a significant change in viscoelastic properties can be observed: an increase in internal friction (by 25%) and a change in elastic modulus in tensile samples. The increase in internal friction during martensitic transformation after stress-induced martensite aging is associated with the oriented growth of thermal-induced martensite. After stress-induced martensite aging, the elastic modulus of martensite (EM) increased by 8 GPa, and the elastic modulus of austenite (EA) decreased by 8 GPa. It was shown that stress-induced martensite aging strongly affects the functional and viscoelastic properties of material and can be used to control them.

Use of 4D-printing and shape memory alloys to fabricate customized metal jewels with functional properties

PurposeThis paper aims to examine customized NiTi jewels with functional properties fabricated through four-dimensional (4D)-printing.Design/methodology/approachTwo opened rings are fabricated through selective laser melting starting from 55.2Ni-Ti (wt.%) micrometric powder. After the additive process the two rings present the one-way shape memory effect (OWSME). A specific training is accomplished on one of the two printed rings to promote the two-way shape memory effect (TWSME). Both the samples, namely, the rings, respectively, presenting the OWSME and TWSME property, follow a series of post-processing routes to improve the surface finish. Furthermore, a thermal treatment at high temperature is used to create a thin colored oxide layer on the sample surface.FindingsResults show that the change of shape owing to the OWSME and TWSME properties allows the customized 4D-printed rings to be adaptable to environmental changes such as load and temperature variations. This adaptability improves comfort and fit of the jewels.Originality/valueTo the best of the authors’ knowledge, in this work, first cases of additively manufactured NiTi jewels are reported to propose innovative solutions in the design and processing industry of jewels.

Two-way shape memory effect with excellent cycling stability in TiNiCuNb alloy

Two-way shape memory effect (TWSME) and its cycling stability is of crucial importance for engineering applications. In present work, (Ti54Ni34Cu12)90Nb10 alloy with stable TWSME was developed. A two-way shape memory strain of 0.89% was obtained after proper training, which was decreased by 0.14% after 500 thermal cycles. The excellent cycling stability of TWSME is due to the improved geometric compatibility between martensite and parent phase and the introduction of β-Nb phase.

Prototyping of 4D-printed self-shaping building skin in architecture: Design, fabrication, and investigation of a two-way shape memory composite (TWSMC) façade panel

The article seeks to demonstrate the potential architectural utility of reversible 4D-printed material for flexible climate adaptation of building. This work presents the engineered design, fabrication, and performative effectiveness of a responsive façade morphing with the use of thermo-responsive shape-memory composites (SMCs). Load-free bidirectional motion of an SMC is configured by combining programmed shape-memory alloy (SMA) fibers and 3D-printed shape-memory polymer (SMP) matrix. Different thermomechanical properties were tested and applied to make building shape change possible according to the variation of outside temperature. For design experiments, the SMC models were fabricated and deployed over the exterior surface of a test building scale model. To help architectural communities better understand responsive material phenomena for building design application, the self-shaping material performance was modeled and evaluated through digital simulation, using theoretical constitutive equations and physical observation of the test building model. The findings reveal merits and opportunities of the smart material use and 4D-printed adaptive architecture, as well as several limitations in current technology and material development for building applications.

Thermomechanical training and structural tests for adaptive SMA bumps with two-way shape memory effect

In this paper, shape memory alloy (SMA) bumps with two-way shape memory effect (TWSME) are trained by simple but effective training approaches, which provides a new idea for the actuations of the shock control bump (SCB) on airfoil. Two different configurations of bump structures (2D and 3D SMA bumps) are designed and fabricated. The bumps are required to exhibit TWSME so that it can change its shape by heating and cooling between two stable states at austenitic phase and martensitic phase, respectively. To obtain the TWSME, the material is trained in the range of martensitic finish temperature and austenitic finish temperature whilst a displacement boundary condition is imposed. A set of fixtures, which can be assembled to the universal testing machine (UTM), are designed to achieve the clamped boundary condition during thermal cycles of the training process. After training, SMA bumps with the TWSME, that bulge at low-temperature and become flat at high, are obtained. Structural tests and deformation control are then carried out afterwards to show the deformation performance of the trained SMA bumps.

4D-printed parametric façade in architecture: prototyping a self-shaping skin using programmable two-way shape memory composite (TWSMC)

PurposeThis study aims to present an architectural application of 4D-printed climate-adaptive kinetic architecture and parametric façade design.Design/methodology/approachThis work investigates experimental prototyping of a reversibly self-shaping façade, by integrating the parametric design approach, smart material and 4D-printing techniques. Thermo-responsive building skin modules of two-way shape memory composite (TWSMC) was designed and fabricated, combining the shape memory alloy fibers (SMFs) and 3D-printed shape memory polymer matrices (SMPMs). For geometry design, deformation of the TWSMC was simulated with a dimension-reduced mathematical model, and an optimal arrangement of three different types of TWSMC modules were designed and fabricated into a physical scale model.FindingsModel-based experiments show robust workability and formal reversibility of the developed façade. Potential utility of this module for adaptive building design and construction is discussed based on the results. Findings help better understand the shape memory phenomena and presented design-inclusive technology will benefit architectural communities of smart climate-adaptive building.Originality/valueTwo-way reversibility of 4D-printed composites is a topic of active research in material science but has not been clearly addressed in the practical context of architectural design, due to technical barriers. This research is the first architectural presentation of the whole design procedure, simulation and fabrication of the 4D-printed and parametrically movable façade.

