A laboratory-numerical approach for modelling scale effects in dry granular slides

Granular slides are omnipresent in both natural and industrial contexts. Scale effects are changes in physical behaviour of a phenomenon at different geometric scales, such as between a laboratory experiment and a corresponding larger event observed in nature. These scale effects can be significant and can render models of small size inaccurate by underpredicting key characteristics such as ow velocity or runout distance. Although scale effects are highly relevant to granular slides due to the multiplicity of length and time scales in the flow, they are currently not well understood. A laboratory setup under Froude similarity has been developed, allowing dry granular slides to be investigated at a variety of scales, with a channel width configurable between 0.25-1.00 m. Maximum estimated grain Reynolds numbers, which quantify whether the drag force between a particle and the surrounding air act in a turbulent or viscous manner, are found in the range 102-103. A discrete element method (DEM) simulation has also been developed, validated against an axisymmetric column collapse and a granular slide experiment of Hutter and Koch (1995), before being used to model the present laboratory experiments and to examine a granular slide of significantly larger scale. This article discusses the details of this laboratory-numerical approach, with the main aim of examining scale effects related to the grain Reynolds number. Increasing dust formation with increasing scale may also exert influence on laboratory experiments. Overall, significant scale effects have been identified for characteristics such as ow velocity and runout distance in the physical experiments. While the numerical modelling shows good general agreement at the medium scale, it does not capture differences in behaviour seen at the smaller scale, highlighting the importance of physical models in capturing these scale effects

Wpływ tarcia na proces tłoczenia blach stosowanych w lotnictwie

An important factor in the possibility of obtaining correct drawn parts with the desired functional properties is the friction between the stamped sheet and the tool. The article discusses the impact of technological lubricants developed according to our own formulas, based on vegetable oils, on the stamping process taking into account the strain distributions in the drawn parts. Biodegradable lubricants based on rapeseed oil with an addition of stearic acid or boric acid were used. The results of the friction coefficient in a strip drawing test and the numerical analysis results of the stamping process of a spherical cap from sheet metal: aluminium 2024, commercially pure titanium Grade 2, steel 5604 in dry friction and lubrication conditions, are presented. Strain distributions and changes in the drawn part wall thickness were analysed.Istotnym czynnikiem decydującym o możliwości uzyskania poprawnych wytłoczek o żądanych właściwościach użytkowych jest tarcie występujące pomiędzy tłoczoną blachą a narzędziem. Tarcie występujące w procesach obróbki plastycznej ma bezpośredni wpływ na: rozkład naprężeń i odkształceń w objętości kształtowanego materiału, graniczną - możliwą do uzyskania wysokość wytłoczki oraz wielkość siły tłoczenia. Podstawowym sposobem ograniczania wielkości oporów tarcia w obróbce plastycznej jest odpowiednie smarowanie. Dodatkowo smary technologiczne zapobiegają bezpośredniemu kontaktowi obrabianego materiału z narzędziem, a tym samym zacieraniu i nalepianiu kształtowanego materiału na powierzchniach roboczych narzędzia, przez co znacząco wpływają na jakość otrzymywanych elementów oraz trwałość narzędzi. Smary dobiera się do konkretnych procesów oraz rodzaju kształtowanych materiałów, wielkości nacisków, stanu współpracujących powierzchni oraz prędkości poślizgu i temperatury pracy. Wpływ poszczególnych czynników na opory tarcia jest złożony i wymaga prowadzenia szeregu badań doświadczalnych z zakresu przydatności smaru technologicznego do poszczególnych procesów formowania. W artykule omówiono wpływ smarów technologicznych opracowanych według własnych receptur na przebieg procesów tłoczenia z uwzględnieniem rozkładów odkształceń w wytłoczkach. Zastosowano biodegradowalne smary oparte na olejach roślinnych tj. oleju rzepakowym z dodatkiem kwasu stearynowego lub kwasu borowego. Przedstawiono wyniki badań współczynnika tarcia w próbie przeciągania pasa blachy oraz wyniki analiz numerycznych procesu tłoczenia czaszy kulistej z blach: aluminiowej 2024, tytanowej Grade2 i stalowej 5604 w warunkach tarcia technicznie suchego oraz w warunkach smarowania. Analizowano rozkłady odkształceń oraz zmiany grubości ścianek wytłoczek

