Criterion for Selecting Composite Materials for Explosion Containment Structures (Review)

Experimental data on the dynamic response and strength of simple shells of fiber composites are used to justify the choice of these materials for the load-bearing shells of blast-proof structures. It is shown that in such structures composites are preferred to homogeneous metal alloys (structural steels) to eliminate strong scale effects of an energetic nature. A criterion for selecting fibers is proposed and justified experimentally, and reinforcement patterns are determined to obtain optimal (in the strength-mass ratio) compositions for the load-bearing shells of blast-proof containers and chambers. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 3–13, September–October, 2005.     

Optical–microphysical properties of smoke haze from Siberian forest fires in summer 2012

A comprehensive experiment on the study of dynamics of optical and microphysical characteristics of submicron aerosols in the near-ground air layer was carried out in June–August of 2012 under conditions of extremely strong smoke haze originating from vast forest fires in Siberia. Variations of the spectral angular scattering coefficients and the degree of linear polarization in the visible wavelength range are studied, as well as the mass concentrations of dry fractions of aerosol and black carbon, relative content of black carbon (BC fraction), single scattering albedo, particle size distribution function, complex refractive index of the particulate matter, and parameter of condensation activity of aerosol. Peculiarities of differences between optical and microphysical characteristics of near-ground aerosol in smoke haze and under smokeless conditions are revealed. This study is important for validation of results of remote sensing of the composition of smoke haze and background atmosphere obtained from satellite data and sun photometric measurements at the Aerosol Robotic Network (AERONET).     

Microstructure of hardened gypsum pastes

Specific surface areas and pore size distribution analysis were taken as essential parameters to explore the microstructure of hardened gypsum pastes. The hydration of gypsum plaster is essentially affected by the water/plaster ratio of the mix, and by the presence of additives which might act as retarders or accelerators to the hydration process. Affecting the microstructure would mutually lead to variations of the compressive strength of the hardened pastes, and these variations are also discussed. Results are mainly expressed in terms of the solid (measured by the extent of its specific area) to the space (pore) ratios. Dual distribution of pore sizes was observed and the two groups of pores are designed as S (small) and L (large) pores. Similarities to the microstructure of hardened Portland cement pastes are indicated. Accelerators appear to function differently from retarders, and the effects of water/plaster ratios were investigated in both cases. The results obtained may carry many significant practical implications to the future use of hardened gypsum pastes.     

Evaluation of the Nonuniformity of Filaments Based on Data from Pulsed-Acoustic Tests of Complex Chemical Fibres

The values of the elongation at break of filaments in a complex fibre are found by the method of combining the stress-strain diagrams and acoustic emission spectra of fracture of complex fibres. Experimental data are used to assess the correspondence of the empirical law of distribution of the elongation at break of filaments to the theoretical (normal) law. The behavior of filaments in extension of a complex fibre to breaking is described with the concepts of reliability theory and the statistical indexes characterizing the nonuniformity of the filaments and the working capacity of a complex fibre in elongation close to the elongation at break are calculated. Complex fibres fabricated by melt spinning (polyester, polypropylene) have higher reliability reserves than fibres wet-spun from solution (viscose). The results are of practical importance and can be used for optimizing industrial manufacture and processing of complex fibres.     

Dependence of spall strength of metals on the amplitude of a shock-wave load

Arzamas. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 1, pp. 94–98, January–February, 1992.     

Thermal decomposition and pore structure of pure and doped stannic oxide gel

The surface properties of a stannic oxide gel and its thermal dehydration products obtained both in vacuo and in the presence of air in the temperature range 100–600°C have been examined by N₂ adsorption. Phase and structural changes have been followed by differential thermal analysis and X-ray diffractometry. Complete pore structure analysis showed that samples dehydrated at or below 250°C were microporous. Above 250°C the pores were found to widen with increase of temperature, the widening occurring concurrently with the crystallisation process. Doping with cations of lower valency (Li⁺ and Al³⁺) than the host cation (Sn⁴⁺) had little effect on the pore structure and specific surface area for the low temperature samples (≤250°), whereas at higher temperatures, e.g. 600°C, it increased the specific area remarkably. The dope ions produce oxygen vacancies and hinder or retard sintering in SnO₂.     

Morphology and microstructure of autoclaved clinker and slag-lime pastes in presence and in absence of silica sand

Development of microstructure in four hydrothermal reactions has been undertaken using scanning electron microscopy. These are clinker, clinker-sand, slag-lime and slag-lime-sand hydrothermal reactions. The microstructure of clinker hydration products displayed crumpled foils and tabular masses of calcium silicate hydrates; few cubic crystals of hydrogarnet appeared only during the initial stage of the reaction. In clinker-sand mixture the C-S-H phase was the only product identified. In slag-lime hydration the microstructure displayed both of the hydrogarnet crystals and the C-S-H phase. The hydration of slag-lime-sand mixture (an optimum composition) was associated with the formation of ill-crystallized tobermorite and crystalline 11A tobermorite as the main products.     

Dimensions of the average pore,the number of pores,and the surface area of hardened Portland cement paste

In the course of their small angle x-ray scattering work, Winslow and Diamond also calculated the radius of gyration of the pores. Using its value for a paste, Diamond adopted two models for the average pore: a sphere and a cylinder of equal height and diameter. This model leads to absurd values for the surface area of the paste. Using a cylindrical model, and the radius of gyration plus the hydraulic radius, the present authors calculated for a similar paste the dimensions of the average pore and obtained the values: $\text{diameter}\text{= 47.2}\text{A}\text{?}\text{,}\text{length}\text{= 466}\text{A}\text{?}$. The number of pores per gram of paste was 2.26 × 10¹⁷. The paper also discusses the surface area of hardened paste, and points out the extremely important contributions of Winslow and Diamond to the subject.