Nominal Pressure Research Articles

Analysis of Elastic Normal Contact of Surfaces With Regular Microgeometry Based on the Localization Principle

Formulations of periodic contact problems for an elastic half-plane and an elastic half-space interacting with a rigid body, having regular microgeometry, and a method for their approximate solution based on the localization principle are proposed. General relations, connecting contact characteristics of the interface (contact pressure distribution and dependence of the real contact area on the nominal pressure) with a single asperity shape and the distance between them, are obtained. The examples, illustrating the use of the obtained approximate relations for the contact characteristics analysis in the case of wavy and wedged profiles, as well as for a periodic system of cylindrical asperities are presented. The comparison of obtained results with the available exact solutions is carried out. It was established that the approximate dependences coincide with the exact solution up to high values of the nominal pressures. It is also shown that the ratio of the contact zone size to the distance between asperities, at which the interaction effect becomes significant, only slightly depends on asperities shape.

Time stability characterization of quadrupole mass spectrometers

• Time stability of eight QMSs was investigated over 2-years period. • Stability of sensitivity of Faraday cup detector and SEM gain for He and N 2 . • Stability of peak position and peak width of He and N 2 . • Stability of minimum detectable partial pressure for He. • Measurements were carried out according to ISO TS 20175:2018. This study focuses on the time stability of different metrological characteristics of quadrupole mass spectrometers (QMSs). Investigated parameters were the sensitivity, when using a Faraday cup as a detector, the peak position, the peak width, the gain of a secondary electron multiplier, and the minimum detectable partial pressure. Eight different commercial QMSs were investigated at seven national metrology institutes under three different nominal calibration pressures of 5 × 10 −6 Pa, 5 × 10 −5 Pa, and 5 × 10 −4 Pa for N 2 and He. The measurements were carried out using a periodicity of approximately 3 months for a total duration of 2 years. Sensitivity calibrations were conducted either through a comparison method using calibrated ionization gauges or by applying a primary vacuum calibration system. In the case of ionization gauges, they were periodically recalibrated to ensure their stability and traceability to a primary pressure standard.

Experimental and mathematical characterization of coronary polyamide-12 balloon catheter membranes.

The experimental quantification and modeling of the multiaxial mechanical response of polymer membranes of coronary balloon catheters have not yet been carried out. Due to the lack of insights, it is not shown whether isotropic material models can describe the material response of balloon catheter membranes expanded with nominal or higher, supra-nominal pressures. Therefore, for the first time, specimens of commercial polyamide-12 balloon catheters membranes were investigated during uniaxial and biaxial loading scenarios. Furthermore, the influence of kinematic effects on the material response was observed by comparing results from quasi-static and dynamic biaxial extension tests. Novel clamping techniques are described, which allow to test even tiny specimens taken from the balloon membranes. The results of this study reveal the semi-compliant, nonlinear, and viscoelastic character of polyamide-12 balloon catheter membranes. Above nominal pressure, the membranes show a pronounced anisotropic mechanical behavior with a stiffer response in the circumferential direction. The anisotropic feature intensifies with an increasing strain-rate. A modified polynomial model was applied to represent the realistic mechanical response of the balloon catheter membranes during dynamic biaxial extension tests. This study also includes a compact set of constitutive model parameters for the use of the proposed model in future finite element analyses to perform more accurate simulations of expanding balloon catheters.

Shock tube ignition delay time measurements for methyl propanoate and methyl acrylate: Influence of saturation on small methyl ester high‐temperature reactivity

AbstractWe report ignition delay time measurements for methyl propanoate (MP) and methyl acrylate (MA), carried out in a high‐pressure shock tube. Experiments were performed behind reflected shock waves across a temperature range of 989‐1 367 K, for fuel‐air mixtures at equivalence ratios of ϕ = 0.5, 1.0, and 2.0, and nominal pressures of 1 and 4 MPa. Ignition delay times were found to decrease with increasing temperature, equivalence ratio, and pressure, and are well described with correlations involving Arrhenius temperature dependence and power‐law dependence on equivalence ratio and pressure. Ignition delay times are compared with model predictions from literature kinetic models, with the models of Zhang et al (Energy & Fuels 2014; 28(11): 7194‐7202) and Bennadji et al (International Journal of Chemical Kinetics 2011; 43(4): 204‐218.) in good agreement with measured ignition delay times for MP and MA, respectively. Kinetic sensitivity analysis shows that the reactions most important for modeling ignition fall into two categories: initiation reactions (ie, decomposition and H‐atom abstraction) and C0‐C1 chemistry controlling the pool of small radicals. The unsaturated MA was observed to have lower reactivity than MP, due to its greater bond strengths for C─C and C─H bonds, resulting in slower rates for initiation reactions.

