Kinetics of the plastic zone of a fatigue crack in the body of a grain during cyclic loading

Moscow. Translated from Problemy Prochnosti, No. 5, pp. 49–52, May, 1989.     

Investigation of CL‐20 and RDX Nanocomposites

Nanocrystalline explosives offer a number of advantages in comparison to conventional energetics including reduced sensitivity and improved mechanical properties. In this study, formulations consisting of 90 % hexanitro‐hexaazaisowurtzitane (CL‐20) or cyclotrimethylene trinitramine (RDX) and 10 % polyvinyl alcohol (PVOH) were prepared with mean crystal sizes ranging from 200 nm to 2 μm. The process to create these materials used a combination of aqueous mechanical crystal size reduction and spray drying. The basic physical characteristics of these formulations were determined using a variety of techniques, including scanning electron microscopy, X‐ray diffraction, and Raman spectroscopy. Compressive stress‐strain tests on pressed pellets revealed that the mechanical properties of the compositions improved with decreasing crystal size, consistent with Hall‐Petch mechanics. In the most extreme case (involving CL‐20/PVOH formulations), crystal size reduction from 2 μm to 300 nm improved compressive strength and Young’s modulus by 126 % and 61 %, respectively. These results serve to highlight the relevance of structure‐property relationships in explosive compositions, and particularly elucidate the substantial benefits of reducing the high explosive crystal size to nanoscale dimensions.     

Production and Sensitivity Evaluation of Nanocrystalline RDX‐based Explosive Compositions

The initiation sensitivity of cyclotrimethylenetrinitramine (RDX) was investigated as a function of crystal size. For this study, RDX powders with mean crystal sizes of ca. 200 and 500 nm were prepared by rapid expansion of supercritical solutions (RESS) with carbon dioxide as the solvent. Initiation sensitivity testing to impact, sustained shock, and electrostatic discharge stimuli was performed on uncoated as well as wax‐coated specimens. The test data revealed that in a direct comparison to coarser grades the nanocrystalline RDX‐based samples were substantially less sensitive to shock and impact stimuli. Furthermore, the 500 nm RDX‐based specimens exhibited the lowest sensitivity values, an indication that minima in shock and impact sensitivities with respect to crystal size exist.     

Tobacco-specific nitrosamines in new tobacco products.

New tobacco products, designed to attract consumers who are concerned about the health effects of tobacco, have been appearing on the market. Objective evaluation of these products requires, as a first step, data on their potentially toxic constituents. Tobacco-specific nitrosamines (TSNAs) are an important class of carcinogens in tobacco products, but virtually no data were available on their levels in these products. In the present study, we analyzed several new products-Ariva, Stonewall, Exalt, Revel, Smokey Mountain, and Quest-for TSNAs and compared their TSNA levels with those in nicotine replacement products and conventional smokeless tobacco and cigarette brands. TSNAs were not detected in Smokey Mountain, which is a tobacco-free snuff product. The lowest levels among the new products containing tobacco were in Ariva and Stonewall (0.26-0.28 microg/g wet weight of product). The highest levels in the new products were found in Exalt (3.3 microg/g tobacco), whereas Revel and Quest had intermediate amounts. Only trace amounts were found in nicotine replacement products, and conventional brands had levels consistent with those reported in the literature. These results demonstrate that TSNA levels in new tobacco products range from relatively low to comparable with those found in some conventional brands.     

Metric classifier using multilevel network of templates

A new approach is proposed to constructing a classifier of two-dimensional (2D) objects in a space of multiresolution object representations. The approach is based on constructing tree-structured covers (TSCs) of clusters of a training set by spheres in the space of the object representations taken at the maximum resolution level. The covering spheres and their projections of all resolution levels generate a multilevel network of templates in which the sphere centers yield the templates, while the spheres themselves form the influence regions of the templates at the corresponding resolution levels. Using the multilevel structure of the template network, a hierarchical search algorithm is proposed for making a decision group of the templates by a given voting criterion. A computational complexity of this algorithm is evaluated. An efficiency of the proposed TSC classifier is demonstrated by estimates of error rates in experiments on signature, hand gesture and face recognition, as well as by the comparative error rates obtained for these sources using the known SVM classifier.     

Methods of determining coke quality

Methods of determining coke quality are compared.     

Evaluation of the Constrained Blister Test for Measuring Adhesion

The constrained blister test (CBT) was evaluated as a method for measuring adhesion using a model system, electrical tape bonded to polystyrene. Pressure is applied through a circular inlet hole in the substrate, causing the adhesive to “blister” up and peel radially away from the substrate. A glass constraint, placed some distance above the adhesive, limits deformation of the adhesive in the vertical direction and promotes radial peel. By operating at low spacer height (the distance of the constraint above the adhesive) and very low growth rates, the energy spent for deformation of the adhesive and viscoelastic dissipation is minimized. Blister radial growth was linear with time, and growth rate increased linearly with the second power of the energy input. An intrinsic, rate-independent adhesion energy was obtained by extrapolation to zero crack growth rate. The CBT was compared with two peel tests. The dependence of the growth rate on energy input was different, but the extrapolation to zero growth rate gave the same value of the intrinsic adhesion energy.     

Reducing the phenol content in coal tar and in coke-plant water flows

The influence of coking-product pyrolysis within the coke furnace on the phenol content in coal tar and in the water in the gas-collection cycle and at the biochemical-treatment unit is considered.