The validity of various fracture mechanics methods at creep temperatures

The application of stress intensity factors derived from linear elastic fracture mechanics (LEFM) to fracture at creep temperatures has been considered. From tensile creep rupture tests on single edge notched and notched centre hole specimens of solution treated A.I.S.I. type 316 stainless steel, it is shown that a LEFM approach is inapplicable to predicting creep crack growth rates, whilst the net section stress is found to correlate well with the crack growth rates. These observations have been explained by considering the creep relaxation that takes place at the notch root, smoothing out the local stresses and thus making the LEFM stress distribution inapplicable. The resulting stress distribution supports the observation that the net section stress is a successful criterion on which to predict creep rupture in stainless steel. The limitations as a fracture mechanics method are explored and it is found that a criterion based on the amount of creep rather than stress would have advantages in some respects. In this context the “crack opening displacement” and the “fracture angle” criteria are considered and their use is found to hinge upon the development of suitable methods for relating the local displacement to the applied stress.     

Effects of SEBS-g-MA copolymer on non-isothermal crystallization kinetics of polypropylene

The non-isothermal crystallization kinetics of pure PP and PP/SEBS-g-MA blends up to volume fraction, Φ _d (0–0.50) was studied by differential scanning calorimetry at four different cooling rates. Crystallization parameters were analyzed by Ozawa and Liu models. The Ozawa model fits in the PP/SEBS-g-MA blends and indicates the effect of SEBS-g-MA copolymer on the crystallization process of polypropylene. Augis–Bennet model has been used to calculate activation energy, ?E, during non-isothermal crystallization process. The value of ?E decreased with SEBS-g-MA due to flexibility of SEBS-g-MA by which movements of chains of PP become easier.     

Asphalt concrete modification with waste PMMA/ATH

This paper presents recycling of waste PMMA/ATH powder in asphalt concrete mixture. Waste PMMA/ATH is generated in large amounts during shaping process of acrylic sheets. Recycling waste polymers rationally and efficiently has become one of the priorities of road pavement industry in recent years. Therefore, in this study waste PMMA/ATH powder was incorporated in an asphalt mixture. In one case waste PMMA/ATH was used as an asphalt binder modifier and in other case as a partial replacement for fine aggregate fraction. Basic performance characteristics of asphalt mixtures were evaluated by measuring material properties such as rutting potential and stripping resistance. Binder characteristics were determined also on artificially aged samples. With both modification methods, improved performance characteristics of asphalt mixture were achieved which can increase road pavement durability. Finally, waste PMMA/ATH allowed us to prepare an asphalt mixture that had strongly enhanced mechanical properties regarding to the wheel tracking test and could also have less negative effects on the environment as indicated by moisture susceptibility test results.     

Basic issues in the mechanics of high cycle metal fatigue

Mechanics issues related to the formation and growth of cracks ranging from subgrain dimension to up to the order of one mm are considered under high cycle fatigue (HCF) conditions for metallic materials. Further efforts to improve the accuracy of life estimation in the HCF regime must consider various factors that are not presently addressed by traditional linear elastic fracture mechanics (LEFM) approaches, nor by conventional HCF design tools such as the S-N curve, modified Goodman diagram and fatigue limit. A fundamental consideration is that a threshold level for ΔK for small/short cracks may be considerably lower than that for long cracks, leading to non-conservative life predictions using the traditional LEFM approach. Extension of damage tolerance concepts to lower length scales and small cracks relies critically on deeper understanding of (a) small crack behavior including interactions with microstructure, (b) heterogeneity and anisotropy of cyclic slip processes associated with the orientation distribution of grains, and (c) development of reliable small crack monitoring techniques. The basic technology is not yet sufficiently advanced in any of these areas to implement damage tolerant design for HCF. The lack of consistency of existing crack initiation and fracture mechanics approaches for HCF leads to significant reservations concerning application of existing technology to damage tolerant design of aircraft gas turbine engines, for example. The intent of this paper is to focus on various aspects of the propagation of small cracks which merit further research to enhance the accuracy of HCF life prediction. Predominant concern will rest with polycrystalline metals, and most of the issues pertain to wide classes of alloys.     

