Search

In this paper, we give a characterization of a hypercyclic weighted composition operator on ℓ p {\ell^{p}} ( 1 ≤ p < ∞ {1\leq p ). We also obtain some necessary conditions and sufficient conditions for the supercyclicity and cyclicity of a weighted composition operator on ℓ p {{\ell}^{p}} ( 1 ≤ p < ∞ {1\leq p ).

Ceramic composites are extremely sensitive to the surrounding environment. Their tribological performance may degrade drastically if they are polluted by some external agent. The present article was aimed to investigate the unidirectional sliding characteristics of brake oil treated woven carbon-carbon (C/C), and carbon-carbon-silicon carbide (C/C-SiC) composites. The laminate orientation, surface conformity, normal load, and sliding velocity were varied. It was depicted that the quantity of oil absorbed by the composites depends on the laminate orientation. The decay rate in friction coefficient revealed that C/C composites are more prone to brake oil in comparison to C/C-SiC composites. The results showed that it is difficult to make an assumption regarding the wear and friction behavior of laminated composites in low conformity contacts concerning normal load and sliding velocity. However, friction coefficient increased with increment in sliding velocity and normal load, for non-conformal Hertzian contacts. The generation of friction film was arduous in the presence of absorbed oil. SEM analysis of worn surfaces revealed different surface morphology for low, and non-conformal contacts which depicted distinct tribological mechanisms.

Reinforced polymers have gained a significant interest in the research community in recent years due to their enhanced performance as compared to their parent polymers. Nanosized reinforcement-based polymer composites have shown a considerable enhancement in performance as compared to micro-/macro-sized fillers. But achieving a high degree of filler alignment in nanocomposites via conventional manufacturing techniques continues to be a challenging task. Additive manufacturing (AM) is a possible solution to this challenge and has undergone a significant development in recent years. AM is an efficient technique to fabricate nanocomposites in complex shapes which uses a layer-by-layer method to fabricate materials and thereby eliminates the need for multi-step processing and the use of fasteners/joints to fabricate complex structures. Due to a wide range of properties and the existence of carbon in a variety of forms, carbon filler-based polymer matrix composites are suitable for applications in several technical sectors. AM of carbon-based structures and fiber-reinforced polymer composites enables the production of highly customized parts with a high degree of filler alignment. AM techniques which are generally employed for the fabrication of carbon-based fillers/fiber-reinforced polymer composites are fused deposition modeling, stereolithography, direct ink writing and selective laser sintering. Although AM techniques are efficient, some critical issues such as voids and defects between interlayers, the low adhesion strength between filaments, part curling and insufficient curing of layers need to be addressed to utilize its full potential.

The cooling rate during fabrication affects the microstructural features and interface strength in metal matrix composites (MMCs). Thus, the present investigation is focused on characterizing the effect of quenching medium on wear and friction response of self-lubricating Al-Cu dual matrix composites. Mica was reinforced in Al-Cu metal matrix composites with the variation of weight percentage as 1%, 2%, 3%, 5%, 8% and 10%. A standard powder metallurgy route was adopted for fabrication. The sintered composites were normalized, and quenched in water, and oil. A pin on disc study was carried to investigate the friction and wear behavior of normalized, oil quenched, water quenched and as-prepared (green) composites. The results revealed that oil quenched composites exhibited the lowest friction coefficient and highest wear loss. The highest friction coefficient of ~0.8 was observed for normalized composites, whereas the highest friction coefficient for water quenched composites was ~0.6. The oil quenched composites exhibited about 8 ~ 15 times higher wear loss as compared to normalized and water quenched composites. Worn surfaces were analyzed under a scanning electron microscope to know the dominant wear mechanisms. The developed composites find potential applications in automotive industry such as pistons for petrol and diesel engines.

The interest in two-dimensional (2D) nanomaterials has been increased rapidly after the discovery of graphene. The 2D graphene Analogs (2DGAs) with ultrathin layered feature exhibit unique property...

