bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of planar continuous current sources with arbitrary shapes for generation of desired radiation patterns by methods of moments and least squares
Authors: Parsa Ali , Oraizi Homayoon
Published: January 2020

Synthesis of planar continuous current sources (planar CCSs) with arbitrary shapes is developed for the generation of specified radiation patterns by method of moments (MoM) and method of least squares (MLS). First, an integral equation is expressed, which relates planar CCS current distribution to its radiation pattern. Second, the planar CCS region is divided into several segments and its current distribution is expressed in terms of the pulse expansion functions to discretise the integral equation. Third, the resulting discretised integral equation is converted to a linear equations system by MoM and MLS. Fourth, the resulting linear equations system is solved to determine unknown coefficients of planar CCS current distribution. To evaluate and compare the efficacy of proposed methods, two parameters of synthesis error (SE) and superdirectivity ratio (SR) are used. It is shown that the number of segments should be properly determined to achieve specified SE and SR. If resulting radiation pattern does not meet design goal, a perturbation procedure is applied to current distribution in order to improve the characteristics of radiation patterns of the planar CCS, such as side‐lobe level and pattern ripple. Several examples are given to validate the efficacy of the proposed methods.
Low‐profile microstrip patch antenna with simultaneous enhanced bandwidth, beamwidth, and cross‐polarisation under dual resonance
Authors: Liu Neng‐Wu , Gao Sen , Zhu Lei , Ji Lu‐Yang , Yang Lin , Zheng Hui‐Li
Published: January 2020

A low‐profile microstrip patch antenna (MPA) with wide bandwidth, wide beamwidth, and reduced cross‐polarisation is proposed here. Firstly, the far‐zone radiated fields of the MPA are deeply studied to improve its radiation performance. It demonstrates that the E‐plane half‐power beamwidth (HPBW) of the antenna could be progressively widened by using a single equivalent slot instead of two equivalent slots. Meanwhile, its high cross‐polarisation of the H‐plane radiation patterns could be successfully decreased down by enlarging the width of the rectangular patch and loading the shorting pins. Secondly, the input impedance of the MPA operating in the fundamental mode is extensively investigated. The results illustrate that the resonant frequencies of its dual modes could be reallocated in proximity to each other for bandwidth enhancement by properly selecting the dimension of radiating patches. Finally, the proposed antenna is fabricated and tested. Experimental results show that the antenna has gained an improved bandwidth (|S11|<–10 dB) of about 12% ranging from 2.70 to 3.03 GHz, while keeping a thin thickness of about 0.029 free‐space wavelength. Besides, its H‐plane cross‐polarisation is kept below −20 dB. Most importantly, the E‐plane HPBW of the antenna is extended to around 140° over the wide band.
Hybrid resampling scheme for particle filter‐based inversion
Authors: Zafar Taimoor , Mairaj Tariq , Alam Anzar , Rasheed Haroon
Published: January 2020

A novel online hybrid resampling (HR) scheme based on the combination of residual and multinomial resampling schemes is proposed. It can be implemented within the framework of the sequential Monte Carlo‐based inversion algorithm, also known as particle filter (PF). Based upon the degeneracy of each particle, the choice of best resampling scheme among both candidates is made at each instant iteratively. Consequently, the inversion performance of PF improves by reducing the computational complexity of the resampling scheme. The proposed online HR scheme is incorporated here within the framework of the PF‐based inversion scheme once applied on nuclear power plant steam generator non‐destructive testing measurement data. The promising results showcase the efficacy of the technique.
Effects of cost optimised grid configuration on earthing system performance: a comparative assessment
Authors: Sengar Kaushal Pratap , Chandrasekaran Kandasamy
Published: January 2020

This study presents the comparative analysis of earthing grid configurations to determine the optimum design in terms of safety parameters and cost for 66/11 kV substation. For different grid configurations, a fixed earthing area of 9000 m2 was considered. Rectangular, triangular, L‐shaped and T‐shaped grids buried in two‐layer soil model were considered for this study. Three methods, i.e. ANSI/IEEE standard 80‐2000, finite element method and genetic algorithm, were used to design the grids. All safety constraints as mentioned in the IEEE standard were followed for designing the earthing grid. A new mathematical cost function (CF) was proposed for designing an effective and economic L‐shaped, T‐shaped and triangular earthing systems. The CFs used in this study include grid depth, dimensions of earthing rod and horizontal conductor, number of rods and conductors, revetment and excavation area. The economic earthing grid obtained through the proposed method reduces the total cost related to grid materials, installation and excavation. Analysis also showed that the rectangular grid showed preferred results in terms of safety parameters while the triangular grid showed optimum cost design for the earthing system under study. Good agreements were found with the rectangular earthing grid in comparison with triangular, T‐shape and L‐shape configurations.
Design of a flat‐type magnetic position sensor using a finite‐difference method
Authors: Mirzaei Mehran , Machac Jan , Ripka Pavel , Chirtsov Andrey , Vyhnanek Jan , Grim Vaclav
Published: January 2020

