Reversible Shape Research Articles

The Effect of Ceo2 Addition on Transformation Temperatures and Wear Resistance of Cu-Al-Ni Shape Memory Alloys

SMAs can switch from one crystallographic structure to another in response to temperature or stress stimuli. When SMAs are exposed to mechanical cyclic stress, they can absorb and discharge mechanical energy by experiencing a reversible hysteretic shape change. SMAs are widely used for sensing, actuation, impact absorption, and vibration damping. This work studied the effect of CeO2 addition on the transformation temperature and wear resistance of Cu-Al-Ni SMAs. WhereCeO2 was added at different percent’s 0.5, 1, and 3 wt% to the base alloy, followed by casting and homogenization at 900oC. Some tests were carried out: Differential scanning calorimeter, Optical Microscope, Scanning Electron microscopy, Energy dispersion spectrometer, X-Ray Diffraction, and Wear and Hardness tests. OM and SEM tests reveal that both phases of martensite β and γ are found. Also, the additions of CeO2 show a visible effect on phase formation and transformation temperatures. It was observed that increasing of CeO2 particles in Cu-based SMAs owing to improve interfacial bonding between matrix and reinforcement and also observed that the variants become thicker with increasing in percent. Additions of different percentages of cerium oxide increase the hardness of Cu-Al-Ni SMAs. Due to the addition of CeO2 particles, the sample's wear rate decreases compared to pure SMAs.

Solvent‐Driven Biomimetic Soft Sensors and Actuators

AbstractThe emergence of soft actuators that exhibit large, complex, programmable, and reversible shape deformation is of fundamental interest having potential applications in optics, medicals, and robotics fields. However, existing soft actuators are generally driven by only few given external stimuli such as temperature, humidity, or light which limit their interactions with their surroundings. Here, biomimetic soft actuators that respond to a variety of solvent vapors via programmable motion studied by Finite Element Modeling (FEM) are presented. A versatile micromachining process is used to fabricate these biomimetic soft actuators able to bend, curve, and twist in different manners according to their designs mimicking stamen, seed pots, and petals of Bauhinia variegate and Dendrobium orchids. The kinetic parameters of the transient response and recovery actuation are taken as the input feature in principal component analysis (PCA) to discriminate analyte molecules. Finally, to broaden the accessible 3D motions and thus functions of these smart actuators, an origami approach is employed to provide further flexibility and novel controlled structural changes in continuum structures such as snake‐like soft actuators, walkers, and grippers.

Photopolymerization of ceramic/zeolite reinforced photopolymers: Towards 3D/4D printing and gas adsorption applications

Normally, 3D printed objects via photopolymerization usually don’t have fully optimized mechanical properties and functions. In this context, the addition of single filler usually can improve these properties through the access to composite materials. However, the addition of filler inevitably has a negative influence on the light penetration inside the composites strongly reducing the depth of cure. Hence, the fabrications of photo-composites based on a combination of two inorganic fillers (alumina Al2O3 and zeolite LTA-5A) are reported in this work. Compared to pure poly(ethylene glycol) diacrylate (PEGDA) and its other corresponding single filler-based composites, PEGDA with 25 wt% LTA-5A and 25 wt% Al2O3-200 had several improved properties: better depth of cure (DOC), good mechanical properties (the storage modulus, tensile strength, the Young’s modulus). Direct laser write (DLW) was used to manufacture 3D patterns and 3D cross-shaped objects with good resolution. Under the hydrothermal stimuli, a 4D printing behavior (reversible shape change) was observed on the 3D cross-shaped objects. In addition, the 3D object with the condition of 4D printing had the ability of withstand a heavy stuff (the mass difference was more than 100 times). This is the first time to report the fabrication of the double filler-based (50 wt%) composite (ceramic and zeolite) with 4D printing behavior and good mechanical properties. Interestingly, calcinated composites had a certain structure strength and good CO2 adsorption performance. Therefore, this work not only paves the way for the investigation of photo-composites filled with multiple fillers combinations (how to improve the mechanical properties and keep good depth of cure for composites via photopolymerization), but also shows us the potential applications in the field of 3D/4D printing, microlithography and functional composites.

Two-Dimensional Mechanics of Atomically Thin Solids on Water.

