Co-reporter:Hongqiu Wei, Qiwei Zhang, Yongtao Yao, Liwu Liu, Yanju Liu, and Jinsong Leng
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 1) pp:
Publication Date(Web):December 20, 2016
DOI:10.1021/acsami.6b12824
Four-dimensional (4D) active shape-changing structures based on shape memory polymers (SMPs) and shape memory nanocomposites (SMNCs) are able to be controlled in both space and time and have attracted increasing attention worldwide. However, conventional processing approaches have restricted the design space of such smart structures. Herein, 4D active shape-changing architectures in custom-defined geometries exhibiting thermally and remotely actuated behaviors are achieved by direct-write printing of ultraviolet (UV) cross-linking poly(lactic acid)-based inks. The results reveal that, by the introduction of a UV cross-linking agent, the printed objects present excellent shape memory behavior, which enables three-dimensional (3D)–one-dimensional (1D)–3D, 3D–two-dimensional (2D)–3D, and 3D–3D–3D configuration transformations. More importantly, the addition of iron oxide successfully integrates 4D shape-changing objects with fast remotely actuated and magnetically guidable properties. This research realizes the printing of both SMPs and SMNCs, which present an effective strategy to design 4D active shape-changing architectures with multifunctional properties. This paves the way for the further development of 4D printing, soft robotics, flexible electronics, minimally invasive medicine, etc.Keywords: 4D shape-changing structures; direct-write fabrication; remotely actuated behavior; shape memory nanocomposite; shape memory polymer;
Co-reporter:Jianping Gu, Jinsong Leng, Huiyu Sun
Mechanics of Materials 2017 Volume 111(Volume 111) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.mechmat.2017.04.008
•A thermoviscoelastic finite deformation constitutive model is proposed.•An internal state variable modeling approach based on thermodynamics is used.•The temperature dependence of the model parameters is studied.Shape memory polymers (SMPs) are a class of smart materials which can recover a large pre-deformed shape in response to external stimulus. A thermoviscoelastic finite deformation constitutive model incorporated with structural and stress relaxation to capture the material behavior in the vicinity of the glass transition is developed for thermally activated amorphous SMPs in the paper. The incorporation of the Adam–Gibbs model for structure relaxation and the modified Eying model for viscous flow into a thermoviscoelastic finite deformation modeling framework is the main feature of the model. Differing from the traditional phenomenological fictive temperature modeling approach, an internal state variable modeling approach developed recently based on thermodynamics is used in the model. Besides, the temperature dependence of the model parameters is studied in the research. Comparisons between the simulation results and the experimental data show good agreement. Furthermore, the predictability of the model is examined by a parametric study and the results also demonstrate the validity of the model.
Co-reporter:Jian Huang, Qiuhua Zhang, Fabrizio Scarpa, Yanju Liu, Jinsong Leng
Composite Structures 2017 Volume 179(Volume 179) pp:
Publication Date(Web):1 November 2017
DOI:10.1016/j.compstruct.2017.07.091
This work describes the out-of-plane bending performance, shape memory effect and variable stiffness of a zero Poisson’s ratio honeycomb structure made from the tessellation of re-entrant hexagons and thin plates. The re-entrant hexagons are fabricated with ABS plastics and the thin plates are made from thermosetting styrene-based shape memory polymers (SMPs). The hexagons and the SMP plates are bonded within the groove joints in the thickness direction of the re-entrant cell units. The re-entrant hexagons generate out-of-plane flatwise compressive stiffness and in-plane compliance, while the SMPs thin plates support out-of-plane flexibility, the shape memory effect and a variable bending stiffness. Because the ABS plastics possesses a significantly higher glass transition temperature than the SMPs, the ZPR honeycomb structure features a higher out-of-plane flexibility when the environmental temperature rises from room temperature to the glass transition temperature of the SMPs. On the contrary, the flatwise compressive stiffness of the ZPR honeycomb remains unchanged. Three-point bending tests have also been performed to determine the out-of-plane bending performance of the ZPR structures at varying temperatures.
Co-reporter:Tianzhen Liu, Tianyang Zhou, Yongtao Yao, Fenghua Zhang, Liwu Liu, Yanju Liu, Jinsong Leng
Composites Part A: Applied Science and Manufacturing 2017 Volume 100(Volume 100) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.compositesa.2017.04.022
This review is focused on the most recent research on multifunctional shape memory polymer nanocomposites reinforced by various nanoparticles. Different multifunctional shape memory nanocomposites responsive to different kinds of stimulation methods, including thermal responsive, electro-activated, alternating magnetic field responsive, light sensitive and water induced SMPs, are discussed separately. This review offers a comprehensive discussion on the mechanism, advantages and disadvantages of each actuation methods. In addition to presenting the micro- and macro- morphology and mechanical properties of shape memory polymer nanocomposites, this review demonstrates the shape memory performance and the potential applications of multifunctional shape memory polymer nanocomposites under different stimulation methods.
Co-reporter:Jian Huang, Qiuhua Zhang, Fabrizio Scarpa, Yanju Liu, Jinsong Leng
Composites Part B: Engineering 2017 Volume 110(Volume 110) pp:
Publication Date(Web):1 February 2017
DOI:10.1016/j.compositesb.2016.11.011
This work presents a novel negative Poisson's ratio honeycomb design composed by two parts (a re-entrant hexagonal component and a thin plate part) that provide separate contributions to the in-plane and out-of-plane mechanical properties. The re-entrant hexagons provide the in-plane negative Poisson's ratio, the in-plane compliance and the out-of-plane compressive strength, while the thin plate part connecting the re-entrant hexagonal section bears the large out-of-plane flexibility. This paper focuses on the in-plane mechanical properties of the auxetic cellular structure. Theoretical models related to the in-plane uniaxial tensile modulus, the shear modulus, and the Poisson's ratios have been built and validated using the finite element techniques. The in-plane behavior of the honeycomb has also been investigated against the geometrical parameters of the unit cell using a parametrical analysis. The theoretical and numerical models illustrate good agreement and show the potential of its application in morphing structures. We also provide a benchmark of the auxetic configuration proposed in this work against negative Poisson's ratio topologies from open literature.
Co-reporter:Junyao Shen, Yongtao Yao, Yanju Liu and Jinsong Leng
Journal of Materials Chemistry A 2016 vol. 4(Issue 32) pp:7614-7621
Publication Date(Web):15 Jul 2016
DOI:10.1039/C6TC01912A
We demonstrate a facile, template-free route for Fe nanowires (NWs) with an average diameter of 100 nm through magnetic-field-assisted hydrothermal conditions. The aspect ratio of the Fe NWs reaches 50. Fe NWs are constructed with interconnected bead-like nanospheres, which are composed of primary nanocrystals (NCs) with an average size of 8 nm. This shows that the polycrystalline Fe NWs have a body-centred cubic (bcc) structure with preferential growth on the 〈110〉 zone axis. Such hierarchical structures involve orientational growth in the presence of an external magnetic field. The molarity of the reducing agent, reaction time and temperature, are further investigated to understand the influence of these parameters on the growth process of Fe NWs. Compared with those of Fe nanoparticles (NPs), the magnetic properties of Fe NWs show both higher saturation magnetization (154.03 emu g−1) and coercivity (360.84 Oe). The peak value of reflection loss (RL) reaches up to −27.28 dB at 3.68 GHz, indicating the excellent microwave absorption performance of the Fe NWs for low gigahertz usage (2–6 GHz). This mild approach to control Fe NWs is easy to scale-up for other iron-related magnetic nanodevice applications.
Co-reporter:Hetao Chu, Zhichun Zhang, Yanju Liu, Jinsong Leng
Carbon 2016 Volume 98() pp:557-566
Publication Date(Web):March 2016
DOI:10.1016/j.carbon.2015.11.036
The high temperature infrared stealth glassfiber reinforced polymer composite based on silver particles modified carbon nanotube paper (SMCNP) material is fabricated successfully by a facile method, which possesses thin, lightweight, broad wavelength band and low infrared emissivity features. The conductivity increases 673% after being modified by small amount silver particles retaining the original mechanical property. Infrared emissivity decreases more than 38.9–55.7% from 0.85 to 0.65 in 3–5 μm and 0.45 to 0.2 in 8–14 μm, respectively. The specific radiant energy decreases by 43.2% in full wavelength after modified and the radiant power maximally reduce 72.5%. Above all, compare with the as-prepared CNP, the SMCNP broaden the absorption wavelength of the infrared spectra, especially in the range of 3–5 μm indicating the silver particles have significant contribution to increase the property. Considering the engineering application, this modified material was integrated with engineering matrix material, using glassfiber prepreg as an example, and still showed excellent energy saving results. Therefore, the SMCNP is a progressive candidate for infrared stealth application.