Synthesis,structural and optical characterization of ZrO2 core–ZnO@SiO2 shell nanoparticles prepared using co-precipitation method for opto-electronic applications

Nanocrystalline Zirconia (ZrO₂) and Zinc oxide (ZnO) as well as Silica (SiO₂) coated ZrO₂ core–shell structures were synthesized by both Co-precipitation and seeded polymerization technique. The phase analysis and the core–shell structure formation were confirmed by X-ray diffraction (XRD), FESEM and high resolution transmission electron microscopy (HRTEM) analysis. The existence of SiO₂ on ZrO₂@ZnO was characterized by FT-IR measurement. UV–Vis study reveals coating of ZnO over Zirconia shows red shift in the absorption spectra. Photoluminescence studies show the non-monotonous variation in luminescence behavior of these core–shell nanoparticles. This investigation explains that the interfacial effect between the core (ZrO₂) and the shell materials (ZnO and SiO₂) can be exploited to tune the optical properties of the material. This implies that we can envisage the core–shell materials as potential candidates for optical–electronic devices.     

Study on electromechanical characterization of piezoelectric polymer PVDF in low-frequency band

Polyvinylidene fluoride (PVDF), a piezoelectric polymer material, is well known as one of the best smart materials to be used for tactile sensors in robots for its good performance. It has been used in many applications including sensors, actuators and surface acoustic wave (SAW) devices. This paper presents an experimental setup and experimental procedures for studying the electromechanical characterization of piezoelectric polymer films, by which the electromechanical characterization of the PVDF films under quasi-static loads and dynamic loads in a wide range of frequency can be researched. Through quasi-static tests, the stress–strain relationships of PVDF films in different directions were obtained. Furthermore, the viscoelastic and piezoelectric properties of PVDF films were analyzed based on the measurement results of dynamic tests under low frequency from 5 Hz to 200 Hz, and some suggestions of the applications of PVDF piezoelectric films in robot tactile sensor are presented.     

Thermo-optical,DSC and microfractographic investigation of PE-PE mixtures

The nucleation effect of high-density polyethylene (HDPE) to low-density polyethylene (LDPE) and the structure of the resulting directional LDPE morphology was studied using thermo-optics, differential scanning calorimetry (DSC), X-ray diffraction and microfractography. Thermo-optics and DSC showed a higher nucleation activity of HDPE compared with the heterogeneities within the LDPE melt. The parallel and more perfect arrangement of the chain segments in transcrystalline LDPE resulted in a higher melting temperature, a difference in unit-cell spacing and a less ductile behaviour during fracture than with spherulitic LDPE.     

Structure of reconstituted collagen hollow fibre membranes

Small- and wide-angle X-ray scattering (SAXS and WAXS) methods were employed to study the structure of reconstituted collagen hollow fibre membranes and the changes that ensue upon entry of water. The tails of the SAXS curves were analysed and were shown to obey Porod's Law. WAXS and water absorption measurements as a function of relative humidity were combined with density measurements to determine the relative volume fractions of water in the “free” and “bound” states. Treating the hollow fibre as a two phase system and employing Porod's Law, average length parameters transverse to the fibre axis were extracted for the collagen fibrils and the water filled pores. All this information was synthesized to yield a model of the structural changes in the hollow fibre caused by water. Implications of such a model for qualitative and quantitative prediction of changes in properties were studied.     

How are collaboration and productivity correlated at various career stages of scientists?

Collaboration is believed to be influential on researchers’ productivity. However, the impact of collaboration relies on factors such as disciplines, collaboration patterns, and collaborators’ characters. In addition, at different career stages, such as the growth or the establishment career stages of scientists, collaboration is different in scale and scope, and its effect on productivity varies. In this paper, we study the relationships between collaboration and productivity in four disciplines, Organic Chemistry, Virology, Mathematics and Computer Science. Our study found that the productivity is correlated with collaboration in general, but the correlation could be positive or negative on the basis of which aspect of collaboration to measure, i.e., the scale or scope of the collaboration. The correlation becomes stronger as individual scientists progress through various stages of their career. Furthermore, experimental disciplines, such as Organic Chemistry and Virology, have shown stronger correlation coefficients than theoretical ones such as Mathematics and Computer Science.     

Magnetic and Structural Study of FeNi3 Nanoparticles: Effect of Calcination Temperature

Bimetallic Fe–Ni alloy nanoparticles (NPs) with molar ratio of Fe to Ni 1:3 were synthesized via chemical reduction using hydrazine in aqueous solution and then calcined at different temperatures. The prepared NPs have been characterized utilizing X-ray diffraction (XRD), energy-dispersive X-ray (EDS) spectroscopy, and vibrating sample magnetometer (VSM). XRD results show that FeNi₃ NPs with face-centered cubic (FCC) crystalline structure were formed. FeNi₃ phase completely disappeared and pure NiO and NiFe₂O₄ phases observed on further heating at 550° C. VSM results reveal a superparamagnetic characteristic for the synthesized NPs when calcined at 50° C. An increased coercivity and decreased saturation magnetization has been observed with increasing calcination temperature up to 550° C.     

Synthesis and thermal analysis of aluminium nitride filled epoxy composites and its effective application as thermal interface material for LED applications

The improvement of heat conduction in any electronic devices has become a predominant issue in which effective heat dissipation is crucial to enhance the performance of packaged devices. This paper elucidates the application of thermally conductive particles filled composites as thermal interface material for LEDs. Present work aims on reducing the junction temperature and thermal resistance of the device under test with heavily filled ceramic-epoxy composite as the interface material between the device and metal substrate. Silane treated aluminium nitride (AlN) powder was studied for its feasibility as the filler material. The thermal conductivity values obtained by hot disc method (ISO/DIS 22007-2.2) were 0.66, 0.54 and 0.44 W/mK for 60, 50 and 40 wt% AlN filled epoxy composites respectively which were described well by thermal transient measurement of LEDs. The junction temperature and total thermal resistance of the thermal set up was reduced significantly with increased filler loading. The least junction to ambient thermal resistance (R_thJ-A) was achieved for 60 wt% followed by 50 and 40 wt% AlN filled TIM with the values of 24.8, 31.98 and 34.64 K/W respectively. Characteristics of the AlN filled composites for LED applications are discussed extensively in terms of thermogravimetric and thermo-mechanical analysis.     

Flux growth of silicates with vapour transported silicon

As a result of a proposed vapour transport mechanism, silicate crystals have been grown from fluxed melts which originally contained only trace amounts of silicon. The melts were contained in platinum crucibles in a sillimanite, Al₂SiO₅, muffle, and the flux consisted of PbF₂, or PbF₂ + PbO, occasionally with additional MoO₃. It is postulated that a volatile siliceous species resulted from the reaction of PbF₂ vapour with the muffle and that this species transported Si into the fluxed melts. The silicate crystals produced include Er₂SiO₅, Dy₂SiO₅, Mg₂SiO₄·MgF₂, a new material of formula Dy₄SiO₈, and several new rare earth compounds with the apatite structure.     

Carbon fibre composites with rubber toughened matrices

In carbon fibre reinforced plastics (CFRP), the initial resistance to crack propagation parallel to fibres is determined largely by the matrix toughness. The fracture toughness (G _IC) of an epoxide resin can be increased considerably by the addition of butadieneacrylonitrile co-polymers (CTBN). These cause the precipitation of small spheres of a second phase and, for example, increaseG _IC from ～ 300 to ～ 3000 J m^?2 on the addition of 9 wt% CTBN. The large increases obtained in bulk resins are not obtained in CFRP, instead significant but modest increases are achieved. The suppression of toughness is related to the thickness of resin film through which the crack propagates.     

