Comparative analysis of the influence of nano- and microfillers of oxidized Al on the frictional-mechanical characteristics of UHMWPE

The influence of nano- and microfillers, including nanofibers and powder of Al₂O₃ and aluminum oxyhydrides AlO(OH) on the mechanical and tribological characteristics of ultrahigh-molecular-weight polyethylene (UHMWPE) is studied. It is found that modification of UHMWPE with nanofibers of Al₂O₃ within 0.1–0.5 wt % ensures a considerable increase in its hardness and multifold increase in its wear resistance. Modification with ultradisperse powders of Al₂O₃ (200–500 nm) in the same amounts has an insignificant effect on the polymer characteristics. Filling of UHMWPE with micron-sized particles (3–50 μm) in amounts of 20 wt % results in increased wear resistance of the original polymer, comparable with the wear resistance at low nanofiber content. X-ray diffraction analysis, IR spectroscopy, and electron microscopy are used to show that incorporation of Al₂O₃ nanofibers into UHMWPE results in the formation of a fundamentally different supermolecular structure in comparison with the use of microfillers.     

Influence of weave of carbon fabric on abrasive wear performance of polyetherimide composites

Three composites of Polyetherimide (PEI) reinforced with carbon fabric (CF) of three weaves viz. plain, twill and satin-4 H were developed keeping the amount of fabric constant (55% by vol.). Studies on mechanical properties confirmed that the twill weave composite (T) showed the highest strength, modulus (both tensile and flexural) and interlaminar shear strength (ILSS) followed by satin (S) and plain weave (P) composites. The performance order, however, was reverse in the case of toughness and elongation to break. Specific wear rate in a single-pass, unidirectional and un-lubricated abrasive wear mode against SiC paper showed strong influence of weave in mild wear condition (load 10 N). Composite S showed the highest wear resistance (W _R) followed by composites T and P. With increase in load, the difference in performance diminished to the extent that at 40 N, it was almost similar for all the three composites. This was correlated with the difference in the length of the fibers between crossover points which, in turn, allowed the microdisplacement of fibers in the composites during abrasion. This was supported by the SEM.

Investigation of polyelectrolyte for electrochemical detection of uric acid in presence of ascorbic acid

Uric acid (UA) was detected in the presence of ascorbic acid (AA) at GC electrode by cyclic voltametry (CV) and differential pulse voltametry (DPV) in aqueous media of cationic polyelectrolyte (poly(diallyldimethylammonium chloride) (PDDA)). Both, UA and AA are anionic nature and electro-static attraction with cationic solution. This lowered their oxidation potentials and increased anodic current. In CV studies, the UA oxidation potential was decreased by 400 mV in the presence of PDDA along with increase in peak current. Effect of PDDA and pH on E_pa and I_pa were also studied. About 360 mV difference in oxidation peak potentials was observed for AA and UA in PDDA media, which established a quick method for their simultaneous determination. The detection limit of UA in the presence of 200 folds AA was found as 1 μM with correlation coefficient of 0.994 and sensitivity of 0.05 μA μM⁻¹. The proposed method has been also applied for determining the UA in human urine without any pretreatment, and found to be satisfactory.     

Influence of content of carbon fabric on the low amplitude oscillating wear performance of polyetherimide composites

Tribo-potential of bi-directionally (BD) reinforced polymer composites is not yet adequately explored especially in low amplitude oscillating wear (LAOW)/fretting wear mode. Hence five composites of Polyetherimide (PEI) containing carbon fabric (plain weave) in the range 40–85 by vol% were developed by impregnation technique followed by compression molding. These composites along with unfilled PEI were evaluated for their LAOW performance on SRV Optimol tester under different loads using ball-on-plate configuration. The performance was compared with that of composite evaluated in earlier work but developed with different processing technique (hand lay up). With increase in load, specific wear rates of all the composites increased while friction coefficient (μ) decreased. It was concluded that carbon fabric inclusion in all amounts proved significantly beneficial for improving friction and wear performance and limiting load of PEI. Very high and very low amount of CF (85 and 40 vol%) proved least beneficial from strength and tribo-performance point of view. Composites with moderate amount of CF (65 and 55 vol%) proved most promising with almost similar potential in reducing μ and wear rate of PEI. Overall CF in the range of 55–65 vol% appeared to be the optimum range for tailoring the strength properties along with tribo-performance in fretting wear mode. The impregnation technique proved significantly better than the hand lay up technique for enhancement in strength and tribo-performance. SEM studies on worn surface proved helpful in understanding wear mechanisms.