Co-reporter:Xinli Xiao, Xueying Qiu, Deyan Kong, Wenbo Zhang, Yanju Liu and Jinsong Leng
Soft Matter 2016 vol. 12(Issue 11) pp:2894-2900
Publication Date(Web):09 Dec 2015
DOI:10.1039/C5SM02703A
Optically transparent shape memory polymers (SMPs) have potential in advanced optoelectronic and other common shape memory applications, and here optically transparent shape memory polyimide is reported for the first time. The polyimide possesses a glass transition temperature (Tg) of 171 °C, higher than the Tg of other transparent SMPs reported, and the influence of molecular structure on Tg is discussed. The 120 μm thick polyimide film exhibits transmittance higher than 81% in 450–800 nm, and the possible mechanism of its high transparency is analyzed, which will benefit further research on other transparent high temperature SMPs. The transparent polyimide showed excellent thermomechanical properties and shape memory performances, and retained high optical transparency after many shape memory cycles.
Co-reporter:Xinli Xiao, Xueying Qiu, Deyan Kong, Wenbo Zhang, Yanju Liu and Jinsong Leng
Soft Matter 2016 vol. 12(Issue 26) pp:5824-5824
Publication Date(Web):21 Jun 2016
DOI:10.1039/C6SM90109C
Correction for ‘Optically transparent high temperature shape memory polymers’ by Xinli Xiao et al., Soft Matter, 2016, 12, 2894–2900.
Co-reporter:Qiwei Zhang, Hongqiu Wei, Yanju Liu, Jinsong Leng and Shanyi Du
RSC Advances 2016 vol. 6(Issue 13) pp:10233-10241
Publication Date(Web):26 Jan 2016
DOI:10.1039/C5RA24247A
Functional physical behavior, including triple shape memory process and reversible actuation, has attracted great interest in the research field of thermosetting polymers in recent years. Herein, we synthesized a series of covalent crosslinking thermosetting polymers with triple shape memory effects via introducing bisphenol-A cyanate ester (BACE) to bismaleimide (BMI) networks. Due to the complex covalent crosslinking structures, such BMI based triple-shape memory polymers (TSMPs) present broad glass transition temperature ranges, which is a crucial precondition for the triple-shape memory behavior. Results demonstrated that BMI based TSMPs showed excellent thermal stabilities and mechanical properties. Moreover, triple shape memory behavior was achieved successfully by choosing two switching temperatures to fix two separate shapes independently. Upon heating, both the programmed shapes could recover to their former shape separately. This paper provides fundamental attempts for the further development of thermosetting triple shape memory polymers. Combining the superior comprehensive properties with the smart triple shape memory behavior, such materials present great potential to be applied as smart materials and structures, especially for aerospace areas.
Co-reporter:Fang Xie, Chongwen Huang, Fei Wang, Longnan Huang, R. A. Weiss, Jinsong Leng, and Yanju Liu
Macromolecules 2016 Volume 49(Issue 19) pp:7322-7330
Publication Date(Web):September 22, 2016
DOI:10.1021/acs.macromol.6b01785
Aiming at an easy-processing metallo-supramolecular polymer which possesses the shape memory property and large deformation ability, we designed a simple metal coordination complex: the blends of zinc-neutralized carboxyl-terminated polybutadiene and poly(styrene-co-4-vinylpyridine) (PSVP). The two polymers are tightly bound due to the metal coordination interactions between Zn2+ ions from carboxyl-terminated polybutadiene and the pyridine group of the PSVP. The elastomer had reasonably good mechanical properties and was thermoplastic. Improvements in mechanical properties of the blends were realized in the rheology analysis compared with a blend without the introduction of the zinc salt. Small-angle X-ray scattering characterization showed that the microstructure of the elastomeric blend consisted of microphase-separated glassy nanodomains of principally PSVP, which served as cross-link junctions that were connected with polybutadiene chains. The elastomer exhibited good shape memory properties for large deformations, and its shape recovery efficiency could reach 81% in the first cycle and could reach 97% ± 1% in the following seven cycles.
Co-reporter:Lei Chen, Wenbing Li, Yanju Liu, Jinsong Leng
Composites Part B: Engineering 2016 Volume 91() pp:75-82
Publication Date(Web):15 April 2016
DOI:10.1016/j.compositesb.2016.01.019
Low mechanical strength and low thermal stability of pristine epoxy-based shape memory polymer (ESMP) hinder its practical applications, and the usually used reinforcing fillers are expensive. In this study, thermally reduced graphite oxide (TrGO) was used as a low-cost but efficient reinforcement phase for ESMP. Compared with pristine ESMP, an increase of 41%–71% for Young's modulus and 44%–64% for tensile strength were observed for the TrGO/ESMP composites containing only 1–3 wt.% TrGO. Thermogravimetric analysis (TGA) showed that 2 wt.% TrGO can improve the thermal stability of ESMP significantly. The thermal conductivity of TrGO/ESMP composites increased almost linearly with increasing TrGO content. Moreover, The TrGO/ESMP composite containing 2 wt.% TrGO can decrease the shape recovery time of ESMP down to 1 min as a result of enhanced thermal conductivity. The TrGO/ESMP composites with such improved properties may have great potential in smart systems.
Co-reporter:Jian Huang, Xiaobo Gong, Qiuhua Zhang, Fabrizio Scarpa, Yanju Liu, Jinsong Leng
Composites Part B: Engineering 2016 Volume 89() pp:67-76
Publication Date(Web):15 March 2016
DOI:10.1016/j.compositesb.2015.11.032
This work presents a novel zero in-plane Poisson's ratio honeycomb design for large out-of-plane deformations and morphing. The novel honeycomb topology is composed by two parts that provide separate in-plane and out-of-plane deformations contributions. The hexagonal component generates the out-of-plane load-bearing compression and in-plane compliance, while a thin plate part that connects the hexagonal section delivers the out-of-plane flexibility. The paper illustrates the in-plane mechanical properties through a combination of theoretical analysis, FE homogenization and experimental tests. Parametric analyses are also carried out to determine the dependence of the in-plane stiffness versus the geometric parameters that define the zero-ν honeycomb.
Co-reporter:Wenbing Li, Yanju Liu and Jinsong Leng
Journal of Materials Chemistry A 2015 vol. 3(Issue 48) pp:24532-24539
Publication Date(Web):24 Nov 2015
DOI:10.1039/C5TA08513F
In this paper, a new type of multicomposite styrene-based shape memory polymer (SSMP) was fabricated. This new SSMP included three regions: a SSMP matrix filled with multiwalled carbon nanotubes (SSMP–CNT), a SSMP matrix filled with Fe3O4 nanoparticles (SSMP–Fe3O4), and a third neat SSMP region which is located between the two composite regions. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results demonstrated that all the three SSMP materials possessed two well-separated transitions, which were subsequently used for the fixing/recovery of two temporary shapes (triple-shape memory effect) in each region. Furthermore, the unique selective actuation functionality of the multicomposite was demonstrated, based on the principle that Fe3O4 nanoparticles and CNT can selectively induce heat in a 30 kHz alternating magnetic field and 13.56 MHz radiofrequency, respectively. Therefore, well-controlled multiple shape recoveries of the multicomposite SSMP were achieved by applying selective stimuli. This proposed approach of selective actuations can be applied to other stimuli-responsive material systems to generate complex structures for target applications.
