Tube hydroforming compression test for friction estimation—numerical inverse method, application, and analysis

Friction plays an important role in forming processes, in fact it influences the material flow and therefore it affects the process and part characteristics. In particular, friction is a very influencing factor in tube hydroforming (THF), where high die–part contact pressure and area make the material sliding very difficult. As a consequence, the material hardly flows to the expansion zones and the part formability can be compromised. To obtain sound parts, FEM models allow the study of the process and optimize its parameters, but they require the right definition of the friction at tube–die interface. For these reasons, friction represents a key-point in THF processes and its knowledge and prediction are very important even if, nowadays, a comprehensive friction test for THF is not available in literature. With this paper, the authors want to propose and evaluate a method to estimate friction for THF processes. In particular, a numerical inverse method allowing the estimation of the Coulombian friction coefficient combining experimental test and FE simulation results will be described. The method is based on the effects of friction on the tube final thickness distribution when it is pressurized and compressed by two punches under different lubrication conditions without expansion. In particular, how the use of few and fast FE simulations allows to estimate an analytical function that takes into account the process conditions and that can be used in combination with experimental results in order to estimate the friction coefficient in THF processes will be shown.     

Nanoscale chemistry and mechanical properties of tribofilms on Al–Si alloy (A383): interaction of ZDDP,calcium detergent and molybdenum friction modifier

Abstract

The interaction of a friction modifier and a calcium phenate detergent additive, with zinc dialkyl dithiophosphates (ZDDPs) in the formation of antiwear films on A383, has been studied using synchrotron radiation and nanoindentation techniques. X-ray absorption near edge structure (XANES) spectroscopy has shown that films prepared from oils containing both ZDDP and detergent, and ZDDP and molybdenum dithiocarbamate (MoDTC), are chemically similar to, but thicker than those made from oils containing only ZDDP. In addition, wear was greatly reduced in the presence of the detergent which was correlated with the basicity and the presence of the friction modifier. The phosphorus K and L edge XANES spectra show that the tribofilms are polyphosphate glasses of similar nature to those found on steel, but characterised by a shorter chain length. The sulphur K edge shows a MoS₂ like film and under certain conditions, the presence of a sulphate species is detected. High resolution topographic images and mechanical properties were determined by atomic force microscopy and imaging nanoindentation. The films formed in the presence of the detergent exhibited similar mechanical responses independent of the conditions tested. The indentation modulus of the films on the Al matrix always appear much softer than the films formed on the Si grains whether or not the lubricant contains only ZDDP, or both ZDDP and MoDTC.     

Role of thermal,mechanical and oxidising treatment on structure and chemistry of carbon black and its impact on wear and friction: Part 2 – Boundary lubrication condition

Mineral oil formulations with zinc dialkyl dithiophosphate (ZDDP) and dispersant (poly isobutylene succinimide ashless dispersant or ‘PIBSA’) and fully formulated oils with and without carbon black were subjected to thermal and mechanical treatment and tribologically tested on TE 77 (high frequency reciprocating rig or ‘HFRR’) machine to examine the frictional performance during the test. These results were compared to oils without carbon black and oils with diesel soot. Results indicate that oils with just ZDDP and dispersant had the highest friction that remains constant for the duration of the test while oils with carbon black in the milled and oxidised condition had the lowest coefficient of friction and the smallest surface roughness in the tribofilm. The mechanism of wear with treated carbon black and diesel soot was found to be polishing wear as evidenced by the scanning probe microscopy images of the tribofilms. Tribofilms were analysed with X-ray absorption near edge structure (XANES) and it was seen that oils without carbon black or even with untreated carbon black had sulphates at the surface, while the oils with carbon black that were treated had a higher proportion of sulphides. A combination of both FeS and ZnS was found in the tribofilms along with short chain phosphates of Zn.     

