Failure Analysis of Discrete Damaged Tailored Extension-Shear-Coupled Stiffened Composite Panels

The results of an analytical and experimental investigation of the failure of composite is tiffener panels with extension-shear coupling are presented. This tailored concept, when used in the cover skins of a tiltrotor aircraft wing has the potential for increasing the aeroelastic stability margins and improving the aircraft productivity. The extension-shear coupling is achieved by using unbalanced 45 plies in the skin. The failure analysis of two tailored panel configurations that have the center stringer and adjacent skin severed is presented. Finite element analysis of the damaged panels was conducted using STAGS (STructural Analysis of General Shells) general purpose finite element program that includes a progressive failure capability for laminated composite structures that is based on point-stress analysis, traditional failure criteria, and ply discounting for material degradation. The progressive failure predicted the path of the failure and maximum load capability. There is less than 12 percent difference between the predicted failure load and experimental failure load. There is a good match of the panel stiffness and strength between the progressive failure analysis and the experimental results. The results indicate that the tailored concept would be feasible to use in the wing skin of a tiltrotor aircraft

Electrically conductive electrospun polymeric mats for sensing dispersed vegetable oil impurities inwastewater

This paper addresses the preparation of electrically conductive electrospun mats on a base of styrene-isoprene-styrene copolymer (SIS) and multiwall carbon nanotubes (CNTs) and their application as active sensing elements for the detection of vegetable oil impurities dispersed within water. The most uniform mats without beads were prepared using tetrahydrofuran (THF)/ dimethyl formamide (DMF) 80:20 (v/v) as the solvent and 13 wt. % of SIS. The CNT content was 10 wt. %, which had the most pronounced changes in electrical resistivity upon sorption of the oil component. The sensors were prepared by deposition of the SIS/CNT layer onto gold electrodes through electrospinning and applied for sensing of oil dispersed in water for 50, 100, and 1000 ppm. - 2019 by the authors.This publication was supported by the Qatar University Collaborative Grant QUCG-CAM-19/20-2. The findings achieved herein are solely the responsibility of the authors. The publication of this article was funded by the Qatar National Library.Scopu

Preparation of progressive antibacterial LDPE surface via active biomolecule deposition approach

The use of polymers in all aspects of daily life is increasing considerably, so there is high demand for polymers with specific properties. Polymers with antibacterial properties are highly needed in the food and medical industries. Low-density polyethylene (LDPE) is widely used in various industries, especially in food packaging, because it has suitable mechanical and safety properties. Nevertheless, the hydrophobicity of its surface makes it vulnerable to microbial attack and culturing. To enhance antimicrobial activity, a progressive surface modification of LDPE using the antimicrobial agent grafting process was applied. LDPE was first exposed to nonthermal radio-frequency (RF) plasma treatment to activate its surface. This led to the creation of reactive species on the LDPE surface, resulting in the ability to graft antibacterial agents, such as ascorbic acid (ASA), commonly known as vitamin C. ASA is a well-known antioxidant that is used as a food preservative, is essential to biological systems, and is found to be reactive against a number of microorganisms and bacteria. The antimicrobial effect of grafted LDPE with ASA was tested against two strong kinds of bacteria, namely, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), with positive results. Surface analyses were performed thoroughly using contact angle measurements and peel tests to measure the wettability or surface free energy and adhesion properties after each modification step. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the surface morphology or topography changes of LDPE caused by plasma treatment and ASA grafting. Surface chemistry was studied by measuring the functional groups and elements introduced to the surface after plasma treatment and ASA grafting, using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). These results showed wettability, adhesion, and roughness changes in the LDPE surface after plasma treatment, as well as after ASA grafting. This is a positive indicator of the ability of ASA to be grafted onto polymeric materials using plasma pretreatment, resulting in enhanced antibacterial activity. - 2019 by the authors.Funding: This publication was made possible by Award JSREP07-022-3-010 and NPRP10-0205-170349 from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors

Investigation of the temperature-relatedwear performance of hard nanostructured coatings deposited on a s600 high speed steel

Thin hard coatings are widely known as key elements in many industrial fields, from equipment for metal machining to dental implants and orthopedic prosthesis. When it comes to machining and cutting tools, thin hard coatings are crucial for decreasing the coefficient of friction (COF) and for protecting tools against oxidation. The aim of this work was to evaluate the tribological performance of two commercially available thin hard coatings deposited by physical vapor deposition (PVD) on a high speed tool steel (S600) under extreme working conditions. For this purpose, pin-on-disc wear tests were carried out either at room temperature (293 K) or at high temperature (873 K) against alumina (Al2O3) balls. Two thin hard nitrogen-rich coatings were considered: a multilayer AlTiCrN and a superlattice (nanolayered) CrN/NbN. The surface and microstructure characterization were performed by optical profilometry, field-emission gun scanning electron microscopy (FEGSEM), and energy dispersive spectroscopy (EDS).Funding: This research was made possible by an NPRP award NPRP 5-423-2-167 from the Qatar National Research Fund (a member of The Qatar Foundation)

Osservazione del processo di refrigerazione della carne di maiale e quella di manzo

Svrha hlađenja svježeg mesa je smanjivanje temperature u najdubljim dijelovima mišića što je brže moguće, a da se pri tome u što većoj mjeri zadrži njegova masa. Ipak, određeni gubici su poželjni jer su suhe površine otpornije na mikrobiološko kvarenje. U našem pokusu je praćen postupak hlađenja svinjetine i govedine u klaonicama u periodu od 2006. do 2007. godine. U prostorijama za hlađenje mjerena je temperatura u mišićima, a u obzir se uzimalo i trajanje postupka. Po završetku hlađenja, u dva je slučaja (13.3%) temperatura svježeg svinjskog mesa prelazila zahtijevanih +7 °C u dubini mišića.The aim of the chilling of carcasses is to decrease the temperature in the deepest parts of muscles as fast as possible while maintaining its weight as high as possible. However, some losses of the weight are desirable because dried surfaces are more resistant to the microbial spoilage. Monitoring of pork and beef chilling process at the slaughterhouses in period 2006 – 2007 was performed in our experiment. Temperature was measured in the muscles, in the chilling rooms and also duration of the process was taken into account. Finally, in two cases (13.3 %) of pork carcasses temperature exceeded required +7 °C in deep part of muscles at the end of process.Der Zweck der Abkühlung von Frischfleisch ist die Verminderung der Temperatur in den tiefsten Muskelteilen in möglichst kurzer Zeit, jedoch soll dabei das Fleischgewicht in möglichst hohem Maße aufbewahrt werden. Doch, manche Gewichtverminderungen sind wünschenswert, weil die trockenen Flächen auf mikrobiologische Blutung widerstandsfähiger sind. In unserem Experiment wurde die Beobachtung des Abkühlungsverfahrens von Schweineund Rindfleisch durchgeführt, dies in Schlachthöfen in der Zeitspanne von 2006 bis 2007. In den Abkühlungsräumen wurde die Temperatur in den Muskeln gemessen, in Betracht wurde auch die Dauer des Verfahrens gezogen. Am Ende des Verfahrens hat die Temperatur in zwei Fällen (13.3%) des frischen Schweinefleisches die verlangenen + 7 ° C in tiefen Muskelteilen überschritten.Lo scopo di refrigerazione della carne fresca è far diminuire al più presto possibile la temperatura nelle parti più profonde del muscolo, cercando di mantenere il suo peso nella maggior parte. Comunque, certe perdite sono pure desiderabili, essendo le superfici asciutte più resistenti al sanguinamento microbiologico. Nel nostro esperimento è stato osservato il processo della refrigerazione di maiale e di manzo nei macelli durante gli anni 2006 e 2007. Nei locali addatti alla refrigerazione è stata misurata la temperatura nei muscoli, ma è stata presa in considerazione anche la durazione del processo. Alla fine del processo, in due casi (13.3 %) della carne di maiale la temperatura superava i richiesti +7°C nelle parti profonde del muscolo