Movement of a three-dimensional solid at an air–water interface is strongly influenced by the extrinsic interactions between the solid and the water. The finite thickness and volume of a moving solid causes capillary interactions and water-induced drag. In this Letter, we report the fabrication and dynamical imaging of freely floating MoS2 solids on water, which minimizes such extrinsic effects. For this, we delaminate a synthesized wafer-scale monolayer MoS2 onto a water surface, which shows negligible height difference across water and MoS2. Subsequently patterning by a laser generates arbitrarily shaped MoS2 with negligible in-plane strain. We introduce photoswitchable surfactants to exert a lateral force to floating MoS2 with a spatiotemporal control. Using this platform, we demonstrate a variety of two-dimensional mechanical systems that show reversible shape changes. Our experiment provides a versatile approach for designing and controlling a large array of atomically thin solids on water for intrinsically two-dimensional dynamics and mechanics.

Reversible Shape-Shifting of an Ionic Strength Responsive Hydrogel Enabled by Programmable Network Anisotropy.

Reversible shape-shifting hydrogels exhibit great potential in diverse fields. Repeatable programmability for the shape transformation has newly been enabled in thermally responsive hydrogels via engineering of the chain orientation of the polymer network, which substantially promotes the transformation capability. However, diversified responsive behavior and the enabling mechanism require further investigation. Herein, we develop an ionic strength (IS) responsive hydrogel enabling the programmable reversible shape transformation based on a semi-interpenetrating network of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA). Deformation of the hydrogel upon external force can be fixed due to crystallization of PVA that underwent cyclic freezing-thawing. Therefore, the chain orientation can be retained in the deformed area, enabling the programmable IS responsive actuation. In contrast to the thermally responsive actuation originated from the lower critical solution temperature phase transition, the IS responsive actuation does not accompany any phase change and the corresponding mechanism is proposed. Reversible bending providing an actuation angle as large as 80° can be achieved after optimization of the PVA content. The PVA crystals can be melted upon heating, and the responsive actuation can thus be reprogrammed. In addition, utilizing a digital light 3D printer, the hydrogels are further fabricated into arbitrary geometries, thus realizing more complex actuations. Overall, our work provides a general strategy to develop reversible shape-shifting hydrogels and paves the way for soft actuators.

Helical carbon nanotubes filled phase change composites with reversible plasticity shape memory and photo-thermal conversion functions towards wide-temperature-range battery thermal management

The rigidity of battery thermal management systems (BTMS) and harsh environments are the obstacles to the development of fast charging/discharging of lithium-ion batteries. Herein, a straightforward path is provided to solve the above dilemma by synthesizing styrene-b-(ethylene-co-butylene)-b-styrene/paraffin wax/helical carbon nanotubes (SEBS/PW/HCNTs). 2D wide-angle X-ray diffraction demonstrated that the PW solid skeleton of SEBS/PW composites oriented along the stretching direction under the tensile stress resisted the elastic potential energy of SEBS to achieve room-temperature shape fixation. Furthermore, HCNTs as a three-dimensional and photo-thermal conversion filler were incorporated into SEBS/PW to impart the composites with rapid light-actuated shape memory and light-thermal conversion/storage capacities. Finally, a BTMS with high phase change efficiency (95.3%), reversible plasticity shape memory (RPSM), photo-thermal conversion and wide-temperature thermal management range from −60 to 50 °C was manufactured by combining the heating and cooling subsystems, which exhibited vast prospects in battery thermal management fields.

A constitutive model and its numerical implementation for reversible behavior of shape memory hydrogels

Shape memory hydrogels (SMHs) are kinds of smart materials with great importance in many fields, such as drug release and soft robotics. In order to design the structures base on SMHs, it is necessary to reveal the mechanism of the shape memory effect and establish the constitutive model of SMHs. However, the existing constitutive models can not describe some of important mechanical behavior of SMHs, such as reversible shape memory effects. In this paper, a three-dimensional finite deformation constitutive model is developed for SMHs with reversible shape memory effects caused by the conformation transition of N-isopropylacrylamide (PNIPAM). In order to well capture its reversible shape memory effect, the polymer network for PNIPAM is decomposed into two parts, coil PNIPAM and globule PNIPAM, with different reference configurations. Then this model is implemented into a user material subroutine (UMAT) and is used for simulating the equilibrium swelling, isothermal uniaxial tension, reversible shape memory behavior and multiple shape memory cycles of SMHs. Our model is validated by comparing the simulation results with experiments. The deformation of a more complex 3D structure and a bilayer structure containing SMHs are also numerically studied which demonstrates great potential of our model in exploring the application of SMHs.

