Mechanical and dry sliding wear characterization of epoxy–TiO2 particulate filled functionally graded composites materials using Taguchi design of experiment

Titania (TiO₂) reinforced homogeneous and functionally graded epoxy composites are developed by simple mechanical stirring and vertical centrifugal casting technique respectively. Investigations on mechanical and wear characteristics of TiO₂ reinforced homogeneous epoxy composites and its functionally graded composite materials developed for tribological applications are presented. The effect of various operational variables, material parameters and their interactive influences on specific wear behaviour of these composites has been studied systematically. A series of test are conducted on a pin-on-disc machine with three sliding velocities of 105, 209 and 314 cm/s under three different normal loading of 20 N, 30 N and 40 N. Out of all samples 20 wt.% epoxy–TiO₂ epoxy graded composites exhibited lowest specific wear rate TiO₂ particle additions on epoxy graded composites have a dramatic effect on the flexural strength, tensile modulus and impact strength in comparison to homogeneous composites. Scanning electron microscope (SEM) observations also indicate that in homogeneous composites TiO₂ particles are peeled off from the matrix to form holes while in graded composite materials under same experimental conditions the TiO₂ particles remain quite intact to the matrix.     

Size reduction of WO3 nanoparticles by ultrasound irradiation and its applications in structural nanocomposites

The porous WO₃ (pore size 2–5 nm) nanoparticles were synthesized using a high intensity ultrasound irradiation of commercially available WO₃ nanoparticles (80 nm) in ethanol. The high resolution transmission electron microscopic (HRTEM) and X-ray studies indicated that the 2–5 nm uniform pores have been created in commercially available WO₃ nanoparticles without much changing the initial WO₃ nanoparticles (80 nm) sizes. The nanocomposites of WO₃/SC-15 epoxy were prepared by infusion of 1 wt.%, 2 wt.% and 3 wt.% of porous WO₃ nanoparticles into SC-15 epoxy resin by using a non-contact (Thinky) mixing technique. Finally the neat epoxy and nanocomposites were cured at room temperature for about 24 h in a plastic rectangular mold. The cured epoxy samples were removed and precisely cut into required dimensions and tested for their thermal and mechanical properties. The HRTEM and SEM studies indicated that the sonochemically modified porous WO₃ nanoparticles dispersed more uniformly over the entire volume of the epoxy (without any settlement or agglomeration) as compared to the unmodified WO₃/epoxy nanocomposites.     

Improvements in mechanical and thermo-mechanical properties of e-glass/epoxy composites using amino functionalized MWCNTs

The prime objective of this work is to optimize the mechanical and thermo-mechanical properties of e-glass/epoxy composites by utilizing amino-functionalized multi-walled carbon nanotubes (MWCNTs–NH₂) through a combination of dispersion method. At first, 0.1–0.4 wt.% of MWCNT–NH₂ was integrated into SC-15 epoxy suspension using a combination of ultra-sonication and calendaring techniques. E-glass/epoxy nanocomposites were than fabricated at elevated temperature with the modified resin using hand layup and compression hot press. 3-Point flexural and dynamic mechanical analysis (DMA) results demonstrated a linearly increasing trend in properties from 0 to 0.3 wt.% loading. Micrographs of MWCNTs incorporated epoxy and e-glass/epoxy samples revealed uniform dispersion of MWCNTs in epoxy, good interfacial adhesion between CNTs and polymer, and improved interfacial bonding between fiber/matrix at 0.3 wt.% loading. An improved dispersion and hence an improved crosslink interaction between MWCNT–NH₂ and epoxy lead to the stronger shift of the mechanical and thermo-mechanical properties of the composites.     

Effect of processing technique on the transport and mechanical properties of graphite nanoplatelet/rubbery epoxy composites for thermal interface applications

Graphite nanoplatelet (GNP)/rubbery epoxy composites were fabricated by mechanical mixer (MM) and dual asymmetric centrifuge speed mixer (SM). The properties of the GNP/rubbery epoxy were compared with GNP/glassy epoxy composites. The thermal conductivity of GNP/rubbery epoxy composite (25 wt.% GNP, particle size 15 μm) reached 2.35 W m⁻¹ K⁻¹ compared to 0.1795 W m⁻¹ K⁻¹ for rubbery epoxy. Compared with GNP/rubbery epoxy composite, at 20 wt.%, GNP/glassy epoxy composite has a slightly lower thermal conductivity but an electrical conductivity that is 3 orders of magnitude higher. The viscosity of rubbery epoxy is 4 times lower than that of glassy epoxy and thus allows higher loading. The thermal and electrical conductivities of composites produced by MM are slightly higher than those produced by SM due to greater shearing of GNPs in MM, which results in better dispersed GNPs. Compression and hardness testing showed that GNPs increase the compressive strength of rubbery epoxy ∼2 times without significantly affecting the compressive strain and hardness. The GNP/glassy epoxy composites are 40 times stiffer than the GNP/rubbery epoxy composites. GNP/rubbery epoxy composites with their high thermal conductivity, low electrical conductivity, low viscosity before curing and high conformability are promising thermal interface materials.     

