Multiple Shape Memory Effects Research Articles

Multiple Shape Memory Effect for Smart Helical Springs with Variable Stiffness over Time and Temperature

In this study, an analytical solution is presented to simulate the mechanical response of thermo-viscoelastic shape memory polymer materials considering the effects of time, temperature, loading rate, etc. Based on the proposed formulation and based on the curved-bar-torsion theory, the behavior of smart helical springs with variable stiffness concerning time and temperature is studied. Moreover, numerical solutions based on the finite element method are used to validate the proposed formulation. The presented formulations are evaluated for different mechanical loading and temperature conditions, and simulated the behavior of both helical compression and extension springs for force recovery or shape recovery processes of shape memory polymer materials. The presentation of multiple shape memory properties along with the effects of parameters such as temperature and rate of temperature have also been investigated. The proposed method is much faster than the numerical solution and the matching of the responses of the two methods at different loading conditions shows the accuracy of the presented method. Therefore, using this propound method, design or optimization processes can be used with much lower computational cost than numerical solutions.

Force and multiple-shape-recovery in shape-memory-polymers under finite deformation torsion-extension

This paper presents a general semi-analytic solution for the thermomechanical behavior of shape memory polymer (SMP) in large deformation, based on a thermo-viscoelastic constitutive model. The formulation presented in this paper is suitable for describing shape memory behaviors such as fixed-strain, stress-recovery and stress-free, strain-recovery, as well as for multiple shape memory effect in uniaxial and combined extension-torsion problems. To verify the results, a comparison has been carried out among the proposed formulation results and those of experiments and 3D finite element analysis outcomes. Compared to the finite element analysis, semi-analytical solutions are interesting due to their very low computational cost. It was observed that the solution time for the proposed method is much lower than the computational time needed for the FE analyses (around 1%). Therefore, the presented solution can be employed as an efficient tool for examining the effects of changing any of the material or geometrical parameters on smart structures consisting of SMP components under torsion-extension for their design and optimization, which involves a large number of simulations. Additionally, the proposed solution is suitable for calibrating material parameters in both uni-axial and 3D benchmark problem of torsion-extension.

Influence of Long-Term Storage on Shape Memory Performance and Mechanical Behavior of Pre-stretched Commercial Poly(methyl methacrylate) (PMMA).

In this paper, we experimentally investigate the influence of storage at 40 °C on the shape memory performance and mechanical behavior of a pre-stretched commercial poly(methyl methacrylate) (PMMA). This is to simulate the scenario in many applications. Although this is a very important topic in engineering practice, it has rarely been touched upon so far. The shape memory performance is characterized in terms of the shape fixity ratio (after up to one year of storage) and shape recovery ratio (upon heating to previous programming temperature). Programming in the mode of uniaxial tension is carried out at a temperature within the glass transition range to one of four prescribed programming strains (namely 10%, 20%, 40% and 80%). Also investigated is the residual strain after heating for shape recovery. The characterization of the mechanical behavior of programmed samples after storage for up to three months is via cyclic uniaxial tensile test. It is concluded that from an engineering application point view, for this particular PMMA, programming should be done at higher temperatures (i.e., above its Tg of 110 °C) in order to not only achieve reliable and better shape memory performance, but also minimize the influence of storage on the shape memory performance and mechanical behavior of the programmed material. This finding provides a useful guide for engineering applications of shape memory polymers, in particular based on the multiple-shape memory effect, temperature memory effect, and/or low temperature programming.

External Stress-Free Reversible Multiple Shape Memory Polymers.

The present work is focused on developing external stress-free two-way tripleshape memory polymers (SMPs). Accordingly, a series of innovative approaches are proposed for the material design and preparation. Polyurethane prepolymers carrying crystalline polytetrahydrofuran (PTMEG) and poly(ε-caprolactone) (PCL) as the switching phases are respectively synthesized in advance and then cross-linked to produce the target material. The stepwise method is believed to be conducive to manipulation of the relative contribution of PCL and PTMEG. Moreover, the chain extender, 2-amino-5-(2-hydroxyethyl)-6-methylpyrimidin-4-ol (UPy), is incorporated to establish hydrogen bonds among the macromolecules. By straightforward stretching treatment at different temperatures, the hydrogen bond networks are successfully converted into an internal stress provider, which overcomes the challenge of stress relaxation of the melted low melting temperature polymer (i.e., PTMEG) and increases the efficiency of stress transfer. Meanwhile, the contraction force of the switching phases is tuned to match the internal tensile stress. As a result, the internal stress provider can closely collaborate with melting/recrystallization of the crystalline domains, leading to the repeated multipleshape memory effects. The cross-linked polyurethane is thus able to reversibly morph among three shapes and displays its potentials as soft robot and actuator. The strategy reported here has the advantages of easily accessible raw materials, simple reaction, and facile programing/deprograming/reprograming, so that it possesses wide applicability.

Reprocessable and Multiple Shape Memory Thermosets with Reconfigurability

Multiple shape memory thermosets for various engineering applications have been quickly developed in recent years, mainly due to their stable thermomechanical performance, environmental stability, excellent chemical, solvent resistance, etc. However, these thermosets are inherently non-recyclable due to their chemically crosslinked properties, and it is difficult to make the permanent shapes of these thermosets sophisticated and geometrically complex, which significantly restricts a great variety of engineering applications in the industry and technology fields, mainly due to the economic inefficiency and environmental impact. Here, a thermoset with recyclability, multiple shape memory effect (multi-SME), and permanent shape reconfiguration is reported. After recycling, it also exhibits excellent mechanical properties without sacrificing the excellent multi-SME, combined elasticity (shape memory), and solid state plasticity, which can be easily scaled up and generalized to a variety of dynamic covalent networks.

Modeling shape-memory effects in amorphous polymers

Abstract The time-dependent behavior of glass transition can be used to achieve shape-memory behaviors in amorphous polymers. Thus, modeling the shape-memory effect in amorphous polymers requires considering the viscoelastic/viscoplastic behaviour across the glass transition region. Here, we discuss our past efforts to develop constitutive models for the glass transition behavior of amorphous polymers to predict the shape-memory behavior under a variety of conditions. We first demonstrate that a viscoelastic model with multiple relaxation processes can describe the temperature memory effect and multiple shape-memory effect in amorphous thermosets and thermoplastics. The viscoelastic model is further extended to a viscoplastic model. Comparison with experimental results shows that the viscoplastic model can accurately predict the partially constrained shape recovery of polymers programmed below the glass transition temperature. Finally, we present a constitutive model to describe the effect of solvent absorption on the thermomechanical properties and shape-memory behavior of amorphous polymers. We derive an explicit function to describe the influence of solvent concentration on viscosity and implement the model for finite element analysis. The thermo-chemo-mechanical coupled model is able to describe the isothermal recovery of programmed SMPs in water.

High strength hydrogels with multiple shape-memory ability based on hydrophobic and electrostatic interactions.

Hydrogels with multiple shape-memory ability have aroused great interest due to their promising applications in various fields. Nevertheless, the weak mechanical performance of most shape-memory hydrogels seriously impedes the practical application in more complex environments. Herein, we reported a novel hydrogel with both high mechanical and multi-shape memory properties composed of stearyl methacrylate (SMA), acrylic acid (AA) and quaternary chitosan (QCH). The electrostatic interactions between AA and QCH together with the hydrophobic interactions of alkyl chains in SMA endowed the hydrogel with great strain-stress and fatigue resistance. Furthermore, due to the reversible destruction and construction of physical cross-links, the prepared hydrogels also exhibited the shape-memory ability in response to different stimuli, such as temperature, pH and NaCl solution. Additionally, the multiple shape-memory effect could be accomplished via programmable combination because of the relatively independent physical interactions in the hydrogels.

A robotic multiple-shape-memory ionic polymer–metal composite (IPMC) actuator: modeling approach

The multiple-shape-memory ionic polymer–metal composite (MSM-IPMC) actuator can demonstrate complex 3D deformation. The MSM-IPMC has two distinct characteristics, which are the electromechanical actuation effect and the thermal-mechanical shape memory effect. The bending, twisting, and oscillating motions of the actuator could be controlled simultaneously or separately by means of thermal-mechanical and electromechanical transduction. In this study, a theoretical model for the MSM-IPMC was developed and experimentally investigated. Based on previous studies on the electromechanical actuation effect of ionic polymer–metal composite (IPMC), a comprehensive physics-based model of MSM-IPMC which couples the actuation effect and the multiple shape memory effect was developed. To verify the model, an MSM-IPMC sample was prepared and used in experimental testing. The simulation results were shown to be in good agreement with the experimental results obtained. The multiple shape memory and recovery rate of three different polymers, namely the Nafion, Aquivion and GEFC of different ions, which are the hydrogen, lithium and sodium, were also tested. Based on the results, it is shown that all the polymers demonstrate the multiple shape memory effect with varying amounts of programmable shapes. The ion type was shown to have an influence on the broad glass transition range of the polymers, which in turn dictated the number of possible programmable shapes for each membrane. The current study is beneficial for the better understanding of the multiple shape memory effect of MSM-IPMC.

A Facile and General Approach to Recoverable High-Strain Multishape Shape Memory Polymers.

Fabricating a single polymer network with no need to design complex structures to achieve an ideal combination of tunable high-strain multiple-shape memory effects and highly recoverable shape memory property is a great challenge for the real applications of advanced shape memory devices. Here, a facile and general approach to recoverable high-strain multishape shape memory polymers is presented via a random copolymerization of acrylate monomers and a chain-extended multiblock copolymer crosslinker. As-prepared shape memory networks show a large width at the half-peak height of the glass transition, far wider than current classical multishape shape memory polymers. A combination of tunable high-strain multishape memory effect and as high as 1000% recoverable strain in a single chemical-crosslinking network can be obtained. To the best of our knowledge, this is the first thermosetting material with a combination of highly recoverable strain and tunable high-strain multiple-shape memory effects.

Structure and Properties of Porous Alloys Based on NiTi Doped by Al, Fabricated by SHS-method

The effect of aluminum doping of porous TiNi-based alloy on structure, penetrability, strength properties and characteristic temperature intervals of martensitic transformations, multiple shape memory effect (MSME) parameters were studied. In this paper porous alloys from mixture of titanium, nickel and aluminum (CAl=0-2.0 at. %) powders were obtained by self propagation high temperature synthesis (SHS-method). Aluminum additives allow to obtain a material which is characterized by an increased content of fine pores 10-20 mm, uniform pore size distribution, an increased level of strength. The optimum concentration of Al to obtain high properties of material was defined. The porous TiNi-based alloys doped with aluminum are promising to solve a number of complex medical problems, such as in vascular surgery and cellular technologies.

Highly Stretchable, Shape Memory Organohydrogels Using Phase-Transition Microinclusions.

Shape memory effect in polymer materials has attracted considerable attention due to its promising applications in a variety of fields. However, shape memory polymers prepared by conventional strategy suffer from a common problem, in which high strain capacity and excellent shape memory behavior cannot be simultaneously achieved. This study reports a general and synergistic strategy to fabricate high-strain and tough shape memory organohydrogels that feature binary cooperative phase. The phase- transition micro-organogels and elastic hydrogel framework act synergistically to provide excellent thermomechanical performance and shape memory effect. During shape memory process, the organohydrogels exhibit high strain capacity, featuring fully recoverable stretching deformation by up to 2600% and compression by up to 85% beneath a load ≈20 times the organohydrogel's weight. Furthermore, owing to the micro-organogel and hydrogel heterostructures, the interfacial tension derived from heterophases dominates the shape recovery of the organohydrogel material. Simple processing and smart surface patterning of the shape memory behavior and multiple shape memory effects can also be realized. Meanwhile, these organohydrogels are also nonswellable in water and oil, which is important for multimedia applications.

Multiple shape memory effects of trans‐1,4‐polyisoprene and low‐density polyethylene blends

AbstractA novel series of shape memory blends of trans‐1,4‐polyisoprene (TPI) and low‐density polyethylene (LDPE) were prepared using a simple physical blending method. The mechanical, thermal and shape memory properties of the blends were studied and schemes proposed to explain their dual and triple shape memory behaviors. It was found that the microstructures played an important role in the shape memory process. In TPI/LDPE blends, both the TPI crosslinking network and LDPE crystalline regions could work as fixed domains, while crystalline regions of LDPE or TPI could act as reversible domains. The shape memory behaviors were determined by the components of the fixed and reversible domains. When the blend ratio of TPI/LDPE was 50/50, the blends showed excellent dual and triple shape memory properties with both high shape fixity ratio and shape recovery ratio. © 2017 Society of Chemical Industry

Ni–Mn–Ga Single Crystal Exhibiting Multiple Magnetic Shape Memory Effects

Both magnetically induced phase transformation and magnetically induced reorientation (MIR) effects were observed in one Ni50Mn28Ga22 single crystal sample by direct measurement of the magnetic field-induced strain. We investigated various twinning microstructures ranged from single twin interface to fine twinning and crossing twins to evaluate what controls the apparent twinning stress crucial for MIR. The main challenges for the applications of these effects are outlined.

A multiple-shape memory polymer-metal composite actuator capable of programmable control, creating complex 3D motion of bending, twisting, and oscillation.

Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. Here, we report an ionic polymer-metal composite actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. This paper introduces a soft multiple-shape-memory polymer-metal composite (MSMPMC) actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of the authors’ knowledge, this MSMPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability.