Design and Development of High-Strength and Ductile Ternary and Multicomponent Eutectoid Cu-Based Shape Memory Alloys: Problems and Perspectives

An overview is presented on the structural and phase transformations and physical and mechanical properties of those multicomponent copper-based shape memory alloys which demonstrate attractive commercial potential due to their low cost, good shape memory characteristics, ease of fabrication, and excellent heat and electrical conductivity. However, their applications are very limited due to brittleness, reduced thermal stability, and mechanical strength—properties which are closely related to the microstructural features of these alloys. The efforts of the authors of this article were aimed at obtaining a favorable microstructure of alloys using new alternative methods of thermal and thermomechanical treatments. For the first time, the cyclic martensitic transformations during repeated quenching, methods of uniaxial megaplastic compression, or torsion under high pressure were successfully applied for radical size refinement of the grain structure of polycrystalline Cu-Al-Ni-based alloys with shape memory. The design of the ultra- and fine-grained structure by different methods determined (i) an unusual combination of strength and plasticity of these initially brittle alloys, both under controlled heat or hot compression or stretching, and during subsequent tensile tests at room temperature, and, as a consequence, (ii) highly reversible shape memory effects.

Programmable Shape Change in Semicrystalline Liquid Crystal Elastomers.

Liquid crystal elastomers (LCEs) are stimuli-responsive materials capable of reversible and programmable shape change in response to an environmental stimulus. Despite the highly responsive nature of these materials, the modest elastic modulus and blocking stress exhibited by these actuating materials can be limiting in some engineering applications. Here, we engineer a semicrystalline LCE, where the incorporation of semicrystallinity in a lightly cross-linked liquid crystalline network yields tough and highly responsive materials. Directed self-assembly can be employed to program director profiles through the thickness of the semicrystalline LCE. In short, we use the alignment of a liquid crystal monomer phase to pattern the anisotropy of a semicrystalline polymer network. Both the semicrystalline-liquid crystalline and liquid crystalline-isotropic phase transition temperatures provide controllable shape transformations. A planarly aligned sample's normalized dimension parallel to the nematic director decreases from 1 at room temperature to 0.42 at 250 °C. The introduction of the semicrystalline nature also enhances the mechanical properties exhibited by the semicrystalline LCE. Semicrystalline LCEs have a storage modulus of 390 MPa at room temperature, and monodomain samples are capable of generating a contractile stress of 2.7 MPa on heating from 25 to 50 °C, far below the nematic to isotropic transition temperature. The robust mechanical properties of this material combined with the high actuation strain can be leveraged for applications such as soft robotics and actuators capable of doing significant work.

4D Printed Multifunctional Composites with Cooling‐Rate Mediated Tunable Shape Morphing

AbstractMultifunctional composites can accomplish multiple tasks such as shape morphing, sensing, and load bearing using a single structure. Smart materials including liquid crystal elastomers (LCE) and shape memory polymers (SMP) have long been used as the primary components of multifunctional composites because of their shape and property changes in response to external stimuli. However, LCEs can generate rapid and reversible shape changes but are soft and require a constant temperature to retain their deformed shape; SMPs have favorable mechanical properties but few can achieve reversible actuations. Moreover, both LCEs and SMPs have limited capability for tunable shape morphing. Multi‐material 3D printing of smart materials, also known as 4D printing, has seen significant advances enabling the fabrication of composites with novel functionality. In this work, 4D printing is leveraged to create an LCE‐SMP composite that can achieve not only rapid and reversible shape changes, but also cooling‐rate regulated tunable shape morphing. The latter is achieved by harnessing the distinct time‐dependent thermomechanical properties of LCEs and SMPs. Furthermore, the composite has a high stiffness at low temperature to support heavy loads. The LCE‐SMP composite hence offers a novel approach to achieve tunable shape morphing for future engineering applications.