Effect vapor grown carbon nanofiber on thermal and mechanical properties of epoxy

In the present investigation, dynamic mechanical analysis (DMA), thermo gravimetric analysis (TGA), tensile tests, fatigue tests and the single edge notch tensile (SENT) tests were performed on unfilled, 1, 2 and 3 wt.% vapor grown carbon nanofiber (CNF) filled SC-15 epoxy to identify the loading effect on thermal and mechanical properties of the composites. DMA studies revealed that filling the 3% carbon nanofiber into epoxy can produce 65% enhancement in storage modulus at room temperature and 6 °C increase in T _g. However, TGA results show that thermal stability of composite is insensitive to the CNF content. Tensile tests were carried out at the strain rate range from 0.02 min⁻¹ to 2 min⁻¹. Results show that CNF/epoxy are strain rate sensitive materials, the modulus and tensile strength increased with increasing of strain rate. Experimental results also indicate that modulus of the nanophased epoxy increases continuously with increasing CNF content. But the 2% CNF infusion system exhibit maximum enhancement in tensile strength, fatigue performance and fracture toughness as compared with other system.     

A comparison of mechanical and wear properties of plasma sprayed carbon nanotube reinforced aluminum composites at nano and macro scale

The macro- and nano-scale mechanical and wear properties of carbon nanotube (CNT) reinforced Al-Si composite coatings prepared by plasma spraying have been compared in this paper. The composite coatings show a two phase microstructure; one phase being the Al-Si matrix with well dispersed CNTs and the other being the CNT clusters. Nanoindentation testing on the matrix portion with dispersed CNTs indicated an increase in the elastic modulus by 19% and 39% and an increase in the yield strength by 17.5% and 27% by the addition of 5 wt.% and 10 wt.% CNTs respectively. Macro-scale compression tests indicated no improvement in the elastic modulus but an increases in the compressive yield strength by 27% and 77% respectively, by addition of 5 wt.% and 10 wt.% CNTs. Nanoscratch testing carried out on the Al-Si matrix with dispersed CNTs indicated a decrease in scratch volume by 34% and 71% by addition of 5 wt.% and 10 wt.% CNTs respectively. Macro-scale wear tests indicated a decrease in the wear volume by 68% in case of 5 wt.% CNT coatings but an increase in the wear volume by 15% for the 10 wt.% CNT coating. The differences in mechanical and wear properties at nano and macro scales are explained in terms of the bimodal CNT dispersion (well dispersed and clusters) in Al-Si matrix, CNT cluster size and fraction and carbide formation.     

CF/EP composite laminates with carbon black and copper chloride for improved electrical conductivity and interlaminar fracture toughness

An experimental study was conducted to improve the electrical conductivity of continuous carbon fibre/epoxy (CF/EP) composite laminate, with simultaneous improvement in mechanical performance, by incorporating nano-scale carbon black (CB) particles and copper chloride (CC) electrolyte into the epoxy matrix. CF/EP laminates of 65 vol.% of carbon fibres were manufactured using a vacuum-assisted resin infusion (VARI) technique. The effects of CB and the synergy of CB/CC on electrical resistivity, tensile strength and elastic modulus and fracture toughness (K_IC) of the epoxy matrix were experimentally characterised, as well as the transverse tensile modulus and strength, Mode I and Mode II interlaminar fracture toughness of the CF/EP laminates. The results showed that the addition of up to 3.0 wt.% CB in the epoxy matrix, with the assistance of CC, noticeably improved the electrical conductivity of the epoxy and the CF/EP laminates, with mechanical performance also enhanced to a certain extent.     