Co-reporter:F. H. Zhang, Z. C. Zhang, C. J. Luo, I-Ting Lin, Yanju Liu, Jinsong Leng and Stoyan K. Smoukov
Journal of Materials Chemistry A 2015 vol. 3(Issue 43) pp:11290-11293
Publication Date(Web):09 Oct 2015
DOI:10.1039/C5TC02464A
Nonwoven fiber composite Nafion/Fe3O4 films can be programmed to adopt over 5 shapes, and several fast transformations in sequence are demonstrated using different intensities of the same stimulus. We use an alternating magnetic field to activate the transformations remotely and investigate the conditions for tunable actuation control. Since the heat is generated inside the shape-changing films, though locally temperatures >80 or 100 °C are achieved, their surface temperature can be kept below 38–40 °C.
Co-reporter:Wenxin Wang, Dongyan Liu, Yanju Liu, Jinsong Leng, Debes Bhattacharyya
Composites Science and Technology 2015 Volume 106() pp:20-24
Publication Date(Web):16 January 2015
DOI:10.1016/j.compscitech.2014.10.016
In order to explore the enabled design principles of electrically driven epoxy-based shape memory (ER) composites, reduced graphene oxide paper (RGOP) was used for manufacturing the material. Shape memory effect is induced by electrical resistive heating of RGOP possessing excellent heat conductive property and serving as a conductive layer to transmit heat to the polymer. The temperature distribution and shape recovery behavior of the composite have been recorded with infrared video. The investigation on shape recovery behavior of reduced graphene oxide paper/epoxy-based shape memory composites (RGOP/ER) reveals that the shape recovery speed increases with increased applied voltage. It is worth noting that the recoverability of the composite is approximately 100% taking only 5 s under 6 V, which is more energy saving than the previously reported data. The electrical actuation shape recovery rate of the composite can be controlled by programming the synergistic effect between the mass ratio and the applied voltage. This work provides a feasible route to construct efficient electrically actuated shape memory composites and to expand their potential applications.
Co-reporter:Xiaobo Gong, Jian Huang, Fabrizio Scarpa, Yanju Liu, Jinsong Leng
Composite Structures 2015 Volume 134() pp:384-392
Publication Date(Web):15 December 2015
DOI:10.1016/j.compstruct.2015.08.048
This work presents a novel zero Poisson’s ratio (ZPR) honeycomb structure that can achieve deformations along two orthogonal directions and avoid the increase of effective stiffness in the morphing direction by the restraining the Poisson’s effect in the non-morphing direction. Opposite to current ZPR honeycombs for one-dimensional wing morphing the proposed novel zero Poisson’s ratio honeycomb configuration can perform two-dimensional deformation and present a cellular structure with smooth edges. Analytical models related to the uniaxial, in-plane shear and bounds of the out-of-plane (transverse) shear stiffnesses are derived and validated using the finite element techniques. The in-plane behavior of the honeycomb is investigated using a parametric analysis against the geometry of the unit cell, while the out-of-plane transverse stiffness is also evaluated vs. the gauge thickness of the cellular honeycomb structure panels. The theoretical and numerical models exhibit good agreement and show the potential of this novel ZPR configuration for morphing sandwich panel cores.
Co-reporter:Hanqing Wei, Liwu Liu, Zhichun Zhang, Haiyang Du, Yanju Liu, Jinsong Leng
Composite Structures 2015 Volume 133() pp:642-651
Publication Date(Web):1 December 2015
DOI:10.1016/j.compstruct.2015.07.107
Pyrotechnic release devices of spacecraft produce high-shock and contamination, which are hazardous. Mechanical release devices can overcome these disadvantages, but they tend to be complex and costly. In this paper, new kinds of release devices (smart release devices) with the advantages of no pyrotechnic, light weight, and simple structure are proposed, which are made of carbon fiber reinforced styrene-based shape memory polymer composite. The key element of the devices is the shape memory polymer composite cylinder (thin-walled tube). First, the smart release devices are designed based on three different deformation ways of the cylinder. Second, the deformation models are analyzed to verify the feasibility of the smart release devices. Then the smart release devices are made according to the design, they agree well with the simulations obtained from ABAQUS. Finally, the tensile experiments were conducted to get the structural strength of the devices. Different forms of the deformation were tested and compared, obtained the release time of the devices.
Co-reporter:Tsz-ting Wong, Kin-tak Lau, Wai-yin Tam, Jinsong Leng, Wenxin Wang, Wenbing Li, Hongqiu Wei
Composite Structures 2015 Volume 132() pp:1056-1064
Publication Date(Web):15 November 2015
DOI:10.1016/j.compstruct.2015.07.023
Styrene-based and epoxy-based SMPs (SSMPs and EPSMPs) filled with different contents of nano-ZnO particles were fabricated, their decolouration, UVR absorbabilities, surface hardness, dynamic mechanical properties and shape memory effects under UVA degradation test were then investigated. Experimental results showed that all samples subjected to the UVA degradation were yellowish with different degree. By adding 2 wt.% of nano-ZnO particles, all SMPs achieved full UVR blockage. 2 and 4 wt.% nano-ZnO/SSMP and 5 and 7 wt.% nano-ZnO/EPSMP could maintain their surface hardness at moderate level after the UVA degradation. Storage modulus of 4 wt.% nano-ZnO/SSMP and EPSMP before and after UVA degradation obtained satisfactory results compared with their pure forms. It was proven that shape recovery ratio was not affected by nano-ZnO particles inside SMPs. Treated EPSMPs could obtain 100% shape recovery. However, UVA degradation was proven to have effects on the shape memory effect in SSMPs. UVA-degraded SSMPs had better recovery than non-UVA-degraded SSMPs, this could be explained by the degraded surface which was changed to be hardened. 4 wt.% of nano-ZnO particles filled into SSMP and EPSMP could maintain a similar full recovery time before and after UVA degradation and could significantly reduce the recovery reaction time.
Co-reporter:Hongqiu Wei;Fenghua Zhang;Dawei Zhang;Yanju Liu
Journal of Applied Polymer Science 2015 Volume 132( Issue 37) pp:
Publication Date(Web):
DOI:10.1002/app.42532
ABSTRACT
With aim of constructing a class of functional environmentally friendly materials, we electrospun chitosan (CS) blends with various contents of poly(ethylene oxide) (PEO) into a series of composite nanofibrous membranes exhibiting shape-memory behaviors. In the present composite system, CS and PEO served as hard and soft domains, respectively. The CS, presenting no thermal transition, and the PEO, with apparent melting–crystallization, were demonstrated by differential scanning calorimetry testing. Characterizations also revealed that the morphologies of the CS/PEO membranes were controlled by the mass ratios of CS/PEO. The composite fibrous membranes showed great mechanical performances and thermal stabilities as well. Moreover, CS/PEO possessed excellent shape-memory behaviors. Such fibrous membranes could complete their shape-recovery processes within 20 s at the temperature of 20°C above the melting transition temperature (Tm). Both the shape fixity and shape-recovery ratios were higher than 90%, even after five cycles. The CS/PEO fibrous membranes present significant potential applications in the field of biotechnology and tissue engineering, such as in scaffolds and smart tubes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42532.
Co-reporter:Lei Chen;Wenbing Li;Yanju Liu
Journal of Applied Polymer Science 2015 Volume 132( Issue 38) pp:
Publication Date(Web):
DOI:10.1002/app.42502
ABSTRACT
In this article, epoxy shape-memory polymer (ESMP) reinforced with 1 wt % thermally reduced graphite oxide (TrGO) was fabricated by solution blending and three-roll mill (TRM) mixing, respectively. Both blending techniques allowed a uniform TrGO dispersion in ESMP matrix, and the TRM mixing lead to an exfoliation of the TrGO worms. Compared with pristine ESMP, the TrGO/ESMP composites showed 36.4–41.1% increase in Young's modulus and 38.1–44.1% improvement in tensile strength. The TrGO/ESMP composite fabricated by TRM mixing had a T5% (the temperature where the material lost 5% of its initial weight) 16.4°C higher than pure ESMP. Compared with pure ESMP, a significant improvement of recovery force by 84.4% and 311.1% was obtained by TrGO/ESMP composite fabricated by solution blending and TRM mixing, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42502.