This study presents an analysis and the design of a new flat‐type position sensor with an external armature. One excitation coil and two antiserially connected pickup coils are used in the stationary part. Solid iron segments or steel lamination segments are used for the moving armature. The proposed position sensor was modelled using linear movement. A two‐dimensional finite‐difference method was developed and was used for fast analysis for optimising the sensor. The induced eddy currents in the solid armature were taken into account in the finite‐difference analysis. The finite‐difference calculations were compared with 2D and 3D finite‐element method simulations and with experimental results. The sensor has a total error of 0.23 mm root‐mean‐square for 36 mm range without any compensation. Unlike previous designs, the authors’ new sensor has no moving coil.
Sensitivity analysis of inverse problems in EM non‐destructive testing
Authors: Bilicz Sándor
Published: January 2020

The inverse problem of electromagnetic (EM) non‐destructive testing (NdT) consists of reconstructing material defect parameters invoking EM field measurements. Uncertainties of the configuration (e.g. imprecise constitutive and geometrical parameters) are inevitably present; hence, the reconstructed defect parameters are also uncertain. In this study, the different sources of uncertainty are ranked by means of sensitivity analysis. The model‐based inversion (involving EM simulation) is computationally demanding; moreover, sensitivity analysis usually requires a vast number of repeated runs of the inversion. To overcome the computational complexity, surrogate models are applied at different levels. Interpolation on a sparse grid is used as a surrogate model of the EM simulation. The sensitivity of the reconstructed defect parameters concerning configuration uncertainties is characterised by means of Sobol indices. The Sobol indices are obtained from a polynomial chaos expansion surrogate model of the entire inversion scheme. A numerical example drawn from eddy‐current NdT is thoroughly analysed to illustrate the proposed methodology and to demonstrate its performance.
HCN-to-HNC intensity ratio: a new chemical thermometer for the molecular ISM
Authors: Hacar A. , Bosman A. D. , van Dishoeck E. F.
Published: January 2020

Context. The gas kinetic temperature (TK) determines the physical and chemical evolution of the interstellar medium (ISM). However, obtaining reliable TK estimates usually requires expensive observations including the combination of multi-line analysis and dedicated radiative transfer calculations.

Aims. This work explores the use of HCN and HNC observations, and particularly the I(HCN)-to-I(HNC) intensity ratio (I(HCN)/I(HNC)) of their J = 1–0 lines, as direct probe of the gas kinetic temperature in the molecular ISM.

Methods. We obtained a new set of large-scale observations of the HCN and HNC (1–0) lines throughout the Integral Shape Filament (ISF) in Orion. In combination with ancillary gas and dust temperature measurements, we find a systematic temperature dependence of the observed I(HCN)-to-I(HNC) intensity ratio throughout our maps. Additional comparisons with chemical models demonstrate that these observed I(HCN)/I(HNC) variations are driven by the effective destruction and isomerization mechanisms of HNC under low-energy barriers.

Results. The observed variations of I(HCN)/I(HNC) with TK can be described with a two-part linear function. This empirical calibration is then used to create a temperature map of the entire ISF. Comparisons with similar dust temperature measurements in this cloud, as well as in other regions and galactic surveys, validate this simple technique for obtaining direct estimates of the gas kinetic temperature in a wide range of physical conditions and scales with an optimal working range between 15 K ≲ TK ≤ 40 K.

Conclusions. Both observations and models demonstrate the strong sensitivity of the I(HCN)/I(HNC) ratio to the gas kinetic temperature. Since these lines are easily obtained in observations of local and extragalactic sources, our results highlight the potential use of this observable as new chemical thermometer for the ISM.
Organic-Photoacid-Catalyzed Glycosylation
Authors: Wang Ting , Li Juncheng , Zhao Gaoyuan
Published: January 2020

Photoacids are molecules that become more acidic upon absorption of light. They are widely utilized in a variety of fields, such as organic synthesis, molecular switching agents, and photodynamic therapy. Currently, the activity of most photoacids is induced by UV light, which limits their applications by the synthetic community. In this ­Synpacts article, we highlight our recent development of visible-light-­induced photoacids and their application in glycosylation reactions.