Synthesis, characterization and mechanical properties of nano alumina particulate reinforced magnesium based bulk metallic glass composites

Mg₆₇Zn₂₈Ca₅ bulk metallic glass reinforced with 0.66-1.5 vol% of nano alumina particulates were successfully synthesized using disintegrated melt deposition technique. Microstructural characterization revealed reasonably uniform distribution of alumina particulates in a metallic glass matrix. The reinforced particles have no significant effect on the glass forming ability of the monolithic glass matrix. Mechanical characterization under compressive loading showed improved micro hardness, fracture strength and failure strain with increase in nano alumina particulate reinforcement. The best combination of strength, hardness and ductility was observed in Mg/1.5 vol% alumina composite with fracture strength of 780 MPa and 2.6% failure strain.     

Microstructure and mechanical properties of friction stir welded Al/Mg2Si metal matrix cast composite

In this research, friction stir weldability of 15 wt.% Mg₂Si particulate aluminum matrix cast composite and effects of tool rotation speed and number of welding passes on microstructure and mechanical properties of the joints were investigated. Microstructural observations were carried out by employing optical and scanning electron microscopy of the cross sections perpendicular to the tool traverse direction. Mechanical properties including microhardness and tensile strength were evaluated in detail. The results showed fragmentation of Mg₂Si particles and Mg₂Si needles existing in eutectic structure in stir zone. Also, homogeneous distribution of Mg₂Si particles was observed in the stir zone as a result of stirring with high plastic strains. Tension test results indicated that tensile strength of the joint had an optimum at 1120 rpm tool rotation speed and decreased with increasing of the number of welding passes. Hardness of the joint increased due to modification of solidification microstructure of the base composite. This research indicates that friction stir welding is a good candidate for joining of 15 wt.% Mg₂Si aluminum matrix composite castings.     

Dielectric polymer matrix composite films of CNT coated with anatase TiO2

This study presents the fabrication method and the dielectric property of polymer matrix composite films of carbon nanotube (CNT) coated with TiO₂. The TiO₂ was coated with sol-gel method using titanium (IV) butoxide (TNBT), HO₂ and benzyl-alcohol as the surfactant. The configuration of CNT-TiO₂ hybrid was observed with the field emission scanning electron microscope images. The coated TiO₂ was thermally treated and transformed into the anatase structure to enhance the mechanical strength and get the high insulating property. The anatase structure was proved from the diffraction angles of XRD. The CNT-TiO₂ hybrid was mixed with the epoxy resin using 3-roll-mil and casted into the films using film casting method. The structure of CNT-TiO₂ hybrid was ascertained to be maintained against the high shear stress during the mixing and casting processes. The dielectric property of the composite films was measured following IPC-TM-6550. The dielectric property at 1 GHz of the composite film of 5 wt.% CNT is about 10 and the loss tangent at 1 GHz is about 0.06.     

Effect of liquid-forming additives on the sintering and mechanical properties of Al2O3/3Y-TZP (30 vol.%) composite

Al₂O₃/3Y-TZP (30 vol.%) composite was pressurelessly sintered with addition of TiO₂MnO₂ and/or CaOAl₂O₃SiO₂ glass. It was found that TiO₂MnO₂ addition greatly enhanced the densification of the composite by the formation of a low-viscosity liquid at sintering temperature. In contrast, the high-viscosity liquid formed by CaOAl₂O₃SiO₂ glass improved mechanical properties because of its repressing effect on grain growth. The composite could be obtained at a temperature as low as 1400°C by co-doping with TiO₂MnO₂ and CAS glass. Bending strength of 552±64 MPa and fracture toughness of 6.03±0.22 MPa m^1/2 were obtained with a doping level of 2 wt.% TiO₂MnO₂ and 2 wt.% CAS glass.     

An investigation on the capability of equal channel angular pressing for consolidation of aluminum and aluminum composite powder

In this study equal channel angular pressing (ECAP) was used as a technique for consolidation of attritioned aluminum powder (45 μm) with varying concentration of nano alumina powders (35 nm) in tube at 200 °C. The effect of ECAP on consolidation behavior of composite powder and mechanical properties of subsequent compacts are presented. It is found that ECAP has the capability of consolidating pure aluminum powder, Al-5 vol% Al₂O₃ and Al-10 vol% Al₂O₃ to near their theoretical density and also declustering of the agglomerated alumina particles after maximum four passes. However full consolidation of Al-15 vol% Al₂O₃ before emanating the cracks on the tube material was not possible and about 7% porosity remains in the compacted composite which degrades the mechanical properties of this composite in comparison to the aluminum composites with 5 vol% and 10 vol% alumina.     

