Showing papers by "Jinsong Leng published in 2013"

A phenomenological approach for the chemo-responsive shape memory effect in amorphous polymers

Abstract: In this work, we present a phenomenological approach to study the state transition and working mechanism of the chemo-responsive shape memory effect (SME) in shape memory polymers (SMPs) The thermodynamics of polymer solution and free-energy theory are initially applied to quantitatively identify the factors that trigger a chemo-responsive SME After this, a field theory is developed to couple the chemical potential, stress and relaxation time in a polymer system with free-energy functions Furthermore, by means of combining together and utilizing the Gordon–Taylor (GT) theory and Free-Volume (FV) theory, the intrinsic plasticizing effect and generalized plasticizing effect are decoupled and quantitatively determined as the driving forces for the chemo-responsive SME in SMPs In addition, the influence of the intrinsic plasticizing effect and generalized plasticizing effect on the glass transition temperature (Tg) is consequently numerically modeled using the GT and FV equations, respectively Finally, the theoretical model is verified by the available experimental data reported in the literature and then compared with the simulation results of a semi-empirical model This phenomenological approach is expected to provide a powerful simulation tool for extracting the transition temperature parameter, theoretical prediction and experimental substantiation of the response of chemo-responsive SME in amorphous SMPs

Design considerations for shape memory polymer composites with magnetic particles

Abstract: Recent experimental investigations demonstrated that by incorporating magnetic particles into shape memory polymer matrices, a fast and remote heating of materials and shape recovery could be achieved by exposing the shape memory polymer composite to an electromagnetic field. The particles served as internal mini-antennas to transform the electromagnetic energy to inductive Joule heat, and subsequently to initiate the recovery of shape memory polymers (SMPs). In this paper, a three-dimensional computational study was carried out to study the coupling between heat transfer from spherically shaped particles and heat-induced shape recovery of SMP composites. The influence of particle size, particle volume fraction, particle heating temperature and rate to the magnetically induced shape recovery behavior was studied. The results in this paper provided a meaningful guidance for further designs and applications of the magnetic particles reinforced shape memory polymer composites.

The quintuple-shape memory effect in electrospun nanofiber membranes

Abstract: Shape memory fibrous membranes (SMFMs) are an emerging class of active polymers, which are capable of switching from a temporary shape to their permanent shape upon appropriate stimulation. Quintuple-shape memory membranes based on the thermoplastic polymer Nafion, with a stable fibrous structure, are achieved via electrospinning technology, and possess a broad transition temperature. The recovery of multiple temporary shapes of electrospun membranes can be triggered by heat in a single triple-, quadruple-, quintuple-shape memory cycle, respectively. The fiber morphology and nanometer size provide unprecedented design flexibility for the adjustable morphing effect. SMFMs enable complex deformations at need, having a wide potential application field including smart textiles, artificial intelligence robots, bio-medical engineering, aerospace technologies, etc in the future.

Property enhancement of polymer-based composites at cryogenic environment by using tailored carbon nanotubes

Abstract: At high attitude, all polymer-based materials would suffer from degradation at very low temperature in the range between 220 and 77 K (commonly called “at cryogenic environment”) and low atmospheric pressure. Within this temperature range, polymer-based composites behave very brittle and many micro-cracks are formed due to differential thermal coefficients of expansion (CTEs) between polymer matrix and high strength reinforcements. An anti-cracking mechanism in the composites is necessary and can be tailored by using nano-particles. Many studies have addressed that the use of single-walled (SWNTs) and multi-walled carbon (MWNTs) nanotubes could enhance the mechanical properties of polymer-based composites. However, interfacial bonding properties are always an issue as it would affect the efficiency and effectiveness of stress transfer in the composites. This paper addresses the viability of using coiled carbon nanotubes (CCNTs) and randomly-oriented nanoclay-supported nanotubes (NSCNTs) to enhance the mechanical properties of epoxy resin at the cryogenic environment.

