Showing papers by "Shanyi Du published in 2009"
TL;DR: In this article, the progress of electro-activate SMP composites is discussed and the filler types that affect the conductive properties of these composites are discussed, and the mechanisms of electric conduction are addressed.
440 citations
TL;DR: In this article, the shape recovery behavior of thermoset styrene-based shape-memory polymer composite (SMPC) reinforced by carbon fiber fabrics is investigated, and the feasibility of using an SMPC hinge as a deployable structure is demonstrated.
Abstract: This paper investigates the shape recovery behavior of thermoset styrene-based shape-memory polymer composite (SMPC) reinforced by carbon fiber fabrics, and demonstrates the feasibility of using an SMPC hinge as a deployable structure. The major advantages of shape-memory polymers (SMPs) are their extremely high recovery strain, low density and low cost. However, relatively low modulus and low strength are their intrinsic drawbacks. A fiber reinforced SMPC which may overcome the above-mentioned disadvantages is studied here. The investigation was conducted by three types of test, namely dynamic mechanical analysis (DMA), a shape recovery test, and optical microscopic observations of the deformation mechanism for an SMPC specimen. Results reveal that the SMPC exhibits a higher storage modulus than that of a pure SMP. At/above Tg, the shape recovery ratio of the SMPC upon bending is above 90%. The shape recovery properties of the SMPC become relatively stable after some packaging/deployment cycles. Additionally, fiber microbuckling is the primary mechanism for obtaining a large strain in the bending of the SMPC. Moreover, an SMPC hinge has been fabricated, and a prototype of a solar array actuated by the SMPC hinge has been successfully deployed.
437 citations
01 Jan 2009
TL;DR: In this paper, the progress of electro-activate SMP composites is discussed and the filler types that affect the conductive properties of these composites are discussed, and the mechanisms of electric conduction are addressed.
Abstract: 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.
393 citations
TL;DR: Shape-memory polymers (SMPs) offer a number of potential technical advantages that surpass other shapememory materials such as shape-memory metallic alloys and shapememory ceramics as discussed by the authors, such as high recoverable strain (up to 400%), low density, ease of processing and the ability to tailor the recovery temperature, programmable and controllable recovery behavior, and more importantly low cost.
Abstract: Shape-memory polymers (SMPs) offer a number of potential technical advantages that surpass other shape-memory materials such as shape-memory metallic alloys and shape-memory ceramics. The advantages include high recoverable strain (up to 400%), low density, ease of processing and the ability to tailor the recovery temperature, programmable and controllable recovery behavior, and more importantly, low cost. This article presents the state-of-the-art regarding SMPs. First, the architecture, type, and main properties of the traditional and recently developed SMPs are introduced. Second, structural and multifunctional SMP composites are summarized and discussed. These composites greatly enhance the performance of the SMPs and widen their potential applications. Finally, current applications of SMP materials in aerospace engineering, textiles, automobiles, and medicine are presented.
201 citations
TL;DR: In this paper, an interaction energy contour integral is derived for the computation of mixed-mode stress intensity factors (SIFs) in nonhomogeneous materials with continuous or discontinuous properties.
125 citations
TL;DR: In this paper, the microstructure, mechanical and oxidation resistance properties of the composite were investigated and it was found that the low modulus of carbon fiber and a graphitization transition layer between fiber and matrix led to the decreased flexural strength.
125 citations
TL;DR: In this article, the effect of the solubility parameter of the interactive solvent on the shape recovery behavior and glass transition temperature of polystyrene SMP was investigated experimentally.
Abstract: For the thermal response of shape-memory polymer (SMP) it has been experimentally demonstrated that the actuation can be achieved using interactive solvent. In this paper, the effect of the solubility parameter of the interactive solvent on the shape recovery behavior and glass transition temperature of polystyrene SMP was investigated experimentally. The effect of the solubility parameter on the activation energy was separated and qualitatively identified, as expected from the relaxation theory and Eyring equation. This approach should be applicable to other SMPs and their composites and many extension applications and achievements could be based on this outcome.
