Severe Working Conditions Research Articles

CFD and experimental analysis of the coolant flow in cryogenic milling

Abstract Cryogenic cooling could improve the machining performance for hard-to-cut materials. Deployment of this modern technology for milling applications, specifically because of their severe working conditions and complicated physical phenomena inside cryogenic fluids, requires further research to become credible for industrial applications. Obtaining accurate models for coolant behavior is essential for optimum design, prediction of operational limits, and safe control of the cooling process. In this paper, Computational Fluid Dynamics (CFD) were used to determine the behavior of the liquid nitrogen (LN2) inside the coolant delivery system and the interaction of the coolant jet with the cutting area. The role of working conditions as well as nozzle geometry, formation of cavitation inside the tool, coolant pressure, and wall temperature on the efficiency of the coolant delivery were investigated in this study. Initial experimental flow measurements were used to predict the simulation setup and evaluate the results. Experimental milling tests were performed to verify the numerical findings. Cutting forces, coolant mass flow rate, temperature, and pressure were measured during the tests. A mechanistic cutting force model and the morphology of the chips were used to interpret the effect of liquid nitrogen on the cutting mechanisms. Results of this study offer three main suggestions for reliable industrial cryogenic milling: using liquid nitrogen in the range of 2–4 bar, improving the insulation of the feeding line and finding a technical solution for non-insulated parts, and increasing the quality of the liquid in the coolant mixture close to the milling head. Outcomes of this study could help to improve the cooling performance and implement a reliable industrial solution for cryogenic milling.

Wear Resistance Improvement of Austenitic 316 L Steel by Microwave-Processed Composite Clads

Metal matrix composite (MMC) claddings can be effectively used in severe wear working conditions. The present work successfully develops the MMC clad of Ni + 10% WC8Co + Cr3C2-based material on SS-316 L substrate using cost-effective microwave hybrid heating (MHH) technique. The developed composite clads showed the refined microstructure with the existence of randomly dispersed reinforcement particles inside the Ni based matrix. The phase analysis study results of the clad region revealed the formation of various hard phases of Co3W3C4, Cr7Ni3, NiC, NiW, W2C, Fe6W6C, Fe7C3, FeNi3 during microwave heating. The hard phases present in the clad region contributed to the enhancement in the microhardness. The mean microhardness of the clad region was observed as 550 ± 40 HV. Further, composite clad exhibited excellent wear resistance than SS-316 L substrate under different tribological conditions.

Novel Adaptive Search Method for Bearing Fault Frequency Using Stochastic Resonance Quantified by Amplitude-Domain Index

Rotating machinery devices are prone to failure due to severe working conditions, whose failures will further induce other mechanical faults. Therefore, the fault diagnosis of rotating machinery is important, especially in the case of unknown fault types and fault characteristics. A novel adaptive search method is proposed for the bearing fault frequency by using stochastic resonance (SR) with general scale transformation. The amplitude-domain indices, which are independent of the specific fault frequency of vibration signal, are applied to quantify SR response. Simulated bearing fault signal is used to illustrate the good performance of these indices in evaluating SR output. Then, an adaptive search procedure for bearing fault frequency is presented in detail and verified by different vibration signals collected from the multiple working conditions. The searching results demonstrate that the proposed adaptive search method is accurate, effective, and sensitive for detecting unknown failure frequencies of rolling bearings. The proposed method might have significant application value in the condition monitoring of rolling bearings.

Radial impact test of aluminium wheels—Numerical simulation and experimental validation

Safety is a crucial issue for automotive wheels, normally subject to severe dynamic working conditions. Severe indoor tests have been conceived and standardised to guarantee the required safety standards of vehicle wheels. This paper is devoted to the analysis and virtual simulation of the radial impact test of aluminium wheels, one of the most severe tests the wheel has to pass before production.The radial impact test is simulated, for a number of different aluminium wheels, by means of a finite element model. The model includes tyre, wheel, striker and supporting structure. The actual structure of the tyre is modelled. Tyre damping is included through a Rayleigh model, whose parameters are experimentally identified. The wheel material inhomogeneity is taken into account by assigning different stress/strain curves to wheel rim and spokes.A wheel instrumented with strain gauges has been used to validate the finite element model. An additional set of four families of different wheel types, equipped with different tyres, has been considered to asses the experimental variability and to compare the outputs of the corresponding impact models realized by the same procedure. The finite element model of the radial impact test has proven to be effective in reproducing the final plastic deformation of the wheel and thus to predict the compliance of the wheel design with the requirements coming from standards.