1 Introduction

2 Visible-Light-Induced Photoacids

3 Synthesis of 2-Deoxyglycosides by Visible-Light-Induced Photoacid Catalysis

4 Conclusion
Metabolic dysregulation in theAtp7b−/−Wilson’s disease mouse model
Authors: Wooton-Kee Clavia Ruth , Robertson Matthew , Zhou Ying , Dong Bingning , Sun Zhen , Kim Kang Ho , Liu Hailan , Xu Yong , Putluri Nagireddy , Saha Pradip , Coarfa Cristian , Moore David D. , Nuotio-Antar Alli M.
Published: January 2020

Inactivating mutations in the copper transporterAtp7bresult in Wilson’s disease. TheAtp7b−/−mouse develops hallmarks of Wilson’s disease. The activity of several nuclear receptors decreased inAtp7b−/−mice, and nuclear receptors are critical for maintaining metabolic homeostasis. Therefore, we anticipated thatAtp7b−/−mice would exhibit altered progression of diet-induced obesity, fatty liver, and insulin resistance. Following 10 wk on a chow or Western-type diet (40% kcal fat), parameters of glucose and lipid homeostasis were measured. Hepatic metabolites were measured by liquid chromatography–mass spectrometry and correlated with transcriptomic data.Atp7b−/−mice fed a chow diet presented with blunted body-weight gain over time, had lower fat mass, and were more glucose tolerant than wild type (WT) littermate controls. On the Western diet,Atp7b−/−mice exhibited reduced body weight, adiposity, and hepatic steatosis compared with WT controls.Atp7b−/−mice fed either diet were more insulin sensitive than WT controls; however, fastedAtp7b−/−mice exhibited hypoglycemia after administration of insulin due to an impaired glucose counterregulatory response, as evidenced by reduced hepatic glucose production. Coupling gene expression with metabolomic analyses, we observed striking changes in hepatic metabolic profiles inAtp7b−/−mice, including increases in glycolytic intermediates and components of the tricarboxylic acid cycle. In addition, the active phosphorylated form of AMP kinase was significantly increased inAtp7b−/−mice relative to WT controls. Alterations in hepatic metabolic profiles and nuclear receptor signaling were associated with improved glucose tolerance and insulin sensitivity as well as with impaired fasting glucose production inAtp7b−/−mice.
β-lactolin, a whey-derived glycine―threonine―tryptophan―tyrosine lactotetrapeptide, improves prefrontal cortex-associated reversal learning in mice
Authors: Ayabe Tatsuhiro , Ohya Rena , Ano Yasuhisa
Published: January 2020

Dementia and cognitive decline have become worldwide public health problems. We have previously reported that a whey-derived glycine―threonine―tryptophan―tyrosine peptide, β-lactolin, improves hippocampus-dependent memory functions in mice. The supplementation with a whey digest rich in β-lactolin improves memory retrieval and executive function in a clinical trial, but the effect of β-lactolin on prefrontal cortex (PFC)-associated cognitive function was unclear. Here we examined the effect of β-lactolin and the whey digest on PFC-associated visual discrimination (VD) and reversal discrimination (RD) learning, using a rodent touch panel-based operant system. β-Lactolin and the whey digest significantly improved the RD learning, and the whey digest enhanced the response latency during the VD task, indicating that β-lactolin and the whey digest improve PFC-associated cognitive functions. Given the translational advantages of the touch panel operant system, consumption of β-lactolin in daily life could be beneficial for improving human PFC-associated cognitive function, helping to prevent dementia.
Molecular identification of white root fungal pathogens and in vitro effect of nanopesticide
Authors: Noveriza R , Rahajoeningsih S , Harni R , Miftakhurohmah
Published: January 2020

White root is an important disease in plantation crops such as rubber, cashew, clove, coffee, and nutmeg. This study aims to molecularly identify white root fungi isolated from white root disease of rubber and nutmeg plants and in vitro effect of nano formulated citronella and clove oils to the fungi. Few fungi isolated from the rubber and nutmeg plants were identified using 4 pairs of universal primers. Effect of nano-pesticide citronella and clove oils was evaluated in invitro against mycelial growth of white root fungi isolates (K1 and P1). The result showed that DNA of the fungi was successfully extracted from fungi isolated from nutmeg and rubber plants using 4 pairs of universal primers. K1 and P1 isolates were identic to Marasmius palmivora (99.1%) and K2 was closed to Rigidoporus microsporus (97.5%), while KP isolates could not be identified because the DNA was contaminated with Trichoderma harzianum. Nanoformulation of citronella and clove oils at 0.5% concentration inhibited mycelial growth of M. palmivorus isolated from rubber and nutmeg plants. The study implies that nano formulation of clove and citronella oils are potential to be tested at green house scale and then in the field for controlling the white root fungal pathogen.
Sustainability design for development of Gayo’s Science Park’s
Authors: Jaya R , Ferizal M , Ardiansyah R , Husaini  , Mirza I , Ishar  , Asis  , Ismail M , Rahmah F F F , Yusriana
Published: January 2020

