One-way Shape Memory Effect Research Articles

Coiled artificial muscles based on UHMWPE with large muscle stroke

Thermal sensitive сoiled artificial muscles with a large muscle stroke (87%) based on oriented ultrahigh molecular weight polyethylene fibers were created. The storage modulus and the recovery stress were used as indicators to determine the optimal conditions for the orientation process of the UHMWPE fibers. The working mechanism of the coiled artificial muscles was discussed in terms of a one-way shape memory effect (SME).

Stress relaxation behavior of columnar-grained Cu–Al–Mn shape memory alloys

Stress relaxation resistance is one of the key properties needed to shape memory alloys (SMAs) in the applications of fasteners, elastic contact components, etc. In this work, the stress relaxation behaviors in the superelastic (SE) and shape memory processes of columnar-grained (CG) Cu–Al–Mn SMAs were investigated under constant strain conditions for 100 h. The effects of loading strain and ambient temperature on the stress relaxation resistance was studied experimentally. The experimental results indicated that the stress relaxation resistance of CG Cu71.3Al17.0Mn11.7 SMAs could reach over 85% and 62% at 25 °C and 60 °C, respectively, at a loading strain of 2%~10%. The SE stress relaxation resistance almost remained constant in the martensite transformation stage; however, it linearly declined with increasing ambient temperature. The stress relaxation resistance for one-way and two-way shape memory effects (OWSME and TWSME) also reached 70% and 66%, respectively, in CG Cu72.7Al16.8Mn10.5 SMAs. The SE, OWSME and TWSME stress relaxation behaviors could be well described by a logarithmic model.

Buckling-controlled two-way shape memory effect in a ring-shaped bilayer

Shape memory polymers (SMPs) usually have a one-way shape memory effect. In this paper, an easy-operating method to realize a two-way shape memory effect was demonstrated in a ring-shaped bilayer structure where the two layers are SMPs with different thermal transition temperatures. By designing specific thermomechanical processes, the mismatched deformation between the two layers leads to a morphology change of ring-shaped bilayer structures from a smooth ring to a gear-like buckling shape under cooling and a reversible recovery to the smooth shape under heating. Such a morphology change is ascribed to occurrence and recovery of thermoelastic buckling. This method was validated by finite element simulation. We experimentally investigated the influence of pre-strain on buckling, and it was found that both the buckling occurrence and recovery temperature vary with pre-strain. Furthermore, considering a ring-shaped SMP–SMP bilayer structure, finite element analysis was conducted to study the influence of film thickness and modulus ratio of two layers on buckling behavior. The results showed that the critical buckling wavelength was greatly influenced by film thickness and modulus ratio. We made a theoretical analysis that accorded well with the numerical results.

Influence of Detwinning on the Shape Memory Effect in Ni55Fe18Ga27 Single Crystals

Deformation mechanisms, one-way and two-way shape memory effects were studied in the mode of compression in the [011] single crystal of the Ni55Fe18Ga27 alloy where the detwinning occurred during deformation and in the [001] single crystal where the detwinning was forbidden. It was found that the [001] and [011] crystals deformed by different mechanisms during compression to 5% (reorientation was in [001] crystal, and the reorientation and detwinning were in [011] crystal) and from 15 to 20% (the 14 M → L10 transition was in [001] crystal and plastic deformation of 14 M phase was in [011]). The compression of both single crystals from 5 to 15% occurred due to the same mechanisms: the 10 M ↔ 14 M transformation and the plastic deformation of the 14 M martensite. The 14 M and L10 phases were stable under load, and they transformed to the 10 M martensite on unloading. It was shown that the crystal orientation and detwinning hardly affected the value of the one-way shape memory effect since both crystals were in the 10 M martensite after preliminary deformation. In this case, the transformation of 10 M martensite to the austenite on heating was accompanied by a strain of about 5% and this was the maximum value of the shape memory effect. It was found that the detwinning significantly affected the temperature ranges of strain recovery. In the [011] crystal, the strain recovered in a very narrow interval on heating (1-2°C), whereas in the [001] crystal the shape memory effect was observed in “normal” temperature range (~ 10°C). The detwinning resulted in the formation of a large oriented internal stress during the preliminary deformation that increased the value of the two-way shape memory effect that was observed in [011] crystals in comparison with the [001] crystals.

