Wear of ZA27/10SiC/1Gr hybrid composite

Metal matrix composites are extensively researched due to their potential advantages over monolithic alloys. The paper presents the wear characteristics of a hybrid composite based on zinc-aluminium ZA27 alloy, reinforced with silicon-carbide (SiC) and graphite (Gr) particles. The tested sample contains 10 vol.% of SiC and 1 vol.% Gr particles. The experiments on the ZA27/SiC/Gr composite were performed on a computer supported tribometer with “block-on-disc” contact geometry under conditions of dry sliding. The paper contains the procedure for preparation of sample composites and presents the microstructure of the composite material and the base ZA27 alloy observed by metallurgy microscope. The wear behaviour of the alloy and the composite were determined under different test conditions, by varying normal loads and sliding speeds

COMPARISON BETWEEN DIFFERENT CALCULATION PROCEDURES OF LOADS CAUSED BY TEMPERATURE DILATATION IN PIPELINES

The problem of loads caused by the temperature dilatations in pipes and its effect on strain and stress state of the entire pipeline is common problem in engineering practice. This paper describes three methods for calculation of loads that can occur in the pipeline caused by temperature differences. The study presented in the paper analysed the L shaped pipeline configuration with an operating temperature at 200°C, pipeline material P235GH, angle between legs of the L shaped pipeline is 90, pipe dimension DN 300 and operating pressure is 10 bar (absolute pressure). The calculation was presented according to standards EN 13480-3 and AD 2000 and Russian method commonly used in engineering practice. The three methods have different engineering approaches for solving the same type of the problem, so the specific differences were presented in the paper. All the results are presented in unified tables for easier comparison and analysis. It can be conducted that all three presented methods showed similar results and choosing the most suitable one for the practical application is mainly determined by the type of the result needed for the specific application

Design of Modern Concept Tribometer with Circular and Reciprocating Movement

This paper considers construction and advantage of modern tribometer conception. Tribometer TPD-04 enables simulation of different contact and test types. Special device enables pin on disk, circular and linear reciprocating test types. The main purpose of tribometer was investigation of friction and wear of polymer materials with or without lubricant according to appropriate standards. Tribometer concept and design solution of same subassemblies that provide defined requests fulfill were described in details. Measure system and software for data acquisition and processing results are specially described.Publishe

Pushing the limits of self-supervised ResNets: Can we outperform supervised learning without labels on ImageNet?

Despite recent progress made by self-supervised methods in representation learning with residual networks, they still underperform supervised learning on the ImageNet classification benchmark, limiting their applicability in performance-critical settings. Building on prior theoretical insights from ReLIC [Mitrovic et al., 2021], we include additional inductive biases into self-supervised learning. We propose a new self-supervised representation learning method, ReLICv2, which combines an explicit invariance loss with a contrastive objective over a varied set of appropriately constructed data views to avoid learning spurious correlations and obtain more informative representations. ReLICv2 achieves $77.1\%$ top-$1$ accuracy on ImageNet under linear evaluation on a ResNet50, thus improving the previous state-of-the-art by absolute $+1.5\%$; on larger ResNet models, ReLICv2 achieves up to $80.6\%$ outperforming previous self-supervised approaches with margins up to $+2.3\%$. Most notably, ReLICv2 is the first unsupervised representation learning method to consistently outperform the supervised baseline in a like-for-like comparison over a range of ResNet architectures. Using ReLICv2, we also learn more robust and transferable representations that generalize better out-of-distribution than previous work, both on image classification and semantic segmentation. Finally, we show that despite using ResNet encoders, ReLICv2 is comparable to state-of-the-art self-supervised vision transformers