Development of the Gayo’s Science Park’s (GSPs) aims to improve the regional economy based on commodity Gayo coffee. Sustainability aspect assessed including technique, economic, social as well as ecology. The objective of this paper was to design the sustainability development of the (GSPs). In this paper we only limits on qualitative judgment of the GSPs development design. In technical aspect discusses how to increase productivity Gayo coffee which currently ranges 650-700 kg ha−1, even though the potential productivity reaches 1.2-1.5 ton ha−1. For the economic aspect focuses on how the GSPs continuing coffee-based production down-stream. In this design also discussed the ecological, technical and social aspects such as increasing productivity, use of organic matter on agriculture as well in plants cultivation conservation zone. To sustain the GSPs, we design a business that will be developed, namely through construct the small-plants (5 kg per running production) and Gayo coffee superior seeds supplier. Therefore, we use several techniques to construct its planning, such as business plan canvas and qualitative SWOT analysis, as well as introducing the innovative technology and site-plan.
Abrasive flow modelling through active parts water jet machine using CFD simulation
Authors: Pătîrnac I , Ripeanu R G , Laudacescu E
Published: January 2020

This study has the main objective the flow modelling using CFD through active parts waterjet cutting machine, model YCWJ-380-1520. More precisely, the study of flow through the cutting head and estimate the erosion wear caused by abrasion of these parts. The active parts of cutting head are the body of head, high pressure nozzle with jewel and mixing tube made from wolfram carbide. On all these components has previously done measurement in order to create the geometrical model. The most wearing subjected parts water-jet machine are the water nozzle and mixing tube where the erosion wear is accelerated by the high velocity. In the first part of this study is presented the water flow model without regarding the abrasive inlet geometry, using Ansys FLOTRAN CFD. Has been considered three dimensions of water nozzle along with three dimensions of mixing tube in order to evaluate velocity variation at mixing tube outlet and how geometry influences outlet velocity. The second part of this paper is made using CFD software Ansys Fluent regarding a tridimensional geometry and a multiphasic flow. In the framework of flow model is established the abrasive particles velocity, difference of pressure inside tube, contour of streamlines, shear stress on the tube wall in order to accomplish the erosion rate during the process flow. It can be noticed that there are two main streamlines: first at the outlet of water nozzle and second from the inlet of abrasive material. Particles velocity is higher at the contact with water stream and lower at the end of cutting head because the difference of diameters between jewel and mixing tube. The maximum erosion rate is recorded where the shear stress are high values, that means to the interior wall of water nozzle and inlet of mixing tube. Pressure becomes high to the jewel of water nozzle and decreases in value toward at outlet of cutting head.
Research on mechanical and geometrical characteristics of materials used for flexible tubing production
Authors: Hagianu A , Nae I , Ionescu G C , Ripeanu R G
Published: January 2020

Coiled tubing used in operational exploitation of oil and gas wells are made of special steels which have to resists to some special requirements such as: tensile strength, internal pressure resistance, collapsing resistance, fatigue strength, corrosion resistance and action of weakening factors. It is interesting that various producers are using different compositions of their steels obtaining quite different mechanical characteristics of the flexible tubing delivered on the market. This paper is presenting the experimental programme for mechanical tests conducted on materials used for production of flexible tubing and the results obtained during these tests. In addition to the materials testing there were studied geometrical characteristics of the flexible tubing such as wall thickness, ovality, cilindricity and their impact on operational life of the flexible tubing.
Experimental Determination of the Loading Capacity of the Elastic Bracelet Assembly
Authors: Geonea I , Dumitru N , Copilusi C , Margine A
Published: January 2020

In this paper we aim to experimentally determine the bearing capacity (the momentum) of the elastic bracelet assemblies. The moment of torsion transmitted by the assembly depends on the clamping force of the assembly and on the friction coefficient between the bushing mounted on the shaft and the hub of the assembly. An experimental stand is used which comprises a hub shaft assembly with a segmented elastic bracelet. The load bearing capacity of the elastic bracelet is determined depending on the strength of the screws. Experimental determination is made on three types of materials. For this purpose, on the shaft is assembled a bush made of different materials: aluminum, bronze, steel. In order to determine the capable assembly moment, strain gauge transducers are used to measure the elastic strains. The recording of the deformations is done by means of an efficient data acquisition system. The assembly characteristic is plotted, namely the dependence between the torque transmitted according to the tightening of the bolts, for three couples of materials.
Power loss in grease lubricated ball bearings
Authors: Ianuş G , Cojocaru D , Oprişan M C , Paleu V , Olaru D N
Published: January 2020

The authors theoretically investigated and then validated the power loss generated both by sliding and rolling in a modified thrust ball bearing with 3 balls operating at low axial load and grease lubrication. Based on ball forces and moment equilibrium, it has been determined the tangential forces on contact ellipses. The hydrodynamic rolling friction forces have been determined by using Biboulet & Houpert’s methodology considering base oil viscosity of the grease. Total power loss has been obtained as a sum of two components: power loss generated by sliding and power loss generated by rolling. Also, total friction torque has been theoretically determined and, as an alternative method, the total power loss has been calculated as a product between total friction torque and angular speed. Finally, based on previously experimental results, the power loss has been validated as the product between experimentally total friction torque and angular speed. A good correlation between the power losses determined by all three methods for 100, 200, 300 and 400 rpm have been obtained.
Abrasive and Erosion Wear of Composite NiCrSiB Coatings Inflicted with Subsonic Flammable Structure through a Cold Process
Authors: Kandeva M , Penyashki T , Kostadinov G , Kalichin Zh
Published: January 2020