Co-reporter:Xinli Xiao, Deyan Kong, Xueying Qiu, Wenbo Zhang, Fenghua Zhang, Liwu Liu, Yanju Liu, Shen Zhang, Yang Hu, and Jinsong Leng
Macromolecules 2015 Volume 48(Issue 11) pp:3582-3589
Publication Date(Web):May 21, 2015
DOI:10.1021/acs.macromol.5b00654
Shape-memory polymers (SMPs) are synthesized with adjustable glass transition temperature (Tg) ranging from 299 to 322 °C, higher than those reported previously. The polyimide containing thermal stable but flexible linkages within the backbone act as reversible phase, and high molecular weight (Mn) is necessary to form physical cross-links as fixed phase of thermoplastic shape-memory polyimide. The critical Mn is 21.3 kg/mol, and the relationship between Mn and Tg is explored. Thermoset polyimides show higher storage modulus and better shape-memory effects than thermoplastic counterparts due to covalent cross-linking, and the effective cross-link density with the influence on their physical properties is studied. The mechanism of high-temperature shape-memory effect of polyimide on the basis of chain flexibility, molecular weight, and cross-link density is proposed, which will benefit further research on high-temperature SMPs.
Co-reporter:Liwu Liu, Zhen Zhang, Jinrong Li, Tiefeng Li, Yanju Liu, Jinsong Leng
Composites Part B: Engineering 2015 Volume 78() pp:35-41
Publication Date(Web):1 September 2015
DOI:10.1016/j.compositesb.2015.03.069
Experiments are conducted to test the permittivity of dielectric elastomer composites adulterated with multi-walled carbon nanotube (MWCNT). The results show that the permittivity of dielectric elastomer composites can be significantly improved by adding MWCNT conductive particles. A thermodynamic model is presented to investigate the stability of MWCNT particle-doped dielectric elastomer composites. The theoretical investigation proves that the polarization of MWCNT, the electrostriction deformation and material constants of the elastomer significantly affect the stability of the thermodynamic system. The numerical analysis shows that comparing to ideal dielectric elastomer, the stability of dielectric elastomer composites filled with MWCNT coupling between electrostriction and polarization can be significantly enhanced.
Co-reporter:Hongqiu Wei, Yongtao Yao, Yanju Liu, Jinsong Leng
Composites Part B: Engineering 2015 Volume 83() pp:7-13
Publication Date(Web):15 December 2015
DOI:10.1016/j.compositesb.2015.08.019
With the aim of seeking a convenient way for integrating functional materials, a polymeric system, presenting both self-healing property and shape memory behavior, was proposed and constructed based on epoxy based shape memory polymer (ESMP) and poly (ε-caprolactone) (PCL). The synthesis principle of PCL–ESMP composite was based on phase separation phenomenon between the two ingredients. Such phase separated PCL–ESMP composite reserved melting transition of PCL and glassy transition of ESMP, respectively, which was the crucial mechanism for achieving self-healing performance and shape memory behavior. A bending-recovery experiment demonstrated that PCL–ESMP composite possessed excellent thermal-induced dual-shape memory effect. Meanwhile, single edge notched bend testing revealed that such composite exhibited desirable self-healing performance as well. This article introduced a simple contrivable concept and exhibited some experimental results of the PCL–ESMP dual-functional composite system. The promising applications are expected to more widely, such as functional composite matrix and intelligent structures.
Co-reporter:Yongtao Yao, Hongqiu Wei, Jingjie Wang, Haibao Lu, Jinsong Leng, David Hui
Composites Part B: Engineering 2015 Volume 83() pp:264-269
Publication Date(Web):15 December 2015
DOI:10.1016/j.compositesb.2015.08.060
Hybrid materials with nanostructure could exhibit a diverse range of applications as advanced functional materials. This research work, composite membranes with shape memory property based on biocompatible polycaprolactone and polyethylene oxide were successfully fabricated by using electrospinning technique. Electrospun fiber configuration is strongly related to the concentration of polymer and electric field strength. The hydrophilic property of hybrid membrane has been improved and water play a critical role in resulting lower its responsive temperature compared with dry membrane. The mechanism of shape memory PCL/PEO hybrid membrane at wet condition has been proposed.
Co-reporter:Fenghua Zhang, Zhichun Zhang, Yanju Liu, Weilu Cheng, Yudong Huang, Jinsong Leng
Composites Part A: Applied Science and Manufacturing 2015 Volume 76() pp:54-61
Publication Date(Web):September 2015
DOI:10.1016/j.compositesa.2015.05.004
The thermosetting epoxy-based shape memory composite microfibers are successfully fabricated by means of coaxial electrospinning. The PCL/epoxy composite fiber shows core/shell structure, in which epoxy as the core layer is for an enhancing purpose. By incorporating epoxy and PCL, the mechanical strength of composite fibers is greatly reinforced. The deformation is via the heating and cooling process, and the shape memory effect can be demonstrated from the micro level to the macro level. The whole shape recovery performance takes only 6.2 s when triggered by the temperature being at 70 °C. The porosity of woven microfibers changes in response to temperature. In addition, the PCL/epoxy composite microfiber membranes are analyzed in an in vitro cytotoxicity test, which proves that PCL as the shell layer provides the composite microfibers potential capabilities in biomedical science.
Co-reporter:Wenxin Wang, Haibao Lu, Yanju Liu and Jinsong Leng
Journal of Materials Chemistry A 2014 vol. 2(Issue 15) pp:5441-5449
Publication Date(Web):24 Jan 2014
DOI:10.1039/C3TA15204A
With the aim of integrating a family of functional composites, possessing a conspicuous water-induced shape memory effect (SME), a novel sodium dodecyl sulfate–epoxy shape memory composite was constructed. The original fabrication strategy of the composite was designed based on the chemical interaction constructed 3D microvoid on the shape memory composite surface. Compared with the pure epoxy shape memory polymer, the composites display a gratifying water-induced shape memory effect. The results indicate that the water-induced shape recovery rate of the composite is accelerated through increasing the temperature or decreasing the specimen thickness. An immersion test in water suggests that the chemical interaction and physical swelling effect have a significant influence on the water-induced shape memory process. This research advocates the design concept and presents some experimental results of the water-driven smart composite. The potential application range is expected to expand more widely, including a humidity sensor, temperature/humidity switch, underwater deployable structure and a power source transforming chemical energy into mechanical energy for an ultralow-power device.
Co-reporter:Hetao Chu, Zhichun Zhang, Yanju Liu, Jinsong Leng
Carbon 2014 Volume 66() pp:154-163
Publication Date(Web):January 2014
DOI:10.1016/j.carbon.2013.08.053
A meso/macropore carbon nanotube paper (CNP) and a self-heating fiber reinforced polymer composite of CNP/glassfiber/epoxy (CGE) based on the meso/macropore CNP were fabricated in this article. The pore diameters mainly distribute from 30 to 90 nm characterized using nitrogen adsorption isotherms at 77 K. The electric conductivities of the CNP and CGE composite are 77.8 and 64.9 S cm−1. Electric heating performance of CGE was investigated at different heat flux densities, wind speed and ambient temperature. A uniform temperature distributed was observed on the surface of CGE detected by an infrared temperature camera. The electric heating performance was verified by deicing a certain amount of ice at different heat flux densities under two kinds of ambient conditions: −22 °C without wind and −22 °C with 14 m/s of the wind speed. The deicing time under the two conditions were less than 220 and 450 s, respectively. The feasibility of the deicing performance was demonstrated through a series of experiments and the results indicate this material is a promising candidate as an electric heating material for deicing.
Co-reporter:Ruirui Zhang, Xiaogang Guo, Yanju Liu, Jinsong Leng
Composite Structures 2014 Volume 112() pp:226-230
Publication Date(Web):June 2014
DOI:10.1016/j.compstruct.2014.02.018
Recently, the deployable structures fabricated using shape memory polymer composites (SMPC) have been developed for its unique properties such as highly reliable, low-cost, light weight and cost-effective mechanisms compared with traditional deployable structures. Shape memory polymer is a kind of smart materials which can memorize the permanent shape and can recover to original shape when be exposed to external stimulus. In order to eliminating effects of low stiffness and strength of pure shape memory polymer, shape memory polymer composites reinforced by particles, carbon nanotubes and fibers were studied. A deployable truss structure made of SMPC was analyzed and fabricated in this paper. The truss was made of multilayer carbon fiber reinforced epoxy-based shape memory polymer composites. Through DMA tests, the glass transformation temperature and mechanical properties of laminates which consist in deployable truss were obtained. The curves of recovery moment as a function of curvatures were also obtained in this paper. The deployable experiments were carried out in order to verify the rationality of deployable truss model. And the experimental results showed that the trusses fabricated in this paper can unfold smoothly and can also be applied as a space deployable structure in the field of spacecraft.