In our earlier paper [Srivastava et al. Eng. Fract Mech, 180 (2017)] we found that mode I, mode II fracture toughness of carbon nanotubes (CNTs) filled woven carbon fabric composites increases with the addition of nanofillers. In order to prove the effect of nanofillers on adhesively bonded joints of woven carbon fabric laminates, the present study is conducted under double cantilever beam (DCB), end notched flexural (ENF) and single lap shear (SLS) tests. Graphene nanoplates (GnPs) filled epoxy resin, and carbon blacks (CBs) filled epoxy resin, and pure epoxy resin adhesives were used to prepare the DCB, ENF and single lap adhesively bonded joint specimen from two similar woven carbon fabric composite plates to measure them. Fracture toughness (mode I mode II) and shear strength of adhesively bonded joints were determined. The results show that the adhesively bonded woven carbon fabric composite joints with GnPs-filled epoxy resin and CBs-filled epoxy resin adhesives give better fracture toughness mode I, mode II and shear strength compare to pure epoxy resin adhesively bonded composite specimen. Mode I value is lower than mode II value due to the sharp propagation of cracks under tensile stress. Scanning electron microscopy (SEM) was utilized to monitor the distribution of nanofillers within the adhesively bonded texture to examine the effect of fracture surfaces in the bonded DCB, ENF and single lap shear joint specimens respectively.

In this study, sliding behavior of carbon/carbon (C/C) and carbon/carbon-silicon carbide (C/C-SiC) composites was investigated under reciprocating sliding conditions with the variation of laminate orientation and surface conformity. The normal and parallel orientation of laminates with partial and low conformity contacts were considered. The normal load was varied from 50 N to 90 N in the steps of 10 N to investigate the effect of load. The contact pressure changed with surface conformity at the same load. Worn surfaces of composites were analyzed under scanning electron microscope to gain an understanding of the dominant wear mechanisms. The results showed that friction coefficient of composites loaded with parallel orientation of laminates was more stable as compared to normal orientation of laminates but normal orientation of laminates yielded higher value of friction coefficient. Low conformity contacts showed lower value of friction coefficient as compared to partial conformity contacts. When the normal load was increased beyond 80 N in case of parallel orientation of laminates, wear loss increased rapidly. In case of very low conformity contacts, C/C-SiC composites showed almost linear increase in wear loss with load. Friction coefficient decreased almost two times and wear loss decreased about 8 times in case of low conformity contacts as compared to partial conformity contacts. Friction film formation, disruption, adhesion and abrasion of contact conjunctions were main parameters which depicted the tribological behavior of C/C and C/C-SiC composites.

Heterostructures of two-dimensional (2D) nanomaterials such as graphene/transition metal oxide (TMO) have recently attracted great interest due to their unique structures and superior properties that none of the individual conventional 2D nanomaterials could have. These unusual properties are due to alteration of the Fermi energy position, density of states, and work function of those heterostructures rather than their chemical components. The physical and quantum properties, the interfacial layer and the synergistic effect of each component in 2D heterostructures lead to the generation of new behavior and properties. In this review article, we are focusing on the recent progress in studying the characteristics and properties of 2D graphene/TMO heterostructures, and their significant applications in advanced energy storage and conversion devices. In this context, we firstly introduce bottom-up wet chemical approaches for the synthesis of 2D graphene/TMO heterostructures. The electron transfer, bonding chemistry and defects at the interface of these heterostructures are then discussed. Thirdly, the tunable properties of 2D graphene/TMO heterostructures and their applications in advanced energy storage and conversion devices are presented. The final section discusses the challenges and future prospects of 2D graphene/TMO heterostructures.

Natural filler reinforced composites are gaining importance due to their low cost, low density, reduced dermal and respiratory irritation, renewable resource and possible recycling without affecting the environmental damage, and together with biodegradable ability. In this investigation, flexural and impact properties of wheat flour reinforced polymer matrix composites have been investigated. The effect of reinforcing random short glass fibers in wheat flour reinforced polymer matrix composites have also been investigated. Effect of saline water treatment on the wheat flour reinforced polymer matrix composites have also been investigated. The results conclude that flexural and impact properties of wheat flour reinforced composites varies with the variation of wheat flour, saline water treatment and with reinforcing random short glass fibers.

Due to its superior electronic, thermal, and mechanical properties, graphene is considered to be the most promising candidate for constructing energy storage and conversion devices. One important way to exploit the potential of graphene is to create graphene composites with other functional materials. Graphene-based hybrid composites (GHCs) have been fabricated by incorporating inorganic and/or organic species into graphene through covalent and/or noncovalent interactions. Different methods of fabrication resulted in different properties of GHCs. So far, GHCs have found wide applications in various sectors. In this article, recent progress and achievements in the preparation of two- and three-dimensional GHCs are reviewed, followed by detailed discussions on their physical, chemical, and mechanical properties. The article then focuses on the detailed applications of GHCs in energy storage and conversion devices.