High-performance fibrous artificial muscle based on reversible shape memory UHMWPE

Shape memory polymer fibers (SMPFs) are an important branch of intelligent fibers. Due to their ability to deform under external stimuli, shape memory polymer fibers have been used in intelligent textiles, polymer fillers and medical fields, including surgical sutures, thrombectomy devices, compression stockings, etc. There have been many studies on SMPFs, but almost all reported SMPFs only exhibit a one-way shape memory effect (SME). The deformation process of the one-way SMPFs is irreversible, and the transition from temporary shape to permanent shape cannot be replicated by simply reversing the stimulus. To tackle this problem. We selected ultra-high molecular weight polyethylene (UHMWPE) as the polymer matrix to prepare external stress-free two-way SMPFs. UHMWPE powders are gel-spun and then hot drawn to yield raw UHMWPE fibers. After programming, the UHMWPE fibers possess high tensile strength (338.72 MPa) and Young's modulus (2287.34 MPa), as well as one-way SME, quasi two-way SME and external stress-free reversible two-way SME. The reversible strain of the prepared reversible shape memory UHMWPE fibers is 27.42%. Artificial muscles and actuators can be made from the programmed UHMWPE fibers. The programmed UHMWPE fibers can lift more than 250 times their own weight with ∼10% reversible strain. The programmed UHMWPE fibers are appropriate for industrial mass production since the preparation and programming processes are simple.

Deep Learning-Accelerated Designs of Tunable Magneto-Mechanical Metamaterials.

Metamaterials are artificially structured materials with unusual properties, such as negative Poisson's ratio, acoustic band gap, and energy absorption. However, metamaterials made of conventional materials lack tunability after fabrication. Thus, active metamaterials using magneto-mechanical actuation for untethered, fast, and reversible shape configurations are developed to tune the mechanical response and property of metamaterials. Although the magneto-mechanical metamaterials have shown promising capabilities in tunable mechanical stiffness, acoustic band gaps, and electromagnetic behaviors, the existing demonstrations rely on the forward design methods based on experience or simulations, by which the metamaterial properties are revealed only after the design. Considering the massive design space due to the material and structural programmability, a robust inverse design strategy is desired to create the magneto-mechanical metamaterials with preferred tunable properties. In this work, we develop an inverse design framework where a deep residual network replaces the conventional finite-element analysis for acceleration, realizing metamaterials with predetermined global strains under magnetic actuations. For validation, a direct-ink-writing printing method of the magnetic soft materials is adopted to fabricate the designed complex metamaterials. The deep learning-accelerated design framework opens avenues for the designs of magneto-mechanical metamaterials and other active metamaterials with target mechanical, acoustic, thermal, and electromagnetic properties.

Ionic liquid-catalyzed synthesis of carbon/polyurethane triboelectric nanocomposites with excellent flame retardancy and oil leak detection

A high-carbon (expandable graphite flakes and carbon black)–loaded polyurethane foam (PUF) composite was prepared using a green and efficient ionic liquid (IL) catalyst. The carbon/PUF composite exhibited excellent flame retardancy and was highly versatile for application in oil leak detection and as triboelectric nanogenerator (TENG). The effect of the IL on the foamability of the carbon/PUF composite was thoroughly investigated. The IL promoted the expansion of the carbon/PUF composite and the microcellular pore formation in it, thereby affording a sponge with low density, excellent flexibility, and compressibility. Owing to the presence of high-carbon fillers, the resultant sponge exhibited excellent flame retardancy by (i) avoiding melt dripping after ignition by a butane torch (∼1400 °C, applied for 20 s), (ii) self-extinguishing after torch removal, and (iii) preventing foam collapse. Additionally, it can pass the UL-94 V-0 rating and the critical fire retardancy metrics, i.e., peak heat release rate, total heat release, and total smoke release, were reduced by 73%, 78%, and 92%, respectively. A flame retardant (FR)-TENG was designed using the carbon/PUF composite. The FR-TENG could be attached to the insole of a shoe, generating an output of 36 and 100 V upon walking and running, respectively. This output was sufficient to concomitantly glow 38 LEDs. Interestingly, owing to the oil-induced reversible shape change, the carbon/PUF composite can be used for the fabrication of high-efficiency oil leak sensors to detect oil spills in pipelines and different water environments. This study offers a new perspective for the development of flame retardant and multifunctional foam-based materials.

