Evaluation of flyash-filled and aramid fibre reinforced hybrid polymer matrix composites (PMC) for friction braking applications

Flyash-filled and aramid fibre reinforced phenolic based hybrid polymer matrix composites (PMC) were fabricated followed by their characterization and tribo-evaluation. The friction-fade and friction-recovery behaviour has been rigorously evaluated as a function of in situ braking induced temperature rise in the disc at the braking interface on a Krauss friction testing machine as per the ECE regulations. The fade behaviour has been observed to be highly dependent on the weight fraction of resin i.e. followed a consistent decrease with the decrease in the flyash content, whereas the frictional fluctuations (μ_max − μ_min) has been observed to decrease with the increase in flyash content. A higher recovery response is registered when the flyash content is 80 wt.%. The analysis of friction performance has revealed that the fade and static friction response are the major determinants of overall frictional response. Wear analysis has revealed that material integrity and temperature rise of the disc decide the wear behaviour. Worn surface morphology investigation using SEM has revealed that the dynamics of formation–destruction of contact-patches (friction-layers) and topographical attributes largely influence the friction and wear performance of such composite brake-pads.     

芳纶浆粕和纳米钛酸钠晶须在汽车摩擦材料中的协同效应

以包括酚醛树脂、芳纶浆粕、纳米钛酸钠晶须、氧化铝、重晶石和二硫化钼的简化配方为基础制备一种摩擦材料,研究芳纶浆粕和纳米钛酸钠晶须的含量对摩擦材料的物理力学性能和摩擦磨损性能的影响。结果表明：随着芳纶浆粕含量的提高摩擦材料试样的布氏硬度呈现提高的趋势;当芳纶浆粕与钛酸钠晶须的比例为3:1时,材料的冲击强度达到最大值0.392 J/cm²,两种增强纤维的均匀混合为摩擦过程中产生高内聚强度的摩擦膜提供了基础,且这个比例产生最佳的协同效应,摩擦系数稳定在0.38~0.45,磨损率为5%。     

Friction and wear properties of UHMWPE/nano-MMT composites under oilfield sewage condition

A new stabilizer material ultra-high molecular weight polyethylene (UHMWPE) was reinforced with modified nano-montmorillonite (MMT) in different contents. Tribological properties of the materials, together with the polyamide (PA) material used as stabilizer for the purpose of comparison, were tested against a J55 steel counterfact on a reciprocating tribometer under oilfield sewage condition. The experimental conditions were a contact pressure 7.0 MPa, a stroke length of 15 mm, and a reciprocating frequency of 1 Hz. The results show that the 10 wt.% nano-MMT composite exhibits the lowest friction coefficient and the best wear resistance among all specimens; that furrow and larger area of brittleness break are dominant for the PA specimen, and that plowed scratches and abrasive wear are dominant for the 10 wt.% nano-MMT composite. The new material proves to be better than PA material when used as stabilizer materials.     

Low temperature preparation of calcium phosphate structure via phosphorization of 3D-printed calcium sulfate hemihydrate based material

The conversion of newly developed three dimensionally printed calcium sulfate hemihydrate (70–90% wt/wt CaSO₄·0.5·H₂O) based materials to calcium phosphate bioceramics by phosphorization in di-sodium hydrogen phosphate solution at 80°C for 4, 8, 16 and 24 h was studied. It was found that transformation rate, phase composition and mechanical properties were influenced by porosity in the fabricated samples and by the duration of the phosphorization treatment. Formulation with 85% CaSO₄·0.5 H₂O showed the fastest transformation rate and resulted in the highest flexural modulus and strength. Depending on the materials formulation, XRD, FT-IR and EDS revealed that calcium deficient hydroxyapatite (CDHA) or a mixture of CDHA and dicalcium phosphate anhydrous (DCPA) were the resulting phases in the transformed samples. After cell culturing for 14 and 21 days, human osteoblast cells were observed to attach to and attain normal morphology on the surface of the transformed sample containing 85% CaSO₄·0.5 H₂O. Various sizes and shapes of mineralized nodules were also found after 21 days.     

