Scratching Action Research Articles

Hydrodynamics and film formation characteristics in a horizontal self‐cleaning twin‐shaft kneader for polymer devolatilization

AbstractA deep understanding of hydrodynamics and film formation characteristics is a prerequisite for the design of twin‐shaft kneaders. In this work, the hydrodynamics and film formation characteristics of a self‐cleaning twin‐shaft kneader are investigated using computational fluid dynamics method. Because of the intermeshing interaction and scratching action of the kneader rods, both bounded films and free films coexist in the kneader. Since both shafts rotate clockwise, more liquid is accumulated in the left cylinder. The liquid level of the left cylinder is higher which reduces the film formation rate of the left zone. The film formation rate in the right zone is 1.3–1.8 times that of the left zone and overlapping zone. The differences between the left and right cylinders would cause inconsistent devolatilization performances. To reduce the negative effects of asymmetric level, a static kneading rod is used to reduce the liquid level of the left zone and increase the film formation rate by 15%. We notice that adding a static kneading rod reduces the power consumption by 10%–30% compared with increasing the rotating speed to the same film formation rate. It could be an efficient method for polymer devolatilization.

Atomistic understanding toward the improved scratching properties of GaAs coated with monolayer graphene

Molecular dynamics simulation was performed to study the surface nanotribological behavior and subsurface damage of gallium arsenide (GaAs) substrate coated with monolayer graphene when subjected to the scratching action of diamond abrasive. Simulation result shows that the coefficient of friction and wear volume of GaAs/graphene surface are evidently lower than those of the bare GaAs surface for various scratching depths. The material removal of the graphene-coated GaAs workpiece is primarily attributed to compression- and shear-induced plastic deformation of GaAs, whereas abrasive wear is the dominant material-removal mechanism for bare GaAs workpiece. On the contrary, the GaAs workpiece coated with graphene exhibits severe subsurface damage due to the higher stress and that graphene can suppress the stress released within the GaAs workpiece during scratching; hence, the stress has to spread deeply. The scratching-induced slight deformation of graphene occurs when the scratching depth is higher than 15 Å. The deformed graphene induced by scratching is still capable of protecting GaAs substrate to some extent, but its C-C bond is vulnerable to be ruptured at the end of the scratching path due to a scratching-induced bulge structure. Increasing temperature can promote the scratching-induced surface wear and subsurface damage of GaAs workpiece. Monolayer graphene can improve the surface tribological properties of GaAs at each temperature. This work can provide atomic insights into the antifriction and antiwear design for GaAs when graphene is used as a coating.

Nanoscratching on surfaces: the relationships between lateral force, normal force and normal displacement

Abstract The relationship between lateral force, normal force and normal displacement has been investigated. Surfaces of diverse materials were nanoscratched at constant rate. Nanoindents with cube corner, Berkovich or cono-spherical indenter indicate proportionality of (normal force) ~ (normal displacement)3/2 up to considerable forces, sometimes approaching the 10 mN range, but phase transformations under pressure may change the slope. This differs from the varying Meyer exponents reported at forces higher by two to three magnitudes when applied to Vickers indenters. Nanoscratching on diverse materials consistently reveals proportionality of (lateral force) ~ (normal force)3/2. This relationship is valid for amorphous (fused quartz) and crystalline materials such as silicon, silica, strontium titanate and the polar molecular crystals of thiohydantoin and nin-hydrin with hydrogen bonds, or pure van-der-Waals crystals of tetraphenylethylene. Anisotropies of the crystals and the type of destruction (breaking covalent bonds, or hydrogen bonds, or van-der-Waals interactions; abrasion, or molecular movements) do not affect the obviously universal relationship but only the proportionality factor with the dimension μN–0.5 which describes materials response to the scratching action for the particular crystal face and anisotropic direction. The new quantitative relationship is usable for the calculation of scratch work and of other quantities related to the lateral force on the basis of the new empirical constants. Both new relationships from nanoindents and nanoscratches are unified in the (lateral force) ~ (normal displacement)9/4 relationship and experimentally verified.