Natural frequencies of vibration of a class of solids composed of layers of isotropic materials

In a recent paper, the Ritz method with simple algebraic polynomials as trial functions was used to obtain an eigenvalue equation for the free vibration of a class of homogeneous solids with cavities. The method presented is here extended to the study of a class of non-homogeneous solids, in which each solid is composed of a number of isotropic layers with different material properties. The Cartesian coordinate system is used to describe the geometry of the solid which is modelled by means of a segment bounded by the yz, zx and xy orthogonal coordinate planes and by two curved surfaces which are defined by fairly general polynomial expressions in the coordinates x, y and z. The surface representing the interface between two material layers in the solid is also described by a polynomial expression in the coordinates x, y and z. In order to demonstrate the accuracy of the approach, natural frequencies are given for both a two- and three-layered spherical shell and for a homogeneous hollow cylinder, as computed using the present approach, and are compared with those obtained using an exact solution. Results are then given for a number of two- and three-layered cylinders and, to demonstrate the versatility of the approach, natural frequencies are given for a five-layered cantilevered beam with a central circular hole as well as for a number of composite solids of more general shape.     

Technique of Determination of the Piezoelectric Modulus d 33 and Investigation of the Limits of its Use

The classification of the piezoelectric modulus measurement methods for different loading regimes is investigated. It is established that the quasi-static methods make it possible to determine the static piezoelectric constants with the minimum errors. An improved method of measuring the piezoelectric modulus d ₃₃ in the quasi-static regime is developed. The method ensures the minimum effect of changes in the domain orientation and transition processes. Dependences of d ₃₃ on the level of mechanical stresses _n are obtained for TsTS-19, TsTS-23, and TsTBS-3 piezoceramics and it is shown that their nature depends of the ferro-rigidity of the piezoceramics composition. Features of the dependences d ₃₃( _n ) associated with the variation of the contact area of piezoelectric elements in the process of measurements and the effect of changes in the domain orientation are revealed. It is shown that the lower boundary of the compression force amounts to 2 MPa for TsTS-19. It is also established that the optimum dimension of the piezoelectric elements in determining d ₃₃ must satisfy the condition 0:45 < < 1:75. It is calculated that the error in measurements of d ₃₃ in accordance with the method proposed is 4.5% with the confidence probability of 95%.     

A method of controllable pulse-heating for investigation of properties of short-lived liquids

A method of controlled pulse heating of low-inertia thermal probe immersed into the liquid under study with a temperatureT ₀ is described. The control system provides a “temperature plateau”-type heating mode, which consists in a rapid (t ₁∼10 μs) increase in the mass-average probe temperature to a chosen valueT _pl ≫T ₀ and maintains this value for a certain time interval (t ₂∼10³–10² μs) to within 1 K. Thermal effusivity of the substance, in relative units, is determined from the value of its internal heat flux. Sensitivity to changes in the thermal effusivity of a reference substance was 10⁻⁴. Due to the short pulse length and fine tuning of theT _pl value, the method allows one to conduct step-by-step scanning of “instantaneous” thermal properties of a substance in the region of its short-lived states.     

Experimental study of discharge coefficient of trapezoidal arced labyrinth weirs of widened middle cycle

Arced labyrinth weir is a certain type of nonlinear weirs with a very high discharge capacity. Thanks to the increased effective length and the ensuing increased discharge capacity of these weirs, they can be used in dam spillways and water regulating structures. This study focused on trapezoidal Arced labyrinth weirs (TALW) of widened middle cycle. Various experiments were performed to evaluate the effect on discharge coefficient of various geometric parameters, including the ratio of inside apex width of the end cycles to that of the middle cycle (w₂/w₁) and the ratio of the length of labyrinth weir (Apron) in flow direction to the width of the middle cycle (B/w₁). Results of this study showed that with a decrease in w₂/w₁ from 0.42 to 0.30, discharge coefficient (C_d) would increase by 13–33%.     

Choice of place of magnetic-flux registration in the magnetic core of an attachable electromagnet for inspection of articles using their coercive force

The demagnetizing current I _dc is measured in different areas of an electromagnet-article magnetic circuit at the moment of zero crossing of the magnetic flux as the gap between the electromagnet and article changes. The weaker dependence of the I _dce magnitude measured in close proximity to the article on the gap width and the possibility of using the parameter in measuring the coercive force of the article with an attachable transducer (in particular, with a Hall sensor) are demonstrated.     

