Material surface layer damage estimation for cyclic loading conditions using the nanoindenting and nanoscratching techniques

The nanoindenting method is based on the automatic measurement and recording of the force acting on the indenter (10⁻²-5 N) and the depth of indentation (10⁻²-200 μm). The scratch hardness or nanoscratching method is based on the continuous recording of resistance forces to movement of the indenter impressed into the surface. __________ Translated from Problemy Prochnosti, No. 4, pp. 132–139, July–August, 2006.     

Potential of short Si–Ti–C–O fiber-reinforced epoxy matrix composite as electromagnetic wave absorbing material

The effects of fiber electrical properties on electromagnetic wave absorbing potential in short Si–Ti–C–O fiber-dispersed epoxy matrix composites were studied. Six kinds of short Si–Ti–C–O fibers with different respective electrical resistivity were incorporated into an epoxy matrix and the dielectric properties of the composites in a frequency range from 1 MHz to 1 GHz were measured. The penetration depth of electromagnetic wave, which is defined as the distance to reduce 1/e of the incident electromagnetic wave power, is obtained from the measured dielectric properties. It is found that the dielectric properties of the composites are strongly dependent on the electrical resistivity of the fiber: the use of lower electrical resistivity fiber leads to a shorter penetration depth. Independent of the electrical resistivity of fiber, the penetration depth decreases with increase in the frequency. This result demonstrates the potential of the composite as a thin electromagnetic wave absorbing material.

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Analysis of the aluminum alloy resistance to the penetration of a steel rod at impact velocities of up to 500 m/s

The penetration of a steel rod into aluminum alloy plates of various thicknesses is examined. The resistance to penetration at its initial stages prior to the rod fracture is found to be determined by the dynamic strength of the plate material, its viscous component (proportional to the plastic strain rate) prevailing at impact velocities of up to 500 m/s. The depth of penetration varies with the velocity and is conditioned by wave processes in the plate, their scale being dependent on its thickness. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 5, pp. 106–110, September–October, 1998.     

Comparative estimation of mechanical properties of cemented carbides by the kinetics of penetration of a rigid punch under contact cyclic loading

We suggest a method of contact fatigue testing of cemented carbides. It involves cyclic loading of a specimen (half-space) with a flat circular punch by a pulsating compressive stress. Both the loading punch and the test specimens are made of cemented carbides. It is found that the parameters of contact fatigue of a cemented carbide include the depth of the punch penetration into the specimen, σ, after a given number of cycles, the form of the dependence of the penetration depth on the number of cycles, the number of loading cycles between abrupt changes in the growth of the σ values, and the number of these changes. With these parameters determined by laboratory tests on small specimens, we can predict the durability of large carbide components subjected in operation to contact cyclic loads. V. N. Bakul Institute for Superhard Materials, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 28–37, May–June, 1998.     

Nano-scratch as a new tool for assessing the nano-tribological behavior of cement composite

This paper presents a preliminary exploration on tribological properties of cement composite material at micro- and nano-scales by means of the nano-scratch technique, which is a new instrument overcoming the limitations of both the classical stylus scratch test and the atomic force microscope. Measurements were conducted on two very different types of material: cement clinker paste and polymer-based cement clinker. Mechanical parameters related to the nano-tribological performance, i.e. penetration depth, coefficient of friction, and elastic deformation ratio, were obtained from the scratching processes. By statistical deconvolution analysis, microstructure constituents with a large discrepancy in elastic modulus and hardness values can be captured as single peaks, but not for the mixture of C–S–H and Ca(OH)₂ phases. A reverse tendency was observed between penetration depth and coefficient of friction of both the substrate and hard particle phase embedded in. An H/E ratio dependent elasto–plastic behavior was identified, with the elastic deformation to be dominant in high H/E ratio phases. The results confirm this new technique as a promising method for quantitative characterization of elasticity, hardness and mar resistance of heterogonous phases in cement composite.     