Piezoelastic PVDF/TPU nanofibrous composite membrane: Fabrication and characterization

Poly (vinylidene fluoride) nanofibers (PVDF NFs) have been extensively used in energy harvesting applications due to their promising piezoresponse characteristics. However, the mechanical properties of the generated fibers are still lacking. Therefore, we are presenting in this work a promising improvement in the elasticity properties of PVDF nanofibrous membrane through thermoplastic polyurethane (TPU) additives. Morphological, physical, and mechanical analyses were performed for membranes developed from different blend ratios. Then, the impact of added weight ratio of TPU on the piezoelectric response of the formed nanofibrous composite membranes was studied. The piezoelectric characteristics were studied through impulse loading testing where the electric voltage had been detected under applied mass weights. Piezoelectric characteristics were investigated further through a pressure mode test the developed nanofibrous composite membranes were found to be mechanically deformed under applied electric potential. This work introduces promising high elastic piezoelectric materials that can be used in a wide variety of applications including energy harvesting, wearable electronics, self-cleaning filters, and motion/vibration sensors. - 2019 by the authors.The project was funded “partially” by Kuwait Foundation for the Advancement of Sciences under project code: PN17-35EE-02

Aeroelastic Tailoring for Stability Augmentation and Performance Enhancements of Tiltrotor Aircraft

The requirements for increased speed and productivity for tiltrotors has spawned several investigations associated with proprotor aeroelastic stability augmentation and aerodynamic performance enhancements. Included among these investigations is a focus on passive aeroelastic tailoring concepts which exploit the anisotropic capabilities of fiber composite materials. Researchers at Langley Research Center and Bell Helicopter have devoted considerable effort to assess the potential for using these materials to obtain aeroelastic responses which are beneficial to the important stability and performance considerations of tiltrotors. Both experimental and analytical studies have been completed to examine aeroelastic tailoring concepts for the tiltrotor, applied either to the wing or to the rotor blades. This paper reviews some of the results obtained in these aeroelastic tailoring investigations and discusses the relative merits associated with these approaches

Improvement in properties of Ni-B coatings by the addition of mixed oxide nanoparticles

A comparison of properties of electrodeposited Ni-B and Ni-B-ZrO2-Al2O3 nanocomposite coatings is presented to explain the benefits of addition of mixed nanoparticles of ZrO2 and Al2O3 into Ni-B matrix. A comparative study of the properties of Ni-B and Ni-B-ZrO2-Al2O3 nanocomposite coatings in their as deposited condition indicates that the addition of mixed nanoparticles into Ni-B matrix has significant influence on its structural, surface, mechanical and electrochemical properties. Incorporation of mixed nanoparticles into Ni-B matrix shows significant grain refinement, substantial enhancement in mechanical properties and decent improvement in corrosion resistance. The improvement in mechanical properties can be attributed to grain refinement of Ni-B matrix and dispersion hardening effect of insoluble hard ceramic nanoparticles. Similarly, corrosion inhibition efficiency of binary Ni-B coatings is considerably improved which can be presumably regarded as the effect of formation of dense structure and decrease in active area of Ni-B matrix due to incorporation of mixed inactive nanoparticles. There is simultaneous improvement in mechanical and anti-corrosion properties of Ni-B coatings by the incorporation of mixed nanoparticles demonstrating usefulness of Ni-B-ZrO2-Al2O3 nanocomposite coatings for many applications.Scopu