Influence of secondary phase particles Al2O3/SiC on the microstructure and tribological characteristics of AA7075-based surface hybrid composites tailored using friction stir processing

Recently, cylinder liners of automotive and aircraft engines are encountered severe wear due to piston slap occurred by the repeated sliding stroke of piston. This research focuses on providing an alternative material for cylinder liners, which can be obtained through friction stir processing on AA7075 with different weight ratios of reinforcements like Al2O3 and SiC. Friction stir processing is executed with a tool rotational speed of 1000 r/min and traveling speed of 56 mm/min at 2° tool tilt angle. The images of optical microscopy reveal the fine-grains with a homogeneous distribution of secondary phase particles and also offer decrement in particle clustering except at some localized regions. It is identified that addition of 3.7 wt.% Al2O3 + 3.0 wt.% SiC in AA7075 enhanced the microhardness about 33.96% higher than base matrix. Hence, wear resistance of the specimen is improved. Dry sliding wear behavior of specimens is analyzed using pin on disc at 20, 40, and 60 N load conditions to create the actual sliding behavior of piston on cylinder wall. Increasing the wt.% of Al2O3 particles enhanced the wear resistance of AA7075 surface hybrid composites at 20 N load due to the formation of protective tribofilm. Specimen with 3.7% Al2O3 + 3.0% SiC has better lubrication and load-bearing capacity that exhibits superior tribological behavior at 40 and 60 N. Higher Fe content of 5.44 wt.% has been obtained through spectroscopy analysis in S5, which is 8% and 6% higher than S3 (7.5% of Al2O3) and S7 (6% of SiC), respectively. The scratching action of this hard specimen on the counterpart brings more Fe content. Increase of Al2O3 particles paved the way for tribofilm formation and identified through scanning electron microscopy micrographs. The observation from worn specimens shows that finer wear debris had increased by adding more quantity of SiC particles due to abrasive wear mechanism.

Inflammation and airway remodeling of the lung in guinea pigs with allergic rhinitis.

Allergic rhinitis (AR) and asthma belong to the category of type I allergic diseases, whose pathological features are airway remodeling of the lung and allergic inflammation. The aim of the present study was to evaluate inflammation and remodeling of lung tissue in a guinea pig model of AR in order to confirm consistent pathological changes of upper and lower airways in AR. Male guinea pigs were randomly divided into an experimental and a control group (n=10 in each). The AR model was established by sensitization through intraperitoneal injection of ovalbumin for three weeks and bilateral nasal local excitation for twelve weeks. All tissues of nasal mucosa and lung were subjected to hematoxylin and eosin as well as toluidine blue staining, and characteristics of remodeling of lung tissue, including thickness of bronchial wall, epithelial mucosa and smooth muscle were histologically determined. Collagen deposition in lung tissue was observed by Masson's trichrome stain. Severe paroxysmal nose scratching action, frequent sneezing, visible outflow of secretion from the anterior naris and frequent nose friction were observed in the AR model group within 30 min after local excitation. The total symptom scores were significantly increased in the AR model group compared with those in the control group. Obvious inflammatory cell infiltration was observed in the AR model group. Compared with those in the control group, the numbers of eosinophils and mast cells in nasal mucosa and lung tissue were significantly increased. Obvious airway remodeling of the lung was observed in the AR model group. Compared with those in the control group, bronchial wall thickness, epithelial layer thickness and smooth muscle thickness in the airways were significantly increased in the AR model group. Increased collagen deposition was found in the AR model group compared with that in the control group. The results of the present study revealed that inflammation and airway remodeling of lungs arose in guinea pigs with AR, suggesting that pathological changes of upper and lower airways are consistent in this AR model.

Fiber Bragg Grating Sensor for Cutting Speed Optimization and Burr Reduction in Micro-nano Scratching

Abstract Patterning a surface by scratching at micro-nano scale requires precise instrumentation strategies for generation of accurate patterns which are used in variety of surfaces ranging from bacteria resistant surfaces to water repellent ones. The scratching action leads to temperature rise of tool tip causing expansion of tool and work surface. This results in positioning inaccuracies and surface defects of the machined work. In this work a fiber Bragg grating sensor (FBG) is used to record the temperature rise at the tool tip under different scratching/cutting speeds. The surface integrity of the patterned work was evaluated after machining using a profilometer. The optimized value of cutting speed for minimum inaccuracy and minimum burr was found using Lagrangian multiplier based technique. This work thus ensures real time control of scratching speed based on tool tip temperature variations only, which finally results in better surface integrity of patterned profile.