Traction Behavior of No. 4129 Synthetic Oil for Space Lubrication

No. 4129 lubricating oil, a kind of synthetic oil, was widely applied in area of space machinery, while its traction behavior has not been realized. In this work, the elastohydrodynamic properties of No. 4129 have been investigated by subjecting it to our self-made test rig at various experiment conditions. The results revealed that the effect of the load on the traction coefficient is greater when the load exceeds 69 N at a fixed rolling velocity. In addition, the rolling speed exerts a smaller influence on the traction coefficient when rolling speed exceeds 11 m/s at a fixed load. Therefore, this lubricating oil exhibits elastic–plastic rheological properties under the prevailing experimental conditions. Based on the obtained experiment data, we have established a new formulae for calculating the traction coefficients of the lubricating oil. In contrast, the calculated traction coefficients by the formulae were fairly well agreed with the measured data. The resulted theoretical formulae will provide a better direction for No. 4129 used as lubricating oil under a severe working condition in space.

From Miracle to Mirage: The Making and Unmaking of the Korean Middle Class, 1960–2015 by Myungji Yang

Book Review From Miracle to Mirage: The Making and Unmaking of the Korean Middle Class, 1960–2015, by Myungji Yang. Ithaca and London: Cornell University Press, 2018. 204 pages. ISBN-10: 1501710737. $45.00 hardcover. The early 2000s ushered in an academic discussion surrounding South Korea’s social woes and concerns for the collapse of its middle class. It is, as the author epitomized, because of the importance of the middle class as a “carrier of economic and political modernization or as a coalitional actor for political transformations” (p. 8). The aftermath of the Asian financial crisis in the late 1990s has delineated someone who can be still categorized as the middle class from another who does not belong to the middle class anymore. That is to say, chicken restaurants owners who invest their lump sum retirement pay would be straddling on the boundary between the two categories. A more pertinent observation is that of socioeconomically vulnerable people who struggle to survive by enduring longer working hours and severe working conditions—most of whom have probably been thrown from the race for upward mobility. Likewise, the un-making of the middle class has signaled turbulent circumstances across different classes. The collective anger for the collapse of the “middle class myth” followed by exacerbating inequality and economic polarization is expressed in the Korean Studies © 2019 by University of Hawai‘i Press. All rights reserved. 1 term “Hell Chosun,” which Yang Myungji discussed at the beginning of the concluding chapter. In From Miracle to Mirage: The Making and Unmaking of the Korean Middle Class, 1960–2015, Yang explains the political, social, and economic circumstances surrounding the emergence and development of the middle class in Korea, as well as the articulation by the middle class against transient circumstances threatening their social status. Chapters in this book are simple and each chapter carries a clear theme. Excluding the introduction and conclusion chapters, there are three chapters which are periodically aligned: the birth of the middle class as the ideal national goal during the 1960s and 1970s; the heydays, focusing on those who settled down in the Gangnam area during the 1980s and 1990s; and the unmaking process of the middle class myths from the 1990s to the present. As Yang mentioned, the notion of “class,” and by extension “middle class,” is a contestable term that is not neatly defined. Rather than delving into an elaborate definition of class in Korea, this book focuses more on the process and dynamics underlying the making and unmaking, via the educational system and investments on real-estate, particularly high-rise apartments in the Gangnam area. This book is additionally centered on the urban middle class in Korea, including three distinct groups: professionals and technical elites; salaried employees; as well as old middle class or petty bourgeoisie including self-employed small business owners, merchants, and shopkeepers. By complementing the definition of urban middle class based on the elaboration of socioeconomically positioned subjects, the book accords attention to the middle class as a contested notion and structural category, one that is not fixed but dependent on historical dynamics and structural forces. Addressing the dynamics of the middle class in the third chapter, their contradictory position in terms of “dubious” characteristics is described well: when their interests are well-represented by the society, they are a main group supporting the system; however, they can be the most threatening element of the society when their social and economic values are in conflict with the system. When the stable, mundane lifestyle of middle class is threatened, their frustration and collective actions can be articulated into social conflict followed by civil movement. Likewise, the strongest and most stable allies of current political regime can turn into their strongest opponents. In this sense, the most interesting chapter is the concluding chapter that highlights the issue of the dwindling middle class. 2 Korean Studies 2019 It briefly provides parallel situations in other countries that share similar issues regarding the crisis of the middle class, which have resulted in political chaos or economically unstable situations. By positioning Korea’s middle class issue into contemporaneity in the globalized world, the concluding chapter...

