An analytical solution for hydraulic conductivity of concrete considering properties of the Interfacial Transition Zone (ITZ)

As a composite material, hydraulic conductivity of concrete depends on conductivity of its components that are the mortar, aggregates and the Interfacial Transition Zone (ITZ). Since hydraulic conduction is analogous to heat and electrical conduction, analytical models from these analogous areas relating effective conductivity of composite to conductivity of its components can be used to find the effective hydraulic conductivity of concrete as a function of properties of its components, i.e., aggregate, mortar and the ITZ. However, effect of the conduction in the ITZ has not been considered in these models. This paper presents an analytical solution for the hydraulic conductivity of concrete as a three-phase composite material. The solution is an extension to the model originally proposed for conduction of composite media with randomly suspended spheres. Results of the proposed model compare well against the experimental results and those obtained from rigorous numerical analysis using the Finite Element (FE) method. The principal significance of this study lies in the development of a versatile analytical model that can be employed as a quick tool for assessment of hydraulic conductivity of concrete without the need for sophisticated FE models at the meso-scale level. It offers more insight into effect of different components of concrete on its overall conductivity.     

On the low cycle fatigue failure of insulated rail joints (IRJs)

Insulated rail joints (IRJs) are safety critical components in the signalling system of railway corridors which provide a break in the continuity of the rail steel to locate trains. IRJs connect the two rail ends at the discontinuity to achieve geometric and mechanical requirements of rail. The bending stiffness of an IRJ is about one third that of continuous rail. As a result, the IRJs, especially those in heavy haul tracks, exhibit early failure predominantly due to ratchetting or alternating plasticity of railhead metal in the vicinity of the endpost insulators.A three-dimensional (3D) finite element numerical simulation is carried out to examine failures of railhead material in the vicinity of the endpost of an insulated rail joint considering high frequency dynamic wheel loading. A dynamic wheel load of 182 kN is applied through a contact patch; the distribution of contact pressure is considered using a non-Hertzian formulation. A 12 m long global IRJ model and a sub-model for localised analysis are employed. The shakedown theorem is employed in this study. Nonlinear isotropic/kinematic elastic–plastic material modelling is employed in the simulation. A peak pressure load lower than the shakedown limit is considered as the input load.The equivalent plastic strain plot for this load case lower than the shakedown limit demonstrates the railhead damage captured through a localised stress analysis in the vicinity of the endpost using the sub-modelling technique. The sub-surface plastic deformation of railhead material extends down to 8 mm from the railhead top surface. The critical crack initiating stress components are at 2–4 mm sub-surface depth. As such, the railhead material fails due to alternating plasticity through low cycle fatigue. Laboratory tests were performed to verify the simulation results and found that test and simulation results correlated well.     

An enriched element‐failure method (REFM) for delamination analysis of composite structures

This paper develops an enriched element‐failure method for delamination analysis of composite structures. This method combines discontinuous enrichments in the extended finite element method and element‐failure concepts in the element‐failure method within the finite element framework. An improved discontinuous enrichment function is presented to effectively model the kinked discontinuities; and, based on fracture mechanics, a general near‐tip enrichment function is also derived from the asymptotic displacement fields to represent the discontinuity and local stress intensification around the crack‐tip. The delamination is treated as a crack problem that is represented by the discontinuous enrichment functions and then the enrichments are transformed to external nodal forces applied to nodes around the crack. The crack and its propagation are modeled by the ‘failed elements’ that are applied to the external nodal forces. Delamination and crack kinking problems can be solved simultaneously without remeshing the model or re‐assembling the stiffness matrix with this method. Examples are used to demonstrate the application of the proposed method to delamination analysis. The validity of the proposed method is verified and the simulation results show that both interlaminar delamination and crack kinking (intralaminar crack) occur in the cross‐ply laminated plate, which is observed in the experiment. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of a novel versatile poly(amic acid) derived from ethylenediaminetetraacetic dianhydride

The polycondensation reaction between ethylenediaminetetraacetic dianhydride and 1,4-diaminobutane in various aprotic polar solvents is being exploited to create a novel linear aliphatic polymer poly(amic acid) (PAA). PAA samples were characterized by Fourier transform infrared, Proton nuclear magnetic resonance and Carbon nuclear magnetic resonance spectroscopy resulting in the identification of characteristic absorption bands and thereby verifying successful synthesis. Gel permeation chromatography confirmed narrow molecular weight distributions with polydispersity indices ranging from 1.2 to 2.2 and reported low number average molecular weights ranging from 4000 to 6000 g mol⁻¹. X-ray photoelectron spectroscopy and energy dispersive X-ray analysis showed the presence of nitrogen on the surface and also found nitrogen to be homogenously distributed throughout the bulk of the PAA samples.     