A three-dimensional phenomenological model for shape memory alloys including two-way shape memory effect and plasticity

The one-way and two-way shape memory effects (SMEs) as well as the thermal hysteresis represent fundamental properties when dealing with the design of detachable and thermally-stable connection systems based on shape memory alloys (SMAs). Such properties can be induced and tuned by thermo-mechanical processes that include thermal treatments and severe pre-deformation in martensitic state, causing the onset of plastic strains. In such complex conditions, material modeling is of great importance to support the design. This paper proposes a generalization of the three-dimensional phenomenological constitutive model by Souza et al. (1998), in order to describe the behavior of severely pre-strained NiTi-based SMAs. The proposed model allows to describe pseudoelasticity, one-way and two-way SMEs, as well as additional physical phenomena evidenced experimentally, such as transformation temperatures’ evolution, thermal hysteresis, phase transformations at low stresses, thermal strains, and phase-dependent elastic properties. Several numerical simulations, ranging from uniaxial tests to the finite element analysis of two case-studies, are performed. Model results are in good agreement with the results of a performed experimental campaign and allow to discuss SMA behavior under such complex loading conditions.

Phase field simulation to one-way shape memory effect of NiTi shape memory alloy single crystal

Based on the Ginzburg-Landau theory and in the framework of thermodynamics, a three-dimensional phase field model was developed to simulate the one-way shape memory effect (OWSME) of NiTi shape memory alloy (SMA) single crystal originated from the martensite transformation and reorientation. A new reorientation strain was simultaneously introduced when a transformation strain was considered in the proposed model, and the phase field equations corresponding to the martensite transformation and reorientation were derived, respectively. From the simulations to the OWSME, it is found that: the martensite variants are grown in a self-coordinating manner and combined by twinned interfaces to reduce the local elastic energy during the temperature-induced transformation from B2 phase to B19′ one; then, the stress-induced martensite reorientation is completed through the migration of twinned interfaces and the variants with optimal orientations are obtained during the subsequent loading, and a residual strain is produced after the unloading; during the further heating after the unloading, a uniform temperature-induced reverse transformation from the single-oriented martensite variant to B2 austenite phase occurs, and the residual strain produced by the stress-induced martensite reorientation is progressively recovered.

Magnetoresistance properties of magnetic Ni-Mn-Sn-B shape memory ribbons and magnetic field sensor aspects operating at room temperature

Abstract In this study, the magnetotransport properties of the Ni48.95Mn37.74Sn13.32B3 ribbons prepared by melt-spinning technique were investigated in details. The martensitic-austenite phase transition was obtained between 280 K and 285 K which are near the room temperature. From ρ-H measurements, it was found that an anomalous Hall effect at 281, 283 and 285 K between Ms (martensite start temperature) and Mf (martensite finish temperature) temperatures is domianant mechanism. It was seen that a voltage variation of 5 µV (between 0 and 10 kOe) at a constant current of 1 mA is one of the best values found for the Heusler alloys. The ρ-H results revealed that the ribbons showed the magnetic field-induced one-way shape memory effect (SME). High voltage change caused by magnetoresistance was reached at a constant current of 100 mA at 298 K. The results suggest that the Ni-Mn-Sn-B ribbon is a potential candidate to prepare a magnetic field sensor operating at the room temperature.