Contact stiffness of mating surfaces of parts under dynamic loading

The dependences of the relative real contact area of the flat contacting surfaces of steel parts on the nominal pressure under dynamic contact loading are studied. It is determined, that the real contact area under dynamic loading is less than under static one. Keywords dynamic plastic hardness, contact approach, real contact area, contact stiffness. matlin@vstu.ru

Regulation of the three-plunger pump operation

Analytical dependences are proposed for recalculating the operating parameters of three-plunger pumps when changing the rotation frequency of a crankshaft. Keywords three-plunger pump, plunger diameter, nominal pressure, rotation frequency, crankshaft. monolit8@yandex.ru

Dry sliding wear behavior of ultrasonic stir cast boron carbide reinforced aluminium nanocomposites

In the present work ultrasonic stir casting method is used to fabricate aluminium metal matrix nanocomposites reinforced with nano boron carbide (nB4C) particles with varying (0.5, 1, 1.5 and 2) weight percentages. Microhardness and nanoindentaion hardness of the nanocomposite is found to increase with increasing reinforcement content. Pin on disk apparatus is used to study the room temperature dry sliding wear behavior of fabricated composites and base alloy. Nominal contact pressures of 0.354–1.412 MPa and sliding speeds of 0.16–0.66 m s−1 are employed. Each test run is conducted for the fixed contact period of 15 min. Field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS) is used to observe worn surface and wear debris to understand the undergoing wear mechanisms. It is observed that base alloy underwent mild to severe plastic deformation led oxidative delamination wear. Nanocomposites are subjected to combination of oxidative, abrasive and mild delamination wear. Nanocomposites display less mass loss and wear rate as compared to base alloy due to the protective tribolayer formed in the contact interface. Part of the mechanically mixed transfer layer is found to adhere firmly to the composite surface under higher load-speed condition. Extremely hard nB4C particle reinforcement is found beneficial for improving the wear resistance of aluminium alloy at varying combinations of load and speed.

Physiological Motion Artifacts in Capacitive ECG: Ballistocardiographic Impedance Distortions

Capacitive electrocardiogram (cECG), a tried and tested technique for more than 50 years, can replace the gold standard electrocardiogram (ECG) only in certain applications, where unobtrusiveness is aimed at the expense of reduced signal quality. This inferiority is due, among other reasons, to the fragility of the capacitive coupling between the body and the electrode, observed as motion artifacts in the presence of time-variant coupling capacitance. Attempts were made to remove these artifacts in earlier studies using adaptive noise cancellation by assuming statistical independence between motion and ECG signals. This article considers the mechanical vibrations of the human body itself as the source of time-variant coupling capacitances, which can cause motion artifacts. Ballistocardiography (BCG) measurements on cECG electrodes were recorded and analyzed to investigate how these mechanical vibrations influence the coupling impedance of the clothing between the body and the electrode. A novel sensor has been proposed and tested in a test bench for four different nominal pressure values (15, 20, 25, and 30 mmHg) with minute-increasing steps for the measurement of the coupling capacitance. Subsequently, simultaneous measurements of BCG and the coupling capacitance were conducted on three healthy subjects for two different electrode positions. A significant correlation between the coupling capacitance and measured ballistocardiograms was found both in time-domain shapes and time–frequency distributions in all measurements.

Catalytic hydrogenation of levulinic acid in ionic liquid mixtures using hydrogen gas in high-pressure CO2

Hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) in ionic liquid (IL) mixtures with hydrogen gas in high-pressure CO2 was studied to demonstrate tuning of product selectivity. Ethyl- or butyl- imidazolium-based cation with Cl, acetate [OAc], diethylphosphate, bis(trifluoro-methanesulfonyl)imide or tetrafluoroborate anion IL mixtures were used as the reaction phase with Pd/C, Pd/Al2O3 or Ru/Al2O3 commercial catalysts. Experiments were performed with batch reactors using (1 to 5) MPa partial pressure H2 at nominal pressures of 8 MPa at 110 °C. GVL selectivities as high as 88% at 50% conversion were obtained in [EMIM]Cl-[EMIM][OAc] using 3 MPa partial pressure H2 in presence of CO2 at 4 h reaction time. Specific interactions of LA with Cl anion IL and CO2 with [OAc] anion IL are key to the reaction mechanism. Reaction systems containing Cl anion - [OAc] anion IL mixtures with H2 gas and CO2 have wide application to hydrogenation of biomass-related compounds.