Sorption and Preconcentration of Vanadium,Chromium, Manganese,and Lead on Silica Gel Modified with (3‐Mercaptopropyl) Trimethoxysilane

Abstract

3‐mercaptopropyltrimethoxysilane, (CH₃O)₃SiCH₂CH₂CH₂SH, loaded on silica gel was used as a preconcentration sorbent for V, Cr, Mn and Pb prior to their determination by graphite furnace atomic absorption spetrometry (GFAAS). Surface characteristics and surface area of the silica gel before and after chemical modification were determined by elemental analysis. The retention and recovery of the analyte elements were studied by applying batch and column techniques. The experimental parameters, such as the effect of pH of the sample, shaking time in batch technique, flow rate of the eluent, the concentration of acid solution in the column section, and the amount of silica on retention and elution have been investigated. All elements were quantitatively (≥90%) recovered in the batch technique with R.S.D. values of 3.0 for vanadium, 1.8 for chromium, 1.7 for manganese, and 0.4 for lead. The same recoveries were obtained in the column techniques for all elements, while manganese in sea water could not be succesfully recovered. Detection limits of the method for vanadium, chromium, manganese, and lead are 1.1, 1.4, 1.3, and 0.8 ng, respectively.     

Effect of elastic deformation by compression,tension, and torsion on the critical magnetic field distribution in a steel 15XH4Д

Effect of deformation by compression, tension, and torsion on magnetic characteristics and critical magnetic field distribution in a high-strength economically alloyed structural steel 15XH4Д. The coercive force, residual induction, and maximum magnetic permeability vary definitely with changing stresses. This fact gives the principal possibility to use these characteristics as parameters for magnetic testing of elastic strains. Moreover, the studies of critical magnetic field distribution allow us to obtain data on the volume of the ferromagnet, which has changed its state in a given magnetic field under certain mechanical stresses.     

Numerical study of deformation textures, yield locus, rolling components and Lankford coefficients for FCC polycrystals using the new polycrystalline ?-model

In this paper, we discuss results from the new viscoplastic non-linear intermediate ?-model for crystal plasticity. We used this viscoplastic ?-model in order to compute several properties and indicators directly connected to the formability of FCC polycrystalline metals. For instance, the yield locus, the Lankford coefficients and the typical FCC rolling texture component and their evolution during plastic deformation are computed. We also compare our results to those predicted by the tangent viscoplastic self-consistent model as well as those obtained by the upper and lower bounds (Taylor and Static). Results concerning FCC metals subjected to plane strain compression (commonly used for the approximation of the rolling process) are presented. As in the self-consistent scheme, the viscoplastic ?-model takes into account the strength of grains interactions. The influence of the grain interaction on predicted results is discussed. This analysis of the change in predicted results for different values of the parameter controlling the grain interaction strength (from a stiff to a more compliant interaction) shows that the results depend strongly on ?.     

1‐Pyrenemethanol,a Useful Fluorometric Reagent for the Detection and Determination of Carboxylic Acids in Atmospheric Samples

Abstract

A rapid fluorometric procedure for the selective and sensitive determination of carboxylic acids, based on pre‐column derivatization using 1‐pyrenemethanol, was optimized and applied to atmospheric sampling. The optimum conditions for derivatization were determined to be: reaction solvent–dichloromethane, temperature ?44°C, reaction time ?30 min, and reagent/total acid ratio ?15. Separation of the derivatives of acids up to twenty carbons by reversed‐phase (C₈) chromatography was achieved in 25 min using a water/acetonitrile gradient with a limit of detection for the derivatives of 20 pg for a 20 µL injection. A scanning detector with good spectral resolution allows qualitative identification of the components in complex samples. When used in atmospheric analysis, the recoveries of carboxylic acids from spiked samples were >80% with repeatabilities below 10% RSD. Low molecular weight acids were encountered predominantly in the vapor phase (0.20 to 92 ng/m³), whereas higher molecular weight acids were found mostly in particulate form (0.15–129 ng/m³).     

Staging of a localized plastic deformation upon the tension of Д16AT alloy specimens on the basis of acoustic emission,surface deformation mapping,and strain gauging data. II. Specimens with notches of different depths

Studies of the development of deformations and damage in Д16AT alloy specimens with side notches, which modeled cracks in objects, were performed by combining the acoustic emission, surface deformation mapping, and strain gauging methods. It was shown that a significant portion of the loading time is associated with crack propagation, which is accompanied by the appearance of a segment with a negative value of the strain strengthening coefficient in loading diagrams. According to the data from the correlation of digital images at the plastic deformation stage (within stage 2), two substages were distinguished: the first is related to the deformation localization directly at the notch apex, while the second is associated with an increase in the area of this region to dimensions that are comparable with the specimen cross section. It was revealed that, in the case of a significantly localized deformation, the staging-based approach to the analysis of deformation and fracturing processes is characterized by the better correlation between data that are recorded by different in situ methods.     