The influence of thermal history on the mechanical properties of poly(ether ether ketone) matrix composite materials

The purpose of this study is to provide insight into the microstructural factors that affect the flexural fatigue performance of carbon-fibre-reinforced poly(ether ehter ketone) (PEEK) composites. Specifically, the effect of the degree of crystallinity on the mechanical properties is examined at two crystallinity levels of the as-received composites (35%) and of quenched composites (10%). Higher static flexural strength and modulus as well as longer fatigue life are observed for the higher crystallinity level. By varying the loading angle with respect to the fibre direction it is shown that the crystallinity effect is not matrix dependent alone. Rather, a strong effect is evident in the fibre direction, which is attributed to the influence of the transcrystalline layer formed on the fibre surface in the high-crystallinity material. As a result, the longitudinal fatigue life at 1·7GPa of the 35% crystallinity material is three orders of magnitude higher than that of the 10% crystallinity composite.     

Synthesis and characterization of a novel multiblock copolyester containing poly(ethylene succinate) and poly(butylene succinate)

Multiblock copolyester (PBS-b-PES) containing poly(butylene succinate) (PBS) and poly(ethylene succinate) (PES) was successfully synthesized by chain-extension of dihydroxyl terminated PBS (HO-PBS-OH) and PES (HO-PES-OH) using 1,6-hexmethylene diisocyanate (HDI) as a chain extender. The chemical structures, molecular weights, crystallization behaviors, thermal and mechanical properties of the copolyesters were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), wide-angle X-ray diffraction (WAXD), tensile testing and hydrolytic degradation. High-molecular-weight copolyesters with M_w more than 2.0 × 10⁵ g mol⁻¹ were easily obtained through chain-extension. The copolyesters showed a single glass transition temperature (T_g) which increased with PES content. The melting point temperature (T_m) and relative degree of crystallinity (X_c) of the copolyesters decreased first and then increased with PES content. The copolyesters manifested excellent mechanical properties, for example, PBS₅-b-PES₅ had fracture stress of 61.8 MPa and fracture strain of 1173%. The chain-extension reaction provided a very effective way to produce high molecular weight multiblock copolyesters.     

An equation of state for the thermodynamic properties of R143a (1,1,1-trifluoroethane)

Thermodynamic properties of 1,1,1-trifluoroethane (R143a) are expresed in terms of a 32-term modified Benedict-Webb-Rubin (MBWR) equation of state. Coefficients are reported for the MBWR equation and for ancillary equations used to lit the ideal-gas heat capacity, and the coexisting densities and pressure along the saturation boundary. The MBWR coefficients were determined from a multiproperty fit that used the following types of experimental data:PVT: isochoric, isobaric, and saturated-liquid heat capacities: second virial coefficients: speed of sound and properties at coexistence. The equation of state was optimized to the experimental data from 162 to 346 K and pressures to 35 MPa with the exception of the critical region. Upon extrapolation to 500 K and 60 MPa, the equation gives thermodynamically reasonable results. Comparisons between calculated and experimental values are presented.     

Development of a HPMC-based controlled release formulation with hot melt extrusion (HME)

The objective of this study was to develop hydroxypropyl methylcellulose (HPMC) based controlled release (CR) formulations via hot melt extrusion (HME) with a highly soluble crystalline active pharmaceutical ingredient (API) embedded In the polymer phase. HPMC is considered a challenging CR polymer for extrusion due to its high glass transition temperature (T_g), low degradation temperature, and high viscosity. These problems were partially overcome by plasticizing the HPMC with up to 40% propylene glycol (PG). Theophylline was selected as the model API. By using differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and X-ray powder diffraction (XRPD), the physical properties of the formulations were systematically characterized. Five grades of HPMC (Methocel^®) – E6, K100LV, K4M, K15M, and K100M – were tested. The extrusion trials were conducted on a 16?mm twIn screw extruder with HPMC/PG placebo and formulations containing theophylline/HPMC/PG (30:42:28, w/w/w). The dissolution results showed sustained release profiles without burst release for the HPMC K4M, K15M, and K100M formulations. The extrudates have good dissolution stability after being stressed for 2 weeks under 40°C/75% RH open dish conditions and the crystalline API form did not change upon storage. Overall, the processing windows were established for the HPMC based HME-CR formulations.     