Co-reporter:Kai Yu, Yanju Liu and Jinsong Leng
RSC Advances 2014 vol. 4(Issue 6) pp:2961-2968
Publication Date(Web):14 Oct 2013
DOI:10.1039/C3RA43258K
In this paper, the practicability of actuating the shape recovery of thermo-responsive shape memory polymers (SMPs) filled with carbon nanotubes (CNTs) has been investigated. When exposed to microwave radiation, the embedded CNTs were expected to absorb the external electromagnetic energy and act as node heating sources in the SMP/CNT composites. In this way, the SMP could be volumetrically heated and subsequently this would lead to a fast actuation. Although the pure SMP was not responsive to microwave radiation, the microwave absorption ratio in the SMP/CNT composites significantly increased along with the increasing amount of added CNTs or the microwave frequency. The influence of the CNTs on the thermomechanical properties of the SMP composites has been investigated and analyzed using scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) methods. The shape recovery behaviors of the SMP composites with 1 wt%, 3 wt% and 5 wt% CNTs were successfully triggered by microwave radiation. The shape recovery process together with the temperature distribution were recorded with an infrared video camera simultaneously. Furthermore, the selective heating characteristic of the microwaves was also experimentally demonstrated on a SMP composite with a nonuniform CNT concentration. The microwave actuation method is potentially a better choice for the wireless remote shape control of SMP/CNT based functional structures.
Co-reporter:Wenbing Li, Yanju Liu and Jinsong Leng
RSC Advances 2014 vol. 4(Issue 106) pp:61847-61854
Publication Date(Web):18 Nov 2014
DOI:10.1039/C4RA10716K
In this work, a novel type of shape memory polymer nanocomposite was fabricated using chemically cross-linked poly(ε-caprolactone) with allyl alcohol as the matrix and Fe3O4 nanoparticles decorated conductive multiwalled carbon nanotubes (Fe3O4@M) as a magnetism and electricity responsive source. The nanocomposite exhibited excellent shape memory performance with a multistage stimulus recovery from a temporary shape to a permanent shape, triggered by an alternating magnetic field, an electric field and hot water, respectively. Uniquely, the nanocomposite also displayed significant two-way reversible shape memory behavior under constant load conditions, which was not demonstrated previously. An alamar blue assay was also used to prove that the material possessed good biocompatibility. The results showed that the material could have good potential application in sensors, functional tissue engineering constructs and artificial muscles.
Co-reporter:Yongbo Dai, Peng Li, Yanju Liu, Anand Asundi, Jinsong Leng
Optics and Lasers in Engineering 2014 Volume 59() pp:19-24
Publication Date(Web):August 2014
DOI:10.1016/j.optlaseng.2014.02.011
Co-reporter:Tao Fu, Yanju Liu, Kin-tak Lau, Jinsong Leng
Composites Part B: Engineering 2014 Volume 66() pp:420-429
Publication Date(Web):November 2014
DOI:10.1016/j.compositesb.2014.06.004
This paper demonstrates the use of four embedded fiber optic acoustic emission sensors (FOAESs) to identify the impact source of the carbon fiber reinforced polymer (CFRP) plate.The optical waveguide method and computer simulation were both applied to explain the principle of FOAES, which proved that any one of the two output terminals of FOAES was able to reveal frequency response characteristics of stress waves. The response characteristics of the FOAES to the stress waves were calibrated and discussed for comparisons of before-and-after embedded in the CFRP plate. Propagation velocities of stress wave depending on the direction in the CFRP plate were measured by FOAESs as the information for impact source identification. A simple and efficient algorithm based on the intersection of hyperbolic curves was presented to estimate the impact source location. An automatic monitoring system with the tailored program of localization algorithm was introduced for online real-time impact source identification. Experiments of impact source localization were achieved by using the FOAESs array mounted on the surface and embedded in the CFRP plate. The measured results agree well with the actual impact sources in the CFRP plate embedded with FOAESs. Furthermore, the research of composites structures embedded with FOAESs is conductive to developing the intelligent integration of structural health monitoring (SHM).
Co-reporter:Lei Zhang, Haiyang Du, Liwu Liu, Yanju Liu, Jinsong Leng
Composites Part B: Engineering 2014 Volume 59() pp:230-237
Publication Date(Web):March 2014
DOI:10.1016/j.compositesb.2013.10.085
Based on the thermomechanical mechanism of shape memory polymers (SMPs), the three-dimensional thermomechanical constitutive equation that can be used in the ABAQUS finite element simulation was derived. Then this paper compiled UMAT subroutine and simulated the thermomechanical behaviors of SMP smart mandrels. In addition, the properties of shape fixity and shape recovery ratio of SMP were considered in detail. Finally, filament winding experiments were proceeded on bottle-shaped and air duct-shaped mandrels and the simple and efficient demoulding of SMP mandrels were verified. The results showed the feasibility of SMP as the smart mandrels from practical application in the future.
Co-reporter:Yanju Liu, Di Song, Chunxia Wu, Jinsong Leng
Composites Part B: Engineering 2014 Volume 63() pp:34-40
Publication Date(Web):July 2014
DOI:10.1016/j.compositesb.2014.03.014
In this paper, nanocomposites based on epoxy matrix with nano-sized multi-walled carbon nanotubes (MWCNTs), Fe3O4 and Fe fillers have been developed due to the application in electromagnetic interference (EMI) shielding. The nanocomposites specimens with different fillers, as well as varied filler weight fraction have been prepared. The microwave absorption of these nanocomposites specimens have been verified by vector network analyzer. Furthermore, trilayer-type laminated nanocomposites containing a matching layer with 15 wt% nano-Fe3O4, an absorbing layer with 5 wt% CNTs and a reflecting layer with 10 wt% CNTs have been designed and fabricated. Moreover, the permittivity and the permeability for each type of composites are tested as well. Experimental results show that such trilayer-type laminated nanocomposite has excellent micro-wave absorption effect in the frequency band (from 13 GHz to 40 GHz) up to 40 dB, especially in high frequency section. The achieved peak values of the fabricated laminated nanocomposites exceed 100 dB.
Co-reporter:Fang Xie, Longnan Huang, Yanju Liu, Jinsong Leng
Polymer 2014 Volume 55(Issue 23) pp:5873-5879
Publication Date(Web):5 November 2014
DOI:10.1016/j.polymer.2014.07.035
•Shape memory cyanate polymers (SMCPs) with high Tg (up to 255.1 °C) are synthesized.•The SMCPs are modified with polybutadiene/acrylonitrile or polyethylene glycol.•The SMCPs all possess high thermal stability and shape recovery ratios above 95%.•The modified SMCPs possess much higher toughness than unmodified polycyanurate.•The SMCPs are promising material systems of high Tg SMPs for space applications.New thermosetting shape memory cyanate polymers (SMCPs) modified with polybutadiene/acrylonitrile (PBAN) were synthesized and compared with polyethylene glycol (PEG)-modified SMCPs for integration into the family of high temperature shape memory polymers with controllable glass transition temperatures (Tg) used in the aerospace industry. The materials were characterized in terms of microstructure, thermal properties, mechanical properties and shape memory properties by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and tensile tests. Differing from the SMCP with PEG, the new cyanate-based shape memory polymer with PBAN (Tg ∼255.1.0 °C) had better shape memory properties and higher thermal stability (relatively high initial degradation temperature and high char residue value at 800 °C). Both of the SMCPs with PBAN and PEG displayed exceedingly high glass transition temperatures over 241.3 °C and higher toughness than unmodified polycyanurate. These qualities render them desirable candidates as matrices in polymer composites, particularly for space applications.
