Dielectric and pyroelectric properties of a composite of ferroelectric ceramic and polyurethane

Flexible piezo- and pyroelectric composite was made in the thin film form by spin coating. Lead Zirconate Titanate (PZT) ceramic powder was dispersed in a castor oil-based polyurethane (PU) matrix, providing a composite with 0–3 connectivity. The dielectric data, measured over a wide range of frequency (10^–5 Hz to 10⁵ Hz), shows a loss peak around 100 Hz related with impurities in the polymer matrix. There is also an evidence of a peak in the range 10^–4 Hz, possibly originating from the glass transition temperature T_g of the polymer. The pyroelectric coefficient at 343 K is 7.0×10^–5 C·m^–2·K^–1 which is higher than that of β-PVDF (1×10^–5 C·m^–2·K^–1). Electronic Publication     

硅烷偶联剂改性聚氨酯的研究

从原料和工艺两方面出发,对以γ-氨丙基三乙氧基硅烷(KH550)为基础的硅烷改性聚氨酯(SPU)进行了改善.原料方面,改性后的KH550由伯氨基转化为仲氨基,反应活性降低;工艺方面,将KH550加料顺序提前.试验结果表明:这两种方法均有利于降低SPU树脂的黏度和提高反应平稳性;较好解决了由于黏度上升太快引起的KH550自聚凝团问题.     

Removal of lead ions in aqueous solution by hydroxyapatite/polyurethane composite foams

We have prepared hydroxyapatite/polyurehthane (HAp/PU) composite foams with two different HAp contents of 20 and 50 wt.% and investigated their removal capability of Pb2+ ions from aqueous solutions with various initial Pb2+ ion concentrations and pH values of 2-6. HAp/PU composite foams synthesized exhibited well-developed open pore structures which provide paths for the aqueous solution and adsorption sites for Pb2+ ions. With increasing the HAp content in the composites, the removal capability of Pb2+ ions by the composite foams increases owing to the higher adsorption capacity, whereas the removal rate is slower due to the less uniform dispersity of HAp in composite foams. The removal rate of Pb2+ ions is also slower with increasing the initial Pb2+ ion concentration in aqueous solutions. The removal mechanism of Pb2+ ion by the composites is varied, depending on the pH value of aqueous solution: the dissolution of HAp and precipitation of hydroypyromorphite is dominant at lower pH 2-3, the adsorption of Pb2+ ions on the HAp/PU composite surface and ion exchange reaction between Ca2+ of HAp and Pb2+ in aqueous solution is dominant at higher pH 5-6, and two removal mechanisms compete at pH 4. The equilibrium removal process of Pb2+ ions by the HAp/PU composite foam at pH 5 was described well with the Langmuir isotherm model, resulting in the maximum adsorption capacity of 150 mg/g for the composite foam with 50 wt.% HAp content.     

湿热环境对7781/CYCOM 7701玻璃纤维/环氧复合材料典型力学性能的影响

采用7781/CYCOM 7701玻璃纤维/环氧织物预浸料和中温固化工艺制造了复合材料单向层压板试验件。将试验件分为3组,分别对应低温干态（CTD）、室温干态（RTD）和高温湿态（ETW）3种试验环境条件。在这3种试验环境条件下,分别测试了复合材料单向层压板的拉伸、压缩、剪切、孔挤压和拉脱等力学性能。并在试验中适当考虑了复合材料经向和纬向力学性能差异、是否含缺口和是否含冲击损伤等情况。根据试验结果,研究了湿热环境对7781/CYCOM 7701玻璃纤维/环氧复合材料单向层压板典型力学性能的影响。研究表明：以RTD条件为基准,各项强度性能在CTD条件下均上升,而在ETW条件下均下降。其中,在ETW条件下,拉伸强度下降18%~25%,压缩强度下降10%~40%,剪切强度下降30%~50%,孔挤压强度下降约20%,拉脱强度下降接近30%;拉伸和压缩弹性模量受温度和吸湿条件影响较小,均在10%左右或以内;而泊松比和剪切弹性模量则受温度和吸湿条件影响很大,两者在ETW条件下的性能比在RTD条件下的性能分别下降约30%和50%。     

喷涂弹性聚氨酯作为海底输油管道保温材料的性能研究

采用无模旋转喷涂工艺制备了聚氨酯弹性保温防水涂层。通过实验与传统保温材料的吸水率、导热系数、密度、抗静水压等物理参数进行了对比,并对弹性聚氨酯的耐海水腐蚀和深海保温性能进行实验。结果表明,喷涂聚氨酯弹性保温材料可以满足水深在500m以上海域中海底输油管道保温的要求。     

On the reinforcement of concrete sleepers by composite materials

The most important role of sleepers in a railroad system is conveyance of the train load from rail to the ballast. Since the sleepers are under complicated loading in real conditions, the first stage is static analysis of them. Future railway traffic will certainly be even faster than that of today, and at the same time the demanded load capacity of the trains will probably increase. This implies that the demands for concrete sleepers will increase and the need for reliable analytical tools will be extensive in the near future.