A nano-grained layer including line defects was formed on the surface of a Ti alloy (Tialloy, Ti-6Al-4V ELI). Then, the micro- and nano-grained Tialloy with the formation of TiO2 on its top surface was coated with a bioactive Ta layer with or without incorporating an antibacterial agent of Ag that was manufactured by magnetron sputtering. Subsequently, the influence of the charged defects (the defects that can be electrically charged on the surface) on the interfacial bonding strength and hardness of the surface system was studied via an electronic model. Thereby, material systems of (i) Ta coated micro-grained titanium alloy (Ta/MGTialloy), (ii) Ta coated nano-grained titanium alloy (Ta/NGTialloy), (iii) TaAg coated micro-grained titanium alloy (TaAg/MGTialloy) and (iv) TaAg coated nano-grained titanium alloy (TaAg/NGTialloy) were formed. X-ray photoelectron spectroscopy was used to probe the electronic structure of the micro- and nano-grained Tialloy, and so-formed heterostructures. The thin film/substrate interfaces exhibited different satellite peak intensities. The satellite peak intensity may be related to the interfacial bonding strength and hardness of the surface system. The interfacial layer of TaAg/NGTialloy exhibited the highest satellite intensity and maximum hardness value. The increased bonding strength and hardness in the TaAg/NGTialloy arises due to the negative core charge of the dislocations and neighbor space charge accumulation, as well as electron accumulation in the created semiconductor phases of larger band gap at the interfacial layer. These two factors generate interfacial polarization and enhance the satellite intensity. Consequently, the interfacial bonding strength and hardness of the surface system are improved by the formation of mixed covalent-ionic bonding structures around the dislocation core area and the interfacial layer. The bonding strength relationship by in situ XPS on the metal/TiO2 interfacial layer may be examined with other noble metals and applied in diverse fields.

Surface modification via advanced technologies to manufacture durable coatings for increasing mechanical, chemical, and biological efficacy is an active research area for biomedical industries. The...

The present work deals with the characterization of multi-walled carbon nanotubes (MWCNTs) filled and unfilled short carbon fiber reinforced epoxy resin composites. Short carbon fibers (10 mm) were selected at various processing stages such as (i) white color polyacrylonitrile fibers (PAN); (ii) pre-carbonized carbon fibers (Precarb-CF); (iii) oxidized carbon fibers (OCF); (iv) fully carbonized carbon fibers (CF-low); and (v) sized carbon fibers (CF Sized). The investigated composites were characterized by three points bending test, hardness test, dynamic mechanical thermal analysis (DMTA), electrical conductivity test, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results show that the mechanical and electrical properties of the investigated materials markedly depend on the type of short carbon fibers and on the presence of MWCNTs. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

The photoelastic technique was used to analyze the stress field in glass fiber reinforced polymer matrix composite. Two glass fiber bundles with a diameter of 0.2 mm were reinforced in orthogonal directions. The composite was subjected to diametrical compression with two orientation of fibers with respect to the loading axis, i.e. 00/900 and 450/1350. A circular polariscope with dark-field arrangement was used to analyze the stress field. The isochromatic fringe pattern nearby fiber/matrix interface revealed that there was strong adhesion between the fiber and matrix. Distorted fringes were observed nearby fiber region which indicated efficient load transfer from matrix to the fiber. It was observed that composite with 450/1350 orientation of fibers showed more principal stress difference in the direction perpendicular to the loading axis.

In recent years, aluminum alloy-and copper alloy-based metal matrix composites are gaining importance in automobile and aerospace industries. Various reinforcements in particulate form can be used in aluminum alloy- and copper alloy-based metal matrix composites, one of which is mica. Mica has a layered or platy texture due to which it acts as a self-lubricating material. The objective of this investigation is to assess the influence of mica reinforcement on the tribological behavior of aluminum-copper (Al-Cu) dual matrix composites when quenched in different media. The results revealed that the compressive strength of mica-filled aluminum-copper (Al-Cu) dual matrix composites decreases as the percentage of mica increases up to 8% in all media. Compressive strength, Vickers hardness, and wear resistance of normalized and water-quenched specimens were greater than that of oil-quenched and non-heat-treated specimens. The worn surfaces of the samples were examined by scanning electron microscopy (SEM).