Reprogrammable recovery and actuation behaviour of shape-memory polymers

Shape memory is the capability of a material to be deformed and fixed into a temporary shape. Recovery of the original shape can then be triggered only by an external stimulus. Shape-memory polymers are highly deformable materials that can be programmed to recover a memorized shape in response to a variety of environmental and spatially localized stimuli as a one-way effect. The shape-memory function can also be generated as a reversible effect enabling actuation behaviour through macroscale deformation and processing, specifically by dictating the macromolecular orientation of actuation units and of the skeleton structure of geometry-determining units in the polymers. Shape-memory polymers can be programmed and reprogrammed into arbitrary shapes. Both recovery and actuation behaviour are reprogrammable. In this Review, we outline the common basis and key differences between the two shape-memory behaviours of polymers in terms of mechanism, fabrication schemes and characterization methods. We discuss which combination of macromolecular architecture and macroscale processing is necessary for coordinated, decentralized and responsive physical behaviour. The extraction of relevant thermomechanical information is described, and design criteria are shown for microscale and macroscale morphologies to gain high levels of recovered or actuation strains as well as on-demand 2D-to-3D shape transformations. Finally, real-world applications and key future challenges are highlighted. Shape-memory materials can generate programmable movements triggered by an external stimulus, such as an environmental change. In this Review, the authors discuss mechanisms, fabrication schemes, characterization methods and applications of the one-way shape-memory effect enabling shape recovery and of reversible shape-memory effects exhibiting actuation behaviour.

Correction: One-way and two-way shape memory effects of a high-strain cis-1,4-polybutadiene–polyethylene copolymer based dynamic network via self-complementary quadruple hydrogen bonding

Correction for ‘One-way and two-way shape memory effects of a high-strain cis-1,4-polybutadiene–polyethylene copolymer based dynamic network via self-complementary quadruple hydrogen bonding’ by Qi Yang, et al., Polym. Chem., 2019, 10, 718–726.

One-way and two-way shape memory effects of a high-strain cis-1,4-polybutadiene–polyethylene copolymer based dynamic network via self-complementary quadruple hydrogen bonding

A polymer network based on a cis-1,4-polybutadiene–polyethylene copolymer exhibits multi- and two-way shape memory effects as well as a high-strain capacity.

A one-dimensional phenomenological model for the two-way shape-memory effect in semi-crystalline networks

The shape-memory effect (SME) in polymers is a stimuli-responsive feature that is attracting more and more attention, thanks to its usage in fields ranging from the biomedical sector to soft robotics. The two-way SME, in particular, has great potential for applications needing repeated cycling, e.g., actuators, and motivates the development of theoretical and numerical tools to support their design. The present paper aims to propose a one-dimensional finite-strain phenomenological model to describe the one-way SME as well as the two-way SME under stress conditions in thermo-responsive semi-crystalline crosslinked polymers. The model is simple, easy to implement, and based on parameters with a clear and direct physical interpretation and measurability. Model predictions are validated on experiments on semi-crystalline networks based on poly(ε-caprolactone) and demonstrate model ability in describing several material features as the effect of the crosslink density on SME, the dependence of microstructural evolution on applied load and heating/cooling rate, and the presence of thermal strains.

Unusual composition dependence of transformation temperatures in Ti-Ta-X shape memory alloys

Ti-Ta-X (X = Al, Sn, Zr) compounds are emerging candidates as high-temperature shape memory alloys (HTSMAs). The stability of the one-way shape memory effect (1WE), the exploitable pseudoelastic (PE) strain intervals as well as the transformation temperature in these alloys depend strongly on composition, resulting in a trade-off between a stable shape memory effect and a high transformation temperature. In this work, experimental measurements and first-principles calculations are combined to rationalize the effect of alloying a third component to Ti-Ta based HTSMAs. Most notably, an $\textit{increase}$ in the transformation temperature with increasing Al content is detected experimentally in Ti-Ta-Al for low Ta concentrations, in contrast to the generally observed dependence of the transformation temperature on composition in Ti-Ta-X. This inversion of trend is confirmed by the $\textit{ab-initio}$ calculations. Furthermore, a simple analytical model based on the $\textit{ab-initio}$ data is derived. The model can not only explain the unusual composition dependence of the transformation temperature in Ti-Ta-Al, but also provide a fast and elegant tool for a qualitative evaluation of other ternary systems. This is exemplified by predicting the trend of the transformation temperature of Ti-Ta-Sn and Ti-Ta-Zr alloys, yielding a remarkable agreement with available experimental data.

