Effects of potassium titanate whiskers and carbon fibers on the wear behavior of polyetheretherketone composite under water lubricated condition

The tribological behaviors of polyetheretherketone (PEEK) composite reinforced by carbon fiber (CF) and potassium titanate whiskers (PTW) have been investigated using the pin-on-disk configuration at different applied loads under water lubricated condition. The effects of micrometer carbon fiber and sub-micrometer PTW on the wear properties of the hybrid composite have been discussed. It was found that the PEEK/PTW/CF composite showed excellent tribological performance in water condition. High wear resistance and low friction coefficient were achieved under a wide range of loads. It was revealed that the two fillers worked synergetically to enhance the wear resistance of the hybrid reinforced PEEK composite. The carbon fiber carried the main load between the contact surfaces and protected the matrix from further severe abrasion of the counterpart. At the same time, the exposed PTW out of the polymer matrix around the fiber inhibited the direct scraping between the fiber edge and counterpart tip in some degree, so that the fibers could be less directly impacted during the subsequent sliding process and they were protected from severe damage. In addition, the reinforcement effect of PTW on PEEK could reduce the stress concentration on the carbon fiber-matrix interface, and thereby reduce the CF failure/damage. The reinforcement effect of PTW on PEEK might also restrict the crack initiation and propagation on the surface and subsurface of the composite, and therefore to protect the matrix from fatigue failure during the sliding process.     

Morphology and electrical properties of polyamide 6/polypropylene/multi-walled carbon nanotubes composites

Morphology, electrical properties and conductive mechanisms of polyamide 6/polypropylene/muti-walled carbon nanotubes (PA6/PP/MWNTs) composites with varied compositions and different blending sequences were investigated. The MWNTs were found to be located preferentially in the PA6 phase in the composites, whatever the PA6 was continuous or dispersed phase. While the incorporation of MWNTs changed the dispersed PA6 phase from spherical to elongated or irregular shape. The PA6/PP/MWNTs (20/80/4) composite with a dispersed PA6 phase exhibited a higher electrical conductivity in comparison with the PA6/PP/MWNTs (50/50/4) composite which has a co-continuous phase and exhibits double percolation. This was due to the formation of a conductive MWNTs networks in the PA6/PP/MWNTs (20/80/4) composite as proved by means of field emission scanning electron microscopy and rheological measurements. The morphology and electrical properties of the PA6/PP/MWNTs (20/80/4) composites were significantly influenced by blending sequences. When blending 3.9 phr MWNTs with a pre-mixed PA6/PP/MWNTs (20/80/0.1) composite, the dispersed PA6 phase formed an elongated structure, which was beneficial to the electrical properties.     

三维编织复合材料在润滑条件下的摩擦性能

利用树脂传递模塑(RTM)工艺制备了三维编织炭纤维/环氧(C3D/EP)复合材料.采用MM-200型摩擦磨损试验机研究了该材料润滑条件下的摩擦磨损性能,探讨了载荷及滑动速度等外界因素的影响;并采用XL30 ESEM电子显微镜观察磨损表面形貌,分析了其磨损机理.结果表明,润滑条件下复合材料的摩擦磨损性能远优于干摩擦,且磨合期较短;随着载荷的增加,复合材料的摩擦系数和比磨损率降低,但滑动速度对摩擦磨损性能的影响很小;润滑条件下的磨损机理主要是磨粒磨损.     