Ni-Cr-B-Si alloys are commonly used in the thermal spraying of steels. Despite their widespread use, their role in protecting metal surfaces from wear is not yet fully clarified. In order to obtain data and understanding of the wear and wear resistance of these coatings, the present work is studied the characteristics of the abrasive and erosive wear of new Ni-Cr-B-Si composite coatings applied by means of a sonic flame jet when heating the substrate to 180 °C (cold process). The powdered compositions used contain particles with an average size of 40 µm and a different percentage of the chemical elements. The abrasion wear is investigated using the thumb-disc pattern for dry surface friction with rigidly attached abrasive particles. Erosion wear is investigated by the interaction of air-jet coatings carrying abrasion particles. All samples in abrasion and erosion are tested under the same contact conditions. The mechanism, speed, and intensity of wear, and wear resistance of coatings at different normal load and slip speeds were obtained.
Tribological behaviour of sealing materials
Authors: Birleanu C , Pustan M , Cosma C , Merie V , Dranda O
Published: January 2020

The sealing elements are the most critical part of the mechanical sealing assembly and the main aspects of these are the tribological ones. The structural behaviour of the sealing components plays a crucial role in determining the sealing performance. Wide varieties of materials are used as seal face materials in practice. In this paper we focus on a couple of sealing materials CoCrWMo alloy / four different types of materials (copper-zinc alloy – brass, tin-copper alloy-bronze, graphite bronze and Teflon – PTFE). Dry and lubricant friction and ring on ring configuration are considered using a ring on ring tribometer. The rings from CoCrWMo alloy were additive manufactured using selective laser melting (SLM) process. Tribological tests were run at room temperature on different couples. These materials present different tribological behaviours in terms of sliding wear evaluation.
Evaluation of stress risers severity in spur gears meshing
Authors: Creţu Spiridon S
Published: January 2020

The standards for gears design use the maximum value of the normal stress σ
zz
, depicted σH, as critical stress for RCF of gears. This value σH can’t sustain evidences regarding the stress risers influences. The paper uses the von Mises stress σvM as critical stress responsible for the initiation of RCF. For concentrated contacts analyses the drawback of FEM is the very long computing time and therefore the author used a semi-analytical method (SAM) based on the numerical formulation for the involved equations of linear half-space theory. The finite width of gears’ teeth imposes quarter-space limitations and consequently the virtual pressures and correction coefficient were considered in the iterative process for pressures distribution. The pressure distribution was further used to evaluate the stress tensor components and 3D distributions of von Mises stresses. Examples are presented for spur gears with different values for end chamfers.
The Fretting Contact of Coated Bodies. Part I – Contact Parameters
Authors: Spinu S , Cerlinca D
Published: January 2020

In case of a mismatch between the elastic properties of the contacting bodies, the solution of the fretting contact can only be achieved numerically due to the connection between the contact pressure and the shear tractions. The numerical treatment of the contact processes employs an iterative strategy, and therefore requires the computation of the displacement response of the elastic body, assumed as an elastic half-space, subjected to general loadings. Unlike the case of homogeneous bodies with known Green’s functions, a closed-form expression of the response of layered semi-infinite solids to unit point loads has only been attained in the frequency domain. The latter formulas are used in this paper to assess the displacement due to arbitrary normal and shear surface tractions, thus empowering the application of a trial-and-error approach in finding the parameters of a fretting contact: the contact area, the slip and the stick regions, and the distributions of pressure and shear tractions. The contact parameters are assessed in a nested loop strategy, involving three levels of iterations. The inner level, based on the conjugate gradient method for linear systems of equations, finds the pressure when solving the contact problem along the normal direction, disconnected from any tangential effects, or the shear tractions when considering the contact equations in the tangential direction, disconnected from the pressure influence. The middle level stabilizes the pressure with respect to the shear tractions, thus assuring that the global instantaneous contact solution is achieved. The outer level manages the reproduction of the loading history in a fretting loop, by load incrementation. The proposed strategy proves itself as a robust tool for the prediction of the fretting contact process involving coatings.
The Fretting Contact of Coated Bodies. Part II – The Stress State
Authors: Spinu S , Cerlinca D
Published: January 2020

