Utjecaj uvjeta grijanja na strukturnu jednolikost i lomno naprezanje aluminijske pjene

In this paper, the possibility to create uniform porous structure for non- symmetric precursor heating was investigated together with changes in collapse stress and their reproducibility. The statistic relative standard deviation (RSD) of pore size was used to determine the structural uniformity. It was shown that proper adjustment of the foaming parameters leads to formation of the uniform foam structure. The compression testing showed that standard deviation of collapse stress was higher for uniform structure than those obtained for non- uniform structure.U ovome radu istražena je mogućnost stvaranja jednolike porozne strukture nesimetričnim zagrijavanjem prekursora, te su isto tako istražene promjene lomnog naprezanja i njihova ponovljivost. Statistička relativna standardna devijacija (RSD) veličine pora koristila se za određivanje strukturne jednolikosti. Pokazano je da pravilan odabir parametara upjenjavanja dovodi do nastajanja jednolike strukture. Tlačna proba je pokazala da je vrijednost standardne devijacije lomnog naprezanja veća za jednoličnu strukturu od onih ostvarenih za nejednoliku strukturu

Scaling of compression strength in disordered solids: metallic foams

The scaling of compression strength with porosity for aluminium foams was investigated. The Al 99.96, AlMg1Si0.6 and AlSi11Mg0.6 foams of various porosity, sample size with and without surface skin were tested in compression. It was observed that the compression strength of aluminium foams scales near the percolation threshold with Tf ? 1.9 - 2.0 almost independently on the matrix alloy, sample size and presence of surface skin. The difference of the obtained values of Tf to the theoretical estimate of Tf = 2.64 ± 0.3 by Arbabi and Sahimi and to Ashby estimate of 1.5 was explained using an analogy with the Daoud and Coniglio approach to the scaling of the free energy of sol-gel transition. It leads to the finding that, there are two different universality classes for the critical exponent Tf: when the stretching forces dominate Tf = f = 2.1, respectively when bending forces prevail Tf = ?.d = 2.64 seems to be valid. Another possibility is the validity of relation Tf ? f which varies only according to the universality class of modulus of elasticity in foam

Light-toned salty soils and coexisting Si-rich species discovered by the Mars Exploration Rover Spirit in Columbia Hills

Light-toned soils were exposed, through serendipitous excavations by Spirit Rover wheels, at eight locations in the Columbia Hills. Their occurrences were grouped into four types on the basis of geomorphic settings. At three major exposures, the light-toned soils are hydrous and sulfate-rich. The spatial distributions of distinct types of salty soils vary substantially: with centimeter-scaled heterogeneities at Paso Robles, Dead Sea, Shredded, and Champagne-Penny, a well-mixed nature for light-toned soils occurring near and at the summit of Husband Hill, and relatively homogeneous distributions in the two layers at the Tyrone site. Aeolian, fumarolic, and hydrothermal fluid processes are suggested to be responsible for the deposition, transportation, and accumulation of these light-toned soils. In addition, a change in Pancam spectra of Tyrone yellowish soils was observed after being exposed to current Martian surface conditions for 175 sols. This change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface. Sirich nodules and soils were observed near the major exposures of S-rich soils. They possess a characteristic feature in Pancam visible near-infrared (Vis-NIR) spectra that may be diagnostic of hydrated species, and this spectral feature can be used to search for additional Si-rich species. The exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area. Hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the Neutron Spectrometer on Mars Odyssey.We thank NASA for funding the MER Athena Science team and the JPL engineering team for continuing to successfully operate the Mars Exploration rovers.https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2008JE00312

Aluminium foam A new light-weight structural material

Translated from Slovak (Report of the Inst. of Materials and Machine Mechanics, Slovak Academy of Sciences, Bratislava, 1997)SIGLEAvailable from British Library Document Supply Centre-DSC:9023.19000(VR-Trans--8634)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Bending properties of aluminium foam

Translated from Czech (Kovove Mater. 1998 (5) p. 320-333SIGLEAvailable from British Library Document Supply Centre-DSC:9023.190(VR-Trans--8895)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo