Development of the titanium structure in explosive collapse of thick-walled cylinders

The dependence of the titanium structure on the total deformation in the explosive collapse of thick-walled cylinders is studied. It is shown that structure evolution as a whole and the critical parameters for the appearance of an unstable plastic flow in titanium are not the functions of the final deformation of the cylinders. This instability, which is governed by the internal structure of the material, is the principal mechanism of the loss of the axial symmetry of collapse in the given geometry under specified load conditions. It is found that the instability of the plastic flow in titanium is manifested in the formation of adiabatic-shear bands. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 5, pp. 122–129, September–October 1998     

Explosive compaction of aluminum powder and the structure of compacts

Macrodefects of the structure of samples produced by explosive compaction of an aluminum powder were examined. The areas of the new contact particle surfaces produced by high-rate deformation were measured by stereological methods. The eddy current method was used to measure the macroscopic electric conductivity of the compacts. From these data, the mean sizes and number of macrodefects per unit volume of a compact were calculated. The techniques employed can be useful for an analysis of the structure of composite materials produced by various methods. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 105–109, March–April, 2000. The present work was supported by the Russian Foundation for Fundamental Research (Grant No. 99-01-00572) and the Federal target program “State Support of the Integration of Higher Education and Basic Research for 1997–2000” (Grant No. 274 in the direction “Basic Research in the Field of Physics and Advanced Technologies).     

Study of the elastic,viscoelastic, and plastic characteristics of chemical fibres

Methods were developed for dividing the total mechanical work of deformation and the deformation corresponding to it into elastic-reversible and viscoelastic-plastic components which suggests use in both calculation of the resistance of chemical fibres in the dynamic deformation regime and for assessing the ability of materials to resist a mechanical effect and recover the initial shape during use. Incorporation of a coefficient for the irreversibility of deformation allows separating the viscoelastic and plastic components of deformation after the total deformation of chemical fibres is broken down into the constituent components. __________ Translated from Khimicheskie Volokna, No. 6, pp. 52–55, November–December, 2007.     

Deformation of nonfired refractories based on phosphate binders. 5. Creep specifics in cement mixtures

The results of experimental studies of aluminosilicate cement are described identifying two temperature intervals of deformation, which differ in their creep regularities. The first range is typical of composites with an unstable low-temperature structure (heat treatment up to 800°C), and the second interval is typical of relatively stable high-temperature structures (> 1000°C). Two ranges of deformation are identified based on stress. In the first range the deformation process is determined by sintering shrinkage under a load which is lower than the surface tension; the second deformation range is typical of loads exceeding the surface tension. __________ Translated from Novye Ogneupory, No. 5, pp. 47–51, May, 2007. Continuation. See beginning in Vol. 48, Nos. 1–2, 2007.     

Permanent deformation in armos fibre at a temperature below the glass transition temperature

The character of accumulation of permanent deformation of Armos fiber as a function of the temperature was established. The important change in the character of ɛ_per.(_ass.) in the temperature region of 80–100°C can be attributed to breaking of hydrogen bonds of the “polymer-water-polymer’ type. The special character of accumulation of permanent deformation is observed in dried Armos fibre. This is hypothetically explained by the effect of two mechanisms: the absence of hydrogen bonds in the initial stage of deformation and their formation in subsequent deformation as a result of convergence of the molecules. Deceased St. Petersburg State University of Technology and Design. Translated fromKhimicheskie Volokna, No. 3, pp. 36–38, May–June, 1999.     

Dependence of the titanium structure formed under high-rate loading on its initial state

The structure of titanium specimens with different grain sizes and initial defect density that were subjected to large high-rate strains is studied, and the critical parameters of the onset of an unstable plastic flow in the specimens are determined. It is established that the formation of a titanium structure and the critical parameters governed by this structure are determined mainly by twinning. Twinning in shock-loaded titanium is the mechanism of plastic deformation that ensures the minimum change in the internal energy. Twinning in titanium under high-rate strain develops at the earlier stages over all admissible twinning systems and results in fragmentation of the structure. The twins are not the structural elements that contribute to the evolution of a uniform plastic strain. Fragmentation of the structure in the formation of twins decreases the critical parameters of the onset of an unstable plastic flow. It is found that as the strain increases, the twins fill the material up to a certain limit level, after which energy relaxation occurs owing to the formation of adiabatic-shear bands and/or cracking. The titanium structure formed in the deformation is highly stable. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 110–121, March–April, 2000.     