High performance multiple-shape memory behaviors of Poly(benzoxazole-co-imide)s

High temperature triggered multiple-shape memory poly(benzoxazole-co-imide)s with adjustable properties were prepared via facile random copolymerization 3,3′,4,4′-biphenyltetracarbolylic dianhydride (BPDA) with two different diamine of 4,4′-oxydianiline (ODA) and 5-amino-2-(4-aminobenzene) benzoxazole (BOA). The effect of polybenzoxazole on the molecular packing, physical properties and shape memory behaviors of poly(benzoxazole-co-imide)s was investigated systematically. The incorporation of polybenzoxazole into polyimides endows better mechanical properties, higher chain packing, broad glass transition temperature and excellent tunable dual-shape memory behaviors with shape fixity above 98% and shape recovery up to 98%. Besides, multiple-shape memory effects with high switching temperature are first achieved in poly(benzoxazole-co-imide)s, and the multiple-shape memory could be adjusted by choosing the two different switching temperatures. Lastly, the potential mechanism of multiple-shape memory behaviors of poly(benzoxazole-co-imide)s are suggested.

The effect of cobalt additives on martensitic transformations and deformation in sintered porous nickel titanium alloys

Porous nickel titanium (TiNi) shape memory alloys with cobalt additives have been obtained by reaction and diffusion sintering. Analysis of the experimental temperature dependence of the electric resistance and multiple shape memory effect leads to a conclusion that Co additives below 1 at % in reaction-sintered, and even more so in diffusion-sintered, alloys lead to a reduction in intrinsic internal stresses in the TiNi phase. Additives above 1 at % induce dispersion hardening of the alloy. At all concentrations, cobalt additives lead to obstacles for the martensitic phase transformations.

Solvent-driven temperature memory and multiple shape memory effects.

Thermally-activated temperature memory and multiple shape memory effects have been observed in amorphous polymers with a broad glass transition. In this work, we demonstrate that the same shape recovery behaviors can also be achieved through solvent absorption. We investigate the recovery behaviors of programmed Nafion membranes in various solvents and compare the solvent-driven and temperature-driven shape recovery response. The results show that the programming temperature and solvent type have a corresponding strong influence on the shape recovery behavior. Specifically, lower programming temperatures induce faster initial recovery rates and larger recovery, which is known as the temperature memory effect. The temperature memory effect can be used to achieve multi-staged and multiple shape recovery of specimens programmed at different temperatures. Different solvents can also induce different shape recovery, analogous to the temperature memory effect, and can also provide a mechanism for multi-staged and multiple shape memory recovery.

Modeling the multiple shape memory effect and temperature memory effect in amorphous polymers

Multiple pattern transformation can be achieved by combining the mechanical instability and multiple shape memory effect.

Relation between temperature memory effect and multiple-shape memory behaviors based on polymer networks

The temperature memory effect (TME) refers to the capability of shape memory materials to memorize the deformation temperature (Td). In this article, the TME of multiple-shape memory polymer based on a PMMA/PEG semi-interpenetrating polymer network (PMMA/PEG semi-IPN) and a PMMA-PCL covalently crosslinked polymer co-network (PMMA-PCL CPN) are studied, and the relation between the TME and the multiple-shape memory effect (SME) is investigated. The results indicate that both the PMMA/PEG semi-IPN and PMMA-PCL CPN can show the TME in a specific range of response temperatures but not in its entire range of glass transition temperatures (Tg). This paper further confirms that broad transition temperature is the key to realizing the TME and the multiple-SME. Furthermore, we discover that the characteristic temperature of the TME corresponds to the multi-step transition temperature of the multiple-SME for the first time. Consequently, the characteristic temperature of the TME can be directly used as a multi-gradient Td to achieve the multiple-SME. Thus it facilitates the selection of a multi-gradient Td in the multiple-SME. The paper also reveals the internal relation of broad Tg, TME and multiple-SME of PMMA/PEG semi-IPN and PMMA-PCL CPN.

Influence of heat treatment on shape memory effect in porous titanium nickel synthesized by the SHS process

An analysis of the influence of heat treatment on the features of variation in parameters of multiple shapememory effect for porous titanium nickel produced by the method of self propagating high-temperature synthesis (SHS) is presented. It is shown that heat treatment of porous titanium nickel substantially affects its structure and physicomechanical properties. Annealing at the temperatures within T = 400–600°C favors an improvement of its physicomechanical characteristics and manifestation of the maximum shape memory effect. It is revealed that a further increase in the temperature, however, results in deterioration of its properties. An optimal temperature of heat treatment of articles made from pore-permeable titanium nickel is proposed – T = 400–450°C for 1 hour in vacuum.