Rapid penetration of bismuth from solid Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> along grain boundaries in Cu and Cu-based alloys

As well known, bismuth rapidly penetrates into copper grain boundaries at about 550 °C and embrittles copper. In the experiments, the authors have used solid Bi₂Te₃ for the embrittlement of pure copper and copper-based solid solutions containing iron and silver. The investigated alloys were heated in the closed volume together with Bi₂Te₃ for a short time (5–90 min) at 570 °C in the hydrogen atmosphere. Bi₂Te₃ did not contact with copper samples during annealing. After that, the samples were bent and grain boundary cracks were formed (with the depth about 10–500 μm). Experiment showed that silver accelerates the embrittlement in the contrast to iron. The cracks in the silver–copper alloys were deeper than in the iron–copper ones. It was assumed that the depth of cracks is equal to the penetration depth. The reasons for this phenomenon were discussed in terms of the impurities effect on the grain boundary segregation.     

Effect of UV radiation on the relaxation characteristics of ferroelectric thin-film capacitors

The effect of UV radiation with a wavelength near the fundamental absorption edge on the relaxation characteristics of ferroelectric capacitors based on thin (Ba,Sr)TiO₃ (BSTO) films has been studied. The absorption spectra of BSTO films with thicknesses up to 1 μm obtained by RF magnetron sputtering on sapphire substrates have been measured in a 300–600 nm wavelength range, the UV radiation penetration depth in this material was determined, and the optical bandgap width was evaluated. It is established that UV irradiation leads to a significant decrease in the relaxation time of the residual capacitance of BSTO-film-based structures. A minimum relaxation time is achieved upon the irradiation in a 350–360 nm wavelength interval.     

The influence of adhesive on the Al alloy in laser weld bonding Mg–Al process

Laser weld bonding is a new welding technology, being used to join Mg–Al alloys. The penetration depth of LWB Mg–Al joint was larger than that in simply laser welding joint in same welding parameters. The temperature at the edge of the Al fusion zone in LWB Mg–Al joint was higher than that in laser welding joint, which was measured through the thermal couples. The laser-introduced plasma in LWB Mg–Al process is observed by the high-speed camera, which is different from that in laser welding process. The surface temperature and state of the Al alloy were changed because of the addition of the adhesive, thus the laser absorptive of Al alloy was increased in LWB process, comparing with that in laser welding process; and the decomposition of the adhesive would make a depression in the Al fusion zone, which would be beneficial to the formation of keyhole welding in LWB Mg–Al joint.     

Effect of Uniaxial Pressure on the Isotope Effect on the Spectrum of Hamiltonians with Electron–Phonon Coupling

We have studied the effect of a change in the equilibrium nearest neighbour distances on the dynamics of charge and ions on a three-site cluster, identified with an O–Cu–O cluster present in high temperature superconductors. We consider a model Hamiltonian that contains an electronic part represented by a single band Hubbard model with onsite electronic correlations and a phononic part consisting of non-interacting Raman and infrared active phonons. The electron–phonon coupling is introduced through the change in interatomic distances generated by Coulomb repulsion between charges at neighbouring sites. For intermediate and strong values of the electron–phonon coupling, this model generates correlated electron–ion motion, i.e., polaron formation. In order to simulate the effect of change in the equilibrium nearest neighbour distances, we assume that the main effect such a change is a variation of the intersite electron hopping probability, t. We, therefore, studied the excitation spectrum of this model and the local lattice distortion in the Cu–O bond length as a function of t. We also studied the effect of a change in t in the polaron tunnelling energy when we use different oxygen isotopic masses, i.e., O¹⁶ and O¹⁸. We find that as function of t, the isotopic shift does not show a monotonic behaviour, as it does as a function of the electron–phonon coupling constant. It exhibits a minimum for values of t for which the electron–phonon coupling generates local lattice distortions with magnitudes similar to those observed experimentally in high-temperature superconductors. This observation could be related with the observed maximum on T _c as a function of the microstrain of the Cu–O bonds (Sanna et al. in Int. J. Mod. Phys. B 14(29–31), 2000; Bianconi et al. in J. Phys.: Condens. Matter 12:10655, 2000; Agrestini et al. in J. Phys. A: Math. Gen. 36:9133, 2003).     