Research on susceptibility of 7075 aluminium alloy to extrusion welding

Abstract Extrusion welding of the 7xxx series aluminium alloys, especially these of high strengthened containing copper is still a barrier difficult to overcome. The main limitations are: poor weldability of the material which decreases a product quality, low permissible exit speed from the die decreasing the production efficiency, as well as severe thermal and mechanical working conditions for the die. The paper presents the results of weldability testing of the 7075 aluminium alloy, containing 5,59 % of Zn, 2,36 % of Mg and 1,49 % of Cu, with the use of an original authorial device. This device enables modelling the behavior of a material in the welding chamber of a porthole die. The tested material was submitted to non-conventional homogenization, what permitted to increase the solidus temperature of the alloy in comparison to the for cast material. The tests were conducted at 520°C and under the pressure of 200 MPa. The microstructure of the material was investigated both in the region of welds and in the basic material by using light microscope and scanning microscopy SEM. In addition, the chemical composition of the alloy was examined by using the ESD method. The microhardness test was performed perpendicularly to the surface of welding. The results indicate that the high-quality welds were not obtained. As it was stated, for the given temperature of welding, the welding factor limit value, i.e. relation of unit pressure to the yield strength (σn/k), was not reached.

ПОВСЕДНЕВНАЯ ЖИЗНЬ КРЕСТЬЯН В 1941-1945 ГГ. В ВОСПОМИНАНИЯХ ЖИТЕЛЕЙ СТАРОШАЙГОВСКОГО РАЙОНА РЕСПУБЛИКИ МОРДОВИЯ

The article provides the analysis of rural population’s everyday life in the Soviet home front in 1941-1945. The study is based on the materials of a survey conducted among the rural residents of Staroshaigovsky district of Mordovia, who witnessed those events. Severe working conditions on collective farms, food shortage and hunger, poor material and living conditions, oppression from the authorities - the reminiscences of the war years are deeply imprinted in historical memory. The author concludes that the provided examples confirm the available information contained in the Russian archives and published documents.

Image Enhancement for Inspection of Cable Images Based on Retinex Theory and Fuzzy Enhancement Method in Wavelet Domain

Inspection images of power transmission line provide vision interaction for the operator and the environmental perception for the cable inspection robot (CIR). However, inspection images are always contaminated by severe outdoor working conditions such as uneven illumination, low contrast, and speckle noise. Therefore, this paper proposes a novel method based on Retinex and fuzzy enhancement to improve the image quality of the inspection images. A modified multi-scale Retinex (MSR) is proposed to compensate the uneven illumination by processing the low frequency components after wavelet decomposition. Besides, a fuzzy enhancement method is proposed to perfect the edge information and improve contrast by processing the high frequency components. A noise reduction procedure based on soft threshold is used to avoid the noise amplification. Experiments on the self-built standard test dataset show that the algorithm can improve the image quality by 3–4 times. Compared with several other methods, the experimental results demonstrate that the proposed method can obtain better enhancement performance with more homogeneous illumination and higher contrast. Further research will focus on improving the real-time performance and parameter adaptation of the algorithm.

Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718

Electron beam melting (EBM) of Alloy 718 is of rapidly growing interest as it allows cost-effective production of complex components. However, the inherent flaws in the component in as-built state are of concern in view of the severe working conditions in which Alloy 718 components typically operate. The present work entails an investigation of changes in microstructure that accompany some post-treatments that are being widely considered to address defects in EBM processed Alloy 718. The effect of two different post-treatments, namely hot isostatic pressing (HIP) and a combined HIP + heat treatment (HT) carried out inside the HIP vessel, have been studied and results from as-built and post-treated specimens were compared in terms of porosity/lack-of-fusion, microstructure, phase constitution (NbC content, δ-phase) and micro-hardness. Post-treatment resulted in reduction in defect content by more than an order of magnitude. HIPing led to complete dissolution of δ phase. In comparison to as-built material, HIPed specimens exhibited significant drop in hardness. However, a sharp ‘recovery’ of hardness to yield values higher than in as-built condition was observed after HIP + HT and can be attributed to precipitation of γ′′ phase.

Cavitation Erosion Performance of Steel, Ceramics, Carbide, and Victrex PEEK Materials

Abstract Cavitation erosion has to be taken into consideration during material selection in many industrial sectors, e.g., offshore, marine, and oil and gas, in which components operate under severe working conditions. The cavitation erosion equipment, located at the University of Southampton, uses a vibratory apparatus to compare, rank, and characterize the cavitation erosion performance of materials. This article highlights some of the results obtained from industrial research (consultancy) work employing a Hielscher UIP1000hd 20 kHz ultrasonic transducer (Hielscher Ultrasonics GmbH, Teltow, Germany). The transducer is attached to a titanium horn to induce the formation and collapse of cavities in a liquid, creating erosion (material loss) of the specimen undergoing testing. The results from erosion cavitation testing (in accordance with ASTM G32-16, Standard Test Method for Cavitation Erosion Using Vibratory Apparatus (Superseded)) of two commercially available steels are presented herein and are shown to have less resistance to cavitation when compared to polyether(ether ketone), ceramic, and carbide materials. These materials are presented, along with Nickel 200, which was used to normalize the results. A plot of cumulative erosion versus exposure time was determined by periodic interruption of the test.

Destructive Testing of Open Rotor Propeller Blades for Extreme Operation Conditions

Due to the complexity of composite material, accurate manufacturing is very complicated and carry over a large number of uncertainties, the process of optimization and validation being of primary importance.In this paper as part of design technology for rotor blades, the process of mechanical testing against severe working conditions using Acoustic Emission (AE) is discussed. As part of this process, the dynamic behaviour is analysed with validation and model updating of the structure and material properties, followed by structural tests under loads specific to the operational conditions.The results presented show how the appropriate AE technique has been implemented in order to obtain relevant data and focus on specific areas of interest for the design development, for correlation between modelling and experimental testing, the structure being tested to the ultimate load.

A Combined Numerical and Experimental Investigation on the Effect of Dynamics Characteristics of Metal Expansion Bellows

Metal expansion bellows is an important flexible element used to absorb extension or shrinkage and vibrations of the piping system used in various process applications. Failure of the bellows occurs due to the unpredictable behavior in its convolutions due to severe working conditions. Hence, determination of its dynamic characteristics is of prime importance. To find and analyse dynamic characteristics like axial natural frequencies, modal frequency responses and mode shapes of U-shaped convolution bellows as well as the effect of increase in number of convolutions on the dynamic characteristics. In this paper, analytical, numerical simulation and experimental investigations are performed to find the axial natural frequencies of bellows. Numerical simulation is performed using the mathematical model in MATLAB and modal analysis is performed using ANSYS 15. The deformation and axial natural frequency response of bellows with eight, nine and ten convolutions are obtained by FE analysis for various modes when bellows are subjected to different end conditions. As per the simulation and experimental modal analysis, it is seen that the range of axial natural frequencies with less number of convolutions shows maximum deformation and larger number of convolutions shows minimum deformation. To decrease the axial natural frequency for the given flow rate and to avoid resonance, the number of convolutions of the bellows should be increased for designing the new configuration.

