Nondestructive testing of highly inhomogeneous materials

Nondestructive testing (NDT) of highly inhomogeneous materials, such as carbon-filled plastics, composites, especially fiber-reinforced and using coarse-grain fillers, etc., is a quite difficult problem. Thus, when these materials are scanned by sensitive elements of conventional systems for NDT, the instability of initial signals caused by the structure of the material may exceed the signal emitted by the defect which, therefore, remains undetected. We investigate a principal possibility of detecting defects by representing them in the form of finite regions whose spatial signals are characterized by distribution functions whose shapes differ from the shape of the same function for the intact material. We analyze the most difficult case of complete overlapping of these functions. By applying both theoretical methods and numerical simulation, we demonstrate the possibility of detection of defect zones in highly inhomogeneous materials which are not visible in the process of human inspection even under the most favorable conditions for observation. We present a method for the calculation of the optimal statistical filter and a system of scanning of the investigated material in local zones. The experimental data of automatic detection are compared with the data of human control according to the Neumann-Pearson risk criterion. The regions of the optimal application of automatic and manual inspection are indicated. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 4, pp. 97–108, July–August, 1996.     

Contribution to quantification of highly inhomogeneous microstructures

In highly inhomogeneous microstructures with a wide range of grain sizes, the problem arises of defining an effective average grain size. An original method for the estimation of effective average grain size and a parameter describing the homogeneity of microstructure are presented. The coefficients of homogeneity for equiaxed and columnar microstructures are calculated. The effective average grain size is calculated as a weighted sum of the average grain sizes of homogeneous grain groups.     

Filtration and infiltration in a zonally inhomogeneous porous medium

Based on experimental investigations carried out under laboratory conditions, the features of filtration and infiltration of a liquid have been studied in a linear model of a bed. The model consisted of two zones of different permeabilities and was manufactured in the form of a cylindrical tube of length 1.1 m and inside diameter 0.032 m. It has been shown that, in filtration of water from a lower permeability to a higher one, the productivity coefficient increases, on the average, by 15% as compared to infiltration. The mechanism of the phenomena observed has been proposed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 77, No. 6, pp. 120–123, November–December, 2004.     

Auxiliary-wall method of measuring highly inhomogeneous local heat fluxes

The auxiliary-wall method has been examined for measurement of highly inhomogeneous local heat-flux distributions. Equations are given for evaluating the components of the systematic error.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 1, pp. 29–40, July, 1978.     

Propagation of technological filtration combustion waves in porous media of inhomogeneous composition

The article contains results of numerical simulation of propagation of filtration combustion waves with forced supply of gas-phase reagent into a porous medium of inhomogeneous composition. Wave “penetration” and “reflection” effects at the interface of media with different chemical compositions are found and explained. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 1, pp. 46–50, 1998.     

Radiation slip in a highly porous material layer

Expressions are obtained for the coefficient of radiant heat conductivity and the temperature jumps in the radiation slip mode in a highly porous material layer.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 59, No. 4, pp. 606–609, October, 1990.     

Crack opening areas in pressure vessels and pipes

The paper summarizes different methods for the calculation of crack opening areas in pressure vessels and pipes. In the case of constant membrane stresses the crack opening area is related to the stress intensity factor. This concept is applied to axial and circumferential cracks in pipes and to meridional cracks in spherical pressure vessels. Plasticity effects are taken into account in the framework of Dugdale's model. Lower and upper bound values for the leak areas are discussed and related to the problems of leak detection and jet forces acting on leaking pipes.     

高度有序多孔阳极氧化铝模板的制备

为了得到纳米孔排列高度有序的多孔阳极氧化铝模板,以0.3 mol·L-1的草酸为电解液研究了模板的制备工艺.采用场发射扫描电子显微镜(FE-SEM)对多孔氧化铝模板的表面形貌进行表征,X射线衍射分析高纯铝及氧化膜的结构.实验结果表明,铝基体不经过高温退火处理,同样能够得到高度有序的氧化铝膜,简化了多孔氧化铝膜的制备工艺.分别讨论了阳极氧化电压和电解液温度对多孔阳极氧化铝膜的形貌及孔径的影响,并对一步法和两步法制得的多孔氧化铝膜进行比较,结果表明,两步阳极氧化法制备的多孔氧化铝模板的有序性优于一步氧化法.XRD分析证实,多孔氧化铝膜由非晶态的Al2O3组成.     

Absorption of radiation in a layer of highly porous material

Radiative transfer through a porous layer, modeled by a uniform system of opaque particles fixed in space, is investigated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 6, pp. 999–1005, June, 1986.     