The service life of contacting coated machine elements is ultimately determined by the distribution of stresses in the coating and in the substrate. By assuming the elastic bodies as elastic half-spaces, the contact stress computation entails the calculation of convolutions expressing the superposition of effects of unit point loads acting on the boundary. The fundamental solutions of stresses and displacements in multilayered materials have only been calculated in the frequency domain, and are known as the frequency response functions. An additional difficulty arises in the stress calculation, related to frequency response function valuation in the origin of the frequency domain, where a singularity is usually encountered. This case of un-determination is circumvented in this paper by substituting the required value with the mean value of the frequency response function over a vicinity centered in origin. The latter approach is endorsed by the fact that the frequency response function is singular, but numerically integrable in the aforementioned vicinity. The latter technique is validated by comparison with results obtained for the sliding contact, and then applied to derive the elastic stresses arising during a fretting loop in the coating and in the substrate. The stresses due to shear tractions are superimposed to those induced by contact pressure. The calculation is performed in layers of constant depth, and the algorithmic complexity is optimized by using state-of-the-art techniques for discrete convolution computation. The equivalent stress is discontinuous across interface between the two layers, and the location and intensity of the maximum von Mises stress is determined by the frictional coefficient and by the mismatch between the Young moduli of the coating and the substrate. The results obtained with the newly proposed numerical technique may extend the understanding of the fretting contact of coated materials and assist the design of improved coating configurations.
A study of the crack initiation angle in the substrate of spur gear teeth subjected to rolling contact fatigue
Authors: Popa C O
Published: January 2020

Fracture failure of engineering structures is caused by cracks that extend beyond a safe size. For modeling the stable fatigue crack propagation it is necessary to determine the angle of crack initiation, i. e. the angle under the crack growth takes place. There are several criteria that try to model this aspect, such as: Sih, MTS, M, T, Ip.

The S-criterion (Sih) was used to simulate the fatigue growth of an internal crack situated in the substrate of a certain spur gear, taking into account the rolling contact fatigue. S-criterion states that the direction of crack initiation coincides with the direction of minimum strain energy density along a constant radius around the crack tip. Since the stress intensity factor Ki is negligible (because of the compression stresses in the substrate of the gear tooth), calculations were made for these conditions and it was obtained a constant and unique angle of crack initiation angle 9 ∼ 80°, that is in concordance with the experimental observations. This study serves to determine the fatigue crack initiation angle in a compression stresses field, as well as its use in modeling the propagation of the fatigue cracks.
Considerations regarding determination of optimal preventive maintenance periodicity for subsurface sucker rod pumps
Authors: Drumeanu A C
Published: January 2020

The subsurface sucker rod pumps are important equipment used for the secondary oil recovery. In their structure, there are friction couples, which are strongly subjected at wear like barrel-plunger, traveling valve and standing valve. The operating durability of subsurface sucker rod pumps is practically determined by the reliability of these couples depending on the work conditions.

The paper presents a case study on the optimization of preventive maintenance of the subsurface sucker rod pumps. The optimal periodicity, of the preventive maintenance of the above mentioned friction couples, is determined on the basis of their operating reliability. There were analyzed two types of preventive maintenance, at fixed time, and at fixed age respectively. The paper results are embodied in practical charts which can be used for choosing optimal preventive maintenance period of the subsurface sucker rod pumps.
Lubricants condition monitoring by using a global performance passport
Authors: Radulescu I , Radulescu A V
Published: January 2020

Lubricants degradation processes are characterized by the physical and chemical indicators changes for oils composition, caused by internal and external factors and the operating conditions severity. Lubricants condition monitoring involves experimental methods to study their behaviour, for developing a lubricants life cycle assessment methodology. The paper proposes the lubricants behaviour complete characterization by using a global performance passport, to study the rheological, tribological and microscopic properties, for various wear stages. The global rheological lubricant feature is expressed by the maximum film pressure, by using the original rheological experimental module. The reference rheological lubricant feature is obtained by using the viscometer validation module, based on the variation of viscosity by the temperature. The tribological lubricant feature is given by the tribological experimental module, based on friction coefficient variation according to the normal pressing force and sliding speed. The structural microscopic lubricant feature is shown by the wear particles analysis module, analysing the solid particles type identified in the fresh and worn lubricant. The global performance lubricants passport assess the lifetime reserve, function the specific use conditions, to reduce operating costs. To do the initial investment for the preliminary experimental tests conduct it is recommended to determine the economic profitability threshold for the user investment.
A simple analytical model for an elastohydrostatic thrust bearing
Authors: Cicone T , Marinescu A A , Sorohan S
Published: January 2020

A new design of an elastohydrostatic bearing with a structurally elastic pad is theoretically analyzed. A single recess circular thrust bearing has the upper pad provided with a large cavity, covered with an elastic metallic membrane. The latter deflects under the pressure distribution in the bearing, creating a radial convergent gap. A simplified axi-symmetric analytical model based on two assumptions is proposed: (i) parabolic approximation for the elastic component of the film thickness and (ii) the maximum elastic deformation of the membrane is calculated analytically using a simplified linear pressure variation in radial direction on the land. Thus, the coupled equations for fluid film and elastic deformation can be solved successively and the bearing performance characteristics can be easily calculated. A parametric analysis, function of a complex elastic parameter and relative recess radius was performed, showing higher load capacity and lower friction similarly to what was previously obtained using rubber-based compliant bearings. A first stage of validation of the analytical model consisted in using a structural finite element model. For the sake of simplicity, the pressure distribution was written in an APDL code using the ANSYS program. The comparison showed small differences for typical values of the recess radius.
Evaluation of inertia effects in planar squeeze flow inside soft, porous layers
Authors: Lupu G , Turtoi P , Cicone T
Published: January 2020