The Influence of Long-Term Storage on the Functional Properties of Shape Memory Alloys

The influence of long-term storage of TiNi-based and CuZnAl alloys on their functional properties was investigated. It was established that during 30 years’ storage of TiNiFe thermomechanical couplings, the stresses in them practically did not decrease. Couplings with CuZnAl alloy sleeves during storage weakened slightly. The one-way shape memory effect in equiatomic TiNi alloy did not change after 25 years. It was found that the value of two-way shape memory effect in the first cycle after storage at room temperature in martensitic state for more than 15 years was higher than before storage.

Functional Properties of Porous Ti-48.0 at.% Ni Shape Memory Alloy Produced by Self-Propagating High-Temperature Synthesis

The functional behavior of the porous shape memory alloy produced by self-propagating high-temperature synthesis from the Ti-48.0 at.% Ni powder mixture was studied. It was found that a large unelastic strain recovered on unloading and it was not attributed to the pseudoelasticity effect. A decrease in deformation temperatures did not influence the value of strain that recovered on unloading, while the effective modulus decreased from 1.9 to 1.44 GPa. It was found that the porous Ti-48.0 at.% Ni alloy revealed the one-way shape memory effect, where the maximum recoverable strain was 5%. The porous Ti-48.0 at.% Ni alloy demonstrated the transformation plasticity and the shape memory effects on cooling and heating under a stress. An increase in stress did not influence the shape memory effect value, which was equal to 1%. It was shown that the functional properties of the porous alloy were determined by the TiNi phase consisted of the two volumes Ti49.3Ni50.7 and Ti50Ni50 where the martensitic transformation occurred at different temperatures. The results of the study showed that the existence of the Ti49.3Ni50.7 volumes in the porous Ti-48.0 at.% Ni alloy improved the functional properties of the alloy.

Control of phase transformations and microstructure for optimum realization of one-way and two-way shape memory effects in removable surgical clips

The functioning of a newly developed “smart” clip for permanent or temporary clipping of the blood vessels is based on one-way and two-way shape memory effects (SME and TWSME, respectively) of Ti-Ni alloy. The clip remains in the ready-to-close position before it is locally heated up to 40–45°C. Once heated by a specially developed clip-holder device, it closes due to realization of the SME, thus softly clipping the vessel. Upon local cooling, the clip opens due to the TWSME realization and can be easily removed without trauma to the vessel. To solve the problem of realization of SME and TWSME in the required temperature ranges and with the best functional characteristics, a thermomechanical treatment of Ti-50.7at.%Ni alloy for controlled precipitation of Ti3Ni4 phase particles and subsequent martensitic transformations was developed. A special regime of the clip thermomechanical treatment, including hot rolling and post-deformation isothermal annealing (aging), SME training procedures, and special design of the clip, was developed to obtain the best combination of the recovery strain and recovery stress of the clip. The phase transformations and microstructure were studied using differential scanning calorimetry, X-ray diffractometry, and transmission electron microscopy. The functional properties of the clips were determined using a bending method for inducing strain. The bench tests of the clip confirmed the effectiveness of the optimized thermomechanical treatment and training regimes as well as the cross-shaped clip design.

Enhanced photomechanical response of a Ni–Ti shape memory alloy coated with polymer-based photothermal composites

A simple way to enhance the activation of shape memory effects with light in a Ni–Ti alloy is demonstrated. Using polydimethylsiloxane-carbon nanopowder (PDMS+CNP) composites as coatings, the one-way shape memory effect (OWSME) of the alloy can be triggered using low power IR light from a laser diode. The PDMS+CNP coatings serve as photothermal materials capable to absorb light, and subsequently generate and dissipate heat in a highly efficient manner, thereby reducing the optical powers required for triggering the OWSME in the Ni–Ti alloy. Experimental results with a cantilever flexural test using both, bare Ni–Ti and coated samples, show that the PDMS+CNP coatings perform as thermal boosters, and therefore the temperatures required for phase transformation in the alloy can be readily obtained with low laser powers. It is also shown that the two-way shape memory effect (TWSME) can be set in the Ni–Ti alloy through cycling the TWSME by simply modulating the laser diode signal. This provides a simple means for training the material, yielding a light driven actuator capable to provide forces in the mN range. Hence, the use of photothermal coatings on Ni–Ti shape memory alloys may offer new possibilities for developing light-controlled smart actuators.