Magnetically Actuated Reconfigurable Metamaterials as Conformal Electromagnetic Filters

Electromagnetic (EM) metamaterials with tailored properties are developed for wave manipulation, filtering, and cloaking for aerospace and defense applications. While traditional EM metamaterials exhibit fixed behaviors due to unchangeable material properties and geometries after fabrication, reconfigurable EM metamaterials allow for tunable performance through electrical/mechanical reconfiguration strategies. Traditional biasing circuit‐based electrical reconfiguration poses challenges due to complex circuit design, while motor‐driven mechanical reconfiguration can lead to bulky and tethered structures with restricted adaptability. Herein, magnetically actuated structurally reconfigurable EM metamaterials with enhanced adaptability/conformability to different geometries, showing merits of fast, reversible, and programmable shape morphing, are developed. Magnetic actuation enables metamaterial's mechanical reconfiguration between flat deployed, flat folded, curved deployed, and curved folded states for both conformal and freestanding 3D shape morphing. Locally, the EM metamaterials fold subwavelength units for tunable properties, switching between all‐pass and band‐stop behaviors upon structural reconfiguration. Globally, the structure can conform and morph to different curved surfaces. The structurally reconfigurable metamaterial also serves as a medium for customizable subwavelength units by rationally designing attached conductive patterns for varied filtering performances such as narrow‐band, dual‐band, and wide‐band filtering behaviors, illustrating the design flexibility and application versatility of the developed structurally reconfigurable EM metamaterial.

Bio-inspired shape morphing soft magnetic locomotion actuators - a novel method of preparation and testing

Soft magnetic materials have drawn the attention of researchers worldwide due to their field response actuation, reversible shape morphing capability, remote controllability, an extensive penetration range in numerous circumstances, and diverse applications in the field of engineering, robotics, and medical science. The fabrication and programming of these actuators have been difficult, expensive, and complex, specifically in generating locomotion. This work aims at achieving the kinetic locomotion in actuators inspired by the caterpillar, inchworm, and centipede using a very simplistic approach. To achieve this, a programming technique has been developed through which a magnetic elastomer can be programmed on the curing bed to mimic the motion of the organisms mentioned above. The Carbonyl Iron (CI) particles dispersed in a viscous thermoplastic polyurethane (TPU) solution are cured under a magnetic field generated using a rotating permanent magnet. In the presence of a magnetic field, the magnetic particles tend to align in the direction of the magnetic field in the matrix. After curing, the actuator has an initial shape that changes to the programmed shape upon applying the magnetic field. The change in shape depends on the intensity of the magnetic field, i.e. if the magnetic field during programming was 0.5 T, then to achieve the programmed shape, we need to maintain the field value greater than or equal to 0.5 T. At the lower field values, the change in shape is slow. Thus, locomotion of the sample has been achieved by controlling the magnetic field intensity.

A NURBS-based inverse analysis of swelling induced morphing of thin stimuli-responsive polymer gels

Gels are a mixture of cross-linked polymers and solvents, and have been widely studied in recent years for a diverse range of biomedical applications. Because gels can undergo large, reversible shape changes due to swelling, their complex physical response must be modeled by coupling large reversible deformation and mass transport. An ongoing challenge in this field is the ability to capture swelling or residual swelling-induced of such stimuli-responsive gels from initially flat two-dimensional (2D) to three-dimensional (3D) curved shapes. Specifically, because such shape changes typically involve large deformations, shape changes, and the exploitation of elastic instabilities, it remains an open question as to what external stimulus should be prescribed to generate a specific target shape. Therefore, we propose a novel formulation that tackles, using both nonlinear kinematics and material models, the coupling between elasticity and solvent transport using Kirchhoff–Love shell theory discretized using isogeometric analysis (IGA). Second, we propose an inverse methodology that chemomechanically couples large deformation and mass transport to identify the external stimuli prescribed to generate a specific target shape. Our numerical examples demonstrate the capability of identifying the required external stimuli, with the implication that the reconstructed target shapes are accurate, including cases where the shape changes due to swelling involve elastic instabilities or softening. Overall, our study can be used to effectively predict and control the large morphological changes of an important class of stimuli-responsive materials.