Secondary Reactions and the Heat of Pyrolysis of Wood

Since its first estimation in 1909, the heat of pyrolysis of biomass has been found to range from endothermic to exothermic, with the latter attributed to secondary reactions that condense secondary char. Herein, the heats of primary and secondary reaction for pine are isolated using a new method to account for the radiative heat loss discrepancy between the heating cycles of wood and char in open crucibles. The overall heat of pyrolysis is then explored as a function of the tortuous path length as volatiles escape from wood particles and the generated internal pressure which together drive the extent of the secondary reactions. Furthermore, two generalized schemes for these secondary reactions are explored, where heterogeneous and homogeneous secondary reactions either compete for the primary reactive volatiles, or apply only to dedicated fractions of them. Of the schemes, the one with dedicated fractions undergoing heterogeneous and homogeneous reactions best explains the results presented here. This work is useful to designers of biomass pyrolysis reactors, where the extent of reaction and thus the overall heat of pyrolysis can be estimated as a function of the nominal particle size and system pressure.

STUDY OF TORQUE NONUNIFORMITY IN DOUBLE-ACTION HYDRAULIC ROTARY VANE MO-TORS

Abstract. Aim. Hydraulic rotary vane motors rely on the principle of torque maintained at a nominal pressure. In this case, the most important parameter of the torque is its nonuniformity. The problem of determining nonuniform torque in hydraulic motors having ten and twelve vanes is investigated with the aim of ensuring the maximum stability of this parameter.Method. Braking torque occurs on the vanes of hydraulic rotary vane motors due to the pressure of the working fluid on the stator; the theoretical expression for torque does not take the braking effect of the vanes into account. Therefore, an expression is compiled for the braking torque of the vanes with a type of stator curve that provides constant acceleration of the vane relative to the rotor.Results. Plots of changes in braking torques were constructed for 10- and 12-vane motors. Ratios of the minimum and maximum braking torques equal to 0.33 and 0.5 for motors with ten and twelve vanes, respectively, were obtained.Conclusion. The torque nonuniformity coefficients for hydraulic motors for the given parameters of d =11,6% and d = 8,8% for motors having ten and twelve vanes, respectively, were obtained. The results of the analysis of the obtained parameters indicate a slight increase in the nonuniformity of torque in a ten-vane motor. In this case, a decrease in the number of vanes leads to an increase in the mechanical efficiency of the hydraulic machine.

Characterization of particulate matter emissions in urban train braking - An investigation of braking conditions influence on a reduced-scale device.

The particulate matter emissions related to the braking of railway rolling stock are investigated using a reduced scale braking device. Samples of organic materials and cast iron discs are tested for different nominal contact pressures and disc surface temperatures, representative of real conditions. The aim of this work is to investigate the influence of braking conditions on the global amount of particles emitted, their distribution in number and size, and their morphological and chemical characteristics. To be representative, the tested conditions are designed to dissipate the same amount of energy for all the braking events by adjusting the pad application duration. The results show that for the same dissipated energy, a temperature increase above a transition value in the range of 230-280 ∘C depending on the braking conditions modifies the size and number distributions of the generated particles. The results obtained are of interest to better represent their propagation through CFD modelling according to the characteristic of the particle emission.

PEEK Composites as Self-Lubricating Bush Materials for Articulating Revolute Pin Joints.

In this study, bearing bushes made of polyetheretherketone (PEEK), 30 wt % carbon fibre reinforced PEEK, 30 wt % glass fibre reinforced PEEK, each 10 wt % of PTFE, graphite and carbon fibre modified PEEK were investigated on a purpose built pin joint test rig. The unlubricated friction and wear behaviour was assessed in sliding contact with a 300M shaft, subjected to a nominal pressure of 93 MPa, articulating sliding speed of 45 °/s. The worn surface and the subsurface layer were studied using optical profilometry and scanning electron microscopy (SEM). Due to thermal sensitivity of PEEK composites, friction energy and temperature rise were analysed for determining the friction and wear mechanism. The bush made of PTFE, graphite and carbon fibre (each 10 wt %) modified PEEK presented the best performance for friction coefficient, wear loss, friction energy and temperature rise. Current work demonstrated that reinforcement modified PEEK composite possesses desirable properties to perform as a load bearing bush in certain tribological applications.