Post buckling analysis of the shape memory polymer composite laminate bonded with alloy film

Abstract: As a new kind of smart materials, shape memory polymer composites (SMPCs) are being used in large in-space deployable structures. However, the recovery force of pure SMPC laminate is very weak. In order to increase the recovery force of a SMPC laminate, an alloy film was bonded on the surface of the laminate. This paper describes the post bulking behavior of the alloy film reinforced SMPC laminate. The energy term associate with this in-plane post buckling have been given .Based on the theorems of minimum energy, a mathematical model is derived to describe the relation between the strain energy and the material and geometry parameters of the alloy film reinforced SMPC laminate. The finite element model (FEM) is also conducted to demonstrate the validity of the theoretical method. The relation between the recovery force and the material geometry parameters were also investigated. The presented analysis shows great potential in the engineering application such as deployment of space structures.

A constitutive theory for shape memory polymers: coupling of small and large deformation

Abstract: At high temperatures, SMPs share attributes like rubber and exhibit long-range reversibility. In contrast, at low temperatures they become very rigid and are susceptible to plastic, only small strains are allowable. But there relatively little literature has considered the unique small stain (rubber phase) and large stain (glass phase) coupling in SMPs when developing the constitutive modeling. In this work, we present a 3D constitutive model for shape memory polymers in both low temperature small strain regime and high temperature large strain regime. The theory is based on the work of Liu et al. [15]. Four steps of SMP’s thermomechanical loadings cycle are considered in the constitutive model completely. The linear elastic and hyperelastic effects of SMP in different temperatures are also fully accounted for in the proposed model by adopt the neo-Hookean model and the Generalized Hooke’s laws.

Composite flexible skin with large negative Poisson's ratio range: numerical and experimental analysis

Abstract: This paper describes the manufacturing, characterization and parametric modeling of a novel fiber-reinforced composite flexible skin with in-plane negative Poisson’s ratio (auxetic) behavior. The elastic mechanical performance of the auxetic skin is evaluated using a three-dimensional analytical model based on the classical laminate theory (CLT) and Sun’s thick laminate theory. Good agreement is observed between in-plane Poisson’s ratios and Young’s moduli of the composite skin obtained by the theoretical model and the experimental results. A parametric analysis carried out with the validated model shows that significant changes in the in-plane negative Poisson’s ratio can be achieved through different combinations of matrix and fiber materials and stacking sequences. It is also possible to identify fiber-reinforced composite skin configurations with the same in-plane auxeticity but different orthotropic stiffness performance, or the same orthotropic stiffness performance but different in-plane auxeticity. The analysis presented in this work provides useful guidelines to develop and manufacture flexible skins with negative Poisson’s ratio for applications focused on morphing aircraft wing designs. (Some figures may appear in colour only in the online journal)

Active vibration control based on piezoelectric smart composite

Abstract: An aircraft?s vertical fin may experience dramatic buffet loads in high angle of attack flight conditions, and these buffet loads would cause huge vibration and dynamic stress on the vertical fin structure. To reduce the dynamic vibration of the vertical fin structure, macro fiber composite (MFC) actuators were used in this paper. The drive moment equations and sensing voltage equations of the MFC actuators were developed. Finite element analysis models based on three kinds of models of simplified vertical fin structures with surface-bonded MFC actuators were established in ABAQUS. The equivalent damping ratio of the structure was employed in finite element analysis, in order to measure the effectiveness of vibration control. Further, an open-loop test for the active vibration control system of the vertical fin with MFC actuators was designed and developed. The experimental results validated the effectiveness of the MFC actuators as well as the developed methodology.

Theory progress and applications of dielectric elastomers

Abstract: This paper summarizes the research progress of dielectric elastomer (DE) and its composite materials, including the introduction of materials, theoretical research development, and typical applications. First of all, the DE composite materials are introduced. Then, the theoretical research development of DEs is summarized. Finally, some applications as well as research prospects about DEs are listed.

Self-assembled carboxylic acid-functionalized carbon nanotubes grafting onto carbon fiber for significantly improving electrical actuation of shape memory polymers

Abstract: This study presents an effective approach to significantly reduce the electrical resistivity of thermally responsive shape memory polymer (SMP) nanocomposites that show Joule heating triggered shape recovery. Carboxylic acid-functionalized carbon nanotubes (CNTs) self-assembled and grafted onto the carbon fibers, were used to enhance the reliability in bonding between the carbon fiber and the SMP via van der Waals and covalent crosslinking, respectively. It was found that the electrical properties of SMP nanocomposites have been improved by the synergistic effect of carboxylic acid-functionalized CNTs and carbon fibers. Furthermore, the electrically responsive recovery behavior and temperature distribution were monitored and characterized. Finally, the molecular structure and temperature dependent electrical behavior were studied, and verified the electro-activated recovery performance of the SMP nanocomposites.