Assessment of the structural-deformation inhomogeneity of a thin surface layer of materials by the method of scratching

The structural-deformation inhomogeneity of the surface layer is assessed by the method of scratching with recording the variations of the tangential force of resistance to the motion of an indenter. For the depths of penetration of the Vickers indenter comparable with the parameters of surface roughness, we determine a function used to describe the inhomogeneity of structural-deformation properties of the material along the scanning path without making into account the influence of the surface topography. __________ Translated from Problemy Prochnosti, No. 3, pp. 70–81, May–June, 2008.     

Vibrowave action on the bed and the critical area of wells with allowance for the slip effect

The model of the process is constructed and the factors influencing its mechanism are determined. It is shown that the influence of vibrowave action on the process of filtration is significantly improved in the presence of the slip effect. The depth of propagation of elastic waves in the bed as a function of their velocity is determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 358–364, March–April, 2008.     

Application of the least-squares method to the analysis of displacements and stresses in the two-dimensional problem

We solve the two-dimensional problem for a rectangular plate subjected to the action of arbitrary forces. The stress function is represented in the form of a series in eigenfunctions. By the least-squares method, the problem of finding the coefficients of expansion is reduced to the determination of the minimum of a special quadratic form. The proposed method enables one to satisfy the boundary conditions with an error of at most 10⁻³. The stress-strain state of the plate under the action of a model point force is computed. The formula for the approximate evaluation of displacements is deduced. The regularities of the distributions of normal stresses, displacements, and strains are established for the plate loaded by local forces. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 4, pp. 21–25, July–August, 2008.     

Pressure and motion of dry sand: translation of Hagen’s paper from 1852

In a remarkable paper from 1852, Gotthilf Heinrich Ludwig Hagen measured and explained two fundamental aspects of granular matter: The first effect is the saturation of pressure with depth in a static granular system confined by silo walls – generally known as the Janssen effect. The second part of his paper describes the dynamics observed during the flow out of the container – today often called the Beverloo law – and forms the foundation of the hourglass theory. A translation of the original 1852 paper is presented after a brief introduction.     

The effect of chromate pigment on the protective properties of an epoxy prime coat

Conclusions The protective function of strontium chromate pigment in the epoxy prime coat on the galvanized steel is manifested simultaneously with penetration of the corrosive medium to the metal surface and consists of an increase (by an order of magnitude) in polarization resistance and inhibition of corrosion of the galvanized steel at the places of through defects of the polymer coating. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 5, pp. 111–113, September–October, 1999.     

Breakthrough of a composite obstacle by high-velocity particles as a result of realization of the superdeep-penetration effect

The results of investigations of the superdeep penetration of high-velocity microparticles into composite obstacles in the process of their collisions are presented. It is shown that the penetration process can be controlled, in principle. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 2, pp. 35–38, March–April, 2006.     

Measurements of the Thermal Effusivity of a Drop-Size Liquid Using the Pulse Transient Hot-Strip Technique

The thermal effusivity of drop-size liquids was measured by the pulse transient hot-strip technique. A strip sensor, used as a thermometer and heat source, is deposited on a smooth surface of an electrically insulating background material – onto which an insulating liquid sample is applied, completely covering the strip probe. Experiments can be made controlling the thermal penetration depth to within some 10 μm of the liquid sample – here demonstrated by measuring a drop of water at about 1% uncertainty. Measurements were made on water and a series of silicone oils (kinematic viscosity from 5 to 50 cSt; 1 cSt = 10⁻⁶