A new fixture for fracture tests under mixed mode I/II/III loading

In this paper, a new loading device for general mixed mode I/II/III fracture tests is designed and recommended. Finite element analyses are conducted on the proposed apparatus to evaluate the fracture parameters of the tested samples under various mixed mode loading conditions. The numerical results revealed that the designed loading fixture can generate wide varieties of mode mixities from pure tensile mode to pure in‐plane and out‐of‐plane shear modes. The accuracy of the proposed fixture is evaluated by conducting a wide range of fracture tests on compact tension shear (CTS) specimens made of polymethyl methacrylate (PMMA). The experimental results are then compared with the theoretical predictions obtained by the Richard criterion. A good consistency is observed between the experimental results and theoretical predictions.     

Comprehensive power swing detection by current signal modeling and prediction using the GMDH method.

Power swing is an undesirable variation in power flow. This can be caused by large disturbances in demand load, switching, disconnection or reclosing lines. This phenomenon may enter the zones of distance relays and cause relay malfunction leading to the disconnection of healthy lines and undermining network reliability. Accordingly, this paper presents a new power swing detection method based on the prediction of current signal with a GMDH (Group Method of Data Handling) artificial neural network. The main advantage of the proposed method over its counterparts is the immunity to noise effect in signals. In addition, the proposed method can detect stable, unstable, and multi-mode power swings and is capable of distinguishing them from the variety of permanent faults occurring simultaneously. The method is tested for different types of power swings and simultaneous faults using DIgSILENT and MATLAB, and compared with some latest power swing detection methods. The results demonstrate the superiority of the proposed method in terms of response time, the ability to detect power swings of different varieties, and the ability to detect different faults that may occur simultaneously with power swings.     

Antitumor Effects of 5-Aminolevulinic Acid on Human Malignant Glioblastoma Cells

5-Aminolevulinic acid (5-ALA) is a naturally occurring non-proteinogenic amino acid, which contributes to the diagnosis and therapeutic approaches of various cancers, including glioblastoma (GBM). In the present study, we aimed to investigate whether 5-ALA exerted cytotoxic effects on GBM cells. We assessed cell viability, apoptosis rate, mRNA expressions of various apoptosis-related genes, generation of reactive oxygen species (ROS), and migration ability of the human U-87 malignant GBM cell line (U87MG) treated with 5-ALA at different doses. The half-maximal inhibitory concentration of 5-ALA on U87MG cells was 500 μg/mL after 7 days; 5-ALA was not toxic for human optic cells and NIH-3T3 cells at this concentration. The application of 5-ALA led to a significant increase in apoptotic cells, enhancement of Bax and p53 expressions, reduction in Bcl-2 expression, and an increase in ROS generation. Furthermore, the application of 5-ALA increased the accumulation of U87MG cells in the SUB-G1 population, decreased the expression of cyclin D1, and reduced the migration ability of U87MG cells. Our data indicate the potential cytotoxic effects of 5-ALA on U87MG cells. Further studies are required to determine the spectrum of the antitumor activity of 5-ALA on GBM.     

Polyurethane/clay nanocomposites reinforced with carbon and glass fibres: study of mechanical and thermal properties,and the effect of electron beam irradiation

Polyurethane (PU) nanocomposites with 0, 1, 3, 5, and 7?wt-% nanoclay contents were prepared. X-ray diffraction patterns, transmission electron microscopy images, tensile test, and thermogravimetric analysis were utilised to reveal the morphological, mechanical, and thermal-resistant properties of the prepared nanocomposites. The exfoliated structure was obtained for nanoclay contents up to 3?wt-%. Incorporation of nanoclay to the PU matrix prompted the thermal stability of the polymer. A nanocomposite filled with 3?wt-% nanoclay showed the best tensile strength in the prepared nanocomposites. Subsequently, the nanocomposite with the 3?wt-% nanoclay was reinforced with carbon and glass fibres. Reinforcement of the PU/nanoclay matrix with carbon and glass fibres significantly ameliorated the tensile properties. Finally, the effects of the electron beam irradiation on the nanocomposites and fibre-reinforced composites were studied. Irradiation with the doses up to 500?kGy enhanced the mechanical and thermal properties. However, further irradiation deteriorated the mechanical and thermal-resistant properties.     

Microstructural design of phlogopite glass-ceramics

Fluorophlogopite glass-ceramics in the MgO–Al₂O₃–SiO₂ glass systems were crystallized by two stages thermal treatments. Obtained glass-ceramics were characterized by DTA, X-ray diffraction and scanning electron microscopy. The heat treated samples at 705°C/3 h + 1000°C/15 min showed 2570.32 ± 98 MPa microhardness. The effect of heat treatment and preparation methods on microhardness and microstructure were studied. The microstructure of samples showed phlogopite and forsterite phases and solved or soft edge in the semi-rod like crystals was recorded which can explain the small value of microhardness. The various microhardness were determined in the range between 1591.61 to 9610 ± 147 MPa.     