Structural dependence of the deformation characteristics of polypropylene film fibre in stress relaxation

The deformational rigidity increases due to relaxation of stresses in oriented PP fibres. Elongation of PP fibres is accompanied by mechanical failure in all stages, which is a distinctive feature of deformation processes in these materials. Ordering of the structure of amorphous regions, manifested by an increase in the deformational rigidity of these fibres, is the result of stress relaxation in oriented PP fibres. Based on proceedings of the memorial conference dedicated to the 100th birthday of Z. A. Rogovin. __________ Translated from Khimicheskie Volokna, No. 1, pp. 32–35, January–February, 2006.     

Flow of polymer systems in the viscoelastic state through round capillaries. Deformation analysis

Flow of polymer systems in the viscoelastic state through a capillary is considered a deformation process; the deformation characteristics used were the equilibrium shear modulus G_R, equilibrium relaxation time θ_R, and parameter m, and the product of the shear gradient by the equilibrium relaxation time S_o = θ_Rq_o was used as the shear deformation. __________ Translated from Khimicheskie Volokna, No. 2, pp. 39–42, March–April, 2006.     

Mathematical modeling of the deformation properties of nonwoven materials with variable rigidity

The previously elaborated mathematical model of viscoelasticity was generalized with consideration of the irreversible component of deformation for the case of an increase in the deformation rigidity of the nonwoven. Methods were developed for determining the deformation characteristics that allow satisfactorily describing creep and relaxation of nonwovens. A method is proposed for accounting for the increase in deformation rigidity and correspondingly the decrease inflexibility which is quantitatively accounted for by the same very simple elementary function of the reversible component of deformation. __________ Translated from Khimicheskie Volokna, No. 2, pp. 64–67, March–April, 2006.     

Grain-size effect on the properties of materials under dynamic deformation

Some deformation features in fine-grained copper under gradient dynamic stresses are studied which provide a better understanding of the mechanism of the processes involved. The experimentally observed abrupt change in the properties of materials with grain sizes smaller than a certain critical value is shown to be related to intergranular slip during deformation. Materials with a grain size of 5–50 μm are found to exhibit properties characteristic of nanomaterials with a strain rate varying from 10⁴ to 3 · 10⁶ sec⁻¹. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 133–138, May–June, 2008.     

Computer study of the viscoelasticity of polymeric materials

The use of mathematical modeling of viscoelasticity combined with computerized methods of predicting viscoelastic processes in synthetic materials increases the accuracy of calculating deformation processes, including deformation-recovery and reverse-relaxation processes, close to the conditions of use of the articles. Computerization of methods of separating the mechanical work of deformation into elastic and scattering components will allow solving problems of calculating the resistance of synthetic materials to impact loads. A computer-integral criterion of the reliability of the prediction is suggested for increasing the reliability of calculating deformation processes in synthetic materials in selecting a variant of normalized relaxation and lag functions. __________ Translated from Khimicheskie Volokna, No. 5, pp. 53–56, September–October, 2006.     

Effect of polymorphous phase transformations on explosive compression of steel spheres

The effect of polymorphous phase transformations on the structure of stress waves and the fracture of steel spheres under compression by spherically converging shock waves has been studied within the model of a porous elastoplastic medium whose matrix undergoes polymorphous transformations under deformation. Computation results are compared with experimental data available in the literature. Institute of Applied Mathematics and Mechanics of Tomsk State University, Tomsk 634050. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 5, pp. 128–136, September–October, 1997.     

Localization of plastic deformation on contacts, determining the formation of a strong joint

It is shown that a strong joint is formed on the contact surface in explosive welding. A band of material on which plastic deformation is localized is formed along the boundary of the surface, this band representing a qualitatively new structure. Use of the laws governing strain localization, obtained from a study of the collapse of thick-walled cylinders that were subjected to explosive shock loading, makes it possible to predict the collision parameters in explosive welding in accordance with the grain size of the materials that are used. M. A. Lavrent'ev Institute of Hydrodynamics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk. Translated from Fizika Goreniya i Vzryva, No. 5, pp. 122–128, September–October, 1995.     

Reactions of three-layer chambers as the result of detonation in them of extended explosive charges

Conclusions An experimental and numerical investigation was conducted, of the reaction of three-layer explosion chambers to internal explosive loading. It is shown that the use of concrete as an intermediate layer can significantly increase the supporting capacity of the chambers, because of the increase of the inert mass of the structure. Peculiarities of deformation of the concrete layer were recorded, consisting in the formation of blocks with constant thickness, equal to the initial thickness, moving relative to one another. A method is proposed for estimating the supporting capacity of chambers similar to those tested. Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 18, No. 4, pp. 88–93, July–August, 1982.     

