Surface roughness modeling of CBN hard steel turning

Study in the paper investigate the influence of the cutting conditions parameters on surface roughness parameters during turning of hard steel with cubic boron nitrite cutting tool insert. For the modeling of surface roughness parameters was used central compositional design of experiment and artificial neural network as well. The values of surface roughness parameters Average mean arithmetic surface roughness (Ra) and Maximal surface roughness (Rmax) were predicted by this two-modeling methodology and determined models were then compared. The results showed that the proposed systems can significantly increase the accuracy of the product profile when compared to the conventional approaches. The results indicate that the design of experiments modeling technique and artificial neural network can be effectively used for the prediction of the surface roughness parameters of hard steel and determined significantly influential cutting conditions parameters

Stanje površinskog sloja materijala obratka kod visokoučinskog brušenja

This paper focuses on the development of high temperatures in the cutting zone during high performance grinding. In order to identify the influence of grinding temperature on surface integrity, temperatures were measured in the workpiece surface layer under different machining conditions. Beside this, under the same conditions, the surface layer properties of the workpiece material were determined through metallographic examination. Microstructureand microhardness of the workpiece surface layer, as well as the burned surfaces and microcracks phenomena were investigated. The conducted experimental investigations allow the surface layer properties of the workpiece material in high performance grinding to be defined.U članku se ukazuje na pojavu visokih temperatura u zoni rezanja pri visokoučinskom brušenju. Da bi se ustanovio utjecaj temperature brušenja na kvalitet obrađene površine, izmjerene su temperature u površinskom sloju materijala obratka pri različitim uvjetima obrade. Ujedno je pri istim uvjetima obrade određeno stanje površinskog sloja materijala obratka metalografskim ispitivanjima. Ispitane su mikrostruktura i mikrotvrdoća površinskog sloja obratka i pojava nagorjelih površina i mikropukotina. Izvedena eksperimentalna istraživanja defi niraju stanje površinskog sloja materijala obratka kod visokoučinskog brušenja

The role of phenotypic plasticity of life history and behavioural traits during speciation processes in Acanthoscelides obtectus

Fenotipska plastičnost, kao univerzalno svojstvo svih organizama, predstavlja sposobnost jednog genotipa da u različitim uslovima životne sredine razvije različite fenotipske vrednosti osobina. Ovaj fenomen predstavlja važan mehanizam fenotipskog variranja insekatа i nalazi se u osnovi formiranja različitih pravaca evolucionih promena njihovih populacija uzrokujući adaptivnu divergenciju i posledičnu međupopulacionu reproduktivnu izolaciju. Od posebne važnosti je i uloga fenotipske plastičnosti u procesima ekološke specijacije, kada ekološki zasnovana divergentna selekcija između životnih sredina ograničava protok gena između populacija. Koristeći pogodnosti laboratorijske evolucije, ova studija proučava osobine životne istorije, njihova međusobna ograničenja i obrasce plastičnih odgovora, populaciono-ekološke i selekcione obrasce kao i promenu reproduktivnog ponašanja kod dve grupe laboratorijskih populacija fitofagnog insekta, Acanthoscelides obtectus, koje su evoluirale na različitim biljkama domaćinima (pasulj, Phaseolus vulgaris i naut, Cicer arietinum). Populacije selektovane na različitim biljkama pokazuju jasne razlike u životnim strategijama i stepenu plastičnosti osobina životne istorije i ponašanja. Načelno, populacije selektovane na pasulju imaju izraženiju sposobnost plastičnog odgovora na variranje identiteta biljke domaćina u poređenju sa populacijama selektovanim na nautu. Selekcioni režimi pokazuju i umeren stepen reproduktivne izolacije čime se ističe značaj divergentne selekcije u početnim fazama procesa nastanka novih vrsta.Phenotypic plasticity, a universal feature of all organisms, represents genotypes’ ability to produce alternative phenotypes in different environmental conditions. In insects, this phenomenon represents an important mechanism of phenotypic variation and it is fundamental for the establishment of different evolutionary trajectories of their populations causing adaptive divergence and consequential interpopulation reproductive isolation. Phenotypic plasticity is of particular importance during the process of ecological speciation, when ecologically based divergent selection between environments reduces gene flow among populations. Using the benefits of laboratory evolution, this study investigates life history traits, their trade-offs and plasticity patterns, population dynamics and selection patterns, as well as changes in reproductive behaviour, in two sets of laboratory populations of a phytophagous insect, Acanthoscelides obtectus, evolved on different host plants (white beans, Phaseolus vulgaris and chickpeas, Cicer arietinum). Populations selected on different plant hosts demonstrate distinct life history strategies and plasticity levels of life history and behavioural traits. Generally, populations selected on beans demonstrate prominent ability to plastically respond to host plant variation compared to chickpea selected populations. Selection regimes demonstrate moderate level of reproductive isolation emphasizing the importance of divergent selection in the first phases of the speciation

Utjecaj mikrostrukture na proces nastajanja strugotine za konvencionalnu i polutekuću lijevanu Al-Cu leguru

