Effect of temperature and the initial state on the spalling fracture of alloy 36NKhTYu

The article presents the results of an experimental investigation of the effect of the temperature, the sulfur content, and the previous heat treatment on the strength and fracture of the alloy 36NKhTYu under loading by shock waves. The load levels corresponding to different stages of spalling fracture of specimens were determined in the temperature range from −196 to 750‡C. It was established that heating, increase of sulfur content, and hardening of the specimens lead to an imperceptible decrease of the dynamic strength of the alloy. The article presents the results of observations of the structure and nature of spalling fracture of the alloy by optical and electron microscopy. Translated from Problemy Prochnosti, No. 5, pp. 119–122, May, 1996.     

Effect of loading conditions and the initial state on the spalling of an octogen-based high explosive

The results of studies on the spalling of an OTK-90 high-explosive composition under impact loading are presented. Specimens 20–105 mm thick were loaded with the impact of 1.0- and 1.6-mm-thick steel plates explosively accelerated up to velocities of 135–380 m/s. The elastoplastic problem was used to numerically calculate the conditions of loading and spalling. The data obtained were used to derive a simple empirical equation relating maximum tensile stress in a spall plane with the stress gradient in a tensile impulse and maximum stress in a shock wave. The stabilization of specimens is shown to lead to a certain reduction in spalling stresses. Russian Federal Nuclear Center, All-Russian Research Institute for Experimental Physics, Sarov, Russia. Translated from Problemy Prochnosti, No. 2, pp. 43–50, March–April, 2000.     

Effect of heating on the spalling failure of glass-cloth-base laminate

Results are presented for experimental determination of the nominal spalling failure of glass-cloth-base laminate at normal and elevated temperatures. It is established that on heating glass-cloth-base laminate to a temperature of 150°C there is an increase, and with further heating to 250°C there is a decease, in its resistance to spalling failure compared with the similar value under loading conditions at normal temperature.Translated from Problemy Prochnosti, No. 10, pp. 63–64, October, 1990.     

Effect of carbon monoxide and sulphur dioxide on the oxidation state of copper in zeolite

A study is made of the reduction and oxidation of Cu²⁺ in CuNaY zeolites by CO and SO₂, using electron spin resonance. It is observed that the Cu⁺ or Cu^o formed by the reduction of Cu²⁺ with CO can be reoxidized to Cu²⁺ by SO₂ at 400°C. SO₂ can also reduce a fraction of the Cu²⁺ sites in the Cu-exchanged zeolites. SO₂ decomposes and forms elemental S under experimental conditions on the zeolite.     

Influence ff the initial state on the strength of pressed lithium hydride

We present the results of mechanical testing of pressed lithium hydride under the conditions of uniaxial compression, radial compression, and bending. The specimens were made of three different powder fractions. Their density varied depending on the level of compacting pressure. It is shown that, in the investigated range of parameters characterizing the initial state of the material, the dependences of strength on the characteristic size of the original powder d and the density of the material of the specimen ρ can be described by the same formula of the form σ _f =σ₀-klog(d/d ₀)+l(ρ-ρ₀), where d₀ and ρ₀ are arbitrarily chosen reference points, and σ₀, k, and l are coefficients determined by the method of regression analysis. The use of data on the strength of pressed lithium hydride under the conditions of uniaxial and radial tension processed as indicated above enabled us to obtain a similar dependence for the conditions of uniaxial tension. Russian Federal Nuclear Center, All-Russia, Scientific Research Institute for Experimental Physics, Sarov, Russia. Translated from Problemy Prochnosti, No. 6, pp. 134–137, November–December, 1999.     

Effect of microstructure on the spalling damage in a 20Mn2SiCrMo bainitic rail

The effect of microstructure on the spalling damage in a heavy-haul 20Mn2SiCrMo bainitic wing rail was investigated. The results show that spalling damage is strongly correlated to the detailed microstructure factors which contribute to the crack propagation resistance at different levels. It is demonstrated that comparing with blocky martensite/austenite (M/A) constituents, film-like M/A constituents have better performance to retard crack propagation. Moreover, the type and proportion of M/A constituents are affected by the isothermal holding temperature during heat treatment, where typical blocky M/A constituents are found in the temperature range from 360 °C to 400 °C.     

Dynamic systems with random initial state

Summary A perturbation scheme is described to treat time variable cryptodeterministic systems. According to Moyal's degree of randomness criteria the method provides a complete stochastic characterization of the system response. Certain digital computational features, when the perturbation scheme is not applicable, are also outlined. For an assumed random initial state, the results are then applied to describe the transient flapping oscillations of a helicopter blade which in forward flight has periodically varying aerodynamic damping and spring parameters.     

Thermodynamic modeling of the initial microstructural evolution of oxide films grown on bare copper

A thermodynamic model is presented that predicts the initial growth of either a (semi-) coherent crystalline oxide phase or an amorphous oxide phase (with a subsequent amorphous-to-crystalline transition) on a bare metal as function of the substrate orientation, growth temperature and film thickness. The model accounts for possible relaxation of growth stresses by plastic deformation. The direct formation and growth of semi-coherent, crystalline Cu₂O is predicted by application of the model to oxide overgrowth on bare Cu{111}, Cu{100} and Cu{110}. For oxide overgrowths on Cu{111} and Cu{110}, a square grid of misfit dislocations with a dislocation distance of about six Cu₂O unit cells would occur on the basis of the model calculations, which agrees with experimental observations reported for Cu{111} in the literature. On Cu{100} an array of misfit dislocations is formed along the single direction of high lattice mismatch.     