Friction and wear testing of titanium and aluminium alloys

W pracy przedstawiono metodykę badań tarciowo-zużyciowych materiałów przeznaczonych do zastosowań w przemyśle lotniczym. Badaniu poddano próbki wykonane z tytanu technicznego Grade 2 i Grade 4, stopu tytanu Grade 5 oraz stopów aluminium 6061T4, 2017A i 2024. Pomiary siły tarcia oraz zużycia elementów pary trącej typu rolka-klocek przeprowadzono na testerze tribologicznym T-05. Badania prowadzono w warunkach tarcia technicznie suchego, dla skoncentrowanego styku ślizgowego obciążonego siłą 150 N. Droga tarcia dla każdego testu wynosiła 330 m. Podczas badań doświadczalnych próbki współpracowały z przeciwpróbką stalową o twardości 63 HRC. Porównywano średnie wartości współczynników tarcia badanych skojarzeń materiałowych. Zaprezentowano przebiegi sumarycznego zużycia liniowego współpracujących elementów pary trącej rolka-klocek w funkcji drogi tarcia. W trakcie badań wyznaczono również ubytek masy współpracujących elementów par trących „tytan-stal” i „aluminium-stal” oraz przyrost temperatury w węźle tarcia.This study presents a methodology of friction and wear testing of materials for applications in the aviation industry. Tests were carried out for specimens made of technically pure titanium Grade 2 and Grade 4, titanium alloy Grade 5 and aluminium alloys: 6061T4, 2017A and 2024. Measurement of friction and wear of the parts in the block-on-ring frictional pair were carried out on a tribological tester T-05. The study was carried out under conditions of technically dry friction for the concentrated sliding contact loaded with 150 N. Friction distance for each test was 330 m. The specimens used in the experiments were coupled with a steel counter-specimen with hardness of 63 HRC. The average values of friction coefficients for the analysed material pairs were compared. The profiles for total linear wear of both parts of the block-on-ring frictional pair were also presented. The mass loss for the parts of the “titanium-steel” and “aluminium-steel” frictional pairs and temperature increments in the frictional pair were also determined

The Effect of the Use of Technological Lubricants Based on Vegetable Oils on the Process of Titanium Sheet Metal Forming

The paper evaluates the drawability of titanium sheet metal Grade 2, with the focus on friction conditions that are present in the sheet metal forming process. The study aims to present the results of the examinations of the friction coefficient during a strip drawing test. The focus of the experiment was on lubricants based on vegetable oils i.e. rapeseed oil, sunflower oil and olive oil. Boric acid was used to improve the lubricating properties of vegetable oils. The results of numerical simulations of the process of forming a cover with stiffening components made of grade 2 titanium sheet metal was also presented. The numerical simulation was carried out using the FEM method with PAMStamp 2G software. The effect of conditions of friction between the sheet metal and tool parts and pressure force of the blank holder on the forming process were investigated. Numerical calculations were performed with consideration for the phenomenon of material strain hardening and anisotropy of plastic properties of the sheet metal formed. The analysis of the deformations and reduction in wall thickness of the drawn parts can be used for determination of the effect of changes in selected parameters on the process of drawn part forming. The quality of drawn parts was assessed based on the shape inaccuracy determined during simulation of forming. The inaccuracy depended on the conditions of the process and strength properties of the titanium sheet metal

EPR Study of Ammonium Nitrate Doped with Copper(II) Ions

This work is devoted to a study of the structural changes in a single crystal of ammonium nitrate, NH$\text{}_{4}$NO$\text{}_{3}$, doped with copper(II) cations by electron paramagnetic resonance. Ammonium nitrate crystallizes at atmospheric pressure in several polymorphic forms, phase VII → V → IV → III → II → I → melt, with transition temperatures of 103 K, 255 K, 305 K, 357 K, 398 K, and 443 K, respectively. The aim of our work was to study the temperature phase transition V → IV at about 255 K using electron paramagnetic resonance technique. The electron paramagnetic resonance spectra were performed using an X-band spectrometer with microwave frequency of 9.4 GHz and magnetic modulation of 100 kHz in the temperature range of 153-296 K. For a single crystal the angular dependence of the copper(II) electron paramagnetic resonance spectra was measured at 293 K and 168 K. The anisotropic behaviour measured at 293 K points to the existence of one kind of two equivalent copper(II) complexes with inverse g and A tensors. A second pair of equivalent complexes also with inverse g and A tensors was observed. The minimal values of g-factors correspond to the maximum values of A. The angular dependence taken at 168 K shows the existence of two types of non-equivalent copper complexes which differ in comparison with the complexes observed at room temperature. The temperature dependence of the intensities of hyperfine structure lines for all copper(II) complexes observed shows a phase transition V → IV occurring in the temperature range of 237-246 K with a hysteresis. One of the hyperfine structure lines of a copper(II) complex measured at low temperatures shows a superhyperfine structure with line intensities 1:2:3:2:1 originating from the interaction of the copper $\text{}^{63,65}$Cu (I=3/2) nucleus with two $\text{}^{14}$N (I = 1) nuclei of two ammonia, NH$\text{}_{3}$, ligand molecules

Influence of frictional conditions on strain distribution in sheet-metal forming of some parts