Thermal and impact study of PP/PET fibre composites compatibilized with Glycidyl Methacrylate and Maleic Anhydride

In this paper, two grafted copolymers, Glycidyl Methacrylate grafted polypropylene (PP) (PP-g-GMA) and Maleic Anhydride grafted PP (PP-g-MA) were used in PP reinforced with short poly(ethylene terephthalate) (PET) fibre composites. Transcrystallization (TC) of PP on PET fibres was investigated using a polarized optical microscope, which revealed no TC for either of the modified composites at the fibre–matrix interface. Heat deflection temperature (HDT) results of GMA modified composites revealed more enhancement than HDT of MA modified samples. The composite strength results showed enhancement for both modified composites up to 10 wt.%, and this growth was bigger for GMA modified composites. The morphological analysis of GMA modified PP/PET composites pointed out a marked improvement of fibre dispersion and interfacial adhesion as compared to non-compatibilized PP/PET composites. The results of impact strength showed about 43% enhancement for 15 wt.% PET fibre composites. It was found that at low fibre percentages, using either of the modifiers reduces the impact strength a little in comparison to impact strength of the unmodified samples. According to linear elastic fracture mechanics LEFM, impact fracture toughness (G_c) and critical stress intensity factor (K_c) were evaluated for these composites based on the fracture energy obtained from impact tests.     

Tribological behavior of Ni3Al matrix self-lubricating composites containing WS2, Ag and hBN tested from room temperature to 800 °C

Ni₃Al matrix self-lubricating composites (NMSC) containing varied amounts of WS₂, Ag and hBN (WAh) with weight ratio of 1:1:1 were fabricated by in situ technique using spark plasma sintering. The friction and wear properties of NMSC against the commercial Si₃N₄ ceramic ball at the load of 10 N and sliding speed of 0.234 m/s for 80 min from room temperature to 800 °C were investigated. The results showed that the tribological properties of NMSC strongly depended on the addition content of WAh. Moreover, NMSC with 15 wt.% WAh and 5 wt.% TiC exhibited the relatively lower friction coefficients and the less wear rates from RT to 800 °C. The excellent tribological behavior of NMSC with 15 wt.% WAh and 5 wt.% TiC was attributed to the synergetic action of composite lubricants of WAh and reinforced phase of TiC.     

Surface Modification of Aramid Fibres with Graphene Oxide for Interface Improvement in Composites

A novel method of biomimetic surface modification was used for aramid fibres aiming to enhance the interface properties between epoxy resin and the modified aramid fibre. Inspired by the composition of adhesive proteins in mussels, a thin layer of poly(dopamine) (PDA) was self-polymerized onto the surface of the aramid fibre. The graphene oxide (GO) was then grafted on the surface of PDA-coated aramid fibres. The microstructure and chemical characteristics of the pristine and modified fibres were characterised using Scanning Electron Microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), indicating successful grafting of GO on the PDA-coated aramid fibres. Single fibre tensile test and microbond test were carried out to evaluate the mechanical properties of the modified fibres. It was found that the fibre surface modification improved the interfacial shear strength by 210% and the fibre tensile strength was protected by GO-PDA coating.     

Improved tensile properties of basalt fibre reinforced polymer composites using silica nanoparticles

In this study, the effect of silica nanoparticles as the reinforcing filler on the tensile response of basalt fibre reinforced polymer (BFRP) composite was investigated. A 40 wt.% nanosilica gel in epoxy was used to prepare a series of nanocomposites with 5 wt.%, 15 wt.% and 25 wt.% nanosilica. Static uniaxial tensile tests were conducted on the basalt fibre reinforced polymer composite to investigate the stress‐strain response of the unmodified and nanomodified composites. It was found that the incorporation of silica nanoparticles with high specific surface area improved the tensile properties of the basalt fibre reinforced polymer composite. The addition of silica nanoparticles in the composite shows significant improvement in tensile modulus with 6 %, 14 % and 19 % for 5 wt.%, 15 wt.% and 25 wt.% nanosilica content, respectively. The higher content of silica nanoparticles in the matrix increased the stiffness of the material as well as the strength of the basalt fibre reinforced polymer composite without reducing the failure strain.     

A surfactant dispersed SWCNT-polystyrene composite characterized for electrical and mechanical properties

Single wall carbon nanotubes (SWCNTs) were dispersed in polystyrene (PS) at 0.1, 0.2, 0.3 and 1.0 wt.% (weight percent) concentrations using a surfactant assisted method. The resulting nanocomposites were characterized for their electrical conductivity, mechanical strength and fracture toughness properties. Results show a significant improvement in electrical conductivity with electrical percolation occurring by 0.2 wt.% SWCNT loading and the SWCNT-PS nanocomposite fully conductive at 1.0 wt.%. Three-point bend tests showed a decline in flexural strength and break strain with the addition of 0.1 wt.% SWCNTs. Improvements in the flexural modulus, strength and break strain with increasing SWCNT wt.% content followed The fracture toughness of the SWCNT-PS nanocomposites, in terms of the critical stress-intensity factor K_IC, was reduced relative to the neat material. From optical and high resolution scanning electron microscopy the presence of the carbon nanotubes is shown to have an adverse effect on the crazing mechanism in this PS material, resulting in a deterioration of the mechanical properties that depend on this mechanism.     