Pressure distribution data from large double-pendulum ice impact tests

Data from ice impact tests using a large double-pendulum apparatus have been analyzed and high spatial resolution pressure-pattern images, recorded at rates of 500 images per second, are presented. The freshwater ice samples were grown in the lab and were cone-shaped with a base diameter of 1 m and base angle of 30o. Energy of the impacts was controlled by varying the ‘drop angle’ of the pendulum arms. Patterns of high-pressure zones (HPZ's, consisting of relatively intact ice) that were surrounded by low-pressure zones (LPZ's, i.e. shattered spall debris), due to spallation of ice from the HPZ's, were evident. Most of the tests showed consistent results, where the instantaneous average interface pressure of the contact area was relatively consistent (5–8.5 MPa), and found to be constant or slightly increasing with contact area as tests progressed. Maximum pressures (i.e. associated with HPZ's) were in the 35–52 MPa range and generally increased with contact area as tests progressed. Peak loads during tests were in the 410–630 kN range. LPZ contact areas were generally 2–6 times the size of the HPZ contact areas. In most tests the time-averaged total load was shared roughly equally between HPZ and LPZ contact areas. The peak loads were found to be directly proportional to the maximum HPZ contact areas. The detailed characteristics of the total load time series records were generally reflected in the corresponding HPZ load time series records much more so than in the LPZ load time series records. Average pressures on the HPZ's and LPZ's were remarkably consistent, 21 MPa and 3.7 MPa respectively. For all tests the actual average pressure was roughly constant, or slightly increasing, while the nominal pressure followed a decreasing trend.

Friction-induced subsurface densification of glass at contact stress far below indentation damage threshold

It is well known that the densification of oxide glass can occur at high contact pressure (typically >5 GPa) under normal indentation conditions. This study reports that when frictional shear is involved, the subsurface densification of glass can occur under low load conditions that would involve completely elastic deformation if the load is applied along the surface normal direction without any interfacial shear. This phenomenon was observed for a borosilicate glass rubbed with a smooth stainless-steel ball in liquid water at a nominal Hertzian contact pressure of ≤0.5 GPa. Under these frictional conditions, subsurface cracking is completely suppressed, and surface wear occurs through mechanochemical reactions. Since the mechanochemical wear track was sufficiently smooth, it was possible to employ a sub-glass transition temperature (sub-Tg) annealing method to measure the volume recovery of the densified subsurface region. The friction-induced subsurface densification of the wear track was also confirmed through nanoindentation measurements and dissolution tests in pH 13 aqueous solutions. Molecular dynamics (MD) simulations with a ReaxFF reactive force also suggested that the subsurface structural change can occur readily when friction is involved at low contact pressure conditions.

Study on jute twine/polypropylene pre-preg tapes: The effects of surface modification and impregnation

Preparation of natural fiber-reinforced thermoplastic prepreg tapes is impeded by two major challenges: 1) incompatibility between natural fibers and thermoplastic; and 2) difficulty impregnating thermoplastic into fibers, due to thermoplastics’ high viscidity. In this study, we investigated the reaction mechanisms associated with jute twines that were treated with alkali and laccase, to improve the compatibility of jute twine/ polypropylene (PP) tape. Simultaneously, PP with three melt flow indices (MFI, 10.9 g/10 min, 27.8 g/10 min, 50.0 g/10 min) was tested to determine optimal conditions for PP impregnation. The results showed that alkali and laccase treatment can effectively improve the interfacial bonding strength between jute twine and PP; although laccase treatment is milder than alkali treatment, and thus enabled more improvement in the prepreg tapes’ tensile and dynamic mechanical properties. The amount of PP impregnated into the jute twine increased as a function of increasing MFI. However, the impregnation effect must be balanced with the PP’s tensile strength. In summary, the prepreg tapes prepared by laccase-treated jute twine and PP with an MFI of 27.8 g/10 min exhibited the best tensile performance. Based on subsequent calculations, the nominal pressure of a pipe wound with laccase-modified jute twine prepreg tapes, can reach 2.88 MPa.

Substantiation of connection of diagnostic indicators with parameters of technical condition of hydraulic manipulators

At the organization of proactive system of maintenance of mechanisms the technique based on determination of relative probability is applied. But in contrast to the technique, when the machine is for maintenance and adjusted the type and frequency of the hydraulic manipulators (HM) it is necessary to carry out constant monitoring of the technical condition of the main elements of the mechanism. The main elements of the HM, which primarily determine its technical condition, are the distribution system, including the pump, oil pressure distributors in the executive bodies of the HM, as well as the column, the extension-grip joint and the rotator. Nominal and permissible pressure values in the distribution system are determined by the technical documentation on the HM. The paper considers the dependence of the vibration signal on the technical condition of the coupling shaft-gear column HM.