MICROSTRUCTURE INFLUENCE ON FRICTION BEHAVIOR OF THE TI6AL4V BIOMEDICAL ALLOY AT LOW LOADS

Dynamic friction coefficient (COF) between Ti6Al4V and Al2O3 was analyzed under low loads (100 mN, 250 mN, 500 mN, 750 mN, 1000 mN), sliding speed (4 mm/s, 8 mm/s, 12 mm/s) at dry contact and in the Ringer's solution. Different Ti6Al4V microstructures were studied: Sample 1 - fully lamellar; Sample 2 - martensitic; sample 3 - equiaxed; and sample 4 - globular microstructure. The maximum COF values varied as: 0.4 - 1.23 (Sample 1), 0.5 – 2.8 (Sample 2), 0.4 – 1.1 (Sample 3), and 0.4 – 2.3 (Sample 4). Lamellar and martensitic microstructures were not beneficial for the tribological response since they exhibited severe wear and very high COF values. The globular Ti alloy microstructure showed extremely high COF and wear under dry conditions. In general, water quenching was not a favorable treatment for tribological behavior. The lowest COF values and wear volumes were exhibited in the case of equiaxed microstructure

Digital image correlation in analysis of stiffness in local zones of welded joints

Ponašanje zavarenih spojeva u lokalnim zonama, kao i njihov uzajamni utjecaj, jedan je od glavnih problema u projektu zavarene konstrukcije. Naime, osnovni je problem u određivanju mehaničkih svojstava materijala u zavarenom spoju. Ta su svojstva neophodna za točan proračun zavarenih konstrukcija. Mogućnost dobivanja vrijednosti lokalne deformacije/pomaka čini tehniku "Digital Image Correlation" (DIC) pogodnom za ispitivanje zavarenog spoja i određivanje mehaničkih svojstava. Tijekom ovih ispitivanja za opterećenje je korišten uređaj za vlačnu provjeru, a dvije kamere su korištene za 3D analizu deformacije. Upotrijebljen je uzorak s paralelnim stranama dobiven zavarivanjem V spoja. Prije ispitivanja izvršeno je kalibriranje kako bi se dobili što točniji rezultati. U radu je predstavljena primjena DIC tehnike korištenjem Aramis softvera za mjerenje lokalnog pomaka/deformacije u zavarenom spoju. Dobiveni rezultati pokazuju da je zavareni spoj bio nejednako deformiran s prednje i zadnje strane korijena, u području elastične deformacije, tijekom vlačnog opterećenja. Zbog vlaka u uzorku s V-zavarom (osnovni materijal S235JRG2, žica elektrode - VAC 60), postoji uzajamni utjecaj mehaničkih svojstava lokalnih zona, gdje je krutost korijena zavara najviša.The behaviour of welded joints in local zones, as well as their mutual influence, represents one of the main challenges in welded structure design. Namely, the main issue lies in determining the mechanical properties of materials in a welded joint. These properties are necessary for an accurate calculation of welded structure integrity. The possibility of obtaining local strain/displacement values makes the "Digital Image Correlation" (DIC) technique suitable for welded joint testing and determining of mechanical properties. In this paper a tensile testing machine was used for loading and a two camera system was used for 3D strain analysis. A specimen with parallel sides, obtained by welding of a V joint was used. Calibration was performed prior to testing, in order to ensure dimensional consistency of the system. Application of DIC technique using Aramis software for measuring local displacement/strain in a welded joint is presented in this paper. Due to tension in the V-weld specimen (Base material - S235JRG2, electrode wire - VAC 60), mutual influence of mechanical properties of local zones is present, wherein the root weld had the highest stiffness

FRICTION FACTOR OF THE FLUID FLOW THROUGH POROUS MEDIA

This paper deals with the theoretical foundations aimed for modeling and simulation of fluid flow through porous structures and related friction. Different approaches to determination of the analytical solution of the friction factor are presented, as well as formulas that are used in specific flow regimes. Review of fluid types from aspect of viscosity are shown, namely Newtonian and non-Newtonian fluids and related aspects of the fluid behaviour. Review of the established dependencies of the friction factor on the influential factors is presented, such as on Reynolds number, pore geometry, permeability and inertia coefficients. Differences between smooth and rough surfaces in contact with the fluid are observed, from aspects of friction. Geometry of the porous structure essentially influences the flow and governs the friction, as well as the surface roughness. The pressure drop within a porous structure is directly influenced by the permeability and drags force coefficients and can well characterise cellular materials. Wall roughness typically enhances the turbulence and transition from laminar to turbulent flows appears earlier for rough than for smooth surfaces. One short example of CFD modeling of the fluid flow through porous media is shown, as well as generation of the Voronoi based open cell pattern.Publishe