The resistance to flow of a fluid squeezed out from a soft and porous structure under compression, generates high load capacity. The process is dependent on permeability, which is variable during compression of the porous layer. This mechanism (named Ex-Poro-Hydrodynamic Lubrication – XPHD) plays an important role in a wide range of tribological applications (biolubrication, shock absorbers, etc.). A literature search reveals that Darcy’s law is intensively used for modeling flow through porous media. However, for high porosity materials and relatively high velocity flows that may occur during impact, the inertia effects could be significant. The full squeeze solution of high velocity flow inside deformable porous materials including inertia effects and permeability variation with the level of compression could not be found in the literature. A numerical study for planar squeeze flow of a Newtonian liquid inside a soft porous layer, based on the Darcy flow model including Forchheimer correction, is presented in this paper. The porous material is compressed at high speed between two perfectly rigid, parallel and impermeable discs. Finite differences technique is used to solve the system of equations. Pressure distribution, load and Reynolds pore based number variation during compression are obtained and compared with similar values predicted by simple analytical models based on Darcy law. The results define the limits of Darcy approach in XPHD lubrication.
Some considerations about the effect of grooves on the viscous coupling performances
Authors: Stoicescu A I , Predescu A , Gâtu V
Published: January 2020

A viscous coupling transmits torque by viscous shearing of the oil film between one or multiple pairs of discs that are in relative motion one to the other. A viscous coupling uses a viscous fluid as a working medium and performs best in full film lubrication condition. A continuous film of oil must be present at all times between the two surfaces that are in relative motion. Only in this stage, when operating in full film lubrication condition, this coupling can achieve the maximum transmission of torque. This kind of study is of a great importance since this coupling is widely used all around the world in all sorts of applications. In this paper, the effect of grooves on the viscous coupling performances was carried out deeply using a Computational Fluid Dynamics Software. The flow of the fluid film and shear torque between the friction pair are complex and keep changing with the operating conditions, the geometry, the number of grooves, the properties of the working oil and the thickness of the oil film.
Standardization in testing ballistic protection systems
Authors: Ojoc G G , Pirvu C , Sandu S , Deleanu L
Published: January 2020

Even more than in other field of activities, standardization in ballistic protection is in trends of CEN/CENELEC declaration that “standards build trust”, promoting innovation and introduction of new, performant solutions based on test procedures and protocols that are able to point out quality and safety for such systems. Ballistic testing standards have particular specifications for ballistic materials, differentiation of tests being made especially on the purpose of the ballistic protection product. In the last decades, test methods have been refined and measurement devices have become more complex. The main set of standards is developed by military organizations (as NATO), highly industrialized countries, where the military and research in the field are priorities (USA, European Community, Asian countries, South Africa). Some states refer to American standards by using them as guides. Depending on the destination of the ballistic product, specifications in standards are different. The authors give examples of how standards requirements are implemented in testing ballistic protection systems, in order to point out the particularities of introducing and verifying new and classical products in this domain. Generally, the results of the ballistic tests are evaluated by acceptance or rejecting the tested product, based on specific criteria, included in standards.
A survey of Mechanical failure and design for Reliability of MEMS
Authors: Somà A
Published: January 2020

In this paper, several experimental mechanical investigation techniques are presented to evaluate the reliability of micro-electro-mechanical systems (MEMS). Microsystems in recent years have spread in many everyday devices. We find micro-scale sensors and actuators in automotive, biomedical and aerospace applications where are demanded very strict performance requirements. Electromechanical non-linear coupling is often a crucial problem both in design and also for the reliability of the system. Mechanism of failure and failure modes has to be taken into account in order to evaluate the reliability of the final system. Focusing on device failure, it emerges that mechanical damage is the most significant source. In this paper a survey of recent advance in mechanical testing of MEMS is presented including: mechanical fatigue, mechanical strength and plasticity, surface and contact failure and creep. Different design of testing specimens is discussed to identify the material properties and failure modes behavior in order to obtain design rules and strategies.
Validation of professional tooth brushing test device, test methodology and analysis
Authors: Achimescu B M , Ciortan S , Buciumeanu M
Published: January 2020