Comparison of the performance of natural latex membranes prepared with different procedures and PTFE membrane in guided bone regeneration (GBR) in rabbits

This work assessed the performance of membranes made of natural latex extracted from Hevea brasiliensis prepared with three different methods: polymerized immediately after collection without the use of ammonia (L1); polymerized after preservation in ammonia solution (L2); and polymerized after storage in ammonia, followed by Soxhlet technique for the extraction of substances (L3). Polytetrafluoroethylene (PTFE) membrane was used as control. Two 10-mm diameter bone defects were surgically made in the calvaria of thirty adult male New Zealand rabbits. Defects (total n = 60) were treated with guided bone regeneration (GBR) using L1, L2, L3 or PTFE membranes (n = 15 for each membrane). Ten animals were euthanized after 7, 20 and 60 days postoperatively so that five samples (n = 5) of each treatment were collected at each time, and bone regeneration was assessed microscopically. The microscopic analysis revealed defects filled with blood clot and new bone formation at the margins of the defect in all 7-day samples, while 20-day defects were mainly filled with fibrous connective tissue. After 60 days defects covered with L1 membranes showed a significantly larger bone formation area in comparison to the other groups (P < 0.05, ANOVA, Tukey). Additionally, bone tissue hypersensitization for L1 and PTFE membranes was also investigated in six additional rabbits. The animals were subjected to the same surgical procedure for the confection of one 10-mm diameter bone defect that was treated with L1 (n = 3) or PTFE (n = 3). Fifty-three days later, a second surgery was performed to make a second defect, which was treated with the same type of membrane used in the first surgery. Seven days later, the animals were euthanized and samples analyzed. No differences among L1 and PTFE samples collected from sensitized and non-sensitized animals were found (P > 0.05, Kruskal–Wallis). Therefore, the results demonstrated that latex membranes presented performance comparable to PTFE membranes, and that L1 membranes induced higher bone formation. L1 and PTFE membranes produced no hypersensitization in the bone tissue.     

The use of foreign patenting as an internationally comparable science and technology output indicator

Foreign patenting activity in some of the world major patent systems is being compared between countries and industries and is found to be, with a few notable exceptions, relatively unbiased. Furthermore, a brief dynamic analysis of the foreign patenting activity in the USA of a number of OECD-countries in 41 industrial sectors in terms of ‘Revealed Technological Advantage’ indices suggests that foreign patent data might provide a very useful addition to the arsenal of Science and Technology Output Indicators.     

Interfacial energetics in the TD-nickel and TD-nichrome systems

The absolute (mean) interfacial free energies are measured in thoria-dispersed (2 vol %) (TD)-nickel and the TD-nichrome (Ni-20% Cr) systems at 1200° C utilizing techniques of scanning electron and transmission electron microscopy. Values of particle/matrix interfacial energies for TD-NiCr and TD-Ni were measured at 2300 and 2000 erg cm^?2 respectively based upon measured values of 2040 and 2200 erg cm^?2 for the surface free energies for nichrome (80∶20 NiCr) and pure nickel respectively, by the method of zero creep and the measurement of grain-boundary groove angles in the electron microscope. Values of 900 erg cm^?2 and 1040 erg cm^?2 were measured for the surface and grain-boundary free energies for thoria (ThO₂). The particle/matrix adhesive energy for TD-nichrome was measured to be roughly half that for the TD-nickel system based upon the classical interfacial adhesion concept. It is concluded that the apparent difference in particle/matrix interfacial strength between TD-nickel and TD-nichrome results by a more complex mechanism than simple interfacial decohesion involving phase separation.     