Wear properties of rheo-squeeze cast aluminum matrix reinforced with nano particulates

There are many approaches to fabricate nanoparticles reinforced aluminum matrix composites. However, uniform distribution of nanoparticle within aluminum matrix remains a difficult challenge. In this study, a novel method is used by taking the advantages from squeeze casting of semi-solid aluminum slurry combined with electromagnetic field to refine the microstructure of the primary Al and eutectic Si phase, plus to obtain uniform distribution nano alumina particles in the aluminum matrix. It is noted that electromagnetic field plays an important role in the formation of non-dendritic primary α-Al particles and a great microstructure refinement occurs as a consequence of the pressure application. It can be seen that the increase in electromagnetic field causes smaller and rounder primary α-Al particles. A comparative study on abrasive wear behavior of nano Al₂O₃ reinforced aluminum metal matrix composite has been carried out in the present investigation. The mass loss of the pin was used to study the effect of Al₂O₃ addition on the wear resistance of the composite materials.     

Effect of Organoclay Ordering and Agglomeration on Morphology and Mechanical Properties of Uncured and Dynamically Cured Ethylene‐Octene Copolymer Nanocomposites

In this work, the effects of organoclay (OMMT) and cross‐linking agent on thermal and mechanical properties as well as the morphology of dynamically cured nanocomposites based on ethylene‐octene copolymer are studied. The nanocomposites containing 1, 3, 5, and 7 wt% OMMT are first prepared and then cured with 0.5 and 1 wt% dicumyl peroxide. Low angle X‐ray scattering and transmission electron microscopy reveal that the size of clay tactoids is increased with the increase of OMMT content within the nanocomposites especially for the uncross‐linked matrix. In addition, the distance between adjacent clay layers is increased for the cured nanocomposites containing 1 and 3 wt% OMMT, however, it remains relatively unchanged for higher amounts of the nanofiller. In uncross‐linked systems, the nanocomposites containing up to 5 wt% OMMT exhibit a remarkable enhancement in stress and strain at break compared to that of the matrix alone. With the addition of further OMMT content, although the stress and strain at break are both decreased, still remained much higher than that of the pristine copolymer. A mechanism is also proposed to compare the microstructure of the uncured and cured nanocomposites before and after stretching.

     

Evolution of shell formation process in PP/PMMA/PS ternary blends: correlation between the melt rheology and phase morphology

Correlation between the melt rheology and phase morphology of PP/PMMA/PS ternary blends during the shell formation process were studied in detail. In this PP-matrix ternary system, theoretical predictions in agreement with the direct SEM observations demonstrated the core-shell morphology with PMMA and PS phases as core and shell phases, respectively. Morphological observations revealed that the complete shell formation takes place at about 12 and 9 wt% of PS minor phase in ternary blends composed of low and high viscosity PMMAs, respectively. In terms of rheological properties, this was corresponding to the maximum value on the storage modulus versus PS content (shell thickness) curves. Encapsulation of high viscosity PMMA core particles at lower PS contents was related to the bigger particles and low interfacial area in this system compared to the system with low viscosity PMMA core particles. At high PS contents, single and multi-core structures were observed for composite droplets of ternary blends containing low and high viscosity PMMAs, respectively. The single core morphology of low viscosity PMMA particles was related to the coalescence of core particles after the coalescence of the corresponding shells, while high viscosity PMMA cores are less likely to coalescence, leading to creation of multi-core morphology in latter system.     

Electrospun poly(hydroxybutyrate)/chitosan blend fibrous scaffolds for cartilage tissue engineering

In this study, polyhydroxybutyrate (PHB) was blended with chitosan (CTS), and electrospun in order to produce more hydrophilic fibrous scaffolds with higher mass loss rates for cartilage tissue engineering application. First, the effects of diverse factors on the average and distribution of fiber's diameter of PHB scaffolds were systematically evaluated by experimental design. Then, PHB 9 wt % solutions were blended with various ratios of CTS (5%, 10%, 15%, and 20%) using trifluoroacetic acid as a co‐solvent, and electrospun. The addition of CTS could decrease both water droplet contact angle from ～74° to ～67° and tensile strength from, ～87 MPa to ～31 MPa. According to the results, the scaffolds containing 15% and 20% CTS were selected as optimized scaffolds for further investigations. Mass loss percentage of these scaffolds was directly proportional to the amount of CTS. Chondrocytes attached well to the surfaces of these scaffolds. The findings suggested that PHB/CTS blend fibrous scaffolds have tremendous potentials for further investigations for the intended application. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44171.     

A New Integrated MADM Technique Combined with ANP,FTOPSIS and Fuzzy Max-Min Set Method for Evaluating Water Transfer Projects

In sustainable water resources management, it is essential to rank inter-basin water transfer projects. This task is difficult due to many different conflict criteria, complex relations among criteria and various judgments of decision makers. In this paper, an integrated multiple attribute group decision making method consists of ANP (Analytical Network Process), fuzzy TOPSIS and fuzzy max-min set methods is proposed for evaluating water transfer projects. A set of over 60 criteria in social, environmental and economic sectors are used for ranking four water transfer projects in Karun River based on three decision maker judgments. A key novelty of the proposed methodology is its ability to model both complex relations among different criteria in water management and the influence of decision maker judgments’ weights on the final ranking in group decision making problem. The procedure starts by obtaining the priority of water transfer projects and the weight of each decision maker judgments by employing ANP and fuzzy TOPSIS, respectively. These weights are used as inputs in the fuzzy max-min set method. Then the effects of decision maker weights on the final ranking are determined in fuzzy environment. Finally, the sensitivity analysis of decision makers’ weights has been conducted. The results show that the proposed method is an effective tool for group decision making problems by considering different criteria and decision makers’ weights.