Microscopic characterization of petiole anatomy of Asteraceous taxa of Western Himalaya-Pakistan

Petiole anatomy of 15 species of family Asteraceae was examined which aimed to investigate petiolar anatomical structures for species level identification. Shandon Microtome was used for petiole histological preparations. Both qualitative and quantitative features were studied under microscope which showed significant variation in petiole, collenchyma, parenchyma shape/size, vascular bundles arrangement/size, and vessel elements quantity. Artemisia japonica Thunb., Cirsium vulgare (Savi) Ten., Myriactis nepalensis Less., Seriphidium brevifolium Ling & Y.R.Ling, Taraxacum officinale (L.) Weber ex F.H.Wigg., and Xanthium strumarium L. showed winged petioles. Maximum length and width of upper and lower epidermis was found in Tagetes erecta L. which is 23.05 ± 0.89 μm, 24.9 ± 1.257 μm length and 21.75 ± 1.38067 μm, 22.75 ± 0.467 μm width, respectively. Petioles of Parthenium hysterophorus L. was longest one with 9.85 ± 10.45 μm while A. japonica Thunb. showed highest number of vessel elements. Maximum size of vascular bundles was found in T. erecta L. with 5.05 ± 14.25 μm. Artemisia annua L., C. vulgare (Savi) Ten, Cyanthillium cinereum (L.) H.Rob., Helianthus annus L., M. nepalensis Less., P. hysterophorus L., Senecio chrysanthemoides DC. have trichomes while Tussilago farfara L. has highest number of vascular bundles. All species have angular collenchyma type except M. nepalensis Less., P. hysterophorus L., S. brevifolium Ling & Y.R.Ling, Tagetes minuta L., T. officinale L., S. chrysanthemoides DC., and T. farfara L. Cluster analysis implemented that distinct plant species in cluster. Petiolar anatomical structures and taxonomic key will helpful for distinguishing Asteraceous taxa at genus and species level. This taxonomic significant investigation will also provide baseline to taxonomists for other Asteraceae studies and phylogenetic research.     

Determining electrophysical characteristics of metal-oxide-semiconductor structures from the data of voltage-capacitance analysis of the depletion region of a semiconductor surface

The oxide layer in nanotransistors with metal-oxide-semiconductor (MOS) structures may be as thin as 20Å. The physical diagnostics of such structures via conventional methods of voltage-capacitance characteristics (VFCs) is impossible without taking into account the usually disregarded effects of degeneracy and dimensional quantization of the electron gas. However, as the oxide-layer thickness decreases, these effects make an increasingly substantial contribution to capacitance C of the MOS structure not only at C?C _i (where C _i is the “oxide capacitance”) but also at C < C _i . In this study, we have developed a general method for determining the principal characteristics of MOS structures from the data of analysis of the VFCs in the region of the Schottky depletion layer. The doping level, the surface potential, the semiconductor surface charge, the voltage of “flat bands,” oxide capacitance C _i , the voltage drop across the oxide, and the sign and density of the charge fixed in it can be found at an accuracy of ?0.1% within the framework of a single experiment regardless of the oxide-layer thickness and without using fitting parameters and a priori assumptions concerning the properties of the electron gas in the accumulation and inversion layers. The stages and results of the implementation of this method are demonstrated by the results of experiments performed on an n-Si-based MOS structure with a 171.2 Å-thick oxide layer.     

Dependence of the Detectability of Flaws on the Distribution of the Magnetizing Field in the Vicinity of a Flaw

It is shown that the flaw detectability of the magnetic-powder inspection method depends on the ratio of the normal H _n and tangential H _t components of the field in the flaw's vicinity and that H _n/H _t < 3 is a condition that ensures the detectability of surface flaws.     

Effects of NOX on inhibition of oxidation by ZDTPS

Investigations of the effects of nitrogen oxides (NO_X) on liquid phase oxidation and inhibition have been conducted in order to develop an improved understanding of the processes by which NO_x accelerates oil degradation in internal combustion engines. Results from studies of the effects of NO_x on oxidation of hexadecane (HD) alone, and in combination with a radical trapping (hindered phenol) antioxidant, and preliminary studies with zinc dialkyldithiophosphates (ZDTPs) were presented in previous reports.^1-3 The complexity of reactions involving NO_x and the role in lubricant degradation of NO_x from blowby were described. Those results suggested that NO_x accelerates the rate of consumption of antioxidant additives and, thus, shortens the useful life of the oil. This work describes results of additional investigations with ZDTPs.     