Prediction of stress relaxation during high-speed stretching of synthetic thread

The viscoelastic characteristics obtained with a “family≓ of stress relaxation curves can be used to predict distortion of the stress-strain diagram in going to high deformation rates. Translated from Khimicheskie Volokna, No. 1, pp. 41–43, January–February, 1998.     

Evolution of the metal microstructure and conditions of strain localization under high-strain-rate loading

Specific features of evolution of the microstructure of coarse-grained and fine-grained copper are examined on the basis of an available dependence of the critical parameters of strain localization on the grain size, which was derived in an explosive collapse of hollow thick-walled cylinders. Similarity of the properties and mechanisms of deformation of fine-grained and ultrafine-grained materials is established. Based on the analysis of the results obtained, a scenario of the change in deformation mechanisms of fine-grained copper in the course of the development of deformation structures under high-strain-rate loading is proposed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 121–131, May–June, 2006.     

Effect of molecular mobility on the deformation characteristics of polycaproamide fibres

The deformation characteristics of PCA fibres are a function of the deformation temperature to a significant degree. The character of the curves of E(ε), E_max(t), σ_b(t), and ε_b(t) indicate a pronounced change in the mechanical properties of PCA fibres not only in “thawing” of segmental mobility in amorphous regions of the polymer, but also in passage of crystallites into the mesomorphic state, which is characterized by pronounced weakening of interchain interactions in the crystallites. The first segment of σ(ε) is only observed in the curves for PCA fibres in the glassy state. In activation of segmental mobility, the σ(ε) curves only contain the second and third segments. St. Petersburg State University of Technology and Design. Translated fromKhimicheskie Volokna, No. 6, pp. 30–31, November–December, 1999.     

Effect of preliminary loading on the deformation and strength properties of high-strength fibres

High-strength, high-modulus polyethylene fibres fabricated with gel technology is similar to low-modulus fibres of the olefin and amide series (Capron, polypropylene) with respect to the character of the correlation of the stress—strain diagrams and curve of accumulation of the residual component of deformation. The residual deformation component is relatively large both for high-strength PE fibre and for p-polyamide fibres. The differences in the character of accumulation of the plastic component in these fibres are due to the fact that the residual strains arising in high-strength PE fibre, as in other flexible-chain polymer fibres (polypropylene, Capron) is initiated by breaking of bonds in the main chain. In p-polyamide fibres (Armos, SVM, Terlon, Kevlar), plastic strains arise due to highly elastic deformation “frozen≓ by hydrogen bonds and orientation of molecular chains. Preliminary deformation affects the strength properties of high-modulus fibres differently: in PE fibres, the strength decreases, it increases for Armos and SVM fibres, and remains unchanged for Terlon fibre. This difference is to a great degree due to the difference in the types of intermolecular interaction in fibres of the olefin and amide series. For all fibres investigated, the character of accumulation of the residual deformation component can be correlated with the type of stress—strain diagram, which will allow creating simpler methods of evaluating residual strains. Translated from Khimicheskie Volokna, No. 3, pp. 30–33, May–June, 1998.     

Enantioselective hydrogenation of ethyl pyruvate over Pt/alumina: systematic variation of the modifier structure

A series of enantiomerically pure amino alcohols and amines has been prepared and tested as modifiers in the enantioselective hydrogenation of ethyl pyruvate over Pt/alumina. Systematic variation of the modifier structure revealed that an extended aromatic π–system is necessary for the function of the modifier and that the enantioselectivity crucially depends on the structure of the amino function. Surprisingly simple modifiers such as 1–(1–naphthyl)ethylamine and 1–(9–anthracenyl)–2–(1–pyrrolidinyl)ethanol proved to be nearly as effective as 10,11–dihydrocinchonidine. This revised version was published online in June 2006 with corrections to the Cover Date.     

Increasing the spinning stability of acrylic fibres

There are two regions of elevated spinning stability separated by a region of unstable jet formation caused by deformation resonance on the spinning stability curves characterizing the maximum deformation of the jets on the distance to their solidification point. Increasing the concentration of solvent (DMAA) in the spinning bath increases the distance to the solidification point and greater expansion of the jet, intensifying the deformation resonance, detected by an increase in the nonuniformity of the linear density of the filaments. With a concentration of solvent of 80% and higher, the solidification point is so far from the spinneret that it does not affect jet expansion; the deformation resonance phenomenon disappears, manifested by an increase in the deformability of the jet and a decrease in the nonuniformity of the linear density of the filaments. Increasing the spinning bath temperature moves the solidification point closer to the spinneret and suppresses deformation resonance, which also increases the deformability of the jet and decreases the nonuniformity of the linear density of the filaments. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 5, pp. 16–19, September–October, 1999.