For many metal alloys, the process of metal cutting is accompanied by extensive plastic deformation and fracture. To study this process, quick stop sectional samples of hypoeutectic Al-Cu alloy chip formation, either as conventionally cast alloy or as “semi solid metal” are used. The type of chip formation is classified according to crack formation mechanism and propagation. During cutting, in all specimens used, quasi-continuous chips with built-up edge (BUE) are obtained. The formation of BUE is undesirable since it is a highly deformed body with a semi stable top which periodically breaks away giving rise to poor workpiece surface quality.Za mnoge metalne legure, proces rezanja je praćen intenzivnom plastičnom deformacijom i lomom. Za istraživanje tog procesa u radu je korištena metoda brzog zaustavljanja procesa rezanja. Materijal uzorka je podeutektička Al-Cu legura, lijevana konvencionalno i kao „polu čvrsti metal“ (semi solid metal-SSM). Vrsta strugotine koja je obrazovana klasifi cirana je prema mehanizmu nastajanja i širenja pukotina. Tokom rezanja, u svim uzorcima nastajala je, kvazi-kontinuirano strugotina sa naslagama (BUE). Stvaranje BUE je nepoželjan proces, jer je to jako deformirani volumen sa polu stabilnim oblikom, koji povremeno raste i odvaja se, što dovodi do lošeg kvaliteta obrađene površine

The microstructure infl uence on the chip formation process of Al-Cu alloy cast conventionally and in semi solid state

For many metal alloys, the process of metal cutting is accompanied by extensive plastic deformation and fracture. To study this process, quick stop sectional samples of hypoeutectic Al-Cu alloy chip formation, either as conventionally cast alloy or as “semi solid metal” are used. The type of chip formation is classifi ed according to crack formation mechanism and propagation. During cutting, in all specimens used, quasi-continuous chips with built-up edge (BUE) are obtained. The formation of BUE is undesirable since it is a highly deformed body with a semi stable top which periodically breaks away giving rise to poor workpiece surface quality

Comparison of anti-Aspergillus activity of Origanum vulgare L. essential oil and commercial biocide based on silver ions and hydrogen peroxide

The antifungal activities of Origanum vulgare essential oil (EO) and of a biocide based on silver and hydrogen peroxide (Sanosil S003) against seven Aspergillus species isolated from different substrata (stone, brick, silk and paper) of cultural heritage objects in Serbia were evaluated. Microdilution, agar dilution and microatmosphere methods were used to determine minimal fungistatic and minimal fungicidal concentrations (MIC and MFC), and light microscopy to determine structural abnormalities. MIC and MFC values for O. vulgare EO ranged from 0.2 to 5 mg mL−1 and for Sanosil S003 from 5 to 250 mg mL−1. Aspergillus sp. sect. fumigati was the most susceptible isolate, where MIC and MFC values were achieved at 0.5 mg mL−1 for O. vulgare EO, while MIC and MFC values for Sanosil S003 were achieved at 5 and 10 mg mL−1, respectively. Morpho-physiological changes were documented in all isolates, including lack of sporulation, depigmentation of conidiogenous apparatus and conidia, and presence of aberrant fungal structures. O. vulgare EO exhibited stronger anti-Aspergillus activity than Sanosil S003, as demonstrated by the higher MIC and MFC values and fewer morpho-physiological changes observed in the tested Sanosil S003 concentrations. O. vulgare EO could be an excellent alternative to commercial biocides, with high potential in the field of cultural heritage conservation

Chemical reaction and diffusion dynamics

In this paper diffusion with chemical reaction was investigated. The concomitant advances in theory, measuring systems and computer simulation bring the new perspectives to the chemical reaction with diffusion studying. The chemical rate and diffusion rate parameters were considered. The obtained results shows effects the chemical reaction rate and diffusion rate. The obtained results demonstrate characterization of the dynamic and steady state conditions, transition between them and how it can be used to predict the stability of the system

Aksijalno-radijalni ležaj kao segment veze okretne platforme sa nosećom konstrukcijom

The paper presents the connection of rotating platforms in building and transport machines depending on the type of driving mechanism. A special attention is paid to axial-radial bearings having big diameters made by prominent manufacturers. There are some necessary conditions which have to be met by supporting frames because working capacity of the bearings depends on them. Also, the law of distribution of load of moment of external forces is proposed because it provides identification of maximum load as a starting basis for further research on determination of optimal laws of distribution of acting forces which are caused by the moment of forces.Publishe

Prilog analizi krutosti ramova utovarno-istovarnih kolica pretovarnih mosnih dizalica

The paper analyzes the dependence of the stiffness of the support frames of the cranes with loading-unloading trolley on the change of geometrical parameters of the frames. The calculation model of the frames with transverse stiffness was formed because it additionally stiffens the supporting surface of the frames for connection with the axial-radial bearing. The relations of characteristic geometrical sizes of longitudinal and transverse elements were established, at which the necessary stiffness of the frames of loading-unloading trolley was achieved. Also, the variables and constants of geometric size were introduced, as well as the constant values of appropriate coefficients, the variation of which provides the possibility to form the optimal structure of the frames of loading-unloading trolley.Publishe

Stabilnost i optimizacija stuba dizalične staze

This research has presented the built-up column analysis with batten, applied to crane runaway support, where stability is put in the foreground. Also, optimization of all essential geometrical parameters of the built-up column was performed for a given height of the crane column and changing the load capacity. The chord members were composed of as-welded I-sections instead of fabricated hot rolled sections witch are commonly used in these constructions. The mass of the built-up columns, which consists of the chord and Web members (battens) members, was taken as the goal function in this research. Additional stability and load capacity conditions were used as constraint functions, as well as specific design recommendations. The optimization procedure was performed in the Ms. EXCEL software package, using the GRG2 algorithm because certain benefits are essential in this optimization problem. In this way, the justification of applying the proposed model of calculation and optimization was shown because the necessary geometrical parameters can be reached very quickly when designing these types of structures, considering that there are a large number of variables and constraint functions. It is also shown how the mass of the column changes and the optimal geometric parameters when the compression force on the column of the runaway crane support increases.Publishe