The vapor pressure of 1,1,1,2-tetrafluoroethane (R134a) and chlorodifluoromethane (R22)

We measured the vapor pressure of chlorodifluoromethane (commonly known as R22) at temperatures between 217.1 and 248.5 K and of 1,1,1,2-tetrafluoroethane (commonly known as R134a) in the temperature range 214.4 to 264.7 K using a comparative ebulliometer. For 1,1,1,2-tetrafluoroethane at pressures between 220.8 and 1017.7kPa (corresponding to temperatures in the range 265.6 to 313.2K), additional measurements were made with a Burnett apparatus. We have combined our results for 1,1,1,2-tetrafluoroethane with those already published from this laboratory at higher pressures to obtain a smoothing equation for the vapor pressure from 215 K to the critical temperature. For chlorodifluoromethane our results have been combined with certain published results to provide an equation for the vapor pressure at temperatures from 217 K to the critical temperature.     

Poisson's ratio as a sensitive indicator of (fatigue) damage in fibre-reinforced plastics

Even if the extent of damage in fibre‐reinforced plastics is limited, it already affects the elastic properties. Therefore, the damage initiation and propagation in composite structures is monitored very carefully. Beside the use of nondestructive testing methods (ultrasonic inspection, optical fibre sensing), the follow‐up of the degradation of engineering properties such as the stiffness is a common approach. In this paper, it is investigated if the Poisson's ratio can be used as a sensitive indicator of (fatigue) damage in fibre‐reinforced plastics. Static, cyclic and fatigue tests have been performed on [0°/90°]_2s glass/epoxy laminates, and axial and transverse strain were measured continuously. The evolution of the Poisson's ratio ν_xy versus time and axial strain ɛ_xx is studied. It is concluded that the degradation of the Poisson's ratio can be a valuable indicator of damage, in combination with the stiffness degradation.     

Synthesis of densely grafted copolymers with tert-butyl methacrylate/2-(dimethylamino ethyl) methacrylate side chains as precursors for brush polyelectrolytes and polyampholytes

Methacrylate-based densely grafted copolymers were synthesized by atom transfer radical polymerization (ATRP) and activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) techniques. The linear poly(2-(2-bromoisobutyryloxy)ethyl methacrylate) PBIEM prepared by ATRP served as a macroinitiator backbone. The “grafting from” strategy was used to initiate polymerization of tert-butyl methacrylate (tBuMA) from PBIEM under ATRP and/or AGET ATRP conditions yielding densely grafted copolymers PBIEM-graft-P(tBuMA). The low polydispersity indices (PDI) of the synthesized brushes evidenced by SEC analysis were consistent with a controlled/living radical polymerization (CLRP) mechanism. The chlorine-terminated PBIEM-graft-P(tBuMA)-Cl macroinitiators were subsequently employed for chain extension with 2-(dimethylamino ethyl) methacrylate (DMAEMA) yielding densely grafted copolymers with diblock copolymer side chains PBIEM-graft-P(tBuMA)-block-PDMAEMA. Further, PBIEM macroinitiator was used to initiate the copolymerization of a binary mixture of tBuMA and DMAEMA through both ATRP and AGET ATRP initiating systems, yielding densely grafted copolymers with statistical distribution of the side chains. The reactivity ratios for random graft copolymerization of tBuMA and DMAEMA from PBIEM backbone established by three different methods (Finemann-Ross, Kelen-Tüdös and Error-in-Variable) did not substantially differ from literature values for conventional free-radical copolymerization of the same monomers. Polyampholyte brushes with PMAA-stat-PDMAEMA side chains were eventually synthesized by hydrolysis of the shielding tert-butyl groups.     

Effect of Low Molecule Polyamide and Nano-SiO2 on Properties of the Poly （MMA/BA/MAA）

Effects of low molecule polyamide （LMPA） and namometer SiO2 particles on the properties of the poly （MMA/ BA/MAA） adhesive for wearable and nonskid PVC （polyvinyl carbazole） materials were investigated. The experimental results show that the shear strength of poly （MMA/BA/MAA）/LMPA is increased, when the LMPA is added into poly （MMA/BA/MAA）. The optimum addition of LMPA is about 4 wt pct. By adding 3 wt pct nano-SiO2 into poly （MMA/BA/MAA）/LMPA adhesive, its properties such as the shear strength, thermal stability, wear resistance and sea waterproof resistance are increased too.     