Effect of silk fiber to the mechanical and thermal properties of its biodegradable composites

Abstract: In recent years, natural fiber-reinforced biodegradable thermoplastics are being recognized as an emerging new environmentally friendly material for industrial, commercial, and biomedical applications. Among different types of natural fibers, silk fiber is a common type of animal-based fiber, has been used for biomedical engineering and surgical operation applications for many years because of its biocompatible and bioresorbable properties. On the basis of our previous study, a novel biodegradable biocomposite for biomedical applications was developed by mixing chopped silk fiber and polylactic acid (PLA) through the injection molding process. This article is aimed at studying the dynamic mechanical and thermal properties of the composite in relation to its biodegradation effect. At the beginning, it was found that the initial storage modulus of a silk fiber/PLA composite increased while its glass transition temperature decreased as compared with a pristine PLA sample. Besides, the coefficient of linear thermal expansions (CLTE) of the composite was reduced by 28%. This phenomenon was attributed to the fiber–matrix interaction that restricted the mobility of polymer chains adhered to the fiber surface, and consequently reduced the Tg and CLTE. It was found that the degraded composite exhibited lower initial storage modulus, loss modulus and tan delta (tan d) but the Tg was higher than the silk fiber/PLA composite. This result was mainly due to the increase of crystallinity of the composite during its degradation process.

Monitoring static shape memory polymers using a fiber Bragg grating as a vector-bending sensor

Abstract: We propose and demonstrate a technique for monitoring the recovery deformation of the shape-memory polymers (SMP) using a surface-attached fiber Bragg grating (FBG) as a vector-bending sensor. The proposed sensing scheme could monitor the pure bending deformation for the SMP sample. When the SMP sample undergoes concave or convex bending, the resonance wavelength of the FBG will have red-shift or blue-shift according to the tensile or compressive stress gradient along the FBG. As the results show, the bending sensitivity is around 4.07 nm/cm−1. The experimental results clearly indicate that the deformation of such an SMP sample can be effectively monitored by the attached FBG not just for the bending curvature but also the bending direction.

Exploration of the novel stacked structure and one-step fabrication of electrospun silica microbelts with controllable wettability

Abstract: A fairly general and direct synthesis for the preparation of silica microbelts with a novel stacked structure and controllable wetting behavior by using a combination of sol–gel chemistry and electrospinning techniques was explored successfully. The formation mechanism of the stacked structure and the potential application of the silica microbelts were confirmed.

Multifunctional carbon nano-paper composite

Abstract: Carbon Nanotube (CNT), for its excellent mechanical, electrical properties and nano size, large special surface physical property, become the most promising material. But carbon nanotube can still fabricated in micro dimension, and can’t be made into macro size, so to the carbon nanotube filled composite can’t explore the properties of the CNT. Carbon nano-paper is made of pure CNT, with micro pore, and it turn micro sized CNT into macro shaped membrane. Based on the piezo-resistivity and electrical conductivity of the carbon nano-paper, we used the carbon nano-paper as functional layers fabricate functional composite, and studies its strain sensing, composite material deicing and shape memory polymer (SMP) material electric actuation performance. The results shown that the resin can pregnant the nano paper, and there was good bond for nano paper and composite. The functional composite can monitoring the strain with high sensitivity comparing to foil strain gauge. The functional composite can be heated via the carbon nano paper with low power supply and high heating rate. The composite has good deicing and heat actuation performance to composite material. For the good strain sensing, electric conductivity and self-heating character of the carbon nano-paper composite, it can be used for self sensing, anti lightning strike and deicing of composite materials in aircrafts and wind turbine blades.

Fabrication of shape memory nanofibers by electrospinning method

Abstract: Shape memory nanofibers are capable of fixing a temporary shape and recovering a permanent shape in response to stimulus. Nafion nanofibers with shape memory effect are achieved via electrospinning technology. The resulting nanofibres exhibit the smooth, continuous, uniform fibrous structure. The diameter of nanofibers increases after annealing progress at different temperatures. The shape memory effect is evaluated in a fixed force controlled tensile test. Electrospun Nafion nanofibers show excellent shape memory properties upon heat. The shape fixity rates and shape recovery rates are about 95-96% and 87-89% after consecutive three shape memory cycles, respectively. The structure of electrospun nanofibers is stable and reversible for at least three cycles of shape memory tests. These results indicate that shape memory Nafion nanofibers can be used in a wide potential application fields such as smart materials and structures in the future.