A Comparative Study on Taguchi’s SN Ratio, Minimising MSD and Variance for Nominal-the-Best Characteristic Experiment

Taguchi uses a coefficient of variation for the nominal-the-best characteristic to define its signal-to-noise (SN) ratio. Optimisation can be accomplished in two steps: first by maximising the SN ratio; the mean is then adjusted to the target. In addition to Taguchi’s traditional SN ratio (η ₁ ), we can minimise the mean square deviation (MSD), (η ₂ ), and variance (η ₃ ) as an index. The purpose of this paper is to present a comparative study employing three indices and mathematical programming to obtain the optimal parameter design to select the best index. Simulation is used in making the selection. The basis for evaluating efficiency is the percentage reduction of quality loss. Depending on the results, η ₃ is better than η ₁ and η ₂ . If there is no adjustment factor to adjust the mean to the target, η ₂ is better than η ₁ , otherwise the efficiency of η ₁ and η ₂ is the same. Therefore, we recommend employing η ₃ for the nominal-the-best characteristic experiment. ID="A1" Correspondence and offprint requests to: F.-C. Wu, Department of Industrial Management, Van-Nung Institute of Technology, 1 Van-Nung Road, Chung-Li, Taiwan 320. E-mail: shogo@cc.vit.edu.tw     

Development of a high-voltage waveguide photodetector comprised of Schottky diodes and based on the Ge–Si structure with Ge quantum dots for portable thermophotovoltaic converters

This paper demontstrates the possibility of developing a high-voltage waveguide photodetector comprised of Schottky diodes and based on a Au/Ge — Si structure with Ge quantum dots pseudomorphic to a silicon matrix, which ensures an increase in the external quantum yield and open-circuit voltage. It is shown on this photodetector that there is a great increase and broadening in sensitivity up to λ = 2.1 μm, which coincides with the main radiation range of a black (gray) body at the emitter temperatures from 1200 to 1700 °C, practically used in thermophotovoltaic converters. This state of the ensemble of Ge quantum dots by means of molecular beam epitaxy can be obtained only under the condition of low growth temperature (250–300 °C). It is established that, below the Si absorption edge, photoresponse on the photodetectors under consideration is determined by two main mechanisms: absorption on the ensemble of Ge quantum dots and Fowler emission. It is shown by the analysis of the Raman scattering spectra on the optical photons of Ge–Si structures that the quantum efficiency of photodetectors based on them in the first case is due to the degree of nonuniform stress relaxation in the array of Ge quantum dots. The photoresponse directly associated with the Ge quantum dots is manifested on Schottky diodes with a superthin intermediate oxide layer SiO₂, which eliminates the second mechanism. In further development, the proposed photodetector architecture with pseudomorphic Ge quantum dots can be used both for portable thermophotovoltaic converters and fiber-optic data transmission systems at wavelengths corresponding to basic telecommunication standards (λ = 0.85, 1.3 and 1.55, 1.3, and 1.55 μm) on the basis of silicon technologies.     

Comments on “Study and application of discharge calibration for submerged radial gates” by Guo X., Guo Y., Wang T., Fu H., Li J. Flow Meas. Instrum. 78 (2021) 101912, https://doi.org/10.1016/j.flowmeasinst.2021.101912

This paper discusses the capability of Guo et al.'s (2021) equations to determine the discharge of radial gates under submerged flow conditions. It was concluded that Guo et al.'s (2021) equations are associated with error reduction compared to the Incomplete Self-Similarity (ISS) theory and the calibration method. However, it does not have a significant advantage over Energy-Momentum (E-M) approach. Employing E-M principles, new equations were proposed to determine the discharge of radial gates, which has some advantages compared to Guo et al. (2021), such as (1) error reduction under partially and fully submerged flow conditions, (2) least dependence on the empirical constants, (3) uniformity of form over the entire submerged condition, and (4) no need to classify the submerged flow. Field calibration showed that the proposed equations in the present study for a single gate predict the discharge of parallel radial gates with a mean absolute error of less than 4.5% subject to the submerged operation of all open gates.