Porous asymmetric SiO2-g-PMMA nanoparticles produced by phase inversion

A new kind of asymmetric organic–inorganic porous structure has been proposed. Asymmetric lattices of polymer grafted silica nanoparticles were manufactured by casting and phase inversion in water. Silica nanoparticles were first functionalized with 3-(dimethylethoxysilyl)propyl-2-bromoisobutyrate, followed by grafting of poly(methylmethacrylate) (PMMA) segments, performed by atom-transfer radical polymerization. Mechanically stable self-standing films were prepared by casting a dispersion of functionalized nanoparticles in different solvents and immersion in water. The resulting asymmetrically porous morphology and nanoparticle assembly was characterized by scanning electron and atomic force microscopy. The PMMA functionalized SiO₂ hybrid material in acetone or acetone/dioxane led to the best-assembled structures. Porous asymmetric membranes were prepared by adding free PMMA and PMMA terminated with hydrophilic hydroxyl group. Nitrogen flow of 2800 L m^?2 h^?1 was measured at 1.3 bar demonstrating the porosity and potential application for membrane technology.     

The effect of nanographite addition on the physical properties of poly(vinylidene fluoride)/hydroxypropyl cellulose blend

In this study, polymeric films of poly(vinylidene fluoride) (PVDF)/hydroxypropyl cellulose (HPC) blend filled with various graphite-nanoparticles (GNP) contents were prepared via solvent-mixing technique. The compatibility between PVDF and HPC polymers was studied. The variations in structure, dielectric and thermal properties were investigated over the frequency range (20 Hz–3 MHz) and temperature range (20–110 °C). The X-ray diffraction and differential scanning calorimetry results reveal that the crystallinity of PVDF was affected by the presence of HPC and GNP. The dielectric results reveal that the great enhancement of dielectric constant ( \(\upvarepsilon^{{\prime }}\) ) and ac conductivity (σ_ac) were observed. The dielectric properties were explained in terms of the dielectric polarization mechanism. Both HPC and GNP additions enhance the \(\upvarepsilon^{{\prime }}\) of PVDF due to the formation of β-phase polymorph and the interface effect between the GNP and blend matrix. The improvement of the thermal stability was observed due to the regular arrangement of the side chains. The easy processing, high dielectric constant, low tangent loss and high thermal stability of the composites make the composites attractive for practical applications in embedded capacitors.     

Effect of pressure on the phase composition of Li(Na)/W/Mn/SiO2 composites and their catalytic activity for oxidative coupling of methane

The phase state of Li/W/Mn/SiO₂ and Na/W/Mn/SiO₂ composites after exposure to high pressures (2.5 GPa at 500°C) and subsequent exploitation in oxidative coupling of methane (OCM) was studied. Comparison of the catalytic activity of the composites before and after exposure to high pressures indicates that the formation of Li(Na)/W/Mn/SiO₂ composites catalytically active for OCM is significantly influenced by high pressures.     

Deposition of ZnO thin films on Si by RF magnetron sputtering with various substrate temperatures

Undoped ZnO thin films were successfully deposited on Si substrates by RF magnetron sputtering with different substrate temperatures. The dependence was systematically investigated the structural, morphology, chemical state and optical properties of ZnO thin films. Crystal quality, growth orientation and optical properties of ZnO thin films were improved at proper substrate temperature (450 °C) whereas were deteriorated at higher temperature (600 °C). X-ray photoelectron spectroscopy showed that proper substrate temperature promoted the formation of Zn–O bonding, resulting in an improvement of film quality, while higher temperature decreased the formation of the Zn–O bonding and increased the oxygen vacancy due to formation of an amorphous SiO₂ layer at the interface of ZnO and Si, resulting in a degradation of film quality. Moreover, the amorphous SiO₂ layer is formed by oxygen related to the Zn–O bonding, mainly. Therefore, the experimental results indicate that the substrate temperature plays an important role in the deposition of ZnO film on Si substrate and needs to be carefully selected to suppress a formation of an amorphous SiO₂ layer.