Au纳米粒子表面等离子共振效应(SPR)增强Au/Bi2WO6异质纳米结构的光催化活性

采用水热-光还原法在三维Bi₂WO₆的二级结构纳米片表面原位沉积Au纳米粒子(Au NPs), 成功获得了具有可见光响应活性的Au/Bi₂WO₆异质光催化剂, 并借助XRD、FE-SEM、HR-TEM、XPS和 UV-Vis-DRS谱等手段对其物相组成、形貌和光吸收特性进行表征, 以罗丹明B(RhB)和苯酚为模型污染物对其光催化性能进行研究。实验结果表明, 与纯Bi₂WO₆相比, 所得Au/Bi₂WO₆异质纳米结构对染料降解具有较高的活性, 当Au负载量为1.5at%时, Au/Bi₂WO₆复合催化剂的催化活性最好, 其光催化降解RhB和苯酚的表观速率常数分别是纯Bi₂WO₆的1.5倍和2.2倍。自由基捕获实验表明, 光生空穴(h⁺)和∙O₂^-是RhB在Au/Bi₂WO₆催化材料上光催化降解的主要活性物种。机理分析表明, Au/Bi₂WO₆活性增强归因于光生电子从Bi₂WO₆的导带向AuNPs表面迁移, 降低光生电子-空穴对的复合率, 同时, Au NPs 的等离子共振效应(SPR)拓展了催化剂在可见光区的响应范围, 从而显著提高了Au/Bi₂WO₆异质光催化的剂活性。Au NPs修饰Bi₂WO₆异质催化剂光太阳能驱动在污水处理方面具有潜在应用。     

PVA/P(AA-AM)复合水凝胶的制备及性能

采用水溶液聚合方法合成了不同组成的丙烯酸-丙烯酰胺共聚物(P(AA-AM))。将聚乙烯醇(PVA)与所合成的P(AA-AM)共混,以戊二醛为交联剂,制备出了不同结构的PVA/P(AA-AM)复合水凝胶。采用扫描电镜观察了凝胶形貌,研究了复合水凝胶的结构与性能关系。结果表明,复合水凝胶溶胀性能与所用交联剂加量有关,复合水凝胶的溶胀度随着交联剂加量增加先增大后减小,在交联剂加量为0.5%时水凝胶溶胀度达到最大值。复合凝胶中的聚合物组成对溶胀度影响显著,随着P(AA-AM)含量提高,水凝胶的溶胀度逐渐增大。适当结构的复合水凝胶具有pH敏感性,敏感程度随着凝胶中P(AA-AM)含量的增加而增强。     

Fracture behaviors of isotactic polypropylene/poly(ethylene oxide) blends: Effect of annealing

As a part of serial work about the toughening of isotactic polypropylene (iPP) during annealing treatment, this work reports the effect of annealing on fracture behaviors of iPP blend with a little of poly(ethylene oxide) (PEO). Injection-molded bars of an iPP/PEO blend were annealed at different temperatures (50-160 °C) for 12 h and at 100 °C for different durations (12-96 h). The fracture behaviors of the annealed samples, including notched Izod impact fracture, universal tensile fracture, and single-edge notched tensile (SENT) fracture, were comparatively investigated to establish the role of annealing in improving the fracture resistance of the sample. The results showed that the annealing treatment greatly influences the fracture resistance of the blend. The impact-fractured surface morphologies were characterized by scanning electron microscope (SEM) to clarify the possible mechanisms for the improvement of the fracture resistance. It was proposed that, the excellent fracture resistance of iPP with a minor phase of which exhibits relatively low melting temperature can be easily achieved through the simple annealing treatment, even if the minor phase is immiscible with iPP.     

纳米细菌纤维素/聚乙烯醇复合水凝胶在模拟体液中的疲劳行为

聚乙烯醇(PVA)复合水凝胶作为半月板及软骨等长期承重植入体,在生理环境中的疲劳行为关系到植入体的持久性和稳定性。采用弥散增强的方法将纳米细菌纤维素(BC)均匀分散在PVA水凝胶基体中,制备了纳米BC/PVA复合水凝胶。在模拟体液(SBF)环境中,采用压缩疲劳过程分析、疲劳前后刚度变化分析及疲劳前后尺寸稳定性分析3种方法,测试和评价了复合水凝胶的抗疲劳性能和力学稳定性。结果表明:纳米BC/PVA复合水凝胶在模拟人体环境中具有良好的抗疲劳性能,能够满足体内植入物的抗疲劳性能需求;纳米BC的加入可以有效提升复合水凝胶的力学稳定性和抗疲劳性能,但随着纳米BC含量的进一步升高,复合水凝胶的抗疲劳性能有所减弱,当PVA与纳米BC质量比为30∶1时,纳米BC/PVA复合水凝胶疲劳前期与后期最大位移变化量最小(0.002mm),疲劳前后刚度变化最小(5.41%),且疲劳前后尺寸稳定性最强,变形量仅为0.427mm,抗疲劳性能达到最佳。     

