Analysis of free vibrations for Rayleigh — Lamb waves in a microstretch thermoelastic plate with two relaxation times

The propagation of free vibrations in a microstretch thermoelastic homogeneous isotropic plate subjected to stress-free thermally insulated and isothermal conditions is investigated in the context of conventional coupled thermoelasticity (CT) and Green and Lindsay (G—L) theories of thermoelasticity. The secular equations for the microstretch thermoelastic plate in closed form for symmetric and skew-symmetric wave mode propagation in completely separate terms are derived. At short wavelength limits, the secular equations for both modes in a stress-free thermally insulated and isothermal homogeneous isotropic microstretch thermoelastic plate reduce to the Rayleigh surface wave frequency equation. The results for symmetric and skew-symmetric wave modes are computed numerically and presented graphically. The theory and numerical computations are found to be in close agreement. Published in Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 36–46, January–February, 2009.     

Passage of an electromagnetic pulse through a layer of homogeneous plasma (exact solution)

The authors found an exact analytical solution of the problems on reflected and transmitted waves in interaction of a short electromagnetic pulse with a plasma layer of finite extension. The problem is solved assuming the linearity of material equations. Analytical expressions of Green functions are obtained for the corresponding problems that allow one to write solutions for the transmitted and reflected waves with any shape of an incident wave. The exact solutions depend substantially on the plasma density and layer extension, which makes it possible to use them in processing experimental results for extraction of the above-mentioned parameters. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 3, pp. 567–574, May–June, 2000.     

Reliability studies of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu soldered joints with aging treatment

In this study, the interfacial reactions and joint reliabilities of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu were investigated during isothermal aging at 150 °C for aging times of up to 1,000 h. Cu₅Zn₈ IMCs layer is formed at the as-soldered Sn–9Zn/Cu interface. Adding 0.3wt.% Ag results in the adsorption of AgZn₃ on the Cu₅Zn₈ IMCs layer. The as-soldered Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu joints have sufficient pull strength. The thickness of the IMCs layer formed at the interface of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu both increase with increasing aging time. Correspondingly, both the pull forces of the Sn–9Zn and Sn–9Zn–0.3Ag soldered joints gradually decrease as the aging time prolonged. However, the thickness of the IMCs layer of Sn–9Zn–0.3Ag/Cu increases much slower than that of Sn–9Zn/Cu and the pull force of Sn–9Zn–0.3Ag soldered joint decreases much slower than that of Sn–9Zn soldered joint. After aging for 1,000 h, some Cu–Sn IMCs form between the Cu₅Zn₈ IMC and the Cu substrate, many voids form at the interface between the Cu₅Zn₈ layer and solder alloy, and some cracks form in the Cu₅Zn₈ IMCs layer of Sn–9Zn/Cu. The pull force Sn–9Zn soldered joint decreases by 53.1% compared to the pull force measured after as-soldered. Fracture of Sn–9Zn/Cu occurred on the IMCs layer on the whole and the fracture micrograph implies a brittle fracture. While the pull force of Sn–9Zn–0.3Ag soldered joint decreases by 51.7% after aging at 150 °C for 1,000 h. The fracture mode of Sn–9Zn–0.3Ag soldered joint is partially brittle at the IMCs layer, and partially ductile at the outer ring of the solder.     

Properties of a silicon surface exposed to nanosecond laser-radiation pulses

Results of the use of nanosecond laser pulses in the technology of production of very-large-scale integration circuits are presented. It is shown that, depending on the conditions of processing of silicon by these pulses, they can avoid mechanical failure of the silicon crystal lattice and form a gettering layer that cleans the silicon from impurities. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 3, pp. 592–595, May–June, 2008.     

New integral representations of analytical solutions to boundary-value problems of nonstationary transfer in regions with moving boundaries

This article surveys the development of a Green function method in solving boundary-value problems of nonstationary transfer in a region with a moving boundary. For a uniform law of boundary displacement, a modification of the thermal-potential method is suggested that leads to analytical solutions in a new (simplest) integral form. M. V. Lomonosov Moscow Institute of Precision Chemical Technology, Moscow, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 72, No. 5, pp. 825–836, September–October, 1999.     