Synergistic effect of organic and inorganic nano fillers on the dielectric and mechanical properties of epoxy composites

Titanium oxide TiO₂/epoxy and TiO₂ with detonation nano-diamond (DND)/epoxy nanocomposites were prepared by using ultrasonication method. TiO₂ and DND particles as reinforcement species and epoxy as matrix were used to produce nanocomposites. The addition of DND particles into TiO₂/epoxy composite improved the dielectric and mechanical properties of nanocomposites in significant amount. The dielectric properties of TiO₂-DND/epoxy nanocomposite demonstrated increase in permittivity and conductivity after addition of the DND particles. The maximum and minimum reflection losses of TiO₂-DND/epoxy nanocomposite for 0.6 and 0.2 wt% DND loading were detected at ?14.5 and ?1.3 dB, respectively. The flexural and tensile strength of TiO₂-DND/epoxy nanocomposites with the addition of 0.4 wt% DNDs were enhanced to 220% and 223%, respectively. Additionally, the energy to break and percent break strain were 3.9 J and 3.86, respectively for 0.4 wt% DND loading in TiO₂-DND/epoxy nanocomposite. Therefore, the present work findings claim that DND particles are well suitable to enrich the dispersion of TiO₂ nanoparticles in epoxy matrix, which develops a strong load transfer interface between the nanoparticles and epoxy matrix and consequently leads to superior properties.     

Improvements in mechanical properties of a carbon fiber epoxy composite using nanotube science and technology

Carbon fiber reinforced epoxy composite laminates, with strategically incorporated fluorine functionalized carbon nanotubes (f-CNTs) at 0.2, 0.3 and 0.5 weight percent (wt.%), are studied for improvements in tensile strength and stiffness and durability under both tension–tension (R = +0.1) and tension–compression (R = −0.1) cyclic loadings, and then compared to the neat (0.0 wt.% CNTs) composite laminate material. To develop the nanocomposite laminates, a spraying technology was used to deposit nanotubes on both sides of each four-harness satin weave carbon fiber fabric piece for the 12 ply laminate lay up. For these experimental studies the carbon fiber reinforced epoxy laminates were fabricated using a heated vacuum assisted resin transfer molding (H-VARTM®) method followed by a 2 soak curing cycle. The f-CNTs toughened the epoxy resin-fiber interfaces to mitigate the evolution of fiber/fabric-matrix interfacial cracking and delamination under both static and cyclic loadings. As a consequence, significant improvements in the mechanical properties of tensile strength, stiffness and resistance to failure due to cyclic loadings resulted for this carbon fiber reinforced epoxy composite laminate.     

Effect of microfibrillated cellulose on mechanical properties of plain-woven CFRP reinforced epoxy

This investigation concerns about study the effect of natural fiber on high performance composite. Effect of addition microfibrillated cellulose (MFC) as natural fiber to plain woven carbon fiber reinforced plastic (CF) reinforced epoxy on mechanical and thermal properties has been investigated. CF/epoxy composites with addition 0.5, 1 and 2 wt.% of MFC were characterized by different techniques, namely tensile, DMA, fracture toughness (mode I) test and SEM. The results reveal that at 2 wt.% of MFC, initiation and propagation interlaminar fracture toughness in mode I improved significantly by 80% and 44% respectively. Although there is slight tendency to increase tensile strength and Young’s modulus with addition MFC up to 2%, it is still not significant with those low contents of MFC. With addition 2 wt.% MFC, the glass transition temperature increased by about 12 °C compared to neat CF/epoxy composite indicating better heat resistance with addition of MFC.     

Covalent functionalization of graphene with organosilane and its use as a reinforcement in epoxy composites

Functionalized graphene nanosheets (f-GNSs) produced by chemically grafting organosilane were synthesized by a simple covalent functionalization with 3-aminopropyl triethoxysilane. The f-GNSs showed a larger thickness, but smaller width and than the un-treated graphene. The covalent functionalization of graphene with silane was favorable for their homogeneous dispersion in the polymer matrix even at a high nanofiller loading (1 wt.%). The initial thermal degradation temperature of epoxy composite was increased from 314 °C to 334 °C, at a f-GNS content of 1 wt.%. Meanwhile, the addition of 1 wt.% f-GNSs increased the tensile strength and elongation to failure of epoxy resins by 45% and 133%, respectively. This is believed to be attributed to the strong interfacial interactions between f-GNSs and the epoxy resins by covalent functionalization. The experimentally determined Young’s modulus corresponded well with theoretical simulation under the hypothesis that the graphene sheets randomly dispersed in the polymer matrix.     