Influence of the ultraviolet irradiation on the properties of TiO2-polystyrene shape memory nanocomposites

Abstract: To date, majority shape adaptations of shape memory polymer (SMP) are thermo responsive. A desire for isothermal, remotely controlled shape adaptations of SMP has motivated examinations of other stimulus. We successfully construct novel TiO2-polystyrene shape memory nanocomposites and investigate influence of the ultraviolet irradiation on the shape memory effect. This material is facilely fabricated by introducing TiO2 into polystyrene SMP. The properties of TiO2-polystyrene shape memory nanocomposites are characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectra (FT-IR), dynamic mechanical analysis (DMA), and diffused reflectance spectrum (DRS). Deriving from photoelectric foundational properties of TiO2, the TiO2-polystyrene shape memory nanocomposites can absorb light energy and undergo intra-molecular or inter-molecular physical or chemical transformations. Furthermore, the results of this work provide a useful baseline upon which researchers could explore more interesting behaviors of photosensitive SMP composite and investigate other more challenging actuation problems.

Plants and mechanical motion – a synthetic approach to nastic materials and structures

Abstract: Recently, an excellent book entitled Plants and Mechanical Motion – A Synthetic Approach to Nastic Materials and Structures, edited by Dr Norman M. Wereley, from the University of Maryland, and Dr ...

A new release device based on styrene-based SMP reinforced by carbon fiber

Abstract: Shape memory polymer composites (SMPC) release device can be fabricated to solve the disadvantages of traditional explosive release device, such as large weight, bad stability, and strong impact force and damage due to explosion. The release device is made up of two thin-walled tubes, the first one is responsible for the torsion, and the second is used to fit the first tube. The tubes are made from carbon fiber reinforced styrene-based shape memory polymer (SMP). Resistor heater is applied to heat the device and actuate the shape recovery process. This SMPC release device can connect the main device and the device which need released. When the instruction comes, it can separate the two devices immediately. Firstly, the first tube is heated by the resistor heater, then the twisting and stretching force is exited on the heating part of the tube, unloading after cooling, the two thin-walled tubes of release device is connected. Secondly, the twisted part of the first tube is heated, it twisted to the original angle, and then the stretched part drew back to the original shape after heating. So the working part pulled the claws of it out of the second tube automatically, and separated the release device to two parts, thus the release is completed. Optimal solutions are designed to achieve high driving efficiency. This paper has evaluated the strength and verified the feasibility of the SMPC release device, measured the tensile strength and the reverse effect, compared with the theoretical and experimental results. Finite element analysis is used to simulate the deformation.

Modeling mechanical behavior of epoxy-shape memory polymers

Abstract: Smart materials and structures is an international frontier field in current development of engineering and science. Representative of soft smart materials include Electroactive polymers (EAPs) and Shape Memory Polymers (SMPs), etc..As a new kind of smart deformation material, SMPs have a wide range of applications in the field of smart material and structures due to their controllable shape memory effects. Deformation mechanism of SMP material is the basis of its applications. This paper proposed an useful thermoviscoelastic constitutive model by considering thermal expansion, structure relaxation and viscoelastic properties of Epoxy-SMP material. To verify the applicability of the model, various experiments such as isothermal uniaxial tensile tests were carried out and then be simulated. The results showed that the constitutive model could nicely predict mechanical behavior of Epoxy-SMP, the proposed constitutive model is useful for the design of SMPs structures.

Fabrication and characterization of shape memory polystyrene foams

Abstract: In this project, shape memory polystyrene foam was fabricated from shape memory polystyrene and ethyl acetate/n-hexane as physical foaming agent based on suspension polymerization method. The foam of uniform pore structure with porosity ranging from 36%～45% have been made successfully. Both shape memory properties and physical properties were characterized. Shape memory polystyrene foam exhibited good shape memory properties-- completely recovery the initial undeformed shape after multiple cycles. The higher thermal stability was achieved compared with pure shape memory polystyrene. The glassy state property of the foam was increased from 75°C to 85°C as the content of filler increased from 0 to 30%.