WEAR BEHAVIOUR OF HYBRID ZA27/SIC/GRAPHITE COMPOSITES UNDER DRY SLIDING CONDITIONS

The paper deals with tribological behaviour of hybrid composites based on ZA27 alloy reinforced with silicon-carbide (SiC) and graphite (Gr) particles. The tested sample contains 5% of SiC and 1% Gr particles. The experimental tests were performed on a “block-on-disc” tribometer. The main tribological parameter in the analysis was wear scar width, obtained by variation of normal loads and sliding speeds, under dry sliding conditions. Through observation of the changes in wear scar widths in dry sliding conditions, corresponding conclusions were made.Publishe

Morfološke karakteristike fitopatogenih gljiva Leptosphaeria Maculans i Leptosphaeria Biglobosa uzročnika raka stabla uljane repice u Srbiji

Cancer stem and blackleg is economically the most important disease of oilseed rape worldwide. This disease is caused by two species of plant pathogenic fungi of the genus Leptosphaeria: Leptosphaeria maculans (Desm.) ces. and de Not anamorf Phoma lingam (Tode. Fr.) Desmas, i Leptosphaeria biglobosa Shoem and Brun. On nutrient PDA medium at 25 ± 1 º C were studied morphological traits (growth, appearance and color of mycelia, set the edge colonies, the presence of fruiting bodies, the smell and the secretion of pigment, the size, shape and color of pycnidia and piknospora) 12 isolates (isolated in Serbia K -112, K-113, K-114, K-115, K-117, K-8, LJ-3, L-10, GS-27, St-12, S-2 and C-5) and control 2 (Lm, Lb) mushrooms. Isolates K-112, K-113, K-114, K-115, K-117 having a quick and regular increase, secreted yellow brown pigment, while K-8, LJ-3, L-10, GS-27, ST-12, S-2 and C-5 form irregular colonies with no pigment, have slow growth and abundant sporulation. The experiment was set up in the four repeats and mycelial growth isolates listed was measured in cm after 5, 10 and 15 days.Rak stabla i suva trulež korena je ekonomski najvažnije oboljenje uljane repice širom sveta. Ovu bolest prouzrokuju dve vrste fitopatogenih gljiva iz roda Leptosphaeria: Leptosphaeria maculans (Desm.) ces. and de Not anamorf Phoma lingam (Tode. Fr.) Desmas, i Leptosphaeria biglobosa Shoem and Brun. Na hranjivoj PDA podlozi pri temperaturi 25±1ºC proučavane su morfološke osobine (porast, izgled i boja micelije, izgled ivice kolonije, prisustvo plodonosnih tela, miris i lučenje pigmenata, veličina, oblik i boja piknida i piknospora) 12 izolata (izolovanih u Srbiji K- 112, K-113, K-114, K-115, K-117, K-8, LJ-3, L-10, GS-27, St-12, S-2 i C-5) i 2 kontrolna (L.m,L.b) gljive. Izolati K-112, K-113, K-114, K-115, K-117 imaju brz i pravilan porast,luče žuto mrki pigment,dok K-8, LJ-3, L-10, GS-27, St-12, S-2 i C-5 obrazuju nepravilne kolonije bez pigmenta,imaju spor porast i obilniju sporulaciju. Ogled je postavljen u četiri ponavlja a porast micelije navedenih izolata je meren u cm posle 5, 10 i 15 dana

Influence of the biomaterial porosity on the host tissue response, the friction and adhesion

The paper presents short review of different aspects of the introduction of porosity into the bulk biomaterial and effects on different material characteristics, especially related to friction and adhesion. Nowadays, there is a great interest to investigate relations between porosity, different mechanical signals due to controlled topography and cell responses generated accordingly. Examples of current investigations of custom developed scaffolds for tissue engineering related to cell seeding and hip stem component are shown. Friction, adhesion and adhesive forces are briefly defined as related to porous material structures and the relevance of nano- and micro-level surface layers in such structures. Patterning techniques and microfabrication techniques for production of controlled and random porous surface layers are given. Influence of porosity on adhesion and friction is presented through several existing experimental results. However, there is a lack of existing data related to many aspects of these novel porous materials and structures.Publishe