Surface damage of unidirectional carbon fiber reinforced epoxy composites under reciprocating sliding in ambient air

For many technical applications friction and wear are critical issues. Reinforced polymer-matrix composites are widely used under vibrating contact condition in various automotive and aerospace applications as well as in structural engineering. In this paper, the friction and wear of bulk epoxy and unidirectional carbon fiber reinforced epoxy composite have been investigated under reciprocating sliding against either alumina or stainless steel balls in ambient air. The effect of sliding direction with respect to the long and unidirectional carbon fibers has been studied. We demonstrate that the carbon fiber reinforcement greatly improves the tribological properties of the thermoset epoxy: it reduces the coefficient of friction and the debris formation. It was found that on sliding in the anti-parallel direction a more significant degradation takes place than in the parallel direction. The coefficient of friction measured on bulk epoxy sliding against either stainless steel or alumina is around 0.65, whereas the coefficient of friction measured on epoxy reinforced with carbon fibers is significantly lower, namely down to 0.11. It was found that sliding with a stainless steel ball in a direction parallel to the fiber orientation results in a lower coefficient of friction than sliding in anti-parallel direction. The reduced coefficient of friction is largely influenced by the carbon fiber reinforcement due to the auto-protecting film formed as a paste in the contact area and along the wear track edges. The relationship between friction and degradation of the composite material including surface wear and debris formation are discussed based on an in-depth analysis of the worn surfaces by optical and scanning electron microscopy, micro-Raman spectroscopy, and white light interferometry.     

Surface and sub-surface degradation of unidirectional carbon fiber reinforced epoxy composites under dry and wet reciprocating sliding

The role of water on the sub-surface degradation of unidirectional carbon fiber reinforced epoxy composite is examined. The correlation between the debonding of carbon fibers at the fiber–epoxy interface, and the wear behavior of the carbon fiber composite are discussed based on an in-depth analysis of the worn surfaces. We demonstrate that a reciprocating sliding performed along an anti-parallel direction to the fiber orientation under dry conditions results in a large degradation by debonding and breaking of the carbon fibers compared to sliding in parallel and perpendicular directions. Immersion in water has a harmful effect on the wear resistance of the carbon fiber composite. The competition between crack growth and the wear rate of epoxy matrix and/or carbon fibers in the sliding track determines the level of material loss of the composite in both test environments.     

Interconnected multi-walled carbon nanotubes reinforced polymer-matrix composites

A modified method for interconnecting multi-walled carbon nanotubes (MWCNTs) was put forward. And interconnected MWCNTs by reaction of acyl chloride and amino groups were obtained. Scanning electron microscopy shows that hetero-junctions of MWCNTs with different morphologies were formed. Then specimens of pristine MWCNTs, chemically functionalized MWCNTs and interconnected MWCNTs reinforced epoxy resin composites were fabricated by cast moulding. Tensile properties and fracture surfaces of the specimens were investigated. The results show that, compared with pristine MWCNTs and chemically functionalized MWCNTs, the chemically interconnected MWCNTs improved the fracture strain and therefore the toughness of the composites significantly.     

Impact and after-impact properties of carbon fibre reinforced composites enhanced with multi-wall carbon nanotubes

The goal of the present study was to investigate the influence of multi-wall carbon nanotubes (MWCNTs) on the impact and after impact behaviour of carbon fiber reinforced polymer (CFRP) laminates. About 0.5% per weight MWCNTs were dispersed via a high shear device in the epoxy matrix (Bisphenol A) of carbon reinforced quasi-isotropic laminates. Subsequently, the modified CFRPs were subjected to low-energy impact and directly compared with unmodified laminates. In previous studies, the beneficial effect of the MWCNT inclusion to the fracture properties of CFRPs has been demonstrated. In terms of the CFRP impact performance, enhanced performance for the CNT doped specimens was observed for higher energy levels. However, the after-impact properties and more specifically compression after impact were improved for both the effective compression modulus and the compression strength. In addition, compression–compression fatigue after impact performance of the CNT modified laminates was also improved, by extending the fatigue life.     

Tensile and thermomechanical properties of short carbon fiber reinforced polyamide 6 composites

In this study, carbon fiber (CF) reinforced polyamide 6 (PA6) composites were prepared by using melt mixing method. Effects of fiber length and content, on the mechanical, thermal and morphological properties of CF reinforced PA6 composites were investigated. Fiber length distributions of composites were also determined by using an image analyzing program. It was seen that the maximum number of fibers were observed in the range of 0–50 μm. Mechanical test results showed that, increasing CF content increased the tensile strength, modulus and hardness values but decreased strain at break values of composites. DSC results showed that T_g and T_m values of composites were not changed significantly with increasing CF content and length. However, heat of fusion and the relative degree of crystallinity values of composites decreased with ascending CF content. DMA results revealed that storage modulus and loss modulus values of composites increased with increasing CF content.     