Carbon–carbon (C/C) composite is one of the best ceramic matrix composite due to its high mechanical properties and applications at control environments in various sectors. Carbon–carbon composite is made of woven carbon fibers; carbonaceous polymers and hydrocarbons are used as matrix precursors. These composites generally have densities

Surface nanostructures have shown potential as biomaterials, in tissue engineering and regenerative medicine devices since they have been shown to enhance cellular function by modulating cell–surface interactions in a controlled manner. This work studies human stem cell behavior on titanium dioxide (TiO2) nanotubes that were fabricated on nano-grained (NG) and coarse-grained (CG) substrates. The NG substrates were derived by surface mechanical attrition treatment (SMAT), which has the advantage of being simple to implement. The TiO2 nanotube layer formed on the SMATed titanium (Ti) is thicker and has an inner diameter (70 nm) greater than a comparable layer observed on an untreated (40 nm) substrate. The results illustrate that a NG Ti layer favors the growth of TiO2 nanotubes; presumably due to the high density of grain boundaries and dislocations. An increase in adhesion of human mesenchymal stem cells (hMSCs) in short term culture was observed on the TiO2 nanotubes grown on the NG substrate compared to those grown on the CG substrate, which we attribute to the various roughness and hydrophilicity differences between the two surfaces. Additionally, higher specific strengths of the TiO2 nanotubes may also be achieved by taking advantage of the Ti grain changes on the substrate and the subsequent growth of the nanotubes. Furthermore, structural deformations at the nanoscale can be exploited to manufacture advanced biomaterial surfaces that are designed to enable improved stem cell attachment.

Two-dimensional (2D) nanomaterials have recently gained interest due to their unique properties which their bulk counterparts do not exhibit. Several 2D nanomaterials have been developed till date, but particularly, transition metal dichalcogenides (TMDs) and graphene have attracted a considerable worldwide research interest due to their excellent properties. The possibility of forming 2D van der Waals (vdW) heterostructures have opened a new way for combining the meritorious properties of graphene and TMDs in a single unit. Due to alteration of Fermi level and Schottky barrier height, the 2D layered graphene/TMD vdW heterostructures could give rise to new properties which are not indigenous either to graphene or TMDs. In this article, we have focused on the recent advances in understanding the characteristics and behavior of 2D layered graphene/TMD heterostructures in various applications. In this context, we firstly discuss the electron transfer characteristics at the interfaces of graphene and TMD heterostructures. Tunable properties of these heterostructures by considering their different architectures are then evaluated. Thirdly, overview approaches in the synthesis of these heterostructures are illustrated. After that, the current conditions of applications of these heterostructures in energy storage, energy conversion, optoelectronic and sensing devices are discussed. The final section remarks the challenges and prospects of 2D vdW graphene and TMD heterostructures.

The effect of normal load on the reciprocating sliding behavior of plain weave woven carbon fibers (CF) and graphene nanoplatelets (GNPs) coated unidirectional carbon fiber strands (GCF) reinforced polymer (CF-GCF/epoxy) composites was investigated. The normal load was varied from 50 N to 90 N at the interval of 10 N. The high frequency of reciprocating motion (5 Hz) was considered. Nearly 13,500 cycles were employed with a stroke length of 1.5 mm. The tensile behavior of CF-GCF/epoxy composite was also investigated keeping longitudinal direction of GCF along the loading direction. The fractured samples and worn surfaces were analyzed under scanning electron microscopy. It was observed that the surface of GCF was rough which increased its interlocking tendency with the matrix and hence increased the tensile strength. The friction coefficient increased with increase of load up to 80 N and decreased afterward, whereas wear loss exhibited increasing trend with increase in load. However wear loss showed a slight decrease in slope beyond 70 N load. Fiber fragments in wear debris were observed at high loads. Although the friction film was also observed at high loads, the abrasion furrows were not significantly visible. The plasticity of matrix and the formation of friction film depicted the friction and wear behavior of CF-GCF/epoxy composites.

This article discusses the mechanical performance of alumina nanoparticles and randomly distributed short glass/carbon fiber-reinforced hybrid composites through microhardness and wear test. The open mold casting method was adapted to prepare the test coupons. The wear and friction behavior of composites sliding against hardened ground EN 32 steel in a pin-on-disc configuration is evaluated on a wear and friction tester. The microhardness properties of the neat epoxy, alumina nanoparticles, and alumina nanoparticle–embedded glass/carbon fiber–reinforced hybrid composites were determined. The morphology of the worn composites was analyzed with a scanning electron microscope. It was found that the particles as fillers contributed significantly to improve the mechanical properties and wear resistance of the polymer composites. This is because the fillers contributed to enhance the bonding strength between the fiber and the epoxy resin. Moreover, the wear and friction resistance of the glass/carbon fiber comp...

