Shape Memory Polymer Fibers Research Articles

Multiscale modeling of vibration damping response of shape memory polymer fibers

Abstract Health of a structure under vibration loads is highly related to the damping characteristics of the system. This work explores an engineered smart Shape Memory Polymer Fiber (SMPF) system that is capable of adjusting its damping capabilities based on applied load frequency and temperatures. A SMPF based structure with smart vibration/damping capability is of interest to many industries including aerospace, automotive and biomedical sectors. SMPFs enable structure engineers to incorporate smart functionality into their design through programming or training of SMPFs. While SMPF structural applications in the case of static loadings have been studied, the application of SMPFs in mitigating vibration responses of a structure has not been fully addressed in the research arena. The vibration damping response of a SMPF material system is studied with a goal to design damping response of smart structures that can mitigate severe vibrations. In this work vibration damping response of a SMPF bundle is experimentally studied through Dynamic Mechanical Analyzer (DMA) machine, and a numerical model is developed to correlate the loss/storage moduli to the damping/stiffness characteristics of the SMPF system. The model is then applied to study forced vibration responses of SMPFs. DMA data are utilized to verify the performance of the proposed model. The presented experimental data and the numerical model provide insight into vibration damping application of SMPFs in smart structures.

Morphological and mechanical analysis of electrospun shape memory polymer fibers

Shape memory block co-polymer Polyurethane (PU) fibers were fabricated by electrospinning technique. Four different solution concentrations (5wt.%, 10wt.%, 15wt.% and 20wt.%) were prepared by using Tetrahydrofuran (THF)/N,N-dimethylformamide (DMF) (50:50, v/v) as solvents, and three different voltages (30kV, 35kV and 38.9kV) were determined for the electrospinning process. Solution properties were explored in terms of viscosity and electrical conductivity. It was observed that as the polymer concentration increased in the solution, the conductivity declined. Morphological characteristics of the obtained fibers were analyzed through Scanning Electron Microscopy (SEM) measurements. Findings indicated that fiber morphology varied especially with polymer concentration and applied voltage. Obtained fiber diameter ranged from 112±34nm to 2046±654nm, respectively. DSC analysis presented that chain orientation of the polymer increased after electrospinning process. Shape fixity and shape recovery calculations were realized. The best shape fixity value (92±4%) was obtained for Y10K30 and the highest shape recovery measurement (130±4%) was belonged to Y15K39. Mechanical properties of the electrospun webs were also investigated in both machine and transverse directions. Tensile and elongation values were also affected from fiber diameter distribution and morphological characteristics of the electrospun webs.

繊維状形状記憶ポリマーを複合した空気圧ラバーアクチュエータの試作

繊維状形状記憶ポリマーを複合した空気圧ラバーアクチュエータの試作

Stress memory polymers

ABSTRACTLike shape memory polymers, a novel phenomenon of stress memory was shown in which the stress of a material can respond to an external stimulus. This concept was further enlightened by a switch‐spring‐frame model that would eliminate the limitation of existing models which overlooked the stimulus responsive nature of such polymers. The discovery being reported in this article was stemmed from a real case study into shape memory polymer fibers in compression stocking for varicose veins. The breakthrough of stress memory enabled researchers to develop applications needing stimuli‐responsive forces, which can broaden the horizon of such smart polymers in emerging smart products in many multidisciplinary fields such as sensors, stress garments, and massage devices, electronic skins, and artificial muscles. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 893–898

Spider-silk-like shape memory polymer fiber for vibration damping

In this study, the static and dynamic properties of shape memory polyurethane (SMPU) fiber are reported and compared to those of spider dragline silk. Although the polymeric fiber has a lower strength compared to spider dragline silks (0.2–0.3 GPa versus 1.1 GPa), it possesses much higher toughness (276–289 MJ m−3 versus 160 MJ m−3), due to its excellent extensibility. The dynamic mechanical tests reveal that SMPU fiber has a high damping capacity (tan δ = 0.10–0.35) which is comparable to or even higher than that of spider silks (tan δ = 0.15). In addition, we found that, different programming methods change the shape memory and damping properties of the fiber in different ways and cold-drawing programming is more advocated in structural applications. These results suggest that the SMPU fiber has similar vibration damping and mechanical properties as spider silk, and may find applications in lightweight engineering structures.