3-Dimensional printing to predict paravalvular regurgitation after transcatheter aortic valve replacement.

There is no effective method to predict paravalvular regurgitation prior to transcatheter aortic valve replacement (TAVR). We retrospectively analyzed pre-TAVR computed tomography (CT) scans of 20 patients who underwent TAVR for severe, calcific aortic stenosis and subsequently printed 3-dimensional (3D) aortic root models of each patient. Models were printed using Ninjaflex thermoplastic polyurethane (TPU) (Ninjatek Manheim, PA) and TPU 95A (Ultimaker, Netherlands) on Ultimaker 3 Extended 3D printer (Ultimaker, Netherlands). The models were implanted at nominal pressure with same sized Sapien balloon-expandable frames (Edwards Lifesciences, CA) as received in-vivo. Ex-vivo implanted TAVR models (eTAVR) were scanned using Siemens SOMATOM flash dual source CT (Siemens, Malvern, PA) and then analyzed with Mimics software (Materialize NV, Leuven, Belgium) to evaluate relative stent appositions. eTAVR were then compared to post-TAVR echocardiograms for each patient to assess for correlations of identified and predicted paravalvular leak (PVL) locations. A total of 20 patients (70% male) were included in this study. The median age was 77.5 (74-83.5) years. Ten patients were characterized to elicit mild (9/10) or moderate (1/10) PVL, and 10 patients presented no PVL. In patients with echocardiographic PVL, eTAVR 3D model analyses correctly identified the site of PVL in 8/10 cases. In patients without echocardiographic PVL, eTAVR 3D model analyses correctly predicted the lack of PVL in 9/10 cases. 3D printing may help predict the potential locations of associated PVL post-TAVR, which may have implications for optimizing valve selection and sizing.

A comparison of nanoscale measurements with the theoretical models of real and nominal contact areas

In this study, an experimental method is proposed to measure the real area of contact between an alumina sphere and an Al surface based on the adhesive transfer of the Au film and the scanning electron microscope in the back-scattered mode. A thin film of Au is sputtered on the alumina sphere before the indentation with the Al surface. After indentation, the interfaces of the alumina sphere and Al surface are observed by the scanning electron microscope. The contact area can be identified based on both the distributions of the alumina and Au on the alumina sphere and Al surface, respectively. The measured contact area at different nominal pressures are compared to predictions made by several popular theoretical elastic-plastic rough surface contact models.

Управление параметрами газовых горелок отражательных печей горения при плавлении никельсодержащего сырья

The purpose of the reserch is to develop and justify the principles of the energy model of an industrial reverberatory furnace taking into account chemical composition and properties of natural gas, which is widely used as a fuel in metallurgical processes to ensure the efficient operation of open gas furnaces in the production of crude Nickel. Сombustion of natural gas in the burners of the gas brands GGSB-1.4 and GGSB-2,2 (of medium pressure with the heat capacity of 1.4 MW, gas flow rate of 140 m 3 /h and connecting gas pressure before the burner of not more than 40 kPa, nominal gas pressure before the burner of not more than 20 kPa) always results in the production of carbon dioxide and soot, which have an adverse effect on the process flow. High content of hydrogen and carbon in the gas changes the thermal balance of the process of crude Nickel smelting. To study the combustion process of natural gas of different composition taking place in the burners of medium pressure the computer program STANJAN is used with the application of the wet gas-based flowmeter OPTISONIC 7300 for pressure measurement. The flowmeter confirmed the stable operation of the device when the liquid content in the gas is up to 1% of the gas volume. The amount of waste flue gases is measured using MRU Delta 65-3 gas analyzers, which identify the total amount of gases (O 2 , CO, NO), temperature, pressure (vacuum), as well as calculate the content of CO 2 and plant efficiency. The value of the maximum temperature of combustion products and their ratio to the excess values in the balance during the entire heating of the air is obtained. The dependencies for industrial burner automation process optimization while minimizing energy losses and emission of harmful substances are determined. Conducted research allows to reveal the negative effect of excess air on the maximum temperature of melting products and the positive effect of air preheating at this temperature. When the air with the temperature of 50°C (instead of 25°C) arrives to the burner the temperature of flame rises, which increases the heat added to the load and reduces the energy consumption of the process. Excess air and product temperature in a thermal process based on natural gas combustion are the primary factors in the determination of environmental and energy aspects of the process.