Nano scale dispersion due to the size transformation of the reinforced particles from micron size to nano size in the polymer matrix to enhance the mechanical properties of fiber-reinforced hybrid composite is an interesting research topic of the current time. In this study, the nanocomposites test coupons were prepared through the open molding route. The nano scale dispersion is achieved at an optimum concentration of alumina particles (2 wt%), which results in improved thermal stability, impact strength, flexural modulus and flexural strength of composites. The maximum enhancement in impact energy was observed to be 84 % correspond to the addition of 2 wt%, 20 % for the flexural strength correspond to the addition of 3 wt% and 35 % for the flexural modulus correspond to the addition of 5 wt% alumina particles to the epoxy matrix. For the addition of 5 wt% of short glass/carbon fibers to the epoxy, an improvement of 130 % and 170 % for the flexural strength and 55 % and 95 % for the flexural modulus was observed. Furthermore, addition of optimum concentration (i.e. 2 wt%) of alumina nano particle to the 5 wt% glass/carbon fiber reinforced hybrid composites resulted in the improvement of impact properties, flexural strength and flexural modulus of 175 %, 195 %; 18 %, 26 % and 65 %, 85 % as compared to the neat epoxy, and 7 %, 8 %; 82 %, 105 % and 17 %, 5 % as compared to the short fiber reinforced composites. These enhancements in the mechanical properties are mainly due to the better stress transfer properties from fiber and nanoparticle to the matrix, due to the existence of strong interfacial interactions between both epoxy/alumina nanoparticles, which depict the higher resistance to fiber pull out as compare to fiber reinforced composites without alumina nanoparticles.

Human society has been utilising the natural resources from the dawn of its civilisation in varying intensity to improve their living standard. Over the course of time, the extraction of the amenities required for such developmental purpose, affects the resource use pattern and access. This has resulted in a change in the existing land use practices in the region. Thus, socio-economic setting of any region and the land use are interlinked and affect each other. This article presents a new socio-economic index (SEI) to quantify the socio-economic status of any river basin. UNDP’s Human Development Index of 1990 has been used and modified to compute the index, in which various aspects of human life are considered and collected from National Survey Samples to reflect on the basin’s land use scenario. Results of the analysis are presented on Narmada River basin as a case study.

Currently functional materials like ionic liquids, dendrimers, surfactants, biopolymers, polymer blends, nanocomposites, supramolecules, drugs, dyes and others of industrial interest and need integrated physicochemical characterizations due to unavoidable several chemical processes like redox, UV light absorption resulting degradation. The physicochemical properties measuring techniques play significant role in deciding applications and understanding structural stability of the needed materials. Thus the search, research and inventions being made in areas of physicochemical sciences are of utmost importance. Thus, the survismeter and oscosurvismeter, the new breakthroughs for integrated physicochemical properties of functional molecules have been emerged as the most usable and answerable, reliable, authentic research methodologies.

A nano-grained layer including line defects was formed on the surface of a Ti alloy (Ti

Fine wood powder/furanic foams were prepared with a strong predominance of the wood component. Low weight and density are important properties of foamed composites. Focusing on preparing light materials, wood foam composites were made using a chemical foaming method and expanded using diethyl ether as the foaming agent. The additives were added to note their effect on the density and mechanical properties, like impact strength and Young's moduli, of the expanded composites. Various tests and scanning electron microscopy analysis were also performed. The foaming agent resulted in closed cells with varied sizes and more or less regular shapes, and with significant density reductions and acceptable loss of mechanical properties.

The influence of multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GnPs) on epoxy resin was investigated to compare their mechanical properties. MWCNT/epoxy resin and GnP/epoxy resin composites were compared with each other for their tensile strength, compressive strength, Charpy Impact and Izod impact energy with the variation of weight percentage ratio of nanofiller ranging from 0.5, 1.0, 2.0 and 3.0, respectively. The result shows that GnP/epoxy resin composite gave better tensile and compressive strength compared to MWCNT/epoxy resin composite whereas Izod impact energy, Charpy impact energy and dynamic fracture toughness of MWCNT/epoxy resin composite resulted in better impact resistance than the GnP/epoxy resin composite. Thermal stability and microstructural properties of composites were measured using Thermogravimetric analysis (TGA), transmission electron microscope (TEM) and scanning electron microscope (SEM).

Nanostructured materials such as nanocomposites and nanolaminates are currently of intense interest in modern materials research. Nanolaminate materials are fully dense, ultra-fine grained solids that exhibit a high concentration of interface defects. They may be developed for engineering applications that take advantage of enhanced mechanical properties or for devices such as energy storage and memory storage capacitors. Nanolaminates can be grown using atom-by-atom deposition techniques that are designed with different stacking sequences and layer thicknesses. The properties of fabricated nanolaminates depend on their compositions and thicknesses. These can be demonstrated within the synthesis process by thickness control of each layer and interfacial chemical reaction between layers. In fact, dielectrics with the formed thin layer have efficient dielectric constant and high insulation characteristics. Dielectric materials with giant dielectric constants can be fabricated as modified single, binary and perovskite oxides. A review of the advantages offered by nanolaminate structures for high performance energy storage devices is presented. Developments of dielectric materials that are formed from a thin layer approach are evaluated. The influence of the interface layer on the dielectric constant of nanolaminate films is assessed from the perspective of conferring a giant dielectric constant and high insulation characteristics. The incorporation of dopants and site-engineering techniques, as well as layer-by-layer structures, which can both be suitable for improving dielectric properties of dielectric nanolaminates, is detailed. Finally, the current status and development of artificial dielectric materials for high performance energy storage devices formed by dielectric nanolaminates are presented.