Contagious scratching: shared feelings but not shared body locations

Contagious scratching: shared feelings but not shared body locations

Improvement in the Scratch Resistance of Polymers by Roller Burnishing Process

Abstract The ability of engineering polymers to resist scratching action has rapidly become a vital requirement for diverse industrial applications because scratches may greatly reduce the life cycle of the components. Therefore, the present work aims to study the possibility of using roller burnishing process to enhance the scratch resistance of polymers to a single pass scratching action. The effects of burnishing feed rate and roller contact width on the scratch hardness of poly(oxymethylene) and polyurethane were considered. The results revealed that low burnishing feed rate and smaller roller contact width led to an increase in scratch hardness for both polymers. The scratch fractures were also observed using SEM to study the changes in wear modes.

An Experimental Study on the Scratch Characteristics of Bamboo Fibre-Reinforced Epoxy Composite

Bamboo fibre has been used as reinforcement in epoxy. The influence of bamboo fibres orientation on the scratch characteristics has been studied by single pass scratching action and evaluated in terms of scratch force and scratch hardness. The composites are prepared for three different fibre orientations, longitudinal, transverse and 10 mm random. Five values of applied load (2 N, 5 N, 10 N, 12 N, 15 N) and two scratching speeds (5.6 mm s−1, 11.2 mm s−1) are considered. The results revealed that the introduction of bamboo fibres tends to increase the scratch force for all composites considered except for longitudinal orientated fibre composite. The scratch hardness shows improvement when bamboo fibre is introduced, except for the longitudinal case. The best result for scratch hardness is exhibited by transversely orientated bamboo fibre reinforced epoxy corresponding to 35 % improvement.

Study on the Scratch Hardness and Indentation Hardness of Burnished Poly(Oxymethylene) Surfaces

Scratch resistance of engineering polymers has become increasingly important for diverse industrial applications as scratches may greatly reduce the life cycle of the components. In this article, a new polymer surface treatment method has been introduced to enhance scratch resistance to a single-pass scratching action. Ball burnishing is a postmachining operation based on plastic deformation commonly used for metals and non-ferrous surfaces. It was demonstrated that ball burnishing is capable of enhancing the scratch hardness and indentation hardness of poly(oxymethylene) surfaces with a good correlation between these two properties. SEM investigations suggest that ball burnishing will alter the mode of scratch damage from severe ductile ploughing and brittle cutting deformation to a mild brittle fracture. A simple model has been proposed that separates the scratching action into two parts, the elastic behavior during indentation and the ploughing behavior during the scratching motion. The dense surface layer induced by the ball burnishing impedes the initial indentation, resulting in less ploughing depth during scratching.

Friction and Wear Mechanisms of Nanocrystalline Nickel in Ambient and Inert Atmospheres

The role of testing environment on the friction and wear behavior of nanocrystalline (nc) Ni with a grain size of 15 ± 3 nm and a hardness of 519 ± 11 Hv has been studied in comparison with microcrystalline (mc) Ni with a grain size of 20 ± 5 μm and a hardness of 122 ± 5 Hv. Coefficients of friction (COFs) and wear rates were measured in ambient air and argon environments using a pin-on-disc tribometer operated at a constant load of 2 N and a sliding speed of 0.1 m/s against a spherical Al2O3 counterface (H = 1,900 ± 40 Hv). The initial contact pressure exerted by the counterface (1.56 GPa) was sufficiently high to induce plastic deformation on the contact surface of the mc Ni but not on the surface of the nc Ni for which the initial wear rate in the first eight cycles was almost two orders of magnitude smaller (Wi (mc) = 7.88 × 10−3 mm3/m, and Wi (nc) = 0.16 × 10−3 mm3/m). Both samples showed higher wear rates when tested in argon, but again the initial wear rate of the nc Ni was much lower (i.e., during the first eight cycles, WiAr (mc) = 9.97 × 10−3 mm3/m and WiAr (nc)= 0.22 × 10−3 mm3/m). In both atmospheres, the COF curves increased rapidly and exhibited a peak before they decreased to a steady-state value. The peak value of the COF for the nc Ni was less than that of the mc Ni in air (COFp (mc) = 0.71, and COFp (nc) = 0.58) as well as in argon (COFpAr (mc) = 1.14, and COFpAr (nc) = 0.77). Steady-state wear conditions in both samples were reached earlier in air than in argon. Compared to the mc Ni, the nc Ni maintained lower steady-state wear rates in both air (Wss (mc) = 0.13 × 10−3 mm3/m, and Wss (nc) = 0.03 × 10−3 mm3/m) and argon (WssAr (mc) = 0.18 × 10−3 mm3/m, and WssAr (nc) = 0.07 × 10−3 mm3/m) environments. The wear track of the nc Ni was continuously widened by the scratching action of the counterface. In the ambient atmosphere, oxidized debris particles became agglomerated, forming a compacted protective tribolayer on the top of the wear track of the nc Ni. In the argon atmosphere, the tribolayers were discontinuous, covering about half of the wear tracks, and had lower hardness because of their lesser oxide content, resulting in higher steady-state wear rates and COF values (COFss (nc) = 0.41, and COFssAr (nc) = 0.58).