Shear properties and water connectivity of wet granules at high solid content concentration

The inner liquid distribution in wet granules strongly influences their mechanical properties. In this study, we examined the shear properties (internal friction angle, cohesion, storage modulus and loss modulus) of wet granules composed of graphite particles and water, and determined their inner water connectivity using X-ray refraction contrast imaging computed tomography (CT) to elucidate their correlation. At high solid content concentration (C_SC) region (C_SC = 85 wt.%), internal friction angle of wet granules was slightly lower than that of wet granules with lower C_SC, and their cohesion becomes almost zero. Furthermore, storage modulus of wet granules at C_SC = 85 wt.% was the highest among all wet granules. The X-ray CT and scanning electron microscopy (SEM) observations revealed that the water connectivity in the wet granules was in the pendular state and graphite particles fractured under shear test at C_SC = 85 wt.%. From these results, it can be concluded that lower shear cohesion at C_SC = 85 wt.% is caused by an increase in the number of isolated liquid bridges, and particle fracture results in a decrease in the internal friction angle owing to decreasing roughness of shear plane. Furthermore, the particle fracture also resulted in the higher storage modulus at C_SC = 85 wt.% in rheological measurements.     

Influence of CaCO3 Whisker Content on Mechanical and Tribological Properties of Polyetheretherketone Composites

The mechanical and tribological properties of polyetheretherketone (PEEK) composites filled with CaCO3 whisker in various content of 0-45% (wt pct) were investigated. The composite specimens were prepared by compression molding. Tribological testing of composites in dry wear mode against carbon steel ring was carried out on a MM200 block-on-ring apparatus. Data on neat PEEK were also included for comparison. It was observed that inclusion of CaCO3 whisker affected the most mechanical properties and the friction and wear in a beneficial way. With an increase in CaCO3 whisker content, friction coefficient continuously decreased but the trends in wear performance varied. The specific wear rate showed minima as 1.28×10-6 mm3/Nm for 15% CaCO3 whisker inclusion followed by a slow increase for further CaCO3 whisker addition. In terms of friction applications, when the tribological and mechanical properties are combined, the optimal content of CaCO3 whisker in the filled PEEK should be recommended as 15% to 20%. Fairly good correlations are observed in friction coefficient vs bending modulus and wear rate vs bending strength, confirming that the bending properties prove to be the most important tribology controlling parameters in the present work.     

Optimum selection of novel developed implant material using hybrid entropy‐PROMETHEE approach

Optimum selection of appropriate biomaterial with unlike properties for the femoral head material is one of the toughest tasks. Therefore, in this article, a series of implant materials for the femoral head by vacuum casting induction furnace containing cobalt‐30chromium (Co‐30Cr) as a base material and three alloying elements (i. e. molybdenum, nickel and tungsten) were developed and evaluated for physical, mechanical and tribological properties. Density, hardness, compressive strength, coefficient of friction and volumetric wear were considered as material selection criterions. The weight of each criterion has been determined by entropy method, while the ranking of the alternatives has been carried out by the preference ranking organization method for enrichment evaluations (PROMETHEE) method. From this ranking results, it is found that the cobalt‐30chromium‐4molybdenum‐1nickel‐2tungsten (Co‐30Cr‐4Mo‐1Ni‐2W) material at given parameters is the best implant material for the femoral head component of hip joint replacement.     

The influence of magnetic field on ballistic performance of aramid fibre and ultrahigh molecular weight polyethylene

An innovative method is introduced here whereby using two sets of arrays of rare earth magnets aligned opposite each other in order to create a repulsion force owing to the like poles when facing close to each other. Ballistic test samples of aramid fibre (Kevlar K29) and ultrahigh molecular weight polyethylene (UHMWPE) were sandwiched by two sets of opposing magnets. Ballistic test was conducted using a gas gun with a 7.62 mm diameter projectile at a velocity ranging from 160 to 220 m/s. High speed camera was used to capture the ballistics testing and it shows that the magnetic repulsion force created by the opposing rare earth magnets managed to suppress the projectile from advancing into the front face of the aramid fibre. Similarly, when magnets were used, the UHMWPE sample shows the projectile perforated through the first few sheets and finally rested on the last sheet showing partial perforation.     