Antimicrobial Modification of LDPE Using Non-thermal Plasma

Low-density polyethylene (LDPE) represents polymer having good chemical and physical characteristics for which it is widely used in many applications, such as biomedical and food packaging industry. This polymer excels by good transparency, flexibility, low weight and cost which makes it suitable material compared to non-polymer packaging materials. However, its hydrophobicity cause many limitations for antimicrobial activity which can result in absence of some characteristics required in food packaging applications. For that purpose, some researches have done experiments to modify the polymer surface to increase the surface free energy (hydrophilicity). This can be done by introducing some polar functional groups into the LDPE surface which will permit an increment of its surface free energy and so its wettability or adhesion without any disruption in its bulk properties [1]. One of the most preferable modification techniques is known as non-thermal radio-frequency discharge plasma, and it is preferred technique due to the ability to modify only thin surface layer leading to noticable improvement of the surface properties [2].Moreover, it represents environmentally friendly technique since it does not require the use of any hazardous chemicals or dangerous radiations and therefore non-thermal plasma is highly recommended for food packaging applications [1]. In addition, the surface modification of LDPE can lead to the enhancement of the antimicrobial activity, which was the main purpose of this research. Food packaging materials requires preventing any growth of bacteria, fungal, or any other microbial organisms for health and food safety. Some approved preservatives are commonly used directly in foods to preserve them form microorganisms growth and spoilage. Nowadays, some innovative ways are applied to graft acrylic acid on polymers surfaces [3] for biomedical applications to create an effective layer for an immobilization of antibacterial agents and this results in bacteria prevention on the LDPE surface. In this research, we focused on grafting of sorbic acid as one of the most commonly used preservatives in food and beverage for being safe, and effective in bacteria inhibition (whether pathogenic strains or spoilage kinds), molds, and yeasts [4]. It is also used in cosmetic industries since it has good compatibility with skin and it is easily usable [5]. For the potential enhancement of the antimicrobial efficiency, chitosan representing antimicrobial agent was used for the immobilization on sorbic acid created layer. Chitosan (a derivative of chitin polysaccharide) was chosen as a natural occurring antimicrobial agent (from crabs shrimps, and other sea shells [5]) that has strong and effective antimicrobial activity along with its nontoxicity, biofunctionality, biodegradability, and biocompatibility [6]. In this study, the LDPE surface was modified by several modification steps. The first step involved the modification of the LDPE surface by non-thermal radio-frequency discharge plasma as a radical graft initiator for the subsequently polymerization of sorbic acid containing double bonds. In the next step, grafting of sorbic acid was carried out immediately after plasma treatment allowing the interaction of plasma created radicals on LDPE surface with sorbic acid. Final step was focused on the immobilization of chitosan on grafted sorbic acid platform. Each modification step was analyzed by different analytical techniques and methods to obtain detailed information about the modification process. The surface parameters changes after modification of the LDPE surface, such as surface free energy (contact angles measurements), graft yield (gravimetric measurements) surface morphology (scanning electron microscopy and atomic force microscopy) and chemistry (Fourier transform infrared spectroscopy with attenuated total reflectance) were obtained allowing understanding the modification process.Qscienc

Biotechnological production process and life cycle assessment of graphene

The aim of this study is to compare the graphene produced using a biotechnological method (Escherichia coli) with the graphene produced by Hummers' method (a chemical method) and to study the effect on the energy consumption and environment. The results indicated that the chemical reduction process has higher energy consumption, approximately 1642 Wh, than the energy consumption of the biotechnological reduction process, which is 5 Wh. The potential of global warming (GWP 100) improved by 71% using the biotechnological route for the production of graphene. Abiotic depletion, the photochemical ozone creation potential, and marine aquatic ecotoxicity potential were improved when the biological route was employed, compared with the chemical route. The eutrophication potential, terrestrial ecotoxicity, and ozone depletion layer changed very little since the main variables involved in the production of graphene oxide and waste management are the same. The biotechnological method can be considered a green technique for the production of graphene, especially given the reduction in the negative effects on global warming, abiotic depletion, the photochemical ozone creation potential, and the marine aquatic ecotoxicity potential