Wear Behavior of Plasma Sprayed Ni-WC Composite Coatings

Seal materials often lose their effectiveness due to the wear of surface under the combined effect of environment and load. In this research, a metallurgical bonding composite coating reinforced with nickel -coated tungsten carbide (Ni -WC) particles was produced on 40Cr carbon steel substrate by plasma sprayed. The bond strength of the coating/substrate interface and the tensile strength of the coating itself reached 260–330 and 100–132MPa, respectively. Effects of Ni and WC contents on the wear behavior of the coating have been systematically investigated at two different wear conditions, namely the high stress pin-on-disk abrasion and three-body abrasive wear. The results show that the higher the Ni content in the coating, the lower the hardness and wear resistance. In stress pin-on-disk abrasive wear, the mass percent of Ni in the coating having the lowest wear amount was 40%, and which was 60% in three-body abrasion. In view of the above, the WC reinforcement of the composite coating plays an important role in protecting the matrix from being worn-out, whereas in the abrasive wear, the wear mechanism is mainly controlled by the scratching and micro-cutting of the matrix followed by the pull out of WC particles due to the scratching action of abrasives. The wear resistance of the 40Cr carbon steel composite coating (Ni -WC) is better than that of the flame overlaid coating.

Wear Mechanism of Diamond Saw Blades for Dry Cutting Concrete

The wear mechanism of several kinds of diamond circular saw blades was studied in the different sawing parameters during dry cutting of cement concrete, ferroconcrete and steel fiber reinforced concrete. Seven wear forms of diamond grits were obtained in the sawing experiments. The cobalt based bond shown the best wear resistance. It showed that the damage of blade body was caused by thermal damage and the scratching action of concrete chips. The result indicates that the wear of diamond saw blades arises mostly from the difficult chips removing, high cutting temperature and drastic impacting in dry sawing.

Nanoscratching on surfaces: the relationships between lateral force, normal force and normal displacement

The relationship between lateral force, normal force and normal displacement has been investigated. Surfaces of diverse materials were nanoscratched at constant rate. Nanoindents with cube corner, Berkovich or cono-spherical indenter indicate proportionality of (normal force) ∼ (normal displacement) 3/2 up to considerable forces, sometimes approaching the 10 mN range, but phase transformations under pressure may change the slope. This differs from the varying Meyer exponents reported at forces higher by two to three magnitudes when applied to Vickers indenters. Nanoscratching on diverse materials consistently reveals proportionality of (lateral force) ∼ (normal force) 3/2 . This relationship is valid for amorphous (fused quartz) and crystalline materials such as silicon, silica, strontium titanate and the polar molecular crystals of thiohydantoin and ninhydrin with hydrogen bonds, or pure van-der-Waals crystals of tetraphenylethylene. Anisotropies of the crystals and the type of destruction (breaking covalent bonds, or hydrogen bonds, or van-der-Waals interactions; abrasion, or molecular movements) do not affect the obviously universal relationship but only the proportionality factor with the dimension μN -0.5 which describes materials response to the scratching action for the particular crystal face and anisotropic direction. The new quantitative relationship is usable for the calculation of scratch work and of other quantities related to the lateral force on the basis of the new empirical constants. Both new relationships from nanoindents and nanoscratches are unified in the (lateral force) ∼ (normal displacement) 9/4 relationship and experimentally verified.