Procesy tłoczenia blach stanowią jedną z ważniejszych technologii kształtowania wyrobów cienkościennych. Rozpatrując proces tłoczenia jako system tribologiczny, szczególną uwagę należy zwrócić na smar technologiczny, który znacząco wpływa na jakość otrzymywanych elementów. W artykule omówiono wpływ smaru technologicznego na rozkład odkształceń w wytłoczkach. Przedstawiono wyniki badań współczynnika tarcia w próbie przeciągania pasa blachy oraz wyniki analiz numerycznych procesu tłoczenia blach.Sheet-metal forming processes are one of the most important technologies used for forming sheet-metal parts. Considering sheet-metal forming process as a tribological system, particular attention should be paid to the technological lubricant, which significantly affects quality of the produced components. The article discusses an impact of the technological lubricant on a strain distribution in the drawn-parts. The friction coefficients which have been determined in the strip drawing test, as well as the results of numerical analyses of the sheet-metal forming process are given

Examinations of Steel Overlap Joints Obtained Using the Friction Stir Welding Technology

The aim of the study was to analyse mechanical properties and microstructure of joints obtained using friction stir welding (FSW) technology. The focus of the study was on overlap linear FSW joints made of 1.4541 DIN 17441 steel sheets with thickness of 1.2 mm. Tools used during friction stir welding of steel joints were made of W-Re alloy. The joints were subjected to visual inspection and their load bearing capacity was evaluated by means of the tensile strength test with analysis of joint breaking mechanism. Furthermore, the joints were also tested during metallographic examinations. The analysis performed in the study revealed that all the samples of the FSW joints were broken outside the joint area in the base material of the upper sheet metal, which confirms its high tensile strength. Mean load capacity of the joints was 15.8 kN. Macroscopic and microscopic examinations of the joints did not reveal significant defects on the joint surface and in the cross-sections

Assessment Of Joints Using Friction Stir Welding And Refill Friction Stir Spot Welding Methods

FSW (Friction Stir Welding) and RFSSW (Refill Friction Stir Spot Welding) joints have been increasingly used in industrial practice. They successfully replace fusion-welded, riveted or resistance-welded joints. In the last two decades, dynamic development of this method has stimulated investigations of the fast methods for joint diagnostics. These methods should be non-destructive and easy to be used in technological processes. The methods of assessment of joint quality are expected to detect discontinuities in the structures welded using FSW and FSSW methods. Reliable detection of flaws would substantially extend the range of applications of FSW joints across many sectors of industry, including aviation. The investigations carried out in this paper allowed for characterization of defects present in FSW and RFSSW joints. Causes of these defects were also stressed. An overview of the methodologies for assessment of joint quality was presented. Results of assessment of the quality of joints made of 2024T6 aluminium sheet metal using FSW and RFSSW method were presented

Symulacja numeryczna procesu wykrawania dokładnego blach tytanowych

The present study has been undertaken in order to investigate the new possibilities of improvement in quality of the cut-surface of titanium blanks. For the intended purpose, a number of numerical simulations of the blanking process were carried out. Fine blanking is one of the most often used methods of finished product manufacturing. Application of blanking with reduced clearance or blanking with material upsetting by V-ring indenter allows for obtaining the high quality cut-surface which does not need further machining. Application of the finite element method (FEM) for numerical simulations allows for effective analysis of the fine blanking processes. In the paper the results of numerical simulation of fine blanking for a disk made of Grade 2 sheet titanium have been presented. The calculations were carried out using ADINA System v. 8.6 based on FEM. Determination of the effect of clearance between cutting edges, and presence and location of V-ring indenter on the stress and strain distribution in shearing zone was the main goal of the work. The numerical simulations showed the effect of tool geometry on a course of blanking process and consequently on the quality and shape of the cut-surface. Based on the numerical simulation it is only possible to deduce the cut-surface appearance, thus the numerical simulations should be completed with experimental tests.Niniejsza praca została wykonana w celu zbadania nowych możliwości poprawy jakości powierzchni przecięcia wykrojek tytanowych. W tym celu wykonano szereg symulacji numerycznych procesu wykrawania. Wykrawanie dokładne jest najczęściej stosowaną metodą otrzymywania wyrobów gotowych. Zastosowanie wykrawania ze zmniejszonym luzem lub wykrawania ze spęczaniem za pomocą klinowej grani pozwala na otrzymanie wysokiej jakości powierzchni przecięcia, ktä nie wymaga dalszej obróbki mechanicznej. Wykorzystanie w symulacjach numerycznych metody elementów skończonych (MES) pozwala na efektywną analizę procesów wykrawania dokładnego. W artykule zaprezentowano wyniki symulacji numerycznej wykrawania dokładnego krążka z blachy tytanowej Grade 2. Obliczenia wykonano przy użyciu programu ADINA System v. 8.6 opartego na MES. Głównym celem pracy było określenie wpływu luzu pomiędzy krawędziami tnącymi oraz obecności klinowej grani na dociskaczu na rozkład naprężeń i odkształceń w obszarze cięcia. Obliczenia numeryczne wykazały wpływ geometrii narzędzi na przebieg procesu wykrawania, a tym samym na jakość i kształt powierzchni przecięcia. Opierając się na symulacjach numerycznych można jedynie wnioskować o wyglądzie powierzchni przecięcia, dlatego symulacje numeryczne powinny być uzupełnione badaniami doświadczalnymi