High-Strain Shape-Memory Properties of Poly(Carbonate-Urea-Urethane)s Based on Aliphatic Oligocarbonates and L-Lysine Diisocyanate

ABSTRACTThe simultaneous capability of high-strain deformation and high shape recovery ratio constitutes a great challenge in design of the shape-memory polymers. Here we report on poly(carbonate-urea-urethane)s (PCUUs) synthesized by a precursor route, based on oligo(alkylene carbonate) diols, L-lysine diisocyanate (LDI), and water vapor. When programed with a strain of εprog = 800%, the PCUU networks exhibited a one-way shape-memory effect (1W-SME) with excellent shape fixity (> 97%) and shape recovery (> 99%) ratios. The switching temperatures (Tsw) varied between 50 and 56 °C and correlated to the melting transitions of the switching domains. The obtained PCUUs capable of high-strain are interesting candidate materials for degradable biomaterials as required in smart medical devices.

Rapidly quenched ferromagnetic ribbons with shape memory for magnetically controlled micromechanic devices

One-way shape-memory effect (SME) controlled by temperature and magnetic field in rapidly melt-quenched (RMQ) Heusler-alloy (Ni53Mn24Ga23) ribbons is experimentally studied. Two-way SME that results from training is demonstrated for submicron Ni53Mn24Ga23 samples. Reversible thermally and magnetically controlled bending of no less than 1.5% and deflection of no less than 2 μm are reached for composite Ni53Mn24Ga23/Pt microactuators with sizes of 25 × 2.3 × 1.7 μm3 in the presence of magnetic field of μ0 Н = 8 T at an initial temperature of 63°С.

On the origin of residual strain in shape memory alloys: experimental investigation on evolutions in the microstructure of CuAlBe during complex thermomechanical loadings

The behaviors of shape memory alloys (SMAs) strongly depend on the presence of different phases: austenite, thermally-induced martensite and stress-induced martensite. Consequently, it is important to know the phase volume fraction of each phases and their evolution during thermomechanical loadings. In this work, a three-phase proportioning method based on electric resistivity variation of a CuAlBe SMA is proposed. Simple thermomechanical loadings (i. e. pseudoplasticity and pseudoelasticity), one-way shape memory effect, recovery stress, assisted two-way memory effect at different level of stress and cyclic pseudoelasticity tests are investigated. Based on the electric resistivity results, during each loading path, evolution of the microstructure is determined. The origin of residual strain observed during the considered thermomechanical loadings is discussed. A special attention is paid to two-way shape memory effect generated after considered cyclic loadings and its relation with the developed residual strain. These results permit to identify and to validate the macroscopic models of SMAs behaviors.

Shape memory effects in porous Ti – 45.0 at.% Ni alloy produced by self-propagating high-temperature synthesis

One way and two-way shape memory effects were studied on heating and cooling of preliminarily deformed porous Ti – 45.0 at.% Ni alloy produced by self-propagating high-temperature synthesis. The porous samples were initially deformed to different strains at a temperature of 25 °C and then they were subjected to heating and cooling through the temperature range of the martensitic transformations. The maximum given strain during preliminary deformation was 16% because further deformation of the sample resulted in porous sample failure. The results obtained have shown that the functional behavior of porous TiNi alloys differs from the properties of cast TiNi alloy. A strain recovery on heating due to the realization of the one-way shape memory effect, and a strain accumulation on cooling caused by a two-way shape memory effect, were observed if the preliminary strain was equal to 10% or higher. The dependencies of the values of one-way and two-way shape memory effects on preliminarily strain were non-linear; the strain increased significantly when the given strain rose from 7 to 14%, and hardly changed if the given strain was larger than 14%.