Interfacial reactions between Sn-3.5 Ag solder and Ni–W alloy films

Nickel based alloys are currently being investigated in an effort to develop stable barrier films between lead free solder and copper substrate. In this study, interfacial reactions between Ni–W alloy films and Sn-3.5 Ag solder have been investigated. Ni–W alloys films with tungsten content in the range of 5.0–18.0 at.% were prepared on copper substrate by electrodeposition in ammonia citrate bath. Solder joints were prepared on the Ni–W coated substrate at a reflow temperature of 250 °C. The solder joint interface was investigated by Cross-sectional scanning electron microscopy, energy dispersive X-ray spectroscopy and electron back scatter diffraction. It has been observed that a Ni₃Sn₄ layer with faceted morphology formed on the Ni–W alloy film after reflow. The thickness of the bright layer was found to decrease with the increase of tungsten content in the Ni–W film. An additional layer with a bright appearance was also found to form below the Ni₃Sn₄ layer. The bright layer was identified to be a ternary phase containing Sn, W and Ni. The bright layer is found to be amorphous and is suggested to have formed through solid state amorphization caused by anomalously fast diffusion of Sn into Ni–W film.     

Use of the method of green functions for numerical solution of multidimensional stefan problems

It is shown that use of an auxiliary Green function, namely, the Green function of the boundary-value problem for the Laplace operator with a condition of the third kind artificially introduced on part of the boundary, makes it possible to find numerical solutions of multidimensional Stefan problems with any boundary conditions. The efficiency of the method is verified for a Stefan problem that has an exact solution. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 5, pp. 910–916, September–October, 1998.     

Nucleation and growth mechanism of apatite on a bioactive and degradable ceramic/polymer composite with a thick polymer layer

Nucleation and growth mechanism of apatite on a bioactive and degradable PLLA/SiO₂–CaO composite with a thick PLLA surface layer were investigated compared to that on a bioactive but non-degradable polyurethane (PU)/SiO₂–CaO composite with a thick PU surface layer. The bioactive SiO₂–CaO particles were made by a sol–gel method from tetraethyl orthosilicate and calcium nitrate tetrahydrate under acidic condition followed by heat treatment at 600 °C for 2 h. The PLLA/SiO₂–CaO and PU/SiO₂–CaO composites were then prepared by a solvent casting method which resulted in thick PLLA and PU surface layers, respectively, due to precipitation of SiO₂–CaO particles during the casting process. Two composites were exposed to SBF for 1 week and this exposure led to form uniform and complete apatite coating layer on the PLLA/SiO₂–CaO composite but not on the PU/SiO₂-CaO composite. These results were interpreted in terms of the degradability of the polymers. A practical implication of the results is that a post-surface grinding or cutting processes to expose bioactive ceramics to the surface of a composite with a thick biodegradable polymer layer is not required for providing apatite forming ability, which has been considered as one of the pragmatic obstacles for the application as a bone grafting material.     

Wettability of NiAl by a liquid Ni–Si–B alloy

An investigation of the wettability of the intermetallic compound NiAl by a liquid Ni–4.5 wt% Si–3.2 wt% B filler metal is presented in this paper. Dynamic observations of spreading of Ni–Si–B droplets, conducted using hot-stage light microscopy, are correlated with post-cooling microscopy and analysis. The paper examines the influence of the oxide layer on the NiAl substrates, on the progression of spreading of the Ni–Si–B liquid. Termination of spreading of the Ni–Si–B droplets by the onset of isothermal solidification at the spreading front is considered. Spreading of the Ni–Si–B droplets was found to be rapid until the onset of isothermal solidification at the spreading front. However, once isothermal solidification commenced, negligible further spreading was observed. The Ni–Si–B filler metal was observed to spread by undermining of the substrate oxide. However, a marked reaction occurred between the substrate oxide and the Ni–Si–B filler metal. This reaction served to remove the substrate oxide layer. The paper contrasts the mechanisms of substrate oxide undermining and isothermal solidification of liquid Ni–Si–B droplets on NiAl with those occurring during the spreading of the same liquid on pure nickel and Ni–Cr alloys. This revised version was published online in November 2006 with corrections to the Cover Date.     

Spectral characteristics of a spherical radiometer and its role in radiometric calibration of optoelectronic radiating elements

A method of calculating the values of the spectral diffuse reflectance of the coatings of the interior walls of photometric spheres is proposed. Results are presented from calculations for different types of photometric spheres coated with a layer of polytetrafluoroethylene. The influence of the form of the spectral sensitivity function of spherical radiometers on the error of radiometric calibration of optoelectronic radiating elements is demonstrated. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 33–34, March, 1998.     