The aim of this work is to increase the load capacity of the sleepers by means of composite materials and to make the railroad system ready for heavier and faster trains. The first step is applying a closed form solution. Then a finite element model of a concrete sleeper is established, in the nest step. Later a full-scale test of reinforced and non-reinforced sleepers is done, and at last, a validation of the finite element model through comparison with full-scale test results as well as closed form solution is conducted. The percentage of increased load capacity of sleepers and good agreements between the results make the work beneficial and reliable.     

有机蒙脱土/聚氨酯弹性体复合材料的微观形貌及力学性能

以十八烷基三甲基氯化铵（OTAC）为改性剂,通过离子交换法改性钠基蒙脱土（MMT）制得有机蒙脱土（OMMT）;以聚丙二醇（PPG）和4,4'-二苯基甲烷二异氰酸酯（MDI）为单体,1,4-丁二醇（BDO）为扩链剂,合成聚氨酯弹性体（PUE）基体;并采用预聚体法制备了OMMT/PUE复合材料。FTIR和XRD测试结果表明:OMMT在2 921 cm-1和1 469 cm-1处出现-CH₂吸收峰,表明OTAC分子链成功插入到OMMT片层,由OMMT的耐热性推算OTAC的插层量为24%,且OMMT的层间距较MMT增加了0.7 nm。OMMT/PUE复合材料的SEM和XRD结果显示:适量的OMMT在PUE基体中均匀分散,且以完全剥离的形式存在,其主要原因是:一方面由于OTAC分子与PUE软链间存在较强的作用,另一方面OMMT表面活性基团与基体间也存在一定的界面作用,两种作用均有利于提高OMMT/PUE复合材料的力学性能。力学性能测试结果表明:当OMMT的含量为3wt%时,OMMT/PUE复合材料的拉伸强度、扯断伸长率及断裂拉伸强度比PUE分别提高了37%、28%和34%,力学性能得到明显改善。      

Selective elimination of lead(II) ions by alginate/polyurethane composite foams

A new type of adsorbent which is capable of selectively adsorbing lead(II) ions (Pb(2+)) was developed. The adsorbent was generated by reaction of sodium alginate with NB-9000B, a polyisocyanate type of prepolymer of polyurethane. The adsorbent was a hydrophilic and flexible alginate/polyurethane composite foam (ALG/PUCF) with the alginate chemically immobilized in the cell walls of the foam. Acid-base titration was used to quantify the concentration of carboxyl groups, which are present on the alginate molecules of the ALG/PUCF, functioning as the essential sites for binding Pb(2+). For the optimized ALG/PUCF, the carboxyl was found to be 38.2+/-1.2mumol/g of dry weight. The capacity for adsorbing Pb(2+) ions in 1.0g of dry weight of the optimized ALG/PUCF was found to be 16.0+/-2.1mumol, indicating that ion exchange was the essential mechanism for adsorbing Pb(2+) ions. The adsorption capacity was found to be highly sensitive to the pH of the sample solution; lower pH (<3) significantly decreased the adsorption. Competing ions such as Mg(2+), Ca(2+), and Cd(2+) also caused a decrease in selectivity and capacity for Pb(2+) adsorption, although the effect was less pronounced than the effect of pH. The ALG/PUCF is highly stable, flexible and easy to use. ALG/PUCF is also reusable after regeneration with ethylenediamine-N,N,N',N'-tetraacetic acid, disodium salt (EDTA-2Na). Due to these features, this adsorbent may be highly useful for elimination of Pb(2+) ions from contaminated water.     

聚氨酯弹性体国内市场与技术进展浅析

对聚氨酯(PU)弹性体氨纶、热塑性聚氨酯弹性体(TPU)及其上游一些原料国内市场最新动态作了介绍和浅析,指出国内氨纶需提高技术创新能力和国际竞争力;国内TPU产业应发展高端产品;并介绍PU弹性体最新技术进展和新的应用,提出了我国未来PU弹性体重点发展方向.     