98 citations
TL;DR: In this article, the effect of voids on the strength of composite laminates has been investigated in terms of the fracture parameters involved in the fracture criterion and the critical void content has been estimated for each case both for void content and ultrasonic attenuation.
Abstract: An experimental program to characterize the effect of voids on the strength of composite laminates is presented. The adequacy of a fracture criterion to represent the experimental data for the effect of voids on the flexure strength, tensile strength, and interlaminar shear strength of composite laminates is assessed. The experimental program investigates the effect of different pressures and dwell times on the critical void content. Laminates produced with carbon fiber/epoxy resin unidirectional prepreg have been produced with an intentionally high void content. Short beam shear, three-point flexure, and tensile testing are used for mechanical evaluation and the results correlate to void volume fraction and ultrasonic absorption coefficient. The ultrasonic absorption coefficient is measured for all the specimens and its variation is approximately linear with the void content, corroborating previous experimental results. The effects of these factors on the strength of the composite laminates are discussed in terms of the fracture parameters involved in the fracture criterion. The critical void content is estimated for each case both in terms of void content and ultrasonic attenuation.
88 citations
TL;DR: In this paper, an electroactive thermoset styrene-based shape memory polymer (SMP) nanocomposite filled with nanosized (30?nm) carbon powders was investigated.
Abstract: This paper concerns an electroactive thermoset styrene-based shape memory polymer (SMP) nanocomposite filled with nanosized (30?nm) carbon powders. With an increase of the incorporated nanocarbon powders of the SMP composite, its glass transition temperature (Tg) decreases and storage modulus increases. Due to the high micro-porosity and homogeneous distributions of nanocarbon powders in the SMP matrix, the SMP composite shows good electrical conductivity with a percolation of about 3.8%. This percolation threshold is slightly lower than that of many other carbon-based conductive polymer composites. Consequently, due to the relatively high electrical conductivity, a sample filled with 10?vol% nanocarbon powders shows a good electroactive shape recovery performance heating by a voltage of 30?V above a transition temperature of 56?69??C.
88 citations
TL;DR: In this article, a modified factor of extinction coefficient and an equivalent albedo of scattering were defined taking into account anisotropic scattering in fibrous insulation for simultaneous estimation of the conductive and radiative properties using the experimentally measured temperature responses for external temperatures up to 980 K.
Abstract: In present paper, a modified factor of extinction coefficient and an equivalent albedo of scattering were defined taking into account anisotropic scattering in fibrous insulation. An inverse conduction–radiation analysis in an absorbing, emitting and scattering medium was conducted for the simultaneous estimation of the conductive and radiative properties using the experimentally measured temperature responses for external temperatures up to 980 K. The estimated properties were validated by comparing the predicted and measured results under transient and steady-state condition. It was found that the calculated results corresponded well with the experimental data within an average of 3.1% under transient condition and 9.8% under steady-state condition. This confirms the good behavior of the model and the validity of results.
44 citations
TL;DR: In this article, the structural, electronic and vibrational properties of a series of heavily B-doped diamond models have been investigated using the density functional theory within a local density approximation, and the vibrational frequencies and eigenmodes were determined using the linear response approach, while Raman intensities were obtained by the second response method.
Journal Article•
TL;DR: In this article, truss core sandwich panels reinforced by carbon fibers were assembled with bonded laminate facesheets and carbon fiber reinforced truss cores, and both ends of the truss layers were embedded into four layers of top and bottom faceshesets.
TL;DR: In this paper, the effect of sintering temperature and holding time on the microstructure and mechanical properties of ZrB 2 -SiCw composites was investigated. And the results indicated that flexural strength and fracture toughness were improved with hot-pressing temperature.
TL;DR: In this article, a probabilistic thermal analysis of the fibrous insulation subjected to aerodynamic heating conditions was performed to account for the uncertainties such as material properties, loading conditions and geometrical variations.
TL;DR: In this paper, an experimental setup was developed to measure the transient temperature response in fibrous insulation and the radiative properties were modified to take anisotropic scattering of fibrous insulations into account.