Corrosion behavior of Al_(0.4)CoCu_(0.6)NiSi_(0.2)Ti_(0.25) high-entropy alloy coating via 3D printing laser cladding in a sulphur environment

High-entropy alloys(HEAs) are of great interest in materials science and engineering communities owing to their unique phase structure.HEAs are constructed with five or more principal alloying elements in equimolar or near-equimolar ratios.Therefore,they can derive their performance from multiple principal elements ratherthan a single element.In this work,three-dimensional printing laser cladding was applied to produce an Al_0.4CoCu_0.6NiSi_0.2Ti_0.25 HEA coating.The experimental results confirmed that the laser cladding could be used to produce a thin coating of 120 μm in thickness.In the high-temperature laser cladding process,some Fe elements diffused from the substrate to the coating,forming a combination of face-centred cubic and body-centred cubic phase structures.The HEA coating metallurgically bonded well with the substrate.Owing to the increased dislocation density and number of grain boundaries,the HEA coating was harder and had a stronger hydrophobicity than X70 steel.The electrochemistry results showed that the HEA coating had better corrosion resistance than X70 steel.Aluminium oxides formed on the surface of the HEA coating had a certain protective effect.However,because of the laser cladding,the HEA coating generated cracks.In future work,the laser cladding technology will be improved and heat treatment will be implemented to prevent formation of cracks.     

Preparation and physicochemical characterization of soy isoflavone (SIF) nanoparticles by a liquid antisolvent precipitation method

Soy isoflavone (SIF) nanoparticles were prepared using dimethyl sulfoxide as a solvent and water as an antisolvent. Response surface methodology was used to analyse the influences of several process parameters on the mass median diameter (D50). The SIF concentration (20–40 mg/mL), volume ratio of antisolvent to solvent (5–7 mL/mL), stirring speed (800–1600 r/min), and reaction time (2–4 min) were optimized. The optimal conditions were determined to be a SIF concentration, volume ratio of antisolvent to solvent, stirring speed and reaction time of 29 mg/mL, 7 mL/mL, 1533 r/min and 3 min, respectively. Satisfactory D50 of SIF (101.24 ± 12.21 nm) were achieved. The processed and unprocessed SIFs were tested and characterized. By comparing the parameters, the chemical properties of the processed and unprocessed SIFs did not change, but the water dissolution rate of the prepared SIF nanoparticles was greatly enhanced.     

Formation of willow leaf-like structures composed of NH2-MIL68(In) on a multifunctional multiwalled carbon nanotube backbone for enhanced photocatalytic reduction of Cr(VI)

Efficient separation and transfer of photogenerated electron/hole as well as enhanced visible light absorption play essential roles in photocatalytic reactions.To promote the photocatalytic reduction of Cr(Ⅵ),a toxic heavy metal ion,multiwalled carbon nanotube (MWCNT) was introduced as an electron acceptor into NH2-MIL-68(In).This led to the growth of a willow leaf-like metal-organic framework (MOF) on an MWCNT backbone forming MWCNT/NH2-MIL-68(In)(PL-1),which showed a highly efficient transfer of photogenerated carriers.Moreover,MWCNT incorporation introduced more mesopores for Cr(Ⅵ) diffusion and enhanced the visible light adsorption without lowering the conduction band position.As a result,the photocatalytic kinetic constant of PL-1 was found to be almost three times higher than that of the parent NH2-MIL-68(In).Thus,growing MOFs on MWCNTs provides a facile and promising solution for effective remediation of environmental pollution by utilizing solar energy.This work provides the first example of using MWCNT/MOF composites for photocatalytic reactions.     

一种具有网状结构聚苯乙烯聚氨酯的合成及表征

将聚对羟甲基苯乙烯用异佛尔酮二异氰酸酯(IPDI)交联,制备了一种具有网状结构的聚苯乙烯聚氨酯,并用核磁共振法(1H-NMR),红外分析法(FT-IR)对其结构作了表征。用差示扫描量热法(DSC),热失重法(TGA/DTG)测定了其热分解性质,发现聚合物具有良好的热稳定性,增大IPDI的含量,聚合物的热分解温度提高。DSC和扫描电镜(SEM)测试表明,增大IPDI的含量也使聚合物微相分离程度提高。对聚合物进行紫外光照射和微生物催化水解,发现聚合物具有光降解和生物降解性。