Wear behavior of brazed WC/NiCrBSi(Co) composite coatings

A metallurgically bonded composite coating of a Ni–Cr–B–Si alloy reinforced with cobalt-coated tungsten carbide (WC-Co) particles was produced on a carbon steel substrate by high temperature vacuum brazing. The bond strength of the coating/substrate interface and the tensile strength of the coating itself reached 300–360 and 100–140 MPa, respectively. Effects of Co and WC-17Co contents on the wear behavior of the coating have been systematically investigated at two different wear conditions, namely the high speed rotating slurry erosive wear and the wet sand/rubber wheel abrasive wear. Results show that the higher was the Co content in the coating, the lower were the hardness and wear resistance. In the slurry erosive wear, the WC reinforcement of the composite coating plays an important role protecting the matrix from being worn-out, whereas in the abrasive wear, the wear mechanism is mainly controlled by the scratching and micro-cutting of the matrix followed by the pull out of WC particles due to the scratching action of abrasives. The wear resistance of the brazed composite coating (WC/NiCrBSi(Co)) is better than that of the flame overlaid coating.

Micro-scale abrasive wear testing of duplex and non-duplex (single-layered) PVD (Ti,Al)N, TiN and Cr–N coatings

A micro-scale abrasive wear test, based on ball-cratering, has been used to evaluate the wear resistance of duplex and non-duplex (Ti,Al)N, TiN and Cr–N coatings. The term duplex is used here when plasma nitriding is followed by PVD coating. Coatings without the plasma nitriding stage are termed single-layered. Coating properties were evaluated by surface profilometry, hardness and scratch testing. All duplex coatings showed higher micro-abrasive wear resistance than their single-layered counterparts, with the duplex (Ti,Al)N coating achieving the best performance. After a certain number of ball revolutions, the coating material became worn through, exposing the substrate material. After this point, the presence of a hard nitrided case diminished the scratching action of the SiC abrasive particles. The experimental results also indicate that the choice of the PVD coating plays an important role in improving the micro-abrasive wear resistance. Apart from single-layered and duplex Cr–N coatings, all the other coating systems provided a higher micro-abrasive wear resistance than the uncoated substrate (hardened AISI H13 steel). The poor abrasive wear resistance recorded for the single-layered and duplex Cr–N coatings could be attributed to the hardness of the Cr–N being much lower than that of the SiC abrasive particles, which caused tearing of the coating with subsequent delamination. The wear pattern observed was found to change from surfaces characterised by grooves (uncoated substrate, single-layered TiN and Cr–N systems and duplex Cr–N system) to surfaces which exhibited multiply indented surfaces (single-layered and duplex (Ti,Al)N systems), indicating a transition between wear mechanisms. This transition was found to be dependent on the ratio between the hardness of the SiC abrasive particles and surface (coating) or subsurface hardness. By decreasing this ratio, the ability of the SiC abrasive particles to scratch the composite surface was reduced and the resistance to micro-scale abrasion was improved.

Micro-abrasion wear testing of PVD TiN coatings on untreated and plasma nitrided AISI H13 steel

An abrasive wear test, based on the ball-crater technique, has been used to evaluate the wear resistance of PVD TiN coatings, on untreated and plasma nitrided AISI H13 steels. Knoop microhardness measurements and scratch tests were carried out to characterise the coating systems under investigation. The TiN on plasma nitrided “duplex” coatings showed better micro-abrasive wear resistance than the single-layered TiN coatings and uncoated AISI H13 substrate. The best performance of the duplex-treated sample can be attributed to the presence of a nitrided subsurface in comparison with that of the single-layered TiN coating. The presence of a hard nitrided layer seemed to diminish the scratching action of the SiC abrasive particles. The wear patterns also indicated a transition between wear mechanisms, depending on the surface (coating) and subsurface hardness. A grooving wear mechanism was observed for a single-layered TiN coating (deposited on a hardened AISI H13 substrate) whilst a mixed mechanism involving grooving and rolling wear was found to occur in a duplex TiN coating (plasma nitrided AISI H13 substrate).