Active Moving Polymers and Multifunctional Composites: Shape the Future Structures

Abstract: Smart materials can be defined as the materials that have the capability of sensing and reacting to environmental conditions or stimuli. In recent years, a wide range of novel smart materials have been developed, the applications of which now cover various important fields including aerospace, automobile, telecommunications, and so forth. This talk mainly focuses on recent progresses of Active Moving Polymer (i.e. Shape Memory Polymer, SMP), and SMP based composite structures, as well as their applications including aerospace, astronautics and biomedical engineering. This presented work summarizes the recent advances in novel SMP including epoxy-based SMP, styrene-based SMP, cyanate ester-based SMP, polyurethane-based SMP, multiple SMP, design and characterization of SMP composites (SMPCs) filled with nickel chains, short carbon fiber, carbon nanotube chains, carbon nanopaper, and so on. The SMP stimulus methods, including heat, electric, light, magnetic field, and solvent have been introduced. The application of SMPCs used in aircraft morphing and space deployable structures is also investigated.

Modelling of the structure-property relationships in the α- quartz structures

Abstract: The molecular mechanism has been employed to model the structure-property relationships of auxetic material with tetrahedral framework at the atomistic level. The germania α –quartz subject uniaxial stress loading in z direction will be investigated. The strain-dependent structure and mechanical properties will be predicted from the force field based simulations, including the transformation from positive-to-negative Poisson’s ratio behaviour and vice versa.

Structural Optimization of Actuator Distribution in the Sliding Wing

Abstract: In this paper the problem of optimal design of actuator position in the sliding wing structure is described and demonstrated. The executive mode of morphing structure is based on parallelogram structure with two degrees-freedom. With regard to the selection of actuator, the choice and control of size and number would be directly related to the weight of the vehicle. In this paper in the light of each parameter of parallelogram structure, the distribution and position of actuator in the parallelogram structure is properly optimized to obtain the feasible region of most appropriate position.

The electro-mechanical phase transition of Gent model dielectric elastomer tube with two material constants

Abstract: Applied to voltage, a dielectric elastomer membrane may deform into a mixture of two states under certain conditions. One of which is the flat state and the other is the wrinkled state. In the flat state, the membrane is relatively thick with a small area, while on the contrary, in the wrinkled state, the membrane is relatively thin with a large area. The coexistence of these two states may cause the electromechanical phase transition of dielectric elastomer. The phase diagram of idea dielectric elastomer membrane under unidirectional stress and voltage inspired us to think about the liquid-to-vapor phase transition of pure substance. The practical working cycle of a steam engine includes the thermodynamical process of liquid-to-vapor phase transition, the fact is that the steam engine will do the maximum work if undergoing the phase transition process. In this paper, in order to consider the influence of coexistent state of dielectric elastomer, we investigate the homogeneous deformation of the dielectric elastomer tube. The theoretical model is built and the relationship between external loads and stretch are got, we can see that the elastomer tube experiences the coexistent state before reaching the stretching limit from the diagram. We think these results can guide the design and manufacture of energy harvesting equipments.

Numerical modeling of dielectrics electrocaloric effect near the Ferroelectric-Paraelectric phase transformation

Abstract: Dielectrics with great electrocaloric effect (ECE) have great potential to be applied in modern refrigeration industry. Compared with the traditional refrigeration technology, it is environmentally friendly and has a higher efficiency. Researchers have found that compared with ECE occurring in ferroelectric phase, ECE in paraelectric state is giant. This paper is determined on calculating the ECE of several kinds of polar dielectric material so as to find some materials with giant ECE. First, we investigate the theoretical framework of ECE near the Ferroelectric-Paraelectric phase transformation, and we show the formula derivation of ECE near the Ferroelectric-Paraelectric phase transformation in the analytical method of the calculus derivation. Then we deduce the expression of phenomenological study parameters. Finally, we calculate the maximum temperature change, entropy change and the mechanical work of several kinds of dielectrics based on the expression deduced. We successfully find some dielectrics with giant ECE. The paper should offer great help in finding the dielectrics with giant ECE, which is of great value in application.