Active origami by 4D printing

Recent advances in three dimensional (3D) printing technology that allow multiple materials to be printed within each layer enable the creation of materials and components with precisely controlled heterogeneous microstructures. In addition, active materials, such as shape memory polymers, can be printed to create an active microstructure within a solid. These active materials can subsequently be activated in a controlled manner to change the shape or configuration of the solid in response to an environmental stimulus. This has been termed 4D printing, with the 4th dimension being the time-dependent shape change after the printing. In this paper, we advance the 4D printing concept to the design and fabrication of active origami, where a flat sheet automatically folds into a complicated 3D component. Here we print active composites with shape memory polymer fibers precisely printed in an elastomeric matrix and use them as intelligent active hinges to enable origami folding patterns. We develop a theoretical model to provide guidance in selecting design parameters such as fiber dimensions, hinge length, and programming strains and temperature. Using the model, we design and fabricate several active origami components that assemble from flat polymer sheets, including a box, a pyramid, and two origami airplanes. In addition, we directly print a 3D box with active composite hinges and program it to assume a temporary flat shape that subsequently recovers to the 3D box shape on demand.

Active materials by four-dimension printing

We advance a paradigm of printed active composite materials realized by directly printing glassy shape memory polymer fibers in an elastomeric matrix. We imbue the active composites with intelligence via a programmed lamina and laminate architecture and a subsequent thermomechanical training process. The initial configuration is created by three-dimension (3D) printing, and then the programmed action of the shape memory fibers creates time dependence of the configuration—the four-dimension (4D) aspect. We design and print laminates in thin plate form that can be thermomechanically programmed to assume complex three-dimensional configurations including bent, coiled, and twisted strips, folded shapes, and complex contoured shapes with nonuniform, spatially varying curvature. The original flat plate shape can be recovered by heating the material again. We also show how the printed active composites can be directly integrated with other printed functionalities to create devices; here we demonstrate this by creating a structure that can assemble itself.

A self-healing particulate composite reinforced with strain hardened short shape memory polymer fibers

A particulate composite dispersed with thermoplastic particles and strain hardened short shape memory polymer fibers was prepared to evaluate its ability to repeatedly heal wide-opened cracks per the two-step close-then-heal (CTH) self-healing scheme. A two-step coating approach was used to enhance the shape fixity and workability of the cold-drawn programmed short polyurethane fibers. The relationship between recovery-stress and recovery-strain was experimentally determined by partially constrained shape recovery test. Notched beam specimens were prepared and fracture-healing was conducted up to five cycles. It is found that the composite was able to heal the wide-opened crack repeatedly with considerable healing efficiency. It is also found that the healing efficiency increases as the fiber length increases, but in a reduced increasing rate. The recovery stress-recovery strain of the strain hardened shape memory polymer fiber behaves nonlinearly. The coated fiber is more effective than the uncoated fiber in closing wide-opened cracks when the recovery strain is within a certain range.

Structural relaxation behavior of strain hardened shape memory polymer fibers for self‐healing applications

ABSTRACTIn this study, shape‐memory polyurethane (SMPU) fibers were strain hardened by cold‐drawing programming (CDP) process. The programmed fibers are experimentally studied on the physical and thermomechanical properties. Structural relaxation, which determines shape memory capability of the SMP fibers, is quantified by conformational entropy change. Based on the entanglement tube theory and reptation theory, the entropic force is derived as a “bridge” to link the stress relaxation and structural relaxation, and thus structural relaxation can be evaluated by stress relaxation. It was found that the CDP SMPU fibers would still have good crackclosing capability after 13 years of hibernation in polymer matrix composite. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013, 51, 966–977

Effect of strain hardening of shape memory polymer fibers on healing efficiency of thermosetting polymer composites