Metal–ceramic composite layers on stainless steel through the combination of electrophoretic deposition and galvanic processes

The use of metal–ceramic composite layers is of considerable technical interest for many areas of application. The use of electrochemical processes makes it possible to realize coatings on stainless steel which combine the properties of the metals with those of ceramics in an outstanding manner. The process presented here is based on a combination of electrophoretic and electrolytic deposition. At the same time, a very high ceramic ratio is attained in comparison to electrolytic dispersion depositions. It was therefore possible to achieve both nickel–zirconium oxide as well as a copper–zirconium oxide coatings with strong adhesive bonds on stainless steel. A preliminary nickel plating or preliminary copper plating of the stainless steel substrate was first realized. A nanoscale zirconium oxide powder (Tosoh TZ-8Y) from an ethanolic suspension was then applied electrophoretically onto this layer and sintered to an open-porous layer with a porosity of 40–50%. After this, the metal was galvanically infiltrated into the pores. An annealing process was then carried out to improve the layer bonding. Solid-state physical tests reveal that a good material bonding of the composite layer onto the substrate occurred as a result of diffusion processes. Metal–ceramic composite layers can be produced through a combination of electrophoretic and electroplating technology with strongly bond on the substrate by a final heat treatment.     

Practical mathematical representation of the flow due to a distribution of sources on a steadily advancing ship hull

A practical mathematical representation of the flow velocity due to a distribution of sources on the mean wetted hull surface and the mean waterline of a ship that steadily advances along a straight path in calm water, of large depth and lateral extent, is presented. A main feature of this flow representation is a simple analytical approximation—valid within the entire flow region—to the local flow component in the expression for the gradient of the Green function associated with the classical Kelvin–Michell linearized free-surface boundary condition. Another notable feature of the flow representation is that the singularity associated with the gradient of the Green function is removed, using a straightforward regularization technique. The flow representation only involves elementary continuous functions (algebraic, exponential and trigonometric) of real arguments. These functions can then be integrated using ordinary Gaussian quadrature rules. Thus, the flow representation is particularly simple and well suited for practical flow calculations. The specific case of a low-order panel method—in which the hull geometry, the source density, and the flow velocity are consistently represented via piecewise linear approximations within flat triangular hull panels or straight waterline segments—is considered.     

Influence of minor Bi additions on the interfacial morphology between Sn–Zn–xBi solders and a Cu layer

The influence of minor Bi additions on the interfacial morphology between Sn–Zn–xBi (x = 0, 1, 3) solders and a Cu layer after reflowing were investigated by microstructural observations. The addition of minor amount of Bi into Sn–Zn solder reduced the tendency to form cracks at the solder/Cu interface. This is because alloying with Bi reduced the mismatch of the coefficient of thermal expansion (CTE) between the solder alloys and the Cu plate. Moreover, the Sn–Zn solder with Bi reduced the melting temperature of the solder alloy, and, this resulted in the coarsening of the gains and thickening of the intermetallic compound (IMC) layers because solder alloys with a lower melting temperature experienced a longer molten period during reflow. Because the Bi atoms accumulated at the surface of the IMC layers in homogeneously, partially impeding the IMC dissolving into the molten solder, a serrated-like Cu–Zn–Sn IMC layer was formed at the Sn–8Zn–3Bi/Cu interface.     

Formation of hydroxyapatite layer on bioactive Ti and Ti–6Al–4V by simple chemical technique

Bioactive coatings on cp-Ti and Ti–6Al–4V were prepared by a simple chemical technique. Specimens of cp-Ti and Ti–6Al–4V were initially immersed in a 5 M NaOH solution at 60 °C for 24 h which resulted in the formation of a porous network structure composed of Na₂Ti₅O₁₁ and TiO₂. The specimens were then immersed in a Ca-rich solution either at 60 °C or at 36.5 °C for 24 h. During this treatment Na⁺ was released and Ti–OH groups were formed. Subsequently, TiO₂ dissociated from the Ti–OH group and combined with calcium ions to form calcium titanate (CaTiO₃), which was embedded in a titania gel layer during the immersion period. The specimens were then immersed in r-SBF at 36.5 °C for 1–30 days. After immersion in r-SBF for 3 days, HAp (hydroxyapatite) spheroids began to deposit on the substrates, and within a week the surfaces were covered. The HAp spheroids were 5 μm in size with a Ca/P ratio of 1.68 which was close to bone-like apatite (1.67). The average thicknesses of HAp layer after immersion in r-SBF for 3 days, 1 week, and 2 weeks were 3.8, 5.6, and 6.4 μm, respectively. A scratch test, used to evaluate the adhesive strength of the HAp layer, showed that the HAp layer was not scraped off until the applied load reached 26 N.     

Method for calculating the spectrum of scattered photons under conditions of aerialγ-mapping

An analytical method for calculating the spectrum of multiply scattered γ-radiation of radioactive isotopes distributed in soil is proposed. Expressions for intensities of fluxes of photons scattered n times are obtained in the form of sums of multiple integrals of a simple form. The integration is performed numerically. Results of calculations of test examples are presented. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 3, pp. 551–558, May–June, 1998.     