There is global interest in improving the mechanical properties of light metals such as aluminum (Al)-based alloys by tailoring their microstructures at the nanometer scale. On the other hand, gold (Au) has been widely applied as a wire bonding material due to its prominent ductility and conductivity. In this study, the microstructure, hardness and elastic modulus of DC magnetron-sputtered aluminum/gold (Al/Au) composite thin films of different thicknesses were investigated. It is shown that in addition to the formation of AlAu2 phase, additional Al and Au nanosegregated phases also formed. The Al/Au thin films of 600 and 800 nm thickness exhibit the maximum hardness (~5.40 GPa) and elastic modulus (~97.00 GPa). However, film thicknesses of 1000 and 1200 nm demonstrate a reduction in hardness and elastic modulus due to different growth mechanisms and the formation of voids that can be attributed to the Kirkendall phenomenon.

The main theme of this paper is to describe the mechanical properties of multi-walled carbon nanotube (MWCNT)/epoxy resin composites with the variation of MWCNT fillers. The work tried to achieve a uniform distribution of MWCNT filler in the epoxy matrix by modifying the hardener and mixing conditions. The MWCNT fillers were used to fabricate the MWCNT/epoxy resin composites with the variation of weight percentage of 0⋅5, 1, 2 and 3%. The dispersion of MWCNT in epoxy resin was carried out with the help of three ball rolling mill process. A significant improvement in tensile strength, compressive strength and elastic modulus was observed due to the excellent dispersion of the MWCNT filler in the epoxy resin that give higher values of tensile strength, compressive strength and elastic modulus at 3% MWCNT.

Epoxy/alumina nanocomposites were prepared by reducing micron size alumina into nanosize during the casting process. In our current investigation it was found that, at low concentration alumina nanoparticles exhibit uniform dispersion of alumina nanoparticles in epoxy nanocomposite while at higher concentration they depict aggregation of alumina particle. Since uniform dispersion of alumina nanoparticles results in improved thermal stability and viscoelastic behavior. It leads to remarkable improvement in breakdown voltage, and breakdown time of epoxy/alumina nanocomposites as compared to neat epoxy. Epoxy nanocomposites containing 2 wt.% of alumina particles results in increase of breakdown voltage by 91% and breakdown time by 155% as compared to neat epoxy. Hence, the nanocomposites developed can be used as insulating material in electrical instruments which require high breakdown voltage as well as improved viscoelastic behavior and thermal stability.

International audience; Tannin/furanic foams compressive strength and impact resistance are improved by addition of small percentages of multiwall carbon nanotubes after sonication of the mixture of components before blowing of the foam. These improvements although clear are limited by the limited proportion of nanotubes that can be added to the foam, higher proportions causing unhandable increases in viscosity of the blowing mixture. Scanning electron microscopy examination at high magnification of the nanotube filled foams showed an even distribution of the nanotubes imbedded in the foam cell walls in certain zones but an apparent lack of nanotubes in other cell wall zones.

The main objective of the present work is to process porous silicon–silicon carbide (Si–SiC) ceramic by the oxidation of carbon–carbon silicon carbide (C/C–SiC) composites. Phase studies are performed on the oxidized porous composite to examine the changes due to the high temperature oxidation. Further, various characterization techniques are performed on Si–SiC ceramics in order to study the material's microstructure. The effects of various parameters such as fiber alignment (twill weave and short/chopped fiber) and phenolic resin type (resol and novolak) are characterized.

The wear behaviour of carbon-carbon (C/C) and carbon-carbon-silicon-carbide (C/C-SiC) composites were studied using a pin-on-disc test rig under dry condition before and after immersion in 25% concentrated H2SO4. The influence of the weight loss and worn temperature against sliding distance and time were investigated. It was found that the weight loss increases with increasing of sliding distance and time, where worn surface temperature increases slowly up to 1.5 Km sliding distance and then tended to become constant. Also, weight loss and worn surface temperature reduces with the exposure of 25% concentrated sulphuric acid. However, the C/C-SiC composites exhibiting a lower weight loss but higher worn surface temperature compare to C/C composites at constant load. The wear and worn temperature of C/C composite gradually in- creases compare to C/C-SiC composite, with an average fading ratio of 7.7% (C/C composite) and 7.4% (C/C-SiC composite). Scanning electron microscope and projection microscope micrographs show that the graphite film was transferred on the test pin side, which stabilized the increase in test pin temperature after the formation of a thick film of graphite debris.