Tribological behaviour and wear of carbon nanotubes grafted on carbon fibres

Carbon nanotubes (CNTs) grafted on fibres are widely used to reinforce composites in order to improve their mechanical properties. This study concerned the tribological properties of CNTs grafted on carbon fibres by the flame method. The aim of this study was to determine whether CNTs on fibres suffer damage under stress, similar to those applied during composite manufacturing, which can damage composite properties, particularly fibre/matrix adhesion. For this purpose, reciprocating friction tests were performed to examine the resistance of CNTs and highlight a wear mechanism. The results showed that the presence of CNTs increased the coefficient of friction in the first friction cycles and then decreased it to close to the COF of the fibre without CNTs. The wear mechanism showed that after a small number of friction cycles, the CNTs were flattened out and formed a transfer film.     

Vibration damping characteristics of carbon fiber-reinforced composites containing multi-walled carbon nanotubes

Vibration damping characteristic of nanocomposites and carbon fiber reinforced polymer composites (CFRPs) containing multiwall carbon nanotubes (CNTs) have been studied using the free and forced vibration tests. Several vibration parameters are varied to characterize the damping behavior in different amplitudes, natural frequencies and vibration modes. The damping ratio of the hybrid composites is enhanced with the addition of CNTs, which is attributed to sliding at the CNT-matrix interfaces. The damping ratio is dependent on the amplitude as a result of the random orientation of CNTs in the epoxy matrix. The natural frequency shows negligible influence on the damping properties. The forced vibration test indicates that the damping ratios of the CFRP composites increase with increasing CNT content in both the 1st and 2nd vibration modes. The CNT-epoxy nanocomposites also show similar increasing trends of damping ratio with CNT content, indicating the enhanced damping property of CFRPs arising mainly from the improved damping property of the modified matrix. The dynamic mechanical analysis further confirms that the CNTs have a strong influence on the composites damping properties. Both the dynamic loss modulus and loss factor of the nanocomposites and the corresponding CFRPs show consistent increases with the addition of CNTs, an indication of enhanced damping performance.     

Single-walled carbon nanotubes modified by ionic liquid as antiwear additives of thermoplastics

Pristine single-walled carbon nanotubes (CNTs) were dispersed in the room-temperature ionic liquid (IL) 1-octyl, 3-methylimidazolium tetrafluoroborate ([OMIM]BF₄) by grinding and ultrasounds. Excess IL was removed to obtain single-walled carbon nanotubes modified by [OMIM]BF₄ (mCNTs). mCNTs were added in a 1 wt.% to polystyrene (PS), polymethylmethacrylate (PMMA) and polycarbonate (PC) to obtain PS + mCNT, PMMA + mCNT and PC + mCNT. The dry tribological performance of the new nanocomposites was studied against AISI 316L stainless steel pins and compared with that of the neat polymers and with the nanocomposites containing pristine carbon nanotubes without IL (PS + CNT; PMMA + CNT and PC + CNT). The maximum wear rate and friction coefficient reduction is obtained for PS + mCNT. Results are discussed upon the basis of optical, SEM and TEM microscopy, thermogravimetric analysis (TGA), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).     

Fabrication and characterization of Al-matrix composites reinforced with amino-functionalized carbon nanotubes

We report the fabrication of Al-matrix composites reinforced with amino-functionalized carbon nanotubes (fCNTs) using powder metallurgy process. Functionalization of the nanotubes was carried out by ball milling multiwalled carbon nanotubes (MWCNTs) in the presence of ammonium bicarbonate. It has been found that the mechanical properties of Al-fCNT composites were much superior to the composites fabricated using non-functionalized or acid functionalized carbon nanotubes. The enhancement in mechanical properties in these composites are attributed mainly to the better and homogeneous dispersion of fCNT in Al matrix as compared to non-functionalized or acid functionalized carbon nanotubes and the formation of a strong interfacial bonding between fCNT and Al matrix leading to an efficient load transfer from Al matrix to fCNT following high-resolution transmission electron microscopy.     

