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Opis: The paper describes modelling approach to computational simulation of surface crack growth subjected to lubricated rolling-sliding contact conditions. The model considers the size and orientation of the initial crack, normal and tangential loading due to rolling-sliding contact and the influence of fluid trapped inside the crack by a hydraulic pressure mechanism. The motion of the contact sliding load is simulated with different load cases. The strain energy density (SED) and maximum tangential stress (MTS) crack propagation criteria are modified to account for the influence of internal pressure along the crack surfaces due to trapped fluid. The developed model is used to simulate surface crack growth on a gear tooth flank, which has been also experimentally tested. It is shown that the crack growth path, determined with modified crack propagation criteria, is more accurately predicted than by using the criteria in its classical form.
Ključne besede: fracture mechanics, numerical methods, contact loading, finite element analysis, internal pressure, maximum tangential stress, strain energy density, surface crack growth
Objavljeno v DKUM: 01.06.2012; Ogledov: 2689; Prenosov: 96
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Opis: Solid-liquid phase transitions of vanillin, ethylvanillin, o-vanillin and o-ethylvanillin in presence of compressed CO2 were determined with the modified capillary method. Furthermore, the solubilities of the above mentioned vanillins in supercritical CO2 were measured at 313.2, 333.2 and 353.2 K and in the pressure range 8-30 MPa using a static-analytic method. The experimental equilibrium solubility data have been fitted to the Peng-Robinson equation in combination with two parameter van der Waals mixing rules and binary parameters were determined from the best fit. Results showed that the phase equilibria of vanillins in dense CO2 are influenced by the position of the hydroxyl group bound to the aromatic ring. Under the pressure of CO2 the melting point depression and also the solubility of both o-vanillins was higher than those of p-vanillins. Oppositely, the alchoxy group (methoxy or ethoxy) showed no significant influence on the solubility of vanillins.
Ključne besede: chemical processing, high pressure technology, CO2, phase equilibria, vanillin isomers, data, ring substituents
Objavljeno v DKUM: 01.06.2012; Ogledov: 2270; Prenosov: 48
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Opis: Ground fruits of the common juniper (Juniperus communis L), with a particle size range from 0.2500.400 mm, forming a bed of around 20.00 +/- 0.05 g, were extracted with supercritical CO2 at pressures of 80,90, and 100 bars and at a temperature of 40 De. The total amount of extractable substances or global yield (mass of extract/mass of raw material) for the supercritical fluid extraction process varled from 0.65 to 4.00"10 (wt). At each Investigated pressure, supercriticaI CO2 extract fractions collected In successive time intervals over the course of the extraction were analyzed by capillary gas chromatography, using flame ionization (GO-FIO) and mass spectrometric detection (GC-MS). More than 200 constituents were detected In the extracts, and the contents of 50 compounds were reported in the work. Dependence of the percentage yields of monoterpene, sesquiterpene, oxygenated monoterpene, and oxygenated sesquiterpene hydrocarbon groups on the extraction time was investigated, and conditions that favored the yielding of each terpene groups were emphasized. At all pressures, monoterpene hydrocarbons were almost completely extracted from the berries in the first 0.6 h. It was possible to extract oxygenated monoterpenes at 100 bar in 0.5 h and at 90 bar in 1.2 h. Contrary to that, during an extraction period of 4 h at 80 bar, it was possible to extract only 75% of the maximum yielded value of oxygenated monoterpene at 100 bar. Intensive extraction of sesquiterpenes could be by no means avoided at any pressure, but at the beginning of the process (the first 0.5 h) at 80 bar, they were extracted about a and 3 times slower than at 100 and 90 bar, respectively. Oxygenated sesquiterpenes were yielded at fast, constant extraction rates at 100 and 90 bar In 1.2 and 3 h, respectively. This initial fast extraction period was consequently foIlowed by much slower extraction of oxygenated sesquiterpenes.
Ključne besede: chemical processing, high pressure technology, CO2, supercritical fluid extraction, pressure, extraction time, Juniperus communis, oxygenated terpenes, juniper berry oil, carbon dioxide
Objavljeno v DKUM: 01.06.2012; Ogledov: 2229; Prenosov: 57
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Opis: The validity of some limit state solutions, when strictly applied to the basic corresponding state theorem (Caquot, 1934), is limited and valid only for simpler limit states, where stress vectors are either perpendicular to the boundary surfaces or when the direction of stress eigenvalue trajectories in transformation are preserved (Michalowski, 2001). The theorem of corresponding states allows us, in some cases, to attain solutions belonging to the limit states for cohesive-friction materials with the transformation of the known boundary of elasto-plastic solutions of limit states for pure friction materials. We demonstrated that for the selected kinematically admissible model, in general cases of boundary stresses, the indirect application of the corresponding states theorem in modified form is permitted.To determine this, we applied the kinematic approach of limit state analysis and used the upper-bound theorem for determining passive earth pressures. The results of our analyses show that incautious application of the corresponding state theorem in its basic form and for general cases is in admissible because the results obtained can be correct only coincidentally, depending on the boundary conditions
Ključne besede: corresponding state, earth pressure, passive pressure, limit analysis, upper-bound
Objavljeno v DKUM: 31.05.2012; Ogledov: 1941; Prenosov: 102
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Opis: For controlling the degree of crystallinity and crystal form during particle formation using supercritical fluids, knowledge of pressure influence on solid-liquid-gas (S-L-G) equilibrium and solubility data of the system is crucial. S-L-G equilibrium data were determined in pressure range from 50 to 600 bar for systems monostearate/CO2 and tristearate/CO2 using a high-pressure view cell. Results showed a temperature minimum for both systems.The solubilities of CO2 in liquid glycerides were high: maximum solubilities, which were determined at temperatures 70 and 90 °C and pressure range from 50 to 450 bar, were from 50 to 90 mol%. Physical characteristics of micronized monostearate and tristearate samples were studied in detail after micronization and after 3 months of storage at 20 °C.
Ključne besede: chemical processing, high pressure technology, supercritical fluids, micronization, fine particles, Particles from Gas Saturated Solution, degree of crystallinity
Objavljeno v DKUM: 31.05.2012; Ogledov: 2958; Prenosov: 59
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