The present work is focused on developing a test apparatus to simulate the contact situation of the toothbrush used in professional toothbrushing (cleaning and polishing) and a dental biomaterial. Cylindrical samples (8×5 mm) were manufactured from a resin composite (frequently used in practice) in similar manner with the preparation of dental restorations in clinical conditions. The tests were carried by using two different toothpastes: a professional toothpaste and a home used toothpaste. All the experiments were carried out for 15 min, under 280 g normal load applied on the brush and the operating speed was around 5000 rev/min. The preliminary results on the dental restorative material selected for this study indicated that the proposed system is consistent and useful for the investigation of the microabrasion processes that arise at the surface of dental biomaterials.
Fretting manifestations in total hip prosthesis
Authors: Capitanu L , Badita L L , Florescu V , Tiganesteanu C , Isvoranu L F
Published: January 2020

This paper analyses the fretting and fretting wear phenomena to the classical and modular hip prostheses. Theoretical and experimental manifestations are studied, at the interface of the femoral stem with the bone cement mantle, at the taper junction between the femoral stem and the femoral head of the prosthesis, as well as at the tapering of the femoral neck adapter’s connections with the stem and the femoral head. The aim of the paper is to highlight the modularization implications of the femoral component of the Total Hip Prosthesis, especially its tribological implications (fretting wear of modular junctions, fatigue and corrosion by fretting) which can contribute to wear and increasing ion concentrations of the metal in the blood, and the possibility of the femoral shaft fracture at the femoral head junction. Theoretical approach described, allows the “Archard” law implementation to predict the fretting wear. Experimental laboratory studies focused on the analysis of the tribological phenomena occurring at the taper junctions between the femoral head and neck, as well as the neck and femoral stem, highlighting the relevant qualitative tribological aspects. For this purpose, experimental junctions were fabricated and tested on a universal MTS mechanical machine, equipped with a fatigue testing device.
Dynamic and tribological contact study for human fingertips at very low speeds
Authors: Călin A , Tudor A , Stoica M , Stoica N , Subhi K
Published: January 2020

Nonlinear elastic models have been widely used to describe the mechanical behaviour of complex materials such as skin. The subject of skin modelling is fairly new and of great importance to fields such as robotics and the development of skin-like materials to orthopaedics and prosthetics. The present article serves to add to the findings of previous authors and present experimental values gathered using the “Stick-Slip Experimental Stand” within the Machine Elements and Tribology Department on the tribological aspects regarding friction at very low speeds. The scope of this article is to evaluate the static and kinetic friction coefficients of the human skin in contact with different materials. A total of 5 different materials were tested to find the static and kinetic friction coefficient. The tested materials were steel, bronze, and 3 types of materials found on the inside of working gloves in direct contact with human skin: leather (bovine origin) and 2 types of textiles (cotton and nylon). All tests were performed at 1.8 mm/min, with an initial load of 7.5 Newton and a test time of 1000 seconds. The total distance evaluated was 9.25 mm.
Effect of microstructure on wear behaviour of aluminium 2014 (Al2014)
Authors: Bhaumik S , Paleu V , Chowdhury D , Cîrlan Paleu C , Datta S
Published: January 2020

The paper investigates the effect of ageing on the hardness and wearing of Al2014. Precipitation hardening and ageing were carried out on the samples. The samples were solution treated at 550°C and were naturally aged. Quenching was carried out using ice-brine solution. Vickers Hardness were taken at regular intervals till 900 hours. The peak hardness value of the natural aged sample was found to be 86HV (93 hours) as compared to the untreated sample (32.4HV) The wear tests were conducted at 10N, 500rpm for 30 minutes. After the tribo test it was observed that the coefficient of friction increased by 7.06% in the naturally aged sample, but the wear rate in case of as-received samples was 46% higher than that of the naturally aged sample. The change in the microstructure of Al2014 is the primary reason for the difference in wear rate of the samples. The present work will help to understand the influence of heat treatment of aluminium alloy on wear properties.
Temperature influence on mechanical properties of chromium nitride thin films
Authors: şerdean F M , Merie V V , Negrea G , Bîrleanu C , Mărieş I
Published: January 2020

Thin films present interest for researchers due to their applicability in areas such as developing microelecromechanical devices, hard coatings, cutting tools and diffusion barriers. This paper is focused on studying the influence of the testing temperature on the mechanical properties of chromium nitride (CrN) thin films. For this purpose, CrN thin films were deposited by direct current magnetron sputtering on silicon substrate using a chromium target of high purity. All the films were obtained by keeping almost all deposition parameters constant, while the nitrogen flow rate was varied. Hence, three types of samples of CrN thin films were obtained using different nitrogen flow rates namely 2 cm3/min, 4 cm3/min and 6 cm3/min. The mechanical properties of these thin films such as the hardness and Young’s modulus were investigated by performing nanoindentation using an atomic force microscope. All experimental investigations were conducted by varying the testing temperature between 20 oC and 100 oC. The purpose was to find the dependency between the testing temperature and the mechanical properties of CrN films deposited at different nitrogen flow rates. The obtained experimental results indicate a significant influence of the testing temperature on the properties of the studied CrN thin films.