Numerical experiment on interaction of solitons describing recurrence of initial state

A soliton is the wave which propagates in the form of stable bulk with concentrated energy. Zabusky and Kruskal discovered it in 1965 by solving numerically the K-dV equation, and consequently a variety of analytical methods were established for studying its physical property to introduce the new field of modern physics. This paper succeeds in demonstrating computationally interaction of solitons concerning recurrence of the initial state suggested by Zabusky and Kruskal where ambiguity about their numerical analysis has prevented us from obtaining stable solution representing recurrent phenomenon for a long time. Here numerical experiment enables us to examine instability occasioning in the leapfrog method with a function of the initial condition which served as a key parameter. It is clarified that: (i) this finite difference approximation is available to describe only weakly coupled interaction of solitons, (ii) on linear analysis point of view, instability results from increasing unstable numerical mode of the higher Fourier components which was attributed to dispersive property of this difference method and (iii) instability originates in a sharp solitary wave which was standing still at the point of its birth.     

高强混凝土层裂数值仿真

为军事防护工程的安全合理设计提供关键的材料特性参数,研究高强混凝土(HSC)在冲击作用下的动态性能响应,采用软件LS-DYNA对C80级HSC在霍普金森压杆(HPB)装置上的冲击层裂过程进行数值仿真分析。仿真表明:应力波在混凝土试块的传播过程中,波形基本保持不变,且峰值震荡不明显;随着冲击速度的增大,混凝土试块的破坏越来越严重;横截面内层裂裂缝由试块表面向内部扩展。数值仿真结果与试验结果有较好的相似性,基本能够反映出HSC试块在HPB冲击层裂试验过程中的受力与破坏特征,由试验结果修正后的HJC本构参数可为后续HSC层裂性能的进一步研究提供参考。     

Effect of fire exposure on cracking,spalling and residual strength of fly ash geopolymer concrete

Fly ash based geopolymer is an emerging alternative binder to cement for making concrete. The cracking, spalling and residual strength behaviours of geopolymer concrete were studied in order to understand its fire endurance, which is essential for its use as a building material. Fly ash based geopolymer and ordinary portland cement (OPC) concrete cylinder specimens were exposed to fires at different temperatures up to 1000 °C, with a heating rate of that given in the International Standards Organization (ISO) 834 standard. Compressive strength of the concretes varied in the range of 39–58 MPa. After the fire exposures, the geopolymer concrete specimens were found to suffer less damage in terms of cracking than the OPC concrete specimens. The OPC concrete cylinders suffered severe spalling for 800 and 1000 °C exposures, while there was no spalling in the geopolymer concrete specimens. The geopolymer concrete specimens generally retained higher strength than the OPC concrete specimens. The Scanning Electron Microscope (SEM) images of geopolymer concrete showed continued densification of the microstructure with the increase of fire temperature. The strength loss in the geopolymer concrete specimens was mainly because of the difference between the thermal expansions of geopolymer matrix and the aggregates.     

Effect of copper concentration in printable copper inks on film fabrication

Precursor-type Cu inks were formulated by mixing copper (II) formate and hexylamine. The lowest electrical resistivity obtained in Cu films made from these inks was 5.2 μΩ·cm. The Cu concentrations in the inks influenced the impurity content after annealing and the microstructure (specifically, the porosity). Inks with a higher volume of hexylamine had a narrower size distribution of Cu particles, so they formed denser films. However, a large volume of hexylamine could not be fully vaporized during a limited annealing time and reacted with formate, creating impurities having boiling temperatures higher than that of hexylamine. Therefore, the Cu concentration governed two factors, porosity and impurity content, which ultimately determined the electrical resistivity of the films. These findings are expected to facilitate the development of copper-based metallic inks for printed electronics.     

Effect of an initial force in a rivet hole on the longevity of a structural component. Report 1. Analysis of the stressed state on the perimeter of the hole with allowance for the initial force

Kharkov Aviation Institute. Translated from Problemy Prochnosti, No. 1, pp. 93–97, January, 1988.     

Influence of the inhomogeneity of the initial stress-strain state on elastic perturbations in a solid body

We study the influence of inhomogeneities of the field of initial stresses on the time of motion of a pulse of strains in the elastic continuum and its mean velocity. This enables us to estimate an error caused by the application of the integral relations of acoustoelasticity established earlier. The case of a uniaxial inhomogeneous stress field is investigated. According to the applied iterative method, the components of the stress tensor in a given interval are represented in the form of a sum of their mean-integral values and deviations. The solution obtained in the approximation of order zero depends only on the mean-integral stresses. The correction of the solution in the first iteration depends both on the mean-integral values of the components of stresses and on the function of their deviations. The obtained results enable us to conclude that the integral acoustic relations can be used to formulate the inverse problems of tomography of tensor fields. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 5, pp. 7–18, September–October, 2005.     

Effect of preheating on the mechanical properties of tough pitch copper made from copper scraps

When hot rolled tough pitch copper is made from copper scraps, lead is intentionally or unintentionally added to the melt. The major role of this lead seems to be the removal of metallic tin by the formation of PbO–SnO₂. A continuously cast and hot rolled copper rod was preheated at temperatures between 673–1173 K for 1 h prior to cold drawing. The maximum diameter of the PbO–SnO₂, of 1–2 μm, was obtained by preheating at 873 K. This preheating temperature also produced the maximum decrease in the recrystallization temperature and the maximum electrical conductivity of the 89.4% cold drawn wire within the investigated experimental range. This can be attributed to a decrease in the dissolved impurity concentration due to the growth of PbO–SnO₂ particles at that temperature. The decrease in recrystallization temperature enhanced the room temperature multiple upset weldability. When preheated at 1173 K, Zn₂SnO₄ particles were formed, but the recrystallization temperature increased and the electrical conductivity decreased due to the dissolution of PbO–SnO₂. This revised version was published online in November 2006 with corrections to the Cover Date.