Co-reporter:Zhichun Zhang;Fenghua Zhang;Xueyong Jiang;Yanju Liu;Zhanhu Guo
Fibers and Polymers 2014 Volume 15( Issue 11) pp:2290-2296
Publication Date(Web):2014 November
DOI:10.1007/s12221-014-2290-5
Electrical conductive nanocomposite fibers were prepared with polyaniline (PANI), polyacrylonitrile (PAN) and multi-walled carbon nanotubes (MWCNTs) via electrospinning. The morphology and electrical conductivity of the PANI/PAN/MWCNTs nanocomposite fibers were characterized by scanning electron microscope (SEM) and Van De Pauw method. Electrical conductivity of nanocomposite fibers increased from 1.79 S·m−1 to 7.97 S·m−1 with increasing the MWCNTs content from 3.0 wt% to 7.0 wt%. Compared with PANI/PAN membranes, the mechanical property of PANI/PAN/MWCNTs nanocomposites fiber membranes decreased. The microwave absorption performance of composite films was analyzed using waveguide tube, which indicated that with the thickness increasing the value of RL reduced from −4.6 to −5.9 dB.
Co-reporter:Fenghua Zhang;Zhichun Zhang;Yanju Liu
Fibers and Polymers 2014 Volume 15( Issue 3) pp:534-539
Publication Date(Web):2014 March
DOI:10.1007/s12221-014-0534-z
Nanoscaled non-woven fibers with shape memory effect are successfully fabricated via electrospinning method from Nafion solutions consisting of a little poly(ethylene oxide) (PEO). Scanning electron microscopy (SEM) investigation shows the electrospun nanofibers with average diameters in the range 170–410 nm. The electrospun nanofibers exhibit excellent shape memory properties. When deformed Nafion nanofibers are stimulated upon heat, the temporary shape responds rapidly, and then recovers to the permanent shape in less than one minute. The shape recovery ratios and shape fixity ratios of Nafion nanofibers with 0.3 wt%, 0.5 wt% and 0.7 wt% PEO are all above 90 %. In shape memory cycle, fibrous structure is stable after the stretching recovery. Shape memory Nafion nanofibers have various potential applications in smart structures and materials in the future.
Co-reporter:Qiao Tan, Liwu Liu, Yanju Liu, Jinsong Leng
Composites Part A: Applied Science and Manufacturing 2014 Volume 64() pp:132-138
Publication Date(Web):September 2014
DOI:10.1016/j.compositesa.2014.05.003
The ever increasing applications of Shape Memory Polymers (SMPs) and its Composites (SMPCs) have motivated the development of appropriate constitutive models. In this work, based on composite bridging model, a constitutive model for unidirectional SMPCs under thermal mechanical loadings in the small strain range has been developed. The composite bridging model has been adopted to describe the distribution of stress–strain between fiber reinforcement and SMPs matrix. Besides, considering the influence of fiber content and temperature, the storage and release of “frozen strain”, the recovery of stress has been quantified as well. The stress–strain curves of SMPCs laminate under axial tensile indicate that the theoretical data derived from the developed model are basically accordant with the experimental data, and that the proposed model is suitable for machining practice. Furthermore, the model has been applied to predict stress recovery, strain storage and releasing with changing of temperature.
Co-reporter:Tan Qiao, Liwu Liu, Yanju Liu, Jinsong Leng
Composites Part B: Engineering 2013 Volume 53() pp:218-225
Publication Date(Web):October 2013
DOI:10.1016/j.compositesb.2013.04.052
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.
Co-reporter:Haibao Lu;Yanju Liu
Macromolecular Materials and Engineering 2012 Volume 297( Issue 12) pp:1138-1147
Publication Date(Web):
DOI:10.1002/mame.201200235
Co-reporter:Jinsong Leng, Xin Lan, Yanju Liu, Shanyi Du
Progress in Materials Science 2011 Volume 56(Issue 7) pp:1077-1135
Publication Date(Web):September 2011
DOI:10.1016/j.pmatsci.2011.03.001
Shape-memory polymers (SMPs) undergo significant macroscopic deformation upon the application of an external stimulus (e.g., heat, electricity, light, magnetism, moisture and even a change in pH value). They have been widely researched since the 1980s and are an example of a promising smart material. This paper aims to provide a comprehensive review of SMPs, encompassing a fundamental understanding of the shape-memory effect, fabrication, modeling and characterization of SMPs, various actuation methods and multifunctional properties of SMP composites, and potential applications for SMP structures. A definition of SMPs and their fundamentals are first presented. Next, a description of their fabrication, characterization and constitutive models of SMPs are introduced. SMP composites, which act to improve a certain function as functional materials or the general mechanical properties as structural materials, are briefly discussed. Specially, the SMP composites can be developed into multifunctional materials actuated by various methods, such as thermal-induced, electro-activated, light-induced, magnetic-actuated and solution-responsive SMPs. As smart materials, the applications of SMPs and their composites receive much interest, including deployable structures, morphing structures, biomaterials, smart textiles and fabrics, SMP foams, automobile actuators and self-healing composite systems.
Co-reporter:Haibao Lu, Yanju Liu, Jihua (Jan) Gou, Jinsong Leng, Shanyi Du
Composites Science and Technology 2011 Volume 71(Issue 11) pp:1427-1434
Publication Date(Web):28 July 2011
DOI:10.1016/j.compscitech.2011.05.016
We are presenting a method of synthesizing three-dimensional self-assembled multi-walled carbon nanotube (MWCNT) nanopaper on hydrophilic polycarbonate membrane. The process is based on the very well-defined dispersion of nanotube and controlled pressure vacuum deposition procedure. The morphology and structure of the nanopaper are characterized with scanning electronic microscopy (SEM) over a wide range of scale sizes. A continuous and compact network observed from the microscopic images indicates that the MWCNT nanopaper could have highly conductive property. As a consequence, the sensing properties of conductive MWCNT nanopaper are characterized by functions of temperature and water content. Meanwhile, in combination with shape-memory polymer (SMP), the conductive MWCNT nanopaper facilitates the actuation in SMP nanocomposite induced by electrically resistive heating. Furthermore, the actuating capability of SMP nanocomposite is utilized to drive up a 5-gram mass from 0 to 30 mm in height.Highlights► We examine the sensing capabilities of electrical nanopaper to temperature and water content. ► We achieve the actuation of shape-memory polymer by electrically resistive heating from nanopaper. ► The actuating capability of nanopaper is integrated with shape-memory polymer. ► Nanopaper possesses a negative temperature coefficient behavior from 25 to 120 °C.
Co-reporter:Yanju Liu, Haibao Lv, Xin Lan, Jinsong Leng, Shanyi Du
Composites Science and Technology 2009 Volume 69(Issue 13) pp:2064-2068
Publication Date(Web):October 2009
DOI:10.1016/j.compscitech.2008.08.016
Shape-memory polymers (SMPs) have been one of the most popular subjects under intensive investigation in recent years, due to their many novel properties and great potential. These so-called SMPs by far surpass shape-memory alloys and shape-memory ceramics in many properties, e.g., easy manufacture, programming, high shape recovery ratio and low cost, and so on. However, they have not fully reached their technological potential, largely due to that the actuation of shape recovery in thermal-responsive SMPs is normally only driven by external heat. Thus, electro-activate SMP has been figured out and its significance is increasing in years to come. This review focuses on the progress of electro-activate SMP composites. Special emphases are given on the filler types that affect the conductive properties of these composites. Then, the mechanisms of electric conduction are addressed.