Abstract: In this article, an experimental setup was developed to measure the transient temperature response in fibrous insulation The radiative properties were modified to take anisotropic scattering in fibrous insulation into account A model of combined radiation and conduction heat transfer through fibrous insulation was generated based on the two-flux approximation Using the measured transient temperature response, the Levenberg–Marquardt method was utilized to identify the equivalent radiative properties and thermal conductivities of fibrous insulation The identified thermal properties were validated by transient and steady state experimental results of fibrous insulation Satisfactory agreement was obtained
TL;DR: In this article, two NiCoCrAl/YSZ microlaminates and a monolithic NiCo-CrAl foil were fabricated by EB-PVD and the fracture toughness was estimated using measured data in room-temperature tensile testing.
TL;DR: In this paper, the boron-doped amorphous diamond (a-D:B) films were used to improve the conversion efficiency of p-a-Si:H window layer.
TL;DR: In this article, the authors investigated the oxidation behavior of AlN-SiC-TiB 2 composites, synthesized by self-propagating high-temperature synthesis (SHS) and hot isostatic pressing (HIP).
20 Oct 2009
TL;DR: In this article, an unsymmetrical washer was designed and fabricated, taking full advantage of Piezoelectric ceramics (PZT) to play both roles as actuators and sensors, and using energy as the only extracted feature to diagnose abnormality.
Abstract: Research and development efforts are underway to provide structural health monitoring systems to ensure the integrity of
thermal protection system (TPS). An improved analytical method was proposed to assess the fastener integrity of a
bolted structure in this paper. A new unsymmetrical washer was designed and fabricated, taking full advantage of
piezoelectric ceramics (PZT) to play both roles as actuators and sensors, and using energy as the only extracted feature to
identify abnormality. This diagnostic method is not restricted by the materials of the bracket, panel and base structure of
the TPS whose condition is under inspection. A series of experiments on a metallic honeycomb sandwich panel were
completed to demonstrate the capability of detecting bolt loosening on the TPS structure. Studies showed that this
method can be used not only to identify the location of loosened bolts rapidly, but also to estimate the torque level of
loosening bolts. Since that energy is the only extracted feature used to detect bolt loosening in this method, the diagnostic
process become very simple and swift without sacrificing the accuracy of the results.
04 May 2009
TL;DR: In this article, the non-resonant vibrational Raman spectra of nitrogen-doped tetrahedral amorphous carbon have been calculated from first principles, including the generation of a structural model, and the calculation of vibrational frequencies, vibrational eigenmodes and Raman coupling tensors.
Abstract: The non-resonant vibrational Raman spectra of nitrogen-doped tetrahedral amorphous carbon have been calculated from first principles, including the generation of a structural model, and the calculation of vibrational frequencies, vibrational eigenmodes and Raman coupling tensors. The calculated Raman spectra are in good agreement with the experimental results. The broad band at around 500 cm−1 arises from mixed bonds. The T peak originates from the vibrations of sp3 carbon and the G peak comes from the stretching vibrations of sp2-type bonding of C=C and C=N. The simulation results indicate the direct contribution of N vibrations to Raman spectra.
25 Jul 2009
TL;DR: In this article, a bistable unsymmetric hybrid composite laminate with quite high stiffness and large shape change is presented, and the Rayleigh-Ritz method is used to predict the cured shape and the predited results agree well with the experimentals.
Abstract: A bistable unsymmetric hybrid composite laminate with quite high stiffness and large shape change is
presented. Rayleigh-Ritz method is used to predict the cured shape and the predited results agree well
with the experimentals. The critical loads switching between different shapes are tested. It shows that the
critical load for hybrid composite laminates increases greatly (up to 10 times) compared with the pure
fiber reinforced polymer matrix composite laminates. The influence of different geometric and material
properites on the bistable shape is discussed. It reveals that the present hybrid bistable laminate is more
designable and miscellaneous.