Harmonic oscillations of a layer excited by concentrated sources

We determine the wave fields of displacements and stresses in a layer harmonically excited by sources concentrated along a line. The components of the fields are represented in the form of series whose coefficients are expressed in the closed form via the Hankel cylindrical functions. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 75–80, September–October, 2006.     

In vitro corrosion behaviour of Ti–Nb–Sn shape memory alloys in Ringer’s physiological solution

The nearly equiatomic Ni–Ti alloy (Nitinol) has been widely employed in the medical and dental fields owing to its shape memory or superelastic properties. The main concern about the use of this alloy derives form the fact that it contains a large amount of nickel (55% by mass), which is suspected responsible for allergic, toxic and carcinogenic reactions. In this work, the in vitro corrosion behavior of two Ti–Nb–Sn shape memory alloys, Ti–16Nb–5Sn and Ti–18Nb–4Sn (mass%) has been investigated and compared with that of Nitinol. The in vitro corrosion resistance was assessed in naturally aerated Ringer’s physiological solution at 37°C by corrosion potential and electrochemical impedance spectroscopy (EIS) measurements as a function of exposure time, and potentiodynamic polarization curves. Corrosion potential values indicated that both Ni–Ti and Ti–Nb–Sn alloys undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the aggressive environment. It also indicated that the tendency for the formation of a spontaneous oxide is greater for the Ti–18Nb–5Sn alloy. Significantly low anodic current density values were obtained from the polarization curves, indicating a typical passive behaviour for all investigated alloys, but Nitinol exhibited breakdown of passivity at potentials above approximately 450 mV(SCE), suggesting lower corrosion protection characteristics of its oxide film compared to the Ti–Nb–Sn alloys. EIS studies showed high impedance values for all samples, increasing with exposure time, indicating an improvement in corrosion resistance of the spontaneous oxide film. The obtained EIS spectra were analyzed using an equivalent electrical circuit representing a duplex structure oxide film, composed by an outer and porous layer (low resistance), and an inner barrier layer (high resistance) mainly responsible for the alloys corrosion resistance. The resistance of passive film present on the metals’ surface increases with exposure time displaying the highest values to Ti–18Nb–4Sn alloy. All these electrochemical results suggest that Ti–Nb–Sn alloys are promising materials for biomedical applications.     

The formation and evolution of intermetallic compounds formed between Sn–Ag–Zn–In lead-free solder and Ni/Cu substrate

The formation and evolution of intermetallic compounds (IMCs) layer between the Sn–3.7Ag–1.0–In–0.9Zn lead-free solder and Ni/Cu substrate were investigated for different reflow time. The morphology and thickness of the IMCs layer formed at the interface varies apparently with increasing the reflow time. At the early reflow stage, a thin continuous Ni₃Sn₄ dissolved with small amount of Cu is observed. As the reflow time going on, a thick Sn–Ni–Cu ternary intermediate compound layer is formed at the interface after the plated Ni layer is consumed totally. When the reflow time is long enough, a final Cu₆Sn₅ IMC layer dissolved with minor Ni will be formed. The IMCs layer grows very slowly until the plated Ni layer was completely consumed. Once the plated Ni layer disappears, the corresponding growth rate of the IMC layer increases apparently.     

TLP bonding of SiCp/2618Al composites using mixed Al–Ag–Cu system powders as interlayers

Mixed Al–Ag–Cu and Al–Ag–Cu–Ti powders were used as interlayers for transient liquid phase diffusion bonding (TLP bonding) of SiC particulate reinforced 2618 aluminum alloy matrix composite (SiCp/2618Al MMC). The results show that by using mixed Al–Ag–Cu powder with the eutectic composition as an interlayer, SiCp/2618Al MMC can be TLP bonded at 540 °C, however, the joining layer is porous. Adding a certain amount of titanium into the Al–Ag–Cu interlayer, the TLP bonding quality can be improved. The titanium added into the Al–Ag–Cu interlayer has an effect of shortening the solidification time of the joining layer, thus decreasing SiC particles from the parent materials entering into the joining layer. The joints bonded using Al–Ag–Cu–Ti interlayers have a maximum shear strength of 101 MPa when 2.1% titanium is added.     

Analysis of a number of elements in the mechanism of mass entrainment of carbon material within the framework of the complete thermochemical model of its destruction

The results of a numerical solution of the equations constructed for a frozen boundary layer on the surface of a carbon material, with allowance for the complete thermochemical model of the entrainment of its mass, are presented. The results obtained are compared with the data that correspond to the use of the analogy between the processes of heat and mass transfer in a boundary layer and of the simplified model of the mass entrainment of the materials of the class considered. The results of comparison between experimental and calculated-theoretical data on the rate of destruction of the ATJ-grade graphite are also presented. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 127–133, January–February, 2009.