Development of rigid bio-based polyurethane foam reinforced with nanoclay

Integration of organic nanoclay into bio-based polyurethane (PU) foam is a promising alternative to enhance the foam’s properties via green technology. In this paper, modified diaminopropane montmorillonite (DAP-MMT) nanoclay was introduced into palm oil-based PU foam at different weight loadings, namely, 0, 2, 4, 6, 8, and 10 wt.%, in order to investigate the effects on the mechanical and thermal properties of the foam. Several tests and characterizations were carried out to study the surface morphology, density, compressive strength and thermal stability of the foam. It was found that foam exhibited an exfoliated or intercalated microstructure based on the DAP-MMT contents. The X-ray diffraction analysis showed that below 4 wt.%, the foams displayed exfoliated structures while beyond the value, the foams exhibited the intercalated morphologies. Closed cells with different cell sizes were observed when the DAP-MMT contents were varied. Meanwhile, thermal stability and compressive strength of foams increased with increasing DAP-MMT contents up to 4 wt.%, as shown by thermogravimetry analysis and compression test, respectively.     

Mechanics of small damage in fiber-reinforced composite materials

In this work the new concept of small damage is examined within the framework of continuum damage mechanics. In particular, special emphasis is given to a new damage variable that is defined in terms of the elastic stiffness of the material. Only the scalar case is studied in this work. The scalar definition of the new damage variable was used recently by many researchers. The investigation of the new scalar damage variable and the new concept of small damage is carried out on fiber-reinforced composite materials.     

有机硅烷偶联剂对水性聚氨酯材料性能的影响

以IPDI为硬段,PTMG1000为软段,TMP为交联剂,APTES为封端剂,合成了一系列硅烷偶联剂改性水性聚氨酯乳液,并制备了水性聚氨酯的固化膜.FT-IR分析表明,APTES上的一NH2 与聚铵酯的端--NCO发生反应,成功地将硅烷结构引入聚氨酯分子中.TG分析表明,APTES的改性,提高了聚氨酯热稳定性.随着w(...     

Limit analysis of composite materials with anisotropic microstructures: A homogenization approach

A nonlinear mathematical programming approach together with the finite element method and homogenization technique is developed to implement kinematic limit analysis for a microstructure and the macroscopic strength of a composite with anisotropic constituents can be directly calculated. By means of the homogenization theory, the classical kinematic theorem of limit analysis is generalized to incorporate the microstructure - Representative Volume Element (RVE) chosen from a periodic composite/heterogeneous material. Then, using an associated plastic flow rule, a general yield function is directly introduced into limit analysis and a purely-kinematic formulation is obtained. Based on the mathematical programming technique, the finite element model of microstructure is finally formulated as a nonlinear programming problem subject to only one equality constraint, which is solved by a direct iterative algorithm. The calculation is entirely based on a purely-kinematical velocity field without calculation of stress fields. Meanwhile, only one equality constraint is introduced into the nonlinear programming problem. So the computational cost is very modest. Both anisotropy and pressure-dependence of material yielding behavior are considered in the general form of kinematic limit analysis. The developed method provides a direct approach for determining the macroscopic strength domain of anisotropic composites and can serve as a powerful tool for microstructure design of composites.     

In situ monitoring in real time of fatigue-induced damage growth in composite materials by acoustography

There are growing concerns about the effects of accidental impact damage on the structural integrity of aerospace composites and about the possible growth of the damage due to in-service fatigue. There has been some success in the use of established methods (ultrasonic C-scan, thermography, X-rays) to monitor damage development during fatigue experiments by interrupting a test and removing the specimen for damage inspection but this stop-and-restart test procedure is far from satisfactory. Real-time damage monitoring in composite materials during fatigue has now become possible by the emergence of a new ultrasonic imaging technology, acoustography. The successful integration of acoustography and a servo-hydraulic fatigue test machine has resulted in a new measurement system which can be used for the in situ monitoring in real time of damage growth in composite specimens during long-term fatigue tests. Results are presented which show damage-area growth during fatigue cycling under high compressive loads. After an initial small enlargement (stage 1), damage grows at a constant rate (stage 2) until the third stage is reached when there is further growth at an increasing rate to final failure. However, a ‘fatigue limit’ has also been observed. At stresses below this fatigue limit, a zero damage-growth régime has been found in studies of >10⁶ fatigue cycles. The results obtained have important implications for the understanding of the effects of damage on fatigue life and for the design of ‘safe’ damage-tolerant structures.     