Helical Liquid Crystal Elastomer Miniature Robot with Photocontrolled Locomotion

AbstractMiniature liquid crystal elastomer (LCE) based soft robots with multidirectional locomotion ability and multifunctionality have captured the extensive interest of researchers for a wide range of potential applications. Generally, the subsistent actuation modes for most LCE soft robots present several simple shape‐changing under external stimuli. Although elaborately designed for complicated structures, they still achieve limited mobility, restricting the practical applications severely. Herein, a photo‐controllable helical soft robot (PHSR) prepared with near‐infrared (NIR) light active LCE is reported. The 3D helical architecture of PHSR is constructed by manually twisting the LCE strip. The irradiation of NIR light transforms the basic reversible shape deformations (shrinking/elongating, winding/unwinding, and bending) of PHSR to macroscopic photomobility. As the torsional orientation of mesogens generated by manually twisting process, the rolling direction can be controlled by the scanning direction of the NIR spot. The flexible steering motion is in favor of performing various tasks such as traversing gap, climbing, and outputting mechanical work, suggesting that PHSR with directional photomobility and multifunction can be extended to a variety of applications.

Multi-responsive chromatic hydrogel exhibiting reversible shape deformations

In this work, deformable and chromatic hydrogel triggered by multi-stimuli was fabricated. This hydrogel was composed of N-isopropylacrylamide (NIPAAm), acryl-6-aminocaproic acid (A6ACA), and spiropyran (SP) derivatives, which possessed ferric ion (Fe3+) and temperature-triggered shape deformations properties as well as chromatic behavior. Under ultraviolet light irradiation, the SP isomer in the hydrogel transformed to the merocyanine (MC) isomer, and the hydrogel showed the characteristic UV–Vis absorption peak of MC at 540 nm. The hydrogel revealed the selective chromatic response to Fe3+ with the disappearance of the absorption peak of MC. Using ionoprinting technology, the hydrogel deformed programmatically in the presence of Fe3+. Moreover, owing to the anisotropic structure of the chromatic hydrogel, it realized reversible bending deformation triggered by temperature. The behaviors of hydrogels in response to dual stimuli (Fe3+ and temperature) were further investigated, and the hydrogel showed programmable, spatiotemporal, and complex deformation behaviors, accompanying by the color change. This hydrogel will have great application potential in soft robotics, soft actuators, and environmental sensors.

Self-Sensing Actuators Based on a Stiffness Variable Reversible Shape Memory Polymer Enabled by a Phase Change Material.

Soft actuators with integrated mechanical and actuation properties and self-sensing ability are still a challenge. Herein, a stiffness variable polyolefin elastomer (POE) with a reversible shape memory effect is prepared by introducing a typical phase change material, i.e., paraffin wax (PW). It is found that the variable stiffness of POE induced by PW can balance the reversible strain and load-bearing capability of actuators. Especially, carbon nanotubes (CNTs) are concentrated in a thin surface layer by spraying and hot pressing in the soft state of POE/PW blends, providing signal transductions for the strain and temperature perception for actuators. Taking advantage of tunable reversible deformation and mechanical transformation of the POE/PW actuator, different biomimetic robotics, including grippers with high load-bearing capability (weight-lifting ratio > 146), walking robots that can sense angles of joints, and high-temperature warning robots are demonstrated. A scheme combining the variable stiffness and electrical properties provides a versatile strategy to integrate actuation performance and self-sensing ability, inspiring the development of multifunctional composite designs for soft robotics.

Influence of humidity on the rheology of thermoresponsive shape memory polymers

Shape Memory Polymers (SMPs) have the inherent ability to maintain a reversible temporary shape and restore a permanent shape under an external trigger. The class of materials has great potential to contribute to smart applications in soft robotics, aerospace, actuation and biomedicine. In these potential application domains, materials are often exposed to large fluctuations due to humidity influences. Therefore, a novel approach is developed to characterize the stronlgy coupled thermal, humidity and time-dependent behavior of polyurethane-based SMP. Weight gain measurements with disk samples of dimension 35,times 35 times 1.5 text {mm}^text {3} and linear expansion tests with rectangular samples of dimension 10 times 40 times 1.0 text {mm}^text {3} at different relative humidity are carried out to perform the isothermal and isohumid dynamic measurements in thermodynamic equilibrium. The time-temperature superposition is used to characterize and compare the viscoelastic properties at different relative humidity. Concerning effective material properties, a major finding of this investigation is the horizontal shift of the material parameter in the temperature space due to the presence of humidity. Thus, the humidity-dependent material behavior is fully described by a humidity-dependent glass transition temperature. The measured experiments provide a full description of the thermal, humidity and mechanical behavior of SMPs.Graphical abstract