Pristine and amino functionalized carbon nanotubes reinforced glass fiber epoxy composites

Multi-phase composites have been studied by incorporating carbon nanotubes (CNTs) as a secondary reinforcement in an epoxy matrix which was then reinforced with glass fiber mat. Different types of CNTs e.g. amino functionalized carbon nanotubes (ACNT) and pristine carbon nanotubes (PCNT) were homogeneously dispersed in the epoxy matrix and two-ply laminates were fabricated using vacuum-assisted resin infusion molding technique. The issues related to CNT dispersion and interfacial bonding and its affect on the mechanical properties have been studied. An important finding of this study is that PCNT scores over ACNT in composites prepared under certain conditions. This is a very significant finding since PCNT is available at a much lower cost than ACNT.     

Sliding friction and wear behaviour of vinylester and its composites under dry and water lubricated sliding conditions

In this paper, we studied and explored the tribological performance of pure vinylester (V), glass fiber reinforced (GFR), SiC filled glass fiber reinforced vinylester composite under dry and water lubricated sliding conditions. Friction and wear tests were carried out with configuration of a pin on a rotating disc under ambient conditions. Tests were conducted at normal load 10, 30 and 50 N and under sliding speed of 1.6 m/s, 2.8 m/s and 4 m/s. The results showed that the coefficient of friction decreases with the increase in applied normal load values both under dry and water lubricated conditions. On the other hand for pure vinylester specific wear rate increases with increase in applied normal load under dry sliding condition and decreases with increase in applied normal load under water lubricated conditions. However the specific wear rate for GFR vinylester composite and SiC filled GFR vinylester composite decreases with the increase in applied normal load both under dry and water lubricated conditions. Moreover, for the range of load and speeds used in this investigation the coefficient of friction and specific wear rates using water lubricant registered lower values than that of the dry condition. The specific wear rates for pure vinylester and vinylester + 50 wt.% GFR and SiC filled GFR vinylester composite under dry and water lubricated sliding condition were in the order of 10⁻⁷ mm³ N⁻¹ mm⁻¹.     

Hierarchical composites of carbon nanotubes on carbon fiber: Influence of growth condition on fiber tensile properties

Growing carbon nanotubes (CNT) on the surface of high performance carbon fibers (CF) provides a means to tailor the thermal, electrical and mechanical properties of the fiber–resin interface of a composite. However, many CNT growth processes require pretreatment of the fiber, deposition of an intermediate layer, or harsh growth conditions which can degrade tensile properties and limit the conduction between the fiber and the nanotubes. In this study, high density multi-wall carbon nanotubes were grown directly on two different polyacrylonitrile (PAN)-based carbon fibers (T650 and IM-7) using thermal Chemical Vapor Deposition (CVD). The influence of CVD growth conditions on the single-fiber tensile properties and CNT morphology was investigated. The mechanical properties of the resultant hybrid fibers were shown to depend on the carbon fiber used, the presence of a sizing (coating), the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. The CNT density and alignment morphology was varied with growth temperature and precursor flow rate. Overall, it was concluded that a hybrid fiber with a well-adhered array of dense MWCNTs could be grown on the unsized T650 fiber with no significant degradation in tensile properties.     

Friction and wear behavior of three-dimensional braided carbon fiber/epoxy composites under lubricated sliding conditions

The friction and wear characteristics of three-dimensional (3D) braided carbon fiber-epoxy (C_3D/EP) composites under lubricated sliding conditions against a quenched medium-carbon steel counterface were studied. Wear tests were performed under different loads at two velocities. Comparative wear tests under dry conditions were carried out to investigate the influence of lubrication. Tribological properties of the C_3D/EP composites with various fiber loadings and two different fiber-matrix adhesion strengths were assessed. It was found that the lubricated contact promoted lower wear rates and friction coefficients. Compared to dry sliding, the tribological performance of the C_3D/EP composites under lubrication was less dependent on fiber content, fiber-matrix bonding, load, and velocity than dry sliding. The worn surfaces of the C_3D/EP composites were analyzed by scanning electron microscopy (SEM) to explore the relevant mechanisms.     

Electrical and thermal properties of polyamide 12 composites with hybrid fillers systems of multiwalled carbon nanotubes and carbon black

Hybrid filler systems of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) were incorporated into two types of polyamide 12 (PA12) using small-scale melt mixing in order to identify potential synergistic effects on the interaction of these two electrical conductive fillers. Although no synergistic effects were observed regarding the electrical percolation threshold, at loadings well above the percolation threshold higher volume conductivities were obtained for samples containing both, MWCNT and CB, as compared to single fillers. This effect was more pronounced when using a higher viscous PA12 matrix. The formation of a co-supporting network can be assumed. The combined use of CB and MWCNTs improved the macrodispersion of MWCNT agglomerates, which can be assigned as a synergistic effect. DSC measurements indicated an effect of the nanofiller on crystallisation temperatures of PA12; however this was independent of the kind or amount of the carbon nanofiller.     

Friction and wear behavior of the polyurethane composites reinforced with potassium titanate whiskers under dry sliding and water lubrication

A series of polyurethane (PU)/potassium titanate whiskers (PTW) composites modified by a high molecular weight hydroxyl-terminated polydimethylsiloxane (HTPDMS) were prepared. The PTW is modified by 2,4-diisocyanatotoluene (2,4-TDI). The effect of the PTW content on the mechanical and tribological properties of the PU composites was studied. Tensile strength of the PU composites increased with the addition of PTW. The friction and wear experiments were tested on a MRH-3 model ring-on-block test rig at different sliding speeds and loads under dry sliding and water lubrication. Experimental results revealed that the small content of PTW contributed to largely improve the tribological properties of the PU composites. The coefficient of friction (COF) of the composites increased and the wear rate value decreased with increasing PTW. Scanning electron microscopic (SEM) investigations showed that the worn surfaces of the PTW-reinforced PU composites was smoother than pure polyurethane under given load and sliding speed.     

Properties of composites of carbon nanotube fibres

Composites have set the standard for high strength materials for several decades. With the discovery of nanotubes, new possibilities for reinforced composites have arisen, with potential mechanical properties superior to those of currently available materials. This paper reports the properties of epoxy matrix reinforced with fibres of carbon nanotubes (CNTs) which, in many ways, are similar to standard composites reinforced with commercial fibres. The composites were formed by the back diffusion of the uncured epoxy into an array of aligned fibres of CNTs. The fibre density and volume fraction were measured from thermogravimetric analysis (TGA). Properties in tension and compression were measured, and the level of fibre–matrix interaction analysed fractographically. The results show the significant potential for this route to CNT reinforcement.     

Evaluation of thermal stability of ultrafine grained aluminium matrix composites reinforced with carbon nanotubes

The effect of carbon nanotubes on the thermal stability of ultrafine grained aluminium alloy processed by the consolidation of nano-powders obtained by mechanical alloying was evaluated via measurements of grain size and mechanical property changes upon annealing at various temperatures. It was found that the grain size of the samples containing carbon nanotubes is stable up to high temperatures and even after annealing at 450 °C (0.7T_m) no evident grain growth was observed. The limited grain boundary migration was attributed to the presence of entangled networks of carbon nanotubes located at grain boundaries and to the formation of nanoscale particles of aluminium carbide Al₄C₃. It was also revealed that carbon nanotubes decompose at a relatively low temperature of 450 °C and form fine Al₄C₃ precipitates. This transformation does not significantly affect the mechanical properties due to the nanoscale size of the carbides.