Development of bumper shield using low density materials

In order to avoid critical accidents due to space debris, this paper proposes an extra bumper shield called an inflatable bumper. It consists of aluminum (Al2024-T3), high strength fiber Vectran and inflatable polyurethane. Because of this inflatability, it is compactly stored during its transportation. And after the installation outside of the space structures, this bumper is then inflated by the effect of expandable polyurethane. This method saves the amount of the transportation and the involved cost. In this paper the experiments, using several polyurethane's with different areal density, have been conducted, compared and evaluated from the viewpoints of the penetrated areal density, the total thickness penetrated, and mass distribution of the fragments captured inside the shield. As the results of the experiments, it is found that the protection ability of the proposed structure depends on the areal density of polyurethane layers and the optimum areal density is 0.525kg/m². And by using polyurethane between Vectran layers, this expandable structure captures the fragments of the secondary debris, which might cause a secondary impact on the space structure.     

Computationally efficient modelling of the fatigue behaviour of composite materials

Fatigue of composite structures is a complex process involving several types of failure. Existing approaches either neglect this complexity or require large computational effort. In this work, a simple progressive damage model including strength and stiffness degradation is implemented into finite element (FE) software. To reduce computational time, the major part of stress calculations is carried out by classical lamination theory. At single points of time, FE analysis is employed to support these calculations. The simplified model is tested against a reference model using FEA after each load cycle. Calculations are set up for a tensile specimen and a cap profile with quasi-isotropic layup. The simplified model using CLT is shown to be in good agreement with the reference while significantly reducing computational time.     

木质纤维填充改性聚氨酯弹性体性能研究

为了改善聚氨酯弹性体拉伸和热稳定性能,本文以环氧树脂改性木质纤维,再填充至聚氨酯(PU)弹性体中制得生物基复合材料,采用万能试验机、扫描电镜和热分析仪分别对复合材料的拉伸性能、断面形貌和热稳定性进行测试分析。结果表明：与未改性填充木质纤维复合材料相比,经水性环氧和E-51环氧树脂改性木质纤维分别填充4wt.%和2wt.%时,复合材料的拉伸强度分别由18.2 MPa提高至22.4和23.7 MPa,断裂伸长率分别由898%提高至1 124%和2 269%。其中,采用2wt.%E-51环氧树脂溶液改性木质纤维填充2wt.%时,与未改性木质纤维相比,其拉伸强度提高了6.3%,断裂伸长率提高4倍以上,这是由于环氧改性木质纤维提高了木质纤维与树脂基体间的界面相容性。失重率为5%时,与未填充PU相比,复合材料的分解温度由269℃升高至279℃,提高了3.7%。填充木质纤维可提高PU拉伸性能与热稳定性。     

Multi-coating inhomogeneities approach for the effective thermo-electro-elastic properties of piezoelectric composite materials

This work presents a micromechanics-based model to predict the effective thermo-electro-elastic properties of a piezoelectric composite materials containing ellipsoidal multi-coated inhomogeneities. A finite element analysis is also performed for two-phase piezoelectric composite materials using ABAQUS finite element software. The results obtained from the multi-coating homogenization method show good agreement with the existing experimental results and the finite element results. The inhomogeneities’s shape effect as well as the poling direction and the coating effects are investigated. The results show that a proper choice of materials and inhomogeneities’s geometry can lead to the desired thermo-electro-elastic properties.     

Development and testing of a self-deformed composite material

A multifunctional – hybrid – composite material that incorporates carbon and glass fibres embedded into an epoxy matrix was developed. This material can be made to undergo a shape change without inserting activators. This is accomplished by selective heating of the embedded carbon fibres through the application of an electric current (Joule effect). The resulting shape change was determined and the stresses generated during heating were measured via a 3-point bending device. The possibility of using the reinforcing fibres of a multi-directional composite as activators for inducing specific deformation modes is discussed.     

Fabrication of homogeneous titania/MWNT composite materials

MWNT/titania nanocomposites were prepared by an impregnation method and subsequent heat treatment at 400 °C. Precursor compounds such as titanium (IV) propoxide and titanium (IV) ethoxide were used to cover the surface of CNTs under solution conditions. Electron microscopy and X-ray diffraction techniques were carried out to characterize the as-prepared titania layers.