Preparation of highly porous hydroxyapatite from cuttlefish bone

Hydroxyapatite structures for tissue engineering applications have been produced by hydrothermal (HT) treatment of aragonite in the form of cuttlefish bone at 200°C. Aragonite (CaCO₃) monoliths were completely transformed into hydroxyapatite after 48 h of HT treatment. The substitution of CO₃ ²⁻ groups predominantly into the PO₄ ³⁻ sites of the Ca₁₀(PO₄)₆(OH)₂ structure was suggested by FT-IR spectroscopy and Rietveld structure refinement. The intensity of the ν₃PO₄ ³⁻ bands increase, while the intensity of the ν₂CO₃ ²⁻ bands decrease with the duration of HT treatment resulting in the formation of carbonate incorporating hydroxyapatite. The SEM micrographs have shown that the interconnected hollow structure with pillars connecting parallel lamellae in cuttlefish bone is maintained after conversion. Specific surface area (S _BET) and total pore volume increased and mean pore size decreased by HT treatment.     

Numerical investigation of convective flows of a highly inhomogeneous gaseous medium

Equations of convection in a gas are analyzed and a computational algorithm that is efficient when the condition gh/RT1 is satisfied for an arbitrary (fairly large) temperature drop is proposed. Calculations of convection occurring in steady nonuniform heating of walls are performed for axisymmetric argoncontaining volumes of different shape. Results of these calculations demonstrate the establishment of steady and periodic motions of the gas.Academic Scientific Complex A. V. Luikov Institute of Heat and Mass Transfer of the Academy of Sciences of Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 6, pp. 983–990, 1995.     

Fabrication and characterization of highly porous mullite ceramics

Highly porous mullite ceramics were fabricated by a reaction-bonding technique from a powder mixture of Al₂O₃ and SiC, with graphite particles as the pore-forming agent. The effects of sintering temperature on porosity and strength as well as pore size and surface area were investigated. It has been shown that the strength and pore size increase but the porosity and surface area decrease with the increase in sintering temperature. Due to the formation of a fine-grained microstructure with well-developed necks, an average strength up to 106 MPa was achieved at a porosity of 32.4%. On the other hand, a relatively high surface area of 12.4 m² g⁻¹ was obtained for a 61% porous mullite ceramic, which was observed to have a good thermal-shock resistance to crack propagation.     

Theoretical-experimental study of complex heat transfer in highly porous composites

A probabilistic approach is proposed for modeling the physical characteristics of high-porosity randomly nonuniform media. The results of mathematical modeling of complex heat transfer are compared with experimental data.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 59, No. 4, pp. 554–561, October, 1990.     

Effects of exterior gas pressure on the structure and properties of highly porous SiOC ceramics derived from silicone resin

Silicon oxycarbide porous ceramics were obtained through pyrolysis of a silicone resin filled with SiOC powders via a simple self-blowing process. The effects of exterior gas pressure on the porosity, compressive strength and microstructure of the porous ceramics were investigated. The porosity (total and open) generally decreased with increasing exterior gas pressure. It was possible to control the total and open porosity of porous ceramics within a range of 58.3-69.8% and 43.9-58.4% respectively, by adjusting the exterior gas pressure while keeping the silicone resin content at 70 vol.%. The compressive strength increased with increasing the exterior gas pressure, and the average compressive strength of the porous ceramics was in the range of 3.9-14.9 MPa. Micrographs indicated that with the exterior gas pressure increasing, the final pore structure of porous ceramics became more and more regular and equirotal.     

Dynamics of self-similar sub-10-fs-pulses in an inhomogeneous highly nonlinear fibre amplifier

ABSTRACT

We study the propagation of ultrashort pulses of width around sub-10 femtosecond in an inhomogeneous highly nonlinear single-mode fibre within the framework of a generalized higher-order nonlinear Schrödinger equation with derivative non-Kerr nonlinear terms and spatially inhomogeneous coefficients. Additional effects to the cubic model include the distributed third-order dispersion, self-steepening, self-frequency shift due to stimulated Raman scattering, quintic nonKerr nonlinearity, derivative non-Kerr nonlinear terms, and gain or loss. The exact self-similar brightand dark-solitary-wave solutions of the governing equation are derived via a transformation connected with the constant-coefficient higher-order nonlinear Schrödinger equation with non-Kerr nonlinearity. The constraint relations among the optical fibre parameters for the existence of these self-similar structures are also discussed. Based on these exact solutions, we investigate the dynamical behaviours of self-similar localized pulses in a periodic distributed fibre system for different parameters.     

Preparation and application of highly porous aerogel-based bioactive materials in dentistry

In this study, the possibility of preparation and application of highly porous silica aerogel-based bioactive materials are presented. The aerogel was combined with hydroxyapatite and p.tricalcium phosphate as bioactive and osteoinductive agents. The porosity of aerogels was in themesoporous region with a maximum pore diameter of 7,4 and 12.7 nm for the composite materials. The newly developed bioactive materials were characterized by scant electron microscopy. The in vitro biological effect of these modified surfaces was also tested on SAOS-2 osteogenic sarcoma cells by confocal laser scanning microscopy.     

Transient diffusion of gas in a highly dispersee sorbing porous solid

The transient diffusion of gas in a porous sorbent is considered on the basis of the “dusty” (or “dust-laden”) gas model. An equation is derived for the diffusion coefficient.