Recently, shape memory polymer fibers (SMPFs) have been used in a biomimetic two-step (Close-Then-Heal) self-healing system for healing macroscopic cracks. The objective of this study was to investigate the effect of cold-drawing programming of SMPFs on the healing efficiency of conventional thermosetting polymer composites and the possibility of healing wide-opened crack by localized heating. To achieve the objective, continuous SMPF strand reinforced conventional epoxy composite beam specimens, which were dispersed with thermoplastic particles, were prepared. The SMPF strands were cold-drawn to various pre-strain levels before casting the polymer matrix. Repeated fracture/healing test was conducted by uniaxial tension. It is found that the composites were able to repeatedly heal macroscopic cracks. Strain-hardening by cold-drawing increased the healing efficiency considerably. It was demonstrated that healing can be achieved by heating locally surrounding the cracked region. The mechanism for the enhanced recovery stress was due to cold-drawing induced molecular alignment and formation of some perfect crystals in the hard segment domain of the SMPF.

Cyclic Viscoplastic-Viscodamage Analysis of Shape Memory Polymers Fibers With Application to Self-Healing Smart Materials

The cold-drawn, programmed shape memory polymer (SMP) fibers show excellent stress recovery property, which promotes their application as mechanical actuators in smart material systems. A full understanding of the thermomechanical-damage responses of these fibers is crucial to minimize the trial-and-error manufacturing processes of these material systems. In this work, a multiscale viscoplastic-viscodamage theory is developed to predict the cyclic mechanical responses of SMP fibers. The proposed viscoplastic theory is based on the governing relations for each of the individual microconstituents and establishes the microscale state of the stress and strain in each of the subphases. These microscale fields are then averaged through the micromechanics framework to demonstrate the macroscale constitutive mechanical behavior. The cyclic loss in the functionality of the SMP fibers is interpreted as the damage process herein, and this cyclic loss of stress recovery property is calibrated to identify the state of the damage. The continuum damage mechanics (CDM) together with a thermodynamic consistent viscodamage theory is incorporated to simulate the damage process. The developed coupled viscoplastic-viscodamage theory provides an excellent correlation between the experimental and simulation results. The cyclic loading-damage analysis in this work relies on the underlying physical facts and accounts for the microstructural changes in each of the micro constituents. The established framework provides a well-structured method to capture the cyclic responses of the SMP fibers, which is of utmost importance for designing the SMP fiber-based smart material systems.

Nanotube fibers for electromechanical and shape memory actuators

Carbon nanotubes are light, stiff and electroactive materials particularly promising in the field of actuating materials. Indeed, carbon nanotubes can expand and contract upon charge injection and be used for the development of electromechanical actuators. Carbon nanotubes can also be included in polymers to improve their properties and bring specific functionalities. When added to shape memory polymers, carbon nanotubes yield an improved stiffness and the possibility to heat the material through Joule’s heating. Nevertheless, spatial ordering of the nanotubes is a critical issue in all these classes of actively moving materials. It is shown in this article that assembling nanotubes under the form of pure or composite fibers is an effective approach to orient carbon nanotubes on a large scale along a well defined direction. Nanotube alignment achieved via fiber drawing allows the optimization of properties of shape memory polymer fibers and electrochemical actuators. In particular, the mechanical response of pure nanotube fibers to electrical stimulations is investigated in liquid electrolytes. It is observed that the fibers can generate a stress one order of magnitude greater than that achieved with unaligned assemblies of nanotubes. We also present the properties of shape memory polymer fibers loaded with carbon nanotubes. These fibers generate a very large stress when they recover their shape after they have been stretched and cooled under tensile load. Composite nanotube polymer fibers also exhibit a temperature memory behavior, which is still raising fundamental questions regarding its microscopic origin.