The effect of multi-walled carbon nanotube (MWCNT) addition on mechanical properties of epoxy resin was investigated to obtain the tensile strength, compressive strength and Young’s modulus from load versus displacement graphs. The result shows that the tensile strength, compressive strength and Young’s modulus of epoxy resin were increased with the addition of MWCNT fillers. The significant improvements in tensile strength, compressive strength and Young’s modulus were obtained due to the excellent dispersion of MWCNT fillers in the epoxy resin. The dispersion of MWCNT fillers in epoxy resin was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Also, Halpin–Tsai model was modified by considering the average diameter of internal/external of multi-walled nanotube and orientation factor ( α ) to calculate the Young’s modulus of multi-walled carbon nanotubes (MWCNTs)/epoxy resin composite. There was a good correlation between the experimentally obtained Young’s modulus and modified Halpin–Tsai model.

Mechanical properties of C/C–SiC composite were investigated under tension, compression, flexural, Izod and Charpy impact tests. The result shows that the value of dynamic fracture toughness under Charpy impact test was 5 times higher than the Izod impact test, whereas static fracture toughness was more than the dynamic fracture toughness, because of variation of impact load and specimen holding conditions. Also, SEM results reveal that the strong interfacial bonding caused by the mismatch of thermal expansion coefficients between fibre and matrix. Finally, fibre debonds, fibre pull-out and fibre broken fractured were identified under SEM observations.

The main objective of the present work is to processing the porous Si-SiC ceramic by the oxidation of C/C-SiC composite. Phase studies are performed on the oxidized porous composite to examine the changes due to the high temperature oxidation. Further, various characterization techniques are performed on Si-SiC ceramic in order to study the material’s microstructure.

Similar substrates of carbon/carbon (C/C) and carbon/carbon–silicon carbide (C/CSiC) composites were bonded with pure epoxy resin and the one containing 3% multiwall carbon nanotubes (MWCNTs). The results show that MWCNT/filled epoxy resin bonded C/CC/C and C/CSiCC/CSiC substrates have a higher adhesive joint strength than those bonded with epoxy resin alone. MWCNTs increase the toughness and strength of the epoxy resin, which increases the interface bond strength between two similar matching surfaces.

The electrical properties of carbon/carbon (C/C) and carbon/carbon–silicon carbide (C/C–SiC) ceramic composites were measured. The results show that the capacitance decreases rapidly with an increase in frequency and it becomes constant above a frequency of 500 kHz, whereas the dissipation factor increases with increasing frequency. C/C–SiC composites give higher value than C/C composites due to the presence of microcracks.

Nanocomposites consisting of multiwall carbon nanotubes (MWCNT) and epoxy resin were produced by a standard calendaring technique. In this study, 3% multiwall carbon nanotube particles were dispersed in epoxy resin by weight to produce the multiwall carbon nanotubes/epoxy composite. Nanohardness and Raman spectroscopy tests were used to obtain the modulus of elasticity and Raman intensity of MWCNTs/ epoxy resin composite. The results show that the Raman intensity increased with the increase of Raman shift and Raman intensity also affected with the reinforcement of multiwall carbon nanotubes and 1% exposure of laser power. Also, nanohardness increased with increase of modulus of elasticity, which indicated that the toughness of epoxy resin improved with the addition of multiwall carbon nanotubes.

Open globe injuries are a very common cause of unilateral visual loss, with children accounting for up to 20% of all these injuries. The principles of management of ocular injuries are the same for children and adults. However, the management in the case of a child is made much more difficult due to variable cooperation with assessment and continuing therapy as well as the subsequent possibility of amblyopia further complicating the treatment. Here we report the successful management of a 3-year-old child who was brought to this center with a full thickness penetrating injury to her cornea, with a pencil, and the presence of hypopyon, 3 days after the occurrence of the injury.