Arbitrarily Reconfigurable and Thermadapt Reversible Two-Way Shape Memory Poly(thiourethane) Accomplished by Multiple Dynamic Covalent Bonds.

The fabrication of a single polymer network that exhibits a good reversible two-way shape memory effect (2W-SME), can be formed into arbitrarily complex three-dimensional (3D) shapes, and is recyclable remains a challenge. Herein, we design and fabricate poly(thiourethane) (PTU) networks with an excellent thermadapt reversible 2W-SME, arbitrary reconfigurability, and good recyclability via the synergistic effects of multiple dynamic covalent bonds (i.e., ester, urethane, and thiourethane bonds). The PTU samples with good mechanical performance simultaneously demonstrate a maximum tensile stress of 29.7 ± 1.1 MPa and a high strain of 474.8 ± 7.5%. In addition, the fraction of reversible strain of the PTU with 20 wt % hard segment reaches 22.4% during the reversible 2W-SME, where the fraction of reversible strain is enhanced by self-nucleated crystallization of the PTU. A sample with arbitrarily complex permanent 3D shapes can be realized via the solid-state plasticity, and that sample also exhibits excellent reversible 2W-SME. A smart light-responsive actuator with a double control switch is fabricated using a reversible two-way shape memory PTU/MXene film. In addition, the PTU networks are de-cross-linked by alcohol solvolysis, enabling the recovery of monomers and the realization of recyclability. Therefore, the present study involving the design and fabrication of a PTU network for potential applications in intelligent actuators and multifunctional shape-shifting devices provides a new strategy for the development of thermadapt reversible two-way shape memory polymers.

Spinodal decomposition and martensitic transformation of the high manganese Mn‒xCu alloys fabricated by additive manufacturing

Mn‒Cu-based shape memory alloys have great potential owing to their excellent shape memory properties, high damping capacity, low production cost, and ease of fabrication. In this study, a selective laser melting (SLM) technique was used to design and manufacture a series of high-manganese Mn‒xCu (x=10–40 wt.%) alloys by blending the elemental powders. Spinodal decomposition and martensitic transformation of the alloys during SLM and heat treatment (HT) processes were investigated and correlated with the tensile, damping, and shape memory properties of the alloys. The results showed that γ‒(Mn, Cu) was the main constituent phase in all of samples subjected to SLM only (hereafter as-SLMed) and the SLMed + HTed Mn‒Cu alloys. The effect of the chemical composition and manufacturing process on the phase structural evolution of the Mn‒Cu alloys were monitored. The spinodal decomposition, martensitic transformation and α-Mn precipitation reactions occurred in the as-SLMed Mn‒xCu samples with x = 15–20 wt.%, x < 30 wt.%, and x < 15 wt.%, respectively. The tensile properties of the as-SLMed Mn‒xCu alloys followed a general downward trend with increasing Mn content, while the corresponding damping capacity and shape memory recovery strain showed the opposite trend. HT can promote spinodal decomposition and martensitic transformation to form an equiaxed γ‒(Mn, Cu) grain, parallel twin plate structure, tweed microstructure, and α-Mn precipitate in the alloys. The SLMed + HTed Mn‒30% Cu alloy displayed a better combination of tensile properties (764, 540 MPa, and 12.5%), damping capacity (tan δ = 0.072 at a strain amplitude of 900 × 10−6), and one-way and two-way (εsme = 1.6% and εtw = 0.7% under the pre-bending strain of 10%) shape memory properties. In addition, the performance of the as-SLMed Mn‒xCu (x = 15–20 wt.%) and SLMed + HTed Mn‒xCu (x = 30 wt.%) alloys is comparable with and even superior to those of multi-component and commercial Mn‒Cu-based alloys, respectively.

Novel two-way multiple shape memory effects of olefin block copolymer (OBC)/polycaprolactone (PCL) blends

The shape memory properties of olefin block copolymer (OBC)/polycaprolactone (PCL) crosslinked blends at different blend compositions were investigated. This is the first OBC-based two-way shape memory blends processes without external load under thermal and vapor stimuli. The deformation temperature of 80 °C was selected far away between the respective melting temperatures of PCL (56.5 °C) and OBC (110.3 °C) for the thermo-triggered two-way multiple shape memory behavior. The internal stress developed between the unmelted OBC crystalline region and crystallized PCL during cooling under pre-strain conditions played an important role in further melting-induced contraction and cooling-induced elongation without external load, even though the deformation temperature caused the complete melting of the crystalline region of PCL and the crystallinity of unmelted OBC was very small. As for the solvent vapor-triggered cases, the THF and n-hexane solvents were used. The bent sample shrank in response to the vapor stimulation, followed by expanding in the air. The blends remarkably showed rare solvent vapor-triggered reversible shape memory behavior without any external stress and pre-soaking treatment. This interesting finding was not reported earlier until now, to the best of our knowledge. This current finding unveils numerous possibilities to prepare multi-triggered blending systems with reversible shape memory behavior.

Effect of stress-induced martensite ageing on the one-way and two-way shape memory effect of [0 1 1]-oriented TiNiCu crystals under tension

In this paper, for the first time, we found that at tension value of the one-way shape memory effect (SME) was 9.9% at external stresses of 250 MPa of the [011]-oriented Ti50Ni40Cu10 alloy (at%) crystals, which exceeds the theoretical value 7.14% for the B2-B19-B19′ martensitic transformation (MT) under tension. It was shown that stress-induced martensite ageing (SIM-ageing) creates conditions for the realization of a tensile two-way SME (TWSME) of 2.5% and does not decrease the value of the one-way SME.

Correction to “Two-Way Shape Memory Polymers: Evolution of Stress vs Evolution of Elongation”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to “Two-Way Shape Memory Polymers: Evolution of Stress vs Evolution of Elongation”Andrés Posada-MurciaAndrés Posada-MurciaMore by Andrés Posada-Murcia, Juan Manuel Uribe-GomezJuan Manuel Uribe-GomezMore by Juan Manuel Uribe-Gomez, Jens-Uwe SommerJens-Uwe SommerMore by Jens-Uwe Sommer, and Leonid Ionov*Leonid IonovMore by Leonid Ionovhttps://orcid.org/0000-0002-0770-6140Cite this: Macromolecules 2021, 54, 17, 8255Publication Date (Web):August 28, 2021Publication History Published online28 August 2021Published inissue 14 September 2021https://doi.org/10.1021/acs.macromol.1c01562Copyright © 2021 The Authors. Published by American Chemical SocietyRIGHTS & PERMISSIONSArticle Views567Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (465 KB) Get e-Alerts Get e-Alerts

Use of shape memory alloy for active shock control bump application

A shape memory alloy (SMA) with composition of Ni50.1Ti49.9 (at. %) was used for fabrication of a 3-D bump structure intended for use as an active shock control bump (SCB) into a transonic wing. This kind of bump is a variable-geometry structure designed to reduce the drag induced by shock wave ensure wing’s aerodynamic performance over the entire range of operating conditions. To meet this target, the SMA bump requires to exhibit two-way shape memory effect (TWSME) so that it can yield continuous shape change by properly changing the driving temperature. Result from differential scanning calorimetry was first presented to provide material’s phase transformation temperatures. To obtain the TWSME, a thermo-mechanical training procedure was proposed and a set of training devices were designed for training SMA bump. The SMA bump in this paper is trained to have a relatively flat shape in high temperature and can swell up when cooling. After more than 80 times training, the TWSME of the material tends to be stable. Then the thermo-mechanical responses of the SMA bump which is subjected to about 100 times training was tested. The result shows that the trained SMA bump can generate about 1.2 mm maximum recoverable deformation during martensitic transformation, which is about 3% of the ratio of the deformation region. Finally, the influence of external load on the thermo-mechanical response of the trained SMA bump were also studied.

Step-wise R phase transformation rendering high-stability two-way shape memory effect of a NiTiFe-Nb nanowire composite

In this work, we designed a NiTiFe-Nb nanowire composite to achieve a high-stability and small-hysteresis R phase two-way shape memory effect (TWSME). The R-phase TWSME was achieved in the composite in an annealed state without thermomechanical training due to the inherent internal stresses associated with the Nb nanowires, as demonstrated by in situ synchrotron high-energy X-ray diffraction. Transmission electron microscopic analysis also revealed some details of the R-phase transformation process, which render an explanation of the high cyclic stability of the R-phase TWSME. The R-phase transformation in this NiTiFe-Nb nanowire composite was found to proceed over several stages, including the formation of precursor nanodomains of partial lattice distortion for the R phase, the formation of R phase particles of coordinated orientations, the coalescence of the R phase particles into selected plate variants of preferential orientations for TWSME, and the continued evolution of the R phase crystallographic structure for further TWSME with zero hysteresis. Such step-wise process of the R-phase transformation divides the total TWSME strain into segments of smaller magnitudes in the macroscopic behavior, and more importantly reduces the discrete lattice distortion mismatch at the transformation interface on the microscopic scale. This drastically reduces the chances of generating dislocations during the transformation process, thus rendering the high cyclic stability of the R-phase TWSME. Such intricate behavior may be closely related to the unique NiTiFe matrix – Nb nanowire microstructure and its unique inherent internal stress condition.