TL;DR: In this article, a thermal explosion in the Cr-Al-Si-C system in air was reported, and the combustion products, Cr2AlC and Cr5-xSi3-zCx+z, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS).
Abstract: Ternary Cr2AlC and Cr3SiC2 compounds—belonging to the family of Mn+1AXn phases (n=1, 2, 3; M is a transition metal, A is an A group element, and X = C or N)—were prepared by thermal explosion in the Cr-Al-Si-C system in air. After mixing, drying, and compaction, the green powders taken in stoichiometric ratios of Cr: Si: C=3: 1: 2 plus 20 wt % Al were thermally exploded at 1100°C in an SHS reactor. The combustion products, Cr2AlC and Cr5-xSi3-zCx+z, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Chromium-aluminum intermetallics and Al4C3 were identified as intermediate products in the synthesis of Cr2AlC. A Cr5-xSi3-zCx+z compound in the system under study was found to exist as Cr3SiC2.
TL;DR: One multiscalar microlaminate comprising the strong, thin layer stacks of NiCoCrAl/YSZ (ZrO2-8 ¼wt.% Y2O3) and 5 thick tough phase layers, whose thicknesses ranged from 5μm to 25μm, was fabricated by electron beam physical vapor deposition (EB-PVD) and then the foil was annealed at 1050°C for 30min this article.
TL;DR: In this article, the feasibility of shape-memory polymers (SMPs) being activated by swelling effect was investigated. And the authors qualitatively identified the role of swelling effect playing in influencing the transition temperature, leading to free volume of polymeric chains increasing.
Abstract: Recently, there is increasing interest in triggering shape recovery of shape-memory polymers (SMPs) by novel inductive
effect In this paper, many hard works have been carried out to make SMP induced while along with swelling effect
Based on the Free-volume theory, Rubber Elasticity Theory and
Mooney-Rivlin Equation, it is theoretically and
experimentally demonstrated the feasibility of SMP activated by swelling effect The mechanism behind it is solvent
acting as plasticizer, to reduce the glass transition temperature (Tg) and melting temperature (Tm) of polymers, make
them softer and more flexible, facilitating the diffusion of the molecules to polymer chains, and then separating them In
addition to this physical action, the intermolecular interactions among the chains are weakened, because interactions are
hindered at the points where the plasticizer is located Finally, the Dynamic mechanical analysis (DMA), FTIR study and
glass transition temperature measurement tests were used to exemplify the feasibility of SMP driven by swelling effect
And it is qualitatively identified the role of swelling effect playing in influencing the transition temperature Swelling
effect occurs due to the interaction between macromolecules and solvent molecules, leading to free volume of polymeric
chains increasing (namely the flexibility of polymer chains increasing), resulting in the Tg decreasing All above
mentioned investigation can be used to confirm that the shape recovery is induced by swelling effect This actuation
almost is applicable for all the SMP and SMP composite, as the swelling theory is almost applicable for all the polymeric
materials
01 Jan 2009
TL;DR: In this article, the shape recovery in a styrene-based shape-memory polymer (SMP) by coating with conductive carbon nanofiber paper has been demonstrated by applying 8.4 V voltage, with response time of 140 s.
Abstract: To electrically activate the shape recovery in a styrene-based shape-memory polymer (SMP) by coating with conductive carbon nanofiber paper has been demonstrated in this paper. Carbon nanofibers in the form of paper sheet in combination with SMP significantly improve the electrical and thermal conductivity of polymer, leading to the actuation of SMP/nanopaper composite (with 15% volume fraction of carbon nanopaper, dimension of 10.0 cm × 0.5 cm × 0.3 cm) can be carried out by applying 8.4 V voltage, with response time of 140 s. Therefore, electrical conductivity of 6.6 S/cm is obtained. This approach, although demonstrated in styrene-based polymer, is applicable to other type of SMP materials. Furthermore, the morphologies of carbon nanofiber in the form of paper is observed by scanning electron microscopy, and the thermomechanical properties of composites are measured and analyzed by dynamic mechanical analysis.Copyright © 2009 by ASME