The goal of this paper is to assess the variation in morphological behaviour of carbon/carbon and carbon/carbon-silicon carbide composite under reciprocating sliding against uniphase and multiphase substrates with variation of normal load. Chrome steel was chosen as uniphase and carbon/carbon and carbon/carbon-silicon carbide composites were slid in self and complementary mated pairs for multiphase materials. The worn surfaces were analysed under scanning electron microscope. Morphological study of worn surfaces showed that carbon/carbon composites slid against chrome steel did not show much abrasion whereas carbon/carbon-silicon carbide composites showed abrasion and, hard silicon carbide particles abraded the formed friction film. In self-mated pairs, carbon/carbon composites mainly showed delamination wear, and carbon/carbon-silicon carbide composites primarily showed matrix peeling and abrasion. In complementary mated pairs, carbon/carbon composites generated some wear debris with sharp edges. The abrasion and adhesion of carbon/carbon-silicon carbide composite were very less in case of complementary mated pair.

The oxidation behavior of graphite substrates with silicon carbide (SiC) and silicon nitride (Si3N4) coatings, prepared by using a solid-vapor reaction process, was investigated in cyclic oxidation tests. The e ect of the porosity of the substrate on the oxidation behavior was also investigated. Substrates with the SiC coating showed higher weight loss than those with the Si3N4 coating. Oxidation of the substrates with 10 and 13 % porosities with the Si3N4 coating took place at 900 C and at 1000 C, respectively. However, after long term cyclic oxidation tests, the substrate with 13 % porosity with the Si3N4 coating was oxidized at a relatively low temperature of 800 C, even though the weight loss was below 10 %. In the case of the SiC coatings, detachment of the coating region or full oxidation of the substrates took place whereas in the case of the Si3N4 coatings, no evidence of delamination or detachment of the coating region was observed after oxidation. The oxidation was a ected by the coating thickness and by the type of materials coated on the substrate, not by the porosity of the substrate itself, although the coating thickness did depend on the porosity of the substrate.

The main objective of present work was to observe the performance of 3D C/C–SiC composites with the exposure of oxy-acetylene gas flame in open atmosphere. Duration of exposure time was increased to measure the weight loss, elastic modulus, microhardness and thermal degradation. Also, XRD pattern was obtained to compare the behaviour of oxidized and unoxidized C/C–SiC composites. The amount of heat transferred to the base material depends upon the torch distance from the materials. The results clearly indicate that the excess amount of carbon was oxidized with the oxygen to form carbon mono oxide. The matrix materials undergo pyrolysis reactions within short periods, which generate volatiles and leave behind a porous skeleton of carbon fibres. The thermal properties (microvolt) microhardness, tensile stress and elastic modulus of C/C–SiC composite was reduced abruptly with increase of exposure time. XRD pattern also shows that the number of peaks and height of signals reduced with the increase of exposure time, which clearly indicates that the morphological changes were induced within the short period and losses carbon and silicon particles.

Silicon carbide (SiC) and silicon carbide/silicon nitride (SiC/Si3N4) were successfully synthesized on graphite substrates by the use of solid–vapor reaction (SVR) process. Layers of SiC and SiC/Si3N4 were synthesized on graphite substrate through the reaction between SiO and substrate the (SiO(vapor) + 2C(from graphite)) and N2 and substrate the (3SiO(vapor) + 2N2 (vapor) + 3C(from graphite)), respectively. With the increase of dwell time and synthesis temperature the thickness of SiC layers increases up to 1500 °C temperature. Also, with the increase of synthesis temperature hardness value of SiC coatings is increased, which is 10–15 times higher than the substrate. The critical load of SiC coatings for wear resistance is about 22 N, which was observed by scratch tests. The synthesized SiC coatings appear to consist of a β-SiC phase mixed with a minor amount of an α-SiC phase, and its thickness is mainly affected by porosity of the substrate. The thickness of SiC/Si3N4 coatings is much thinner than that of SiC coatings, but gives higher value of surface hardness.

We report the results of detailed electrical resistivity variation with temperature at different twin configurations in Ni49Mn29Ga22. It was noted that in the martensitic region (

The ballistic impact behavior of wired glass has been studied. Three types of commercially available samples, with thin and thick wire mesh, were impacted with steel, glass, and tungsten carbide spheres of various sizes using a gas gun. Impact energies varied from 0.5 to 40 J. A system of cracks was found to develop that comprised primarily a major cone crack. At higher energies, additional radial and lateral cracking developed along with increased damage to the front face of the sample. The extent of damage was assessed in terms of basal cone crack area, number of cracks, mass loss, and fracture load of impacted samples. It was found that damage, at a given impact energy, increased with increasing projectile diameter. Moreover, 10 mm diameter glass spheres caused more damage than smaller (3–4.74 mm diameter) steel spheres. No significant differences were observed with regard to the ballistic behavior of the thin- and thick-wired glass types.