The abrasive wear behaviour of continuous fibre polymer composites

The dry abrasive-dominant wear behaviour of several composite materials consisting of uni-directional continuous fibres and polymer matrices was investigated. Seven materials were examined: neat epoxy (3501-6), carbon fibre epoxy (AS4/3501-6), glass fibre/epoxy (E-glass/ 3501-6), aramid fibre/epoxy (K49/3501-6), neat polyetheretherketone (PEEK), carbon fibre/PEEK (APC2) and aramid fibre/PEEK (K49/PEEK). The wear behaviour of the materials was characterized by experimentally determining the friction coefficients and wear rates with a pin on-flat test apparatus. First, the effects of the operation variables apparent normal pressure, sliding velocity and apparent contact area were observed. The dimensionless wear rate increased linearly as the apparent normal pressure increased and decreased as the apparent contact area increased. Second, through microscopic observations of the worn surfaces and subsurface regions, basic wear mechanisms were identified as a function of fibre orientation. Observations of fibre-abrasive particle interactions allowed for the differentiation of the dominating wear mechanisms. Finally, a network of data was compiled on the wear behaviour in terms of the three material parameters: fibre orientation, fibre material and matrix material. This enabled the systematic selection of an ideal low wear composite material which would consist of a PEEK matrix reinforced with aramid fibres oriented normal to the contacting surface and carbon fibres oriented parallel to the contacting surface.     

On the experimental investigation of crash energy absorption in laminate splaying collapse mode of FRP tubular components

In this experimental work the crash energy absorption of fibre reinforced plastic (FRP) tubular components that collapse in laminate splaying mode is investigated by means of a new testing method, the “curling test”. This test method was used trying rectangular carbon, aramid and glass FRP strips—in which the reinforcing fibres were in the form of reinforcing woven fabric (carbon and aramid FRP specimens) and multi-axial fibre reinforcements (glass FRP specimens). Apart from the analysis of the system of bending and friction forces acting on the specimens during the curling tests in comparison with the forces acting in the case the laminate splaying collapse mode and the observations related to the deformation and crushing induced on the FRP specimens by this force combination, the analysis of the test results focused on the influence of the most important geometric and laminate material properties—such as thickness, flexural rigidity, number of reinforcing fibre layers, laminate stacking sequence and constituent material mechanical properties—on the specific energy absorption and the peak load.     

Tricalcium phosphate based resorbable ceramics: Influence of NaF and CaO addition

Resorbable bioceramics have gained much attention due to their time-varying mechanical properties in-vivo. Implanted ceramics degrade allowing bone in-growth and eventual replacement of the artificial material with natural tissue. Calcium phosphate based materials have caught the most significant attention because of their excellent biocompatibility and compositional similarities to natural bone. Doping these ceramics with various metal ions has significantly influenced their properties. In this study, tricalcium phosphate (TCP) compacts were fabricated via uniaxial compression with five compositions: (i) pure TCP, (ii) TCP with 2.0 wt.% NaF, (iii) TCP with 3.0 wt.% CaO, (iv) TCP with a binary of 2.0 wt.% NaF and 0.5 wt.% Ag₂O, and (v) TCP with a quaternary of 1.0 wt.% TiO₂, 0.5 wt.% Ag₂O, 2.0 wt.% NaF, and 3.0 wt.% CaO. These compacts were sintered at 1250 °C for 4 h to obtain dense ceramic structures. Phase analyses were carried out using X-ray diffraction. The presence of NaF in TCP improved densification and increased compression strength from 70 (± 25) to 130 (± 40) MPa. Addition of CaO had no influence on density or strength. Human osteoblast cell growth behavior was studied using an osteoprecursor cell line (OPC 1) to assure that the biocompatibility of these ceramics was not altered due to the dopants. For long-term biodegradation studies, density, weight change, surface microstructure, and uniaxial compression strength were measured as a function of time in a simulated body fluid (SBF). Weight gain in SBF correlated strongly with precipitation viewed in the inter-connected pores of the samples. After 3 months in SBF, all samples displayed a reduction in strength. NaF, CaO and the quaternary compositions maintained the most steady strength loss under SBF.     