天然歯および歯冠修復材料の衝撃滑走摩耗に関する実験的研究

A number of studies have reported comparisons of wear resistance of dental materials in various ways such as toothbrushing and sliding tests. In this study, an impacting-sliding motion was applied for evaluating the relative wear resistance of dental porcelain, Au-Ag-Pd alloy, hard and soft types of Ni-Cr alloys, acrylic resin and tooth enamel. Hemispherical and flat specimens were prepared, and their surfaces were smoothly polished except for those of the porcelain which were finished by glazing. One stroke of the wear test consisted of dropping of the upper hemispherical specimen onto the lower flat specimen and successive sliding along it under a load of 500gf. Such an impacting and sliding motion was repeated 10, 000 times at a rate of 40 strokes/min. Significantly larger wear was generally observed on the lower flat specimen when the upper slider specimen was made of the same material as the lower. Although the porcelain was extremely harder than any other materials, the porcelain slider caused not so larger wear tracks on the tooth enamel and Ni-Cr alloys. The porcelain was also abraded with the metal and enamel sliders, which was probably due to the scratching action of the small porcelain fragments yielded in impacting. The enamel showed significantly larger wear with the enamel slider. It was less abraded with the porcelain and Ni-Cr alloys, and no detectable wear was found with Au-Ag-Pd alloy and acrylic resin. The finely polished harder type Ni-Cr alloy not only caused smaller wear on the other materials but also was less abraded with them. The softer type Ni-Cr alloy and Au-Ag-Pd alloy exhibited significant relative wear with each other. The acrylic resin showed severe wear with the resin while it caused no perceptive wear on any other materials and enamel. The foregoing findings indicate that the relative wear may not always be affected by the hardness but by the other physical and mechanical properties such as configuration, surface aspect, elasticity, plasticity and impact strength of the materials.

粒子分散強化型合金のＳＥＭ内微小切削 母材変形能による工具摩耗抑制機構

Microcutting of particle dispersion-hardened alloys are performed with SEM direct observation method. These alloys, hypereutectic Al-Si alloy and Al-Ni binary alloy, include second-phase hard particles in the soft matrix with comparatively rich (Al-Ni) or poor (Al-Si) ductility. Tool wear of carbide tool in the turning of Al-Ni alloy is hardly observed; this indicates that the ductility in the matrix would play an important role to reduce the severe tool wear. Summary of the results are shown below. (1) Compressive load to start the fragmentation of a simple particle in both alloys shows almost the same value. (2) The increas-ing rate of percentage of fractured particles in Al-Ni alloy by the compression test is smaller than that in Al-Si alloy. This can be attributed to the load relaxation to second-phase particles induced by the plastic flow of the matrix. (3) Fragmentation of particles and direct collision of particles with the cutting tool were observed in microcutting of these alloys by SEM direct observation method. (4) Rich ductility of the matrix in Al-Ni alloy would produce the elusion of particles in the case of direct collision of particles with the cutting edge; this indicates that the extent of damage to the cutting edge by particles should be small. (5) Poor ductility of the matrix in Al-Si alloy causes higher frequency of the mechanical scratching action by particles for tool flank.

走査電顕内その場観察法によるＡｌ‐Ｓｉ系過共晶合金の微小切削

This paper describes an experimental investigation of a micro-cutting to make clear the severe tool wear mechanism in hypereutectic Al-20%Si alloy. Tool wear of carbide tool is mainly induced by the mechanical scratching action with crushed primary Si particles. In situ observation by using SEM micro-cutting system is found to be very successful for the clarification of the interaction between crushed primary Si particles and a cutting edge of tool. Summary of the results are shown below. (1) Primary Si particles are crushed and/or fine grained in the shearing zone. A part of them are observed to collide directly with a cutting edge of tool by following the micro-cutting. This appears to be a cause of severe tool wear in turning of this alloy. (2) The direction of primary cracks in primary Si particles almost agree with those of principal stress under a compressive value by the elastic stress analysis.