An investigation of super-hydrophilic properties of TiO2/SnO2 nano composite thin films

A sol-gel dip coating technique was used to fabricate TiO₂/SnO₂ nano composite thin films on soda-lime glass. The solutions of SnO₂ and TiO₂ were mixed with different molar ratios of SnO₂:TiO₂ as 0, 3, 4, 6, 8, 9, 10.5, 13, 15, 19.5, 25 and 28 mol.% then the films were prepared by dip coating of the glasses. The effects of SnO₂ concentration, number of coating cycles and annealing temperature on the hydrophilicity of films were studied using contact angle measurement. The films were characterized by means of scanning electron microscopy, X-ray diffraction and atomic force microscopy measurements. The nano composite thin films fabricated with 8 mol.% of SnO₂, four dip coating cycles and annealing temperature of 500 °C showed super-hydrophilicity.     

Grafting of nano-TiO2 onto flax fibers and the enhancement of the mechanical properties of the flax fiber and flax fiber/epoxy composite

In this article, a flax fiber yarn was grafted with nanometer sized TiO₂, and the effects on the tensile and bonding properties of the single fibers and unidirectional fiber reinforced epoxy plates were studied. The flax fiber yarn was grafted with nanometer sized TiO₂ through immersion in nano-TiO₂/KH560 suspensions under sonification. The measured grafting content of the nano-TiO₂ ranged from 0.89 wt.% to 7.14 wt.%, dependent on the suspension concentration. With the optimized nano-TiO₂ grafting content (∼2.34 wt.%), the tensile strength of the flax fibers and the interfacial shear strength to an epoxy resin were enhanced by 23.1% and 40.5%, respectively. The formation of Si–O–Ti and C–O–Si bonds and the presence of the nano-TiO₂ particles on the fiber surfaces contributed to the property enhancements. Unidirectional flax fiber reinforced epoxy composite (V_f = 35.4%) plates prepared manually showed significantly enhanced flexural properties with the grafting of nano-TiO₂.     

Structure and photocatalytic activity studies of TiO2-supported over Ce-modified Al-MCM-41

Ce-Al-MCM-41, TiO₂/Al-MCM-41 and TiO₂/Ce-Al-MCM-41 materials with varying contents of Ce (by impregnation) and TiO₂ loaded (by solid-state dispersion) on Al-MCM-41 support are prepared. The Ce modified and TiO₂ loaded composite systems are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS) techniques. The DRS and XPS of low Ce content (0.2-0.5 wt.%) modified Al-MCM-41 samples are showing more characteristic of Ce³⁺ species wherein cerium in interaction with Al-MCM-41 and that of high Ce (0.8, 3.0 wt.%) content modified samples are showing the characteristic of both Ce⁴⁺and Ce³⁺species. A series of Ce-modified Al-MCM-41 and TiO₂ loaded composite catalysts are evaluated for photocatalytic degradation of phenol under UV irradiation. Low Ce content in Ce³⁺ state on Al-MCM-41 is showing good photoactivity in comparison with high Ce content samples and pure ceria. The composite TiO₂/Ce-Al-MCM-41 is showing enhanced degradation activity due decreased rate of electron-hole recombination on TiO₂ surface by the redox properties of cerium. The photocatalyst TiO₂/Ce-Al-MCM-41 with an optimum of 10 wt.% TiO₂ and 0.3 wt.% Ce is showing maximum phenol degradation activity. The possible mechanism of phenol degradation on the composite photocatalyst is proposed.     

Microstructures and dielectric properties of Ba0.5Sr0.5TiO3–Zn2TiO4 composite ceramics with low sintering temperature for tunable device applications

Ba_0.5Sr_0.5TiO₃–Zn₂TiO₄ composite ceramics with low dielectric constant and high tunability are fabricated at a relatively low sintering temperature of 1200 °C via the conventional solid-state reaction route. Zn₂TiO₄ and Ba_0.5Sr_0.5TiO₃ can be friendly coexistent in the composite material system. The dielectric constant is tailored from 2500 to 83 by manipulating the addition of Zn₂TiO₄ content from 0 wt.% to 80 wt.% weight ratio. The dielectric loss still keeps around 0.002 and the tunability is 10.3% under a DC-applied electric field of 30 kV/cm at 10 kHz for the 80 wt.% Zn₂TiO₄ added Ba_0.5Sr_0.5TiO₃ composite ceramics. These composite ceramics are promising candidates for multilayer low-temperature co-fired ceramics (LTCC) and potential tunable devices applications.