Estimation of length and surface of anisotropic capillaries

Surface density (S_V) and length density (L_V) of myocardial capillaries have hitherto been estimated from their profile boundary length (B_A) and their numerical density (Q_A) on transverse sections by the simplifying assumptions of the Krogh model (perfectly anisotropic, straight, unbranched capillaries with constant cross-sectional area). As the capillaries actually are partially anisotropic, curved, branching cylinders with variable cross-sectional area, a geometrical bias arises from the model-reality discrepancies. We have applied and compared two methods to overcome these inconsistencies: (1) estimation of L_V and S_V by a more realistic model (the Dimroth-Watson distribution); (2) estimation of L_V and S_V from isotropic uniform random (IUR) sections. Twelve male Wistar rats were fixed by retrograde vascular perfusion. One pair of longitudinal and transverse sections, and six IUR sections per animal were selected at random from the left ventricular papillary muscles. Ultrathin sections were silver-impregnated and studied by light microscopic morphometry. Nearly identical estimates of L_V and S_V were found by both methods. The model-based estimation provides biologically meaningful anisotropy constants, but it presupposes knowledge of the anisotropy axis. The IUR method provides no measure of anisotropy, but it can be applied in tissues where the anisotropy axis is not known. Both methods are equally efficient and practically unbiased in S_V estimation, but the model-based estimation is far more efficient in L_V estimation.     

Suppression of flow-induced vibration of a circular cylinder by means of a flexible sheet

In this study, the suppression of flow-induced vibration of an elastically supported circular cylinder by attachment of a flexible sheet was investigated experimentally. In particular, the dependence of flow-induced vibration characteristics of the circular cylinder upon the flow velocity was investigated in detail by axially attaching the flexible poly-ethylene sheet to the cylinder surface. The characteristics of the flow-induced vibration of the cylinder were investigated by changing the attachment angle ?? and the length l of the flexible sheet (rectangular type) as experimental parameters in various combinations. The angle ?? was set at five different angles, 90°, 45°, 0°, ?45° and ?90°. The angle??s base point was the back side stagnation point of the cylinder. The length l of the flexible sheet varied from 0.5 to 3.0 times of the cylinder??s diameter at the interval of 0.5 times. The width T of the flexible sheet along the span of the cylinder also varied in 7 cases from 1.0L to 0.4L (L is the length of the cylinder) in order to discover the minimum width of the sheet necessary to effectively suppress the flow-induced vibration of the cylinder. Furthermore, the flexible sheet of the minimum width was split into 2 to 5 pieces and attached to the cylinder, and changes in the flow-induced vibration characteristics were investigated. Also, vibration characteristics were investigated for a flexible sheet in the shape of an isosceles triangle. As a result, the optimal length l and minimum width T of the flexible rectangular sheet were found to be 2??2.5D and 0.7L, respectively, to suppress the flow-induced vibration of the cylinder. Most importantly, it was found that the sheet located at the back side stagnation point can suppress the flow-induced vibration generated by any directional flow to strike the front surface of the cylinder.     

Lubrication of sliding point contacts of AISI 52100 steel — the influence of curvature

The lubrication mechanism of fully submerged sliding point contacts of non-oxidized AISI 52100 steel has been studied as a function of radius of curvature in the contact area. The results of experiments, performed with hemispherically tipped pins with radii of curvature R₁ ranging from 1 mm to 23 mm in contact with the curved surfaces of rings of 76 mm diameter, corroborate the existence of three well-defined lubrication regimes, i.e. a regime of thin oil film lubrication, a regime of boundary lubrication and a regime of virtually unlubricated contact. At small radii of curvature (i.e.R₁ = 1 mm and 5 mm), the contacts derive their load-carrying capacity almost entirely from the presence of a boundary lubricant film. At R₁ = 23 mm, lubrication is mainly due to the presence of a thin oil film.     