Thermal characteristics of the combined flat plate heat receiver in solar power tower plant

This study presents a combined flat plate heat receiver (FPHR) for a solar power tower plant. Four flat plate heat pipes (FPHPs) as heat transfer units are homogeneously enclosed in a cavity of 150° constituting the combined FPHR. The start-up characteristics of the FPHP were experimentally investigated and quantitatively analysed. In addition, the isothermal performance, heat transfer performance, stability under severe working conditions, and effect of non-condensable gas on the thermal characteristics were experimentally investigated. The results show that the heat transfer limits are not encountered during the start-up process and the FPHP heated on one-side surface could successfully start up. The continuum flow regime established in the FPHP results in a good isothermal characteristic and makes the output power to synchronously respond to the input power without delay under a heat flux fluctuation condition. It is also found that the FPHP possesses potential to inhibit the hotspots under non-uniform heating condition. Besides, the accumulated non-condensable gas would lead to the reduction of the heat transfer performance. The main conclusions drawn from this work will be helpful for further development of the heat receivers used in solar power tower systems.

Ni nanocluster composites for enhanced impact resistance of multilayered arc-PVD ceramic coatings

Optimally, hard protective coatings should effectively absorb impact energy to reduce the likelihood of failure events. In this work, an arc-PVD approach was utilised for the deposition of thick ceramic multilayer AlCrTiN/CrN-based coatings containing a distribution of metallic nickel inclusions throughout sequential CrN-based interlayers. The aim of such coatings is to provide resistance to impact loading in intensive application environments, such as drop forging of steel and turbine blades exposed to abrasive particles. The structure and micro-structural development of the ceramic was first investigated using transmission electron microscopy, where discrete Ni inclusions were observed as both larger discs (d ~ 600–800nm, h ~ 200nm) and smaller (d ~ 50nm) nanoclusters. Confirmation of the distribution and nanocluster chemistry was achieved using atom probe tomography. For mono-block coatings, XRD data showed drastically reduced internal stresses as a result of the Ni inclusions, enabling the creation of thicker protective coatings which minimise substrate stress concentration upon loading. Nickel inclusion additionally provides a softening of the containing hard ceramic layer, allowing for tuning of mechanical properties. Supporting this idea, in situ micropillar compression measurements of the multi-layered coating systems showed that Ni clusters hindered crack propagation through the coating during failure, while the fracture strength could be increased by incorporating both Ti and Ni in the softer CrN-based layer. High-load impact testing highlighted the influence of Ni ‘shock absorbers’ in reducing circumferential cracking, which was further confirmed by an industrial die forging test that demonstrated a 15–22% life-time increase compared to a much thicker hard-chrome plated reference. The results of this study demonstrate an exciting way to produce Ni nanocluster integrated hard ceramic multi-layers using arc-PVD in a single processing step. Such tuneable thin-film composite systems show great promise in minimising damage from impact loading, even under severe working conditions such as in hot forging.

Thermoelastohydrodynamic analysis of misaligned bearings with texture on journal surface under high-speed and heavy-load conditions

Hydrodynamic journal bearings are used to support the planetary gears in the transmission system of a Geared Turbo Fan engine, and they operate under severe working conditions, such as misalignment, high speed, and heavy load. Surface texture is regarded as an effective approach to improve mechanical properties under severe working conditions. However, the effects of surface texture on misaligned journal bearings under severe conditions have not been well studied. Therefore, a thermoelastohydrodynamic (TEHD) lubricating model with a textured and misaligned journal is presented in this study. Solid deformation, heat transfer between oil and the bearing, and heat convection between air and the bearing are considered in the model. The effects of cavitation and viscosity-temperature are also taken into account. The impacts of surface texture parameters and the misalignment angle on lubricating properties are investigated in the model. Results indicate that the bearing lubricating performance is greatly improved by optimal surface texture considering journal misalignment. The maximum oil film pressure and load-carrying capacity of a journal bearing increase with journal misalignment. Meanwhile, the oil film temperature increases sharply while considering misalignment.