Co-reporter:Jinsong Leng;Xuelian Wu;Yanju Liu
Journal of Applied Polymer Science 2009 Volume 114( Issue 4) pp:2455-2460
Publication Date(Web):
DOI:10.1002/app.30724
Abstract
In addition to the fabrication of thermoset styrene-based shape memory polymer (SMP) and its nanocomposite filled with nanocarbon particles, this study presents the effect of nanocarbon particles on infrared light-active shape recovery behaviors of this type of SMP material. The experimental results reveal that both pure SMP and SMP filled with nanocarbon particles can be actuated by infrared light in vacuum, while shape memory effect shown by the composite is stronger than that of in pure SMP. Shape memory effect is evaluated by shape recovery ability and shape recovery speed in detail. Moreover, factors which would influence the infrared light-active shape memory effect in SMP with/without nanocarbon particles are explored by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and infrared absorption characteristic tests. The better shape memory effect of the nanocomposite attributes to its higher storage modulus and higher infrared absorption capability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Co-reporter:Tao Fu, Yanju Liu, Quanlong Li, Jinsong Leng
Optics and Lasers in Engineering 2009 Volume 47(Issue 10) pp:1056-1062
Publication Date(Web):October 2009
DOI:10.1016/j.optlaseng.2009.03.011
A fiber optic acoustic emission sensor based on fused-tapered coupler and its applications in structural health monitoring are proposed in this paper. The fiber optic acoustic emission sensor (FOAES) was tested using pencil lead break tests compared with the commercial acoustic emission sensor (R15 PZT). Besides, the sensor was embedded into the carbon fiber reinforced plastics (CFRP) materials and tested in the same way. It successfully detected the AE signals. FOAES was applied in the structural health monitoring (SHM) of CFRP materials. Damages of carbon fiber/epoxy composite laminates during three-point-bending test were monitored by surface-mounted and embedded FOAES, respectively. Results identified that the sensor embedded into composite structures could monitor damage of composite laminates on-line as the surface-mounted sensor did.
Co-reporter:Jinsong Leng, Wolfgang Ecke
Optics and Lasers in Engineering 2009 Volume 47(Issue 10) pp:1017
Publication Date(Web):October 2009
DOI:10.1016/j.optlaseng.2009.06.002
Co-reporter:Yongbo Dai, Yanju Liu, Jinsong Leng, Gang Deng, Anand Asundi
Optics and Lasers in Engineering 2009 Volume 47(Issue 10) pp:1028-1033
Publication Date(Web):October 2009
DOI:10.1016/j.optlaseng.2009.05.012
A novel fiber Bragg grating (FBG) sensor system for measurement of strain and temperature is proposed in this paper. The proposed sensor technique is based on time-division multiplexing (TDM). A semiconductor optical amplifier (SOA), connected in a ring cavity, is used to serve as a gain medium and switch. The SOA is driven by a pulse generator, which operates the SOA at different periods of time to select reflected pulses from a particular sensor. The FBG sensors have identical center wavelengths and can be deployed along the same fiber. This technique relieves the spectral bandwidth issue and permits the interrogation of up to 100 FBGs along a fiber, if the reflectivity of the individual sensors is sufficiently low to avoid shadowing effects. This system is particularly suitable for the application in structural health monitoring (SHM) where large numbers of sensors are required in wide measurement ranges.
Co-reporter:H. Lv;J. Leng;Y. Liu;S. Du
Advanced Engineering Materials 2008 Volume 10( Issue 6) pp:592-595
Publication Date(Web):
DOI:10.1002/adem.200800002
Co-reporter:J.S. Leng, R.A. Barnes, A. Hameed, D. Winter, J. Tetlow, G.C. Mays, G.F. Fernando
Sensors and Actuators A: Physical 2006 Volume 126(Issue 2) pp:340-347
Publication Date(Web):14 February 2006
DOI:10.1016/j.sna.2005.10.050
This paper is concerned with the design concepts, modelling and implementation of various fibre optic sensor protection systems for development in concrete structures. The design concepts of fibre optic sensor protection system and on-site requirements for surface-mounted and embedded optical fibre sensor in concrete structures have been addressed. The aspects of finite element (FE) modelling of selected sensor protection systems in terms of strain transfer efficiency from the structure to the sensing region have also been focused in this paper. Finally, the experimental validations of specified sensor protection system in concrete structures have been performed successfully. Protected extrinsic Fabry–Perot interferometric (EFPI) and fibre Bragg grating (FBG) sensors have been used to monitor the structural health status of plain and composite wrapped concrete cylinders. Results obtained indicate that the protection system for the sensors performs adequately in concrete environment and there is very good correlation between results obtained by the protected fibre optic sensors and conventional electrical resistance strain gauges.
Co-reporter:Xin Lan, Liwu Liu, Yanju Liu, Jinsong Leng, Shanyi Du
Mechanics of Materials (May 2014) Volume 72() pp:46-60
Publication Date(Web):1 May 2014
DOI:10.1016/j.mechmat.2013.05.012
Highlights•Buckling mechanics of shape memory polymer composites (SMPCs) is investigated.•Strain energy expression of the SMPC thermodynamic system is developed.•Analytical expressions of key parameters during the buckling were determined.•Buckling of carbon fibre generated a large macroscopic structural strain of SMPC.The buckling mechanics of fibre-reinforced shape-memory polymer composites (SMPCs) under finite flexure deformation is investigated. The analytical expressions of the key parameters during the buckling deformation of the materials were determined, and the local post-buckling mechanics of the unidirectional fibre-reinforced SMPC were further discussed. The cross section of SMPC under flexural deformation can be divided into three areas: the non-buckling stretching area, non-buckling compression area and buckling compression area. These areas were described by three variables: the critical buckling position, the neutral plane position and the fibre buckling half-wavelength. A strain energy expression of the SMPC thermodynamic system is developed. According to the principle of minimum energy, the analytical expressions of key parameters in the flexural deformation process is determined, including the critical buckling curvature, critical buckling position, position of the neutral plane, wavelength of the buckling fibre, amplitude of the buckling fibre and macroscopic structural strain of the composite material. The results showed that fibre buckling occurred in the material when the curvature increasing from infinitesimal to the critical value. If the curvature is greater than the critical curvature, the neutral plane of the material will move towards the outboard tensile area, and the critical buckling position will move towards the neutral plane. Consequently, the half-wavelength of the buckling fibre was relatively stabilised, with the amplitude increasing dramatically. Along with the increasing of the shear modulus, the critical curvature and buckling amplitude increase, while the critical half-wavelength of the fibre buckling decrease and the critical strain of the composite material increase. Finally, we conducted experiments to verify the correction of the key parameters describing SMPC materials under flexural deformation. The values determined by the experiments proved that the theoretical prediction is correct. Additionally, the buckling deformation of the carbon fibre generated a large macroscopic structural strain of the composite material and obtained a resulting large flexural curvature of the structure with minimal material strain of the carbon fibre.
Co-reporter:Liwu Liu, Yanju Liu, Kai Yu, Jinsong Leng
Mechanics of Materials (May 2014) Volume 72() pp:33-45
Publication Date(Web):1 May 2014
DOI:10.1016/j.mechmat.2013.05.013
•Influence of temperature and deformation on permittivity is considered.•Relations between different work conjugated parameters are theoretically described.•Allowable energy range of dielectric elastomer is calculated.•Electric induced variation of elastomer’s temperature and entropy is studied.•Results should offer assistances in guiding the design of excellent actuators.In this paper, the influence of both temperature and deformation on dielectric constant is considered during the establishment of free energy function of dielectric elastomers. A constitutive model of the thermodynamic systems undergoing adiabatic process is derived to study its thermoelectromechanical stability. The relations between different work conjugated parameters of dielectric elastomer are theoretically described, including the relations between nominal electric field and nominal electric displacement, entropy and temperature. Under different temperatures and electric fields, the allowable energy range of dielectric elastomer is calculated. Furthermore, the electric-induced variation of dielectric elastomer’s temperature and entropy is also studied under various principal planar stretch ratios. These simulation results should offer assistances in guiding the design and fabrication of excellent actuators featuring dielectric elastomers.