Influence of glass substrate thickness in laser scribing of glass

The thickness of the glass substrate used in liquid crystal displays continues to be decreased from its original thickness of 1.1 mm for the purpose reducing size and weight. The aim of this study was to clarify the influence of the glass substrate thickness during laser scribing with crack propagation caused by laser heating followed by quick quenching. The laser scribe conditions for soda-lime glass substrates with thickness equal to or less than 1.1 mm were obtained in laser irradiation experiments. Two-dimensional thermal elasticity analysis was conducted with a finite element method based on the scribable conditions obtained in the experiment. The laser scribable conditions can then be estimated by the upper limit of the maximum surface temperature, T_max, and the lower limit of the maximum tensile stress, σ_tmax, in the cooling area, regardless of the glass substrate thickness. There is a substrate thickness with which the maximum tensile stress σ_tmax becomes the largest under each scribe condition. The substrate thickness with which σ_tmax becomes the largest is obtained at a faster scribe velocity for thinner glass substrate and at slower scribe velocity for thicker glass substrate. Owing to these relations, the crack depth also has almost the same tendency as σ_tmax.     

Influence of test parameters on the measurement of the coefficient of friction of magnetic tapes

The cylinder friction and the normal stress distribution were calculated for the general case of a magnetic tape wrapped around a cylinder. The coefficient of friction was found to depend on the radius r of the cylinder and the initial tension T₀ according to the relation $\text{(}\text{r}\text{T}{}_0\text{)}{}^{\mathrm{1?n}}$ and to be independent of the wrap angle θ₀. On the basis of tests conducted on five commercial magnetic tapes and on a typical tape substrate (poly(ethylene terephthalate)), n was found to be close to 1. Hence r, T₀ and θ₀ in the ranges used in the tests reported here have no significant influence on the coefficient of friction.For the speed range from 27 to 80 mm s^?1, the sliding speed has no influence on the coefficient of friction, but temperature and humidity do have a significant influence. Therefore, temperature and humidity conditions should be selected on the basis of the application of the machine.     

Design of experiments approach to the study of tribological performance of Cu-concentrate-filled PPS composites

The tribological performance of copper-concentrate (CC) mineral deposit as the filler in polyphenylene sulfide (PPS) was studied as a function of the filler proportions and sliding test variables. CC is a complex mixture of CuS, Fe_xO_y, SiO₂, Al₂O₃, and other trace materials. The design of experiments based upon L₉ (3⁴) orthogonal arrays by Taguchi was used. Sliding tests were performed in the pin-on-disk configuration against a hardened tool steel (55-60 HRC) disk. The improvement in wear resistance of PPS was considerable with the use of fillers. The lowest steady state wear rate of 0.0030 mm³/km was obtained for PPS+20%CC+15%PTFE composition. It was two orders of magnitude lower than that of unfilled PPS. The variations in steady state coefficient of friction with the changes in filler proportions and sliding test variables were small. The transfer film was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). X-ray photoelectron microscopy (XPS) was used to detect chemical reactive species developed during sliding, especially in the interface between transfer film and its counterface. Wear particles and the polymer worn surfaces were analyzed by energy dispersive spectroscopy (EDS) for elemental distribution.     

The mechanism of ductile chip formation in cutting of brittle materials

A theoretical analysis for the mechanism of ductile chip formation in the cutting of brittle materials is presented in this paper. The coexisting crack propagation and dislocation in the chip formation zone in the cutting of ductile materials are examined based on an analysis of the geometry and forces in the cutting region, both on Taylor’s dislocation hardening theory and the strain gradient plasticity theory. It was found that the ductile chip formation was a result of large compressive stress and shear stress in the chip formation zone, which shields the growth of pre-existing flaws by suppressing the stress intensity factor K _I . Additionally, ductile chip formation in the cutting of brittle materials can result from the enhancement of material yield strength in the chip formation zone. The large compressive stress can be generated in the chip formation zone with two conditions. The first condition is associated with a small, undeformed chip thickness, while the second is related to the undeformed chip thickness being smaller than the radius of the tool cutting edge. The analysis also shows that the thrust force F _t is much larger than the cutting force F _c . This indicates that large compressive stress is generated in the chip formation zone. This also confirms that the ductile chip formation is a result of large compressive stress in the chip formation zone, which shields the growth of pre-existing flaws in the material by suppressing the stress intensity factor K _I . The enhancement of material yield strength can be provided by dislocation hardening and strain gradient at the mesoscale, such that the workpiece material can undertake the large cutting stresses in the chip formation zone without fracture. Experiments for ductile cutting of tungsten carbide are conducted. The results show that ductile chip formation can be achieved as the undeformed chip thickness is small enough, as well as the undeformed chip thickness is smaller than the tool cutting edge radius.