Effects of silica nanoparticles on tribology performance of poly(Epoxy Resin‐Bismaleimide)‐based nanocomposites

Introduction of small nanoparticles into polymer matrix increases the mechanical, tribological, and thermal properties of nanocomposites. In this study, poly(epoxy resin‐bismaleimide‐diaminodiphenylmethane) (EP‐BMI‐DDM) copolymers filled with silica nanoparticles (SNPs) were successfully fabricated through in situ suspension polymerization. To enhance the interfacial adhesion of silica particles to the polymer matrix, the nanoparticles were organo‐modified by silane coupling agent. Results of tensile strength test revealed that increased toughness of the composites was attributed to the microcavitations induced by organo‐modified SNPs (OSNPs). Proper loadings of OSNPs can play a critical role in antifriction performance, with optimal friction coefficient of 0.17 (2 wt% OSNPs content). Thermostabilities of the nanocomposites were characterized by differential thermal gravimetric analysis. At the maximum rate of weight loss of EP‐BMI‐DDM/3 wt% OSNP, the temperature measured 452°C, which is 52°C higher than that of pure EP‐BMI‐DDM copolymers (400°C). The produced nanocomposites feature good thermostability and self‐lubrication can be widely used as wearable material under severe working conditions with higher temperature. POLYM. ENG. SCI., 59:274–283, 2019. © 2018 Society of Plastics Engineers

Preparation, Mechanical Properties and Cyclic Oxidation Behavior of the Nanostructured NiCrCoAlY-TiB2 Coating

TiB2-Metal composite coatings with excellent oxidation resistance become ideal candidates using at high temperature ranging from 600 to 1000 °C. In order to maintain both the superior mechanical properties and oxidation resistance in severe working conditions, the nanostructured NiCrCoAlY-TiB2 coating was fabricated by the activated combustion high velocity air-fuel spraying (AC-HVAF) with the composite powders prepared by ball milling and plasma spheroidization. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the phase constituents and microstructure. It was found that the coating with nanostructured TiB2 particles uniformly distributed in the NiCrCoAlY matrix has the same structure as the composite powders. The coating shows excellent mechanical properties, such as high microhardness (991.43 HV0.3), good fracture toughness (4.12 MPa m−1/2) and large bonding strength (75.43 MPa), and excellent oxidation resistance with low weight gain (1.56 × 10−6 mg2 cm−4 s−1). The cyclic oxidation behavior is in accordance with the parabolic law.

Fabrication of N-doped 3C-SiC nanobelts with selected [formula omitted] top surface and their enhanced transverse piezoresistance behaviours

The piezoresistive effect of SiC low-dimensional nanostructures, together with their exclusive benefits of superior mechanical characteristics and could be integrated into the flexible devices that can withdraw large strain, promise to make a wide range of sensing devices application possible in the severe working conditions. In this work, we reported the transverse piezoresistance behaviours of n-type 3C-SiC nanobelts with selected (11¯0) top surface and N dopants. The single-crystalline SiC nanobelts were achieved by the means of direct pyrolysis of polymeric precursors without catalysts, which had an average N doping level of ~ 6.02 at% and a typical width-to-thickness ratio of ~ 8. It was disclosed that the transverse piezoresistance coefficient π[11¯0] reached the maximum 10.29 × 10–11 Pa−1 at a fixed external stress of 67.03 nN. Correspondingly, the gauge factor (GF) was calculated to be of ~ 61.7, which is higher than all the reported n-type SiC, intrinsic SiC, as well as most of the p-type SiC counterparted. The findings shed light on the fact that present n-type SiC nanobelts have the potential of becoming an outstanding contestant for the development of robust pressure sensors having elevated sensitivities.

Enhancement of tribofilm formation from water lubricated PEEK composites by copper nanowires

A high-performance tribofilm is crucial to enhance the tribological performance of tribomaterials. In order to promote tribofilm formation under water lubrication conditions, copper nanowires as a functional nanomaterial were filled into neat polyetheretherketone (PEEK) and PEEK10SCF8Gr (i.e., PEEK filled with 10 vol.% short carbon fibers and 8 vol.% graphite flakes). The results show that the addition of copper nanowires and a greater applied load can enhance materials transfer and tribofilm formation during sliding process. Moreover, copper nanowires can share a part of applied load, and retard the fatigue effect to some extent. In addition, copper nanowires, carbon fibers and graphite can synergistically improve the tribological performance and the tribofilm formation under water lubrication and severe working conditions. In particular, only 0.5 vol.% copper nanowires can form a high-performance tribofilm, which endows superior lubricating property and wear resistance capacity of the PEEK10SCF8Gr. Furthermore, the surface analysis indicates that the tribofilm contains some transferred materials and the products from tribochemical reactions as well.