Co-reporter:Liwu Liu, Kai Yu, Yanju Liu, Jinsong Leng
Mechanics of Materials (February 2014) Volume 69(Issue 1) pp:71-92
Publication Date(Web):1 February 2014
DOI:10.1016/j.mechmat.2013.09.006
•This paper develops a thermodynamic theory of polar elastic dielectric.•Mechanical behavior of polar elastic dielectric is analyzed.•Typical thermodynamics cycles are described as cooling devices and generators.•Thermo-electro-mechanical coupling behavior undergoing phase transition is investigated.The alternation of temperature and entropy induced by an electric field in a polar dielectric material is known as the electrocaloric effect (ECE). This paper develops a thermodynamic theory of the polar elastic dielectric with large ECE and large deformation compatibility. The theory characterizes the equilibrium condition of the polar elastic dielectric which is subjected to mechanical forces, electric field and thermal field. The mechanical behavior and large deformation of the polar elastic dielectric thermo-electro-mechanical system are analyzed under the coupling influence of hyperelastic, polarization, electrostriction and thermal contribution on the system. The typical thermodynamics cycles of the polar elastic dielectric are described as cooling devices and generators and the electrocaloric and pyroelectric energy conversion are calculated. Ferroelectric polymer, as an important category of electroactive polymers, is a typical polar dielectric with a large ECE and a large deformation. As an example, when subjected to different voltage, the ferroelectric polymers are regarded as cooling devices. We calculated their temperature change, entropy change, heat absorptions and work generation. We also calculated the voltage change, electric quantity change and work of the ferroelectric polymer which is regarded as generators when subjected to different temperatures. Finally, we investigated the thermo-electro-mechanical coupling behavior of the ferroelectric polymers undergoing ferroelectric–paraelectric phase transition.
Co-reporter:Liwu Liu, Yanju Liu, Xiaojian Luo, Bo Li, Jinsong Leng
Mechanics of Materials (December 2012) Volume 55() pp:60-72
Publication Date(Web):1 December 2012
DOI:10.1016/j.mechmat.2012.07.009
By applying a voltage, electric charge will be induced on the surface of dielectric elastomers. Generally, the charge increases with the level of voltage. When the voltage reaches to a certain value, the charge would not increase any more due to the polarization saturation of dielectric materials. In this paper, a thermodynamic constitutive model, combined both the nonlinear dielectric and hyperelastic behavior as dielectric elastomers undergoing polarization saturation, has been developed. Analytical solutions have been obtained for situations incorporating strain-stiffening effect, electromechanical instability and snap-through instability. The numerical results reveal the marked influence of the extension and polarization saturation limits of elastomer material on its electromechanical instability and the snap-through instability. The developed constitutive model would be helpful in future research of dielectric elastomer based high-performance transducers.Highlights► Model of dielectric elastomer undergoing polarization saturation has been developed. ► Analytical solutions have been obtained for electromechanical and snap-through instability. ► Numerical results reveal the marked influence of polarization saturation on instability. ► Model would be helpful in future research of elastomer based high-performance transducers.
Co-reporter:Y.J. Chen, F. Scarpa, Y.J. Liu, J.S. Leng
International Journal of Solids and Structures (15 March 2013) Volume 50(Issue 6) pp:996-1004
Publication Date(Web):15 March 2013
DOI:10.1016/j.ijsolstr.2012.12.004
This work describes the theoretical, numerical and experimental in-plane and out-of-plane elastic behavior of a class of anti-tetrachiral lattice structures with in-plane negative Poisson’s ratios and anisotropic behavior. Closed form analytical solutions related to the uniaxial stiffness, in-plane Poisson’s ratio and bounds for the transverse shear modulus are derived, and compared against homogenization-based finite element methods and experimental tests performed on rapid prototyping-made samples. The benchmarked models are then used to investigate the behaviors of the anisotropic negative Poisson’s ratio structures against the geometry parameters defining the unit cell. The results show the existence of large variations in linear elastic constants and degree of anisotropy, which can be achieved by changing the lattice geometry parameters. The analysis presented in this work provides meaningful guidance to assist design anti-tetrachiral anisotropic lattices, which could serve as sandwich panel cores in aerospace applications.Highlights► Novel anisotropic negative Poisson’s ratio (anti-tetrachiral) lattice structures developed. ► Large variations of in-plane negative Poisson’s ratios can be achieved through tuning geometry. ► Anti-tetrachiral anisotropic lattices maximize transverse shear for minimum density.
Co-reporter:Wenxin Wang, Haibao Lu, Yanju Liu and Jinsong Leng
Journal of Materials Chemistry A 2014 - vol. 2(Issue 15) pp:NaN5449-5449
Publication Date(Web):2014/01/24
DOI:10.1039/C3TA15204A
With the aim of integrating a family of functional composites, possessing a conspicuous water-induced shape memory effect (SME), a novel sodium dodecyl sulfate–epoxy shape memory composite was constructed. The original fabrication strategy of the composite was designed based on the chemical interaction constructed 3D microvoid on the shape memory composite surface. Compared with the pure epoxy shape memory polymer, the composites display a gratifying water-induced shape memory effect. The results indicate that the water-induced shape recovery rate of the composite is accelerated through increasing the temperature or decreasing the specimen thickness. An immersion test in water suggests that the chemical interaction and physical swelling effect have a significant influence on the water-induced shape memory process. This research advocates the design concept and presents some experimental results of the water-driven smart composite. The potential application range is expected to expand more widely, including a humidity sensor, temperature/humidity switch, underwater deployable structure and a power source transforming chemical energy into mechanical energy for an ultralow-power device.
Co-reporter:Wenbing Li, Yanju Liu and Jinsong Leng
Journal of Materials Chemistry A 2015 - vol. 3(Issue 48) pp:NaN24539-24539
Publication Date(Web):2015/11/24
DOI:10.1039/C5TA08513F
In this paper, a new type of multicomposite styrene-based shape memory polymer (SSMP) was fabricated. This new SSMP included three regions: a SSMP matrix filled with multiwalled carbon nanotubes (SSMP–CNT), a SSMP matrix filled with Fe3O4 nanoparticles (SSMP–Fe3O4), and a third neat SSMP region which is located between the two composite regions. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results demonstrated that all the three SSMP materials possessed two well-separated transitions, which were subsequently used for the fixing/recovery of two temporary shapes (triple-shape memory effect) in each region. Furthermore, the unique selective actuation functionality of the multicomposite was demonstrated, based on the principle that Fe3O4 nanoparticles and CNT can selectively induce heat in a 30 kHz alternating magnetic field and 13.56 MHz radiofrequency, respectively. Therefore, well-controlled multiple shape recoveries of the multicomposite SSMP were achieved by applying selective stimuli. This proposed approach of selective actuations can be applied to other stimuli-responsive material systems to generate complex structures for target applications.
Co-reporter:F. H. Zhang, Z. C. Zhang, C. J. Luo, I-Ting Lin, Yanju Liu, Jinsong Leng and Stoyan K. Smoukov
Journal of Materials Chemistry A 2015 - vol. 3(Issue 43) pp:NaN11293-11293
Publication Date(Web):2015/10/09
DOI:10.1039/C5TC02464A
Nonwoven fiber composite Nafion/Fe3O4 films can be programmed to adopt over 5 shapes, and several fast transformations in sequence are demonstrated using different intensities of the same stimulus. We use an alternating magnetic field to activate the transformations remotely and investigate the conditions for tunable actuation control. Since the heat is generated inside the shape-changing films, though locally temperatures >80 or 100 °C are achieved, their surface temperature can be kept below 38–40 °C.
Co-reporter:Junyao Shen, Yongtao Yao, Yanju Liu and Jinsong Leng
Journal of Materials Chemistry A 2016 - vol. 4(Issue 32) pp:NaN7621-7621
Publication Date(Web):2016/07/15
DOI:10.1039/C6TC01912A
We demonstrate a facile, template-free route for Fe nanowires (NWs) with an average diameter of 100 nm through magnetic-field-assisted hydrothermal conditions. The aspect ratio of the Fe NWs reaches 50. Fe NWs are constructed with interconnected bead-like nanospheres, which are composed of primary nanocrystals (NCs) with an average size of 8 nm. This shows that the polycrystalline Fe NWs have a body-centred cubic (bcc) structure with preferential growth on the 〈110〉 zone axis. Such hierarchical structures involve orientational growth in the presence of an external magnetic field. The molarity of the reducing agent, reaction time and temperature, are further investigated to understand the influence of these parameters on the growth process of Fe NWs. Compared with those of Fe nanoparticles (NPs), the magnetic properties of Fe NWs show both higher saturation magnetization (154.03 emu g−1) and coercivity (360.84 Oe). The peak value of reflection loss (RL) reaches up to −27.28 dB at 3.68 GHz, indicating the excellent microwave absorption performance of the Fe NWs for low gigahertz usage (2–6 GHz). This mild approach to control Fe NWs is easy to scale-up for other iron-related magnetic nanodevice applications.
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