A prerequisite for the effective transfer of the shape-memory effect to cottonfibers

Subtle interaction between shape-memory polymer and cellulose fibers within fabricsremains a critical issue for understanding their thermal–mechanical properties and thus theshape-memory behavior in cotton fibers. We demonstrate here the efficacy of Ramanspectroscopy to probe the induced stresses in warp and weft fibers, presentingphysicochemical features for cellulose fibers finished with macromolecule polyurethane andsmall-molecule dimethyloldihydroxyethyleneurea. Accordingly, a possible mechanism fortransfer of the shape-memory effect to fabrics is proposed. Forming as a coating on thefiber surface after the finishing process, the shape-memory polymer takes a critical role inreducing the residual stress in weft fibers, establishing the prerequisite for reserving theshape-memory effect to fabric. In addition, this work has demonstrated that Ramanspectroscopy is able to probe the residual stresses in cotton fabrics after being treated bychemicals in addition to that due to physical deformation. Our result provides clearevidence that in the finishing process strength reduction in fibers in general is not onlycaused solely by a chemical reaction, but also by a physical modification of the cottonstructure.

Melt spun thermoresponsive shape memory fibers based on polyurethanes: Effect of drawing and heat‐setting on fiber morphology and properties

AbstractThermoresponsive shape memory (SMP) fibers were prepared by melt spinning from a polyester polyol‐based polyurethane shape memory polymer (SMP) and were subjected to different postspinning operations to modify their structure. The effect of drawing and heat‐setting operations on the shape memory behavior, mechanical properties, and structure of the fibers was studied. In contrast to the as‐spun fibers, which were found to show low stress built up on straining to temporary shape and incomplete recovery to the permanent shape, the drawn and heat‐set fibers showed significantly higher stresses and complete recovery. The fibers drawn at a DR of 3.0 and heat‐set at 100°C gave stress values that were about 10 times higher than the as‐spun fibers at the same strain and showed complete recovery on repeated cycling. This improvement was likely due to the transformation brought about in the morphology of the permanent shape of the SMP fibers from randomly oriented weakly linked regions of hard and soft segments to the well‐segregated, oriented and strongly H‐bonded regions of hard‐segments. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2172–2182, 2007

417 マイクロメカニックスによる SMP 繊維含有インテリジェントマテリアルの剛性解析

A shape memory polymer (SMP) of polyurethane series can be designed for its glass-transition temperature T_g, beyond which a remarkable change in stiffness may occur, with in the range from -30℃ to 70℃. A material containing such SMP fibers may hence be also designed for its macroscopic stiffness by adjusting the type of T_g distribution of fibers. In the present reserch, micromechanical analysis on the macroscopic stiffness of such an intelligent material is performed by taking into cosideration the type of T_g distribution of fibers. Effects of temperature on the macroscopic elastic modulus E^^- and the poisson's ratio v^^- are calculated with respect to various types of T_g distribution of fibers. It can be see from the results that after shape recovery of fibers the value of E^^- increases and the value of v^^- decreases to become below zero.

Stability Control of Active Compressed Rods with Shape Memory Polymers

In structural systems, applied compressive force fields cause second-order effects that may not only influence the buckling behavior, but also enhance the internal stress and the deformation field in the structure. Specifically, slender and thin-walled structural elements subjected to compressive force fields may experience buckling instability, which may affect their service life. In the case of imperfection-sensitive systems, loading and geometric imperfections may drastically affect the buckling response and reduce the buckling resistance. This behavior may be positively influenced by a structural adaptation to bending effects. In this connection, an attempt is made to use the potentials of the adaptive systems to influence the second-order as well as the buckling response of the slender compression elements by means of the actuator components. To this end, the stability control problem of adaptive slender rods with embedded Shape Memory Polymer (SMP) actuators is theoretically treated. The main goal of this investigation was to explore the possibility of minimizing the end deflection of a cantilever rod under eccentrically applied force via actuation of an SMP fiber. First, the stability theory of spatial rods is outlined, and the non-linear governing equations of straight rods are derived. The specific case treated is the problem of a cantilever rod with a single eccentric SMP fiber under eccentrically applied end compressive force. Numerical calculations were carried out with the help of the Runge-Kutta method. It is shown that the response of the rod can be effectively controlled by the appropriate action of the SMP actuator. Specifically, the goal of minimizing the end deflection of the eccentrically loaded cantilever rod through the action of the SMP actuator is achieved. In carrying out the computations, the second-order effects arising from the action of SMP fiber as well as the axial force were taken into consideration. Moreover, the follower action of the SMP force was considered.