Effect of SiC whisker addition on the microstructures and mechanical properties of Ti(C,N)-based cermets

Ti(C, N)-based cermets with addition of SiC whisker (SiC_w) were prepared by vacuum sintering. The microstructures of the prepared cermets were investigated by using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Mechanical properties such as transverse rupture strength (TRS), fracture toughness (K_IC) and hardness (HRA) were also measured. It was found that the grain size of the cermets was affected by the SiC whisker addition. The cermets with 1.0 wt.% SiC whisker addition exhibited the smallest grain size. The porosities of the cermets increased with increasing SiC whisker additions. The addition of the SiC whisker had no influence on the phase constituents of the cermets. Compared with the cermets with no whisker addition, the highest TRS and fracture toughness for cermets with 1.0 wt.% SiC whisker addition increased by about 24% and 29%, respectively. The strengthening mechanisms were attributed to finer grain size, homogeneous microstructure and moderate thickness of rim phase. The toughening mechanisms were characterized by crack deflection, whisker bridging and whisker pulling-out.     

Different reinforcement strategies of hybrid surface composite AA6061/(B4C+MoS2) produced by friction stir processing

Aluminum surface composites have gained huge importance in material processing due to their noble tribological characteristics. The reinforcement of solid lubricant particles with hard ceramics further enriches the tribological characteristics of surface composites. In the current study, friction stir processing was chosen to synthesize hybrid surface composites of aluminum containing B₄C and MoS₂ particles with anticipated improved tribological behavior. B₄C and MoS₂ powder particles in 87.5: 12.5 ratio were reinforced into the AA6061 by hole and groove method. Microstructural observations indicated that reinforcement particles are well distributed in the matrix. The hardness and wear resistance of hybrid surface composites improved as compared to the base material, due to well distributed abrasive B₄C and solid lubricant MoS₂ particles in AA6061. The hybrid surface composites achieved ∼32 % increased average hardness as compared to the base material. Hole method revealed ∼13 % better wear resistance compared to the groove method for friction stir processed hybrid surface composite, attributing to an improved homogeneity of particle distribution shown by zigzag hole pattern. Moreover, friction stir processed AA6061 without reinforcement particles exhibited reduced hardness and wear resistance due to loss of strengthening precipitates during multi-pass friction stir processing.     

Comparison of friction and wear performances of brake materials containing different amounts of ZrSiO4 dry sliding against SiCp reinforced Al matrix composites

Low friction levels for brake materials dry sliding against Al matrix composites (Al-MMCs) were observed. Al matrix composites reinforced with 30 vol.% SiC_p (34 μm) were used first to fabricate a new brake drum in place of the conventional cast iron brake drum for a Chase Machine. Experimental studies on the brake materials differing in amounts of zirconium silicate (0 wt%, 4 wt%, 8 wt%, and 12 wt% ZrSiO₄) dry sliding against the Al-MMCs drum were performed on the Chase Machine in order to examine their effects on friction and wear performances. The test procedures include friction fade and recovery, load and speed sensitivities at 177 °C and 316 °C, and wear. Experimental results show that the brake material containing 8 wt% ZrSiO₄ had the best wear resistance and higher friction level. The brake material containing 12 wt% ZrSiO₄ had the highest friction level, but wear increased rapidly. The deterioration of the latter wear suggests that this brake material is unreliable in commercial applications.     

Optimal design of flyash filled composite friction materials using combined Analytical Hierarchy Process and Technique for Order Preference by Similarity to Ideal Solutions approach

The performances of flyash based fibre reinforced-phenolic composites have been rigorously evaluated on a Krauss friction testing machine following PVW-3212 norms as per the “Economic Commission for Europe” (ECE) regulations and have been discussed in-terms of fade, recovery, performance friction coefficient, wear and disc-temperature rise. The present paper deals with tribo-performance analysis in-terms of sensitivity of the overall performance due to any fluctuations in six selected performance defining attributes (PDA) specifically with regard to friction-fade, friction-recovery, wear, disc-temperature rise and averaged friction performance. The relative weights of importance of the PDAs with respect to overall friction performance have been elicited by the Analytic Hierarchy Process (AHP). The ranking of the friction materials has been carried out by the Technique for Order Preference by Similarity to Ideal Solutions (TOPSIS). In the sensitivity analysis part, the weightage of the PDAs were systematically varied within a specified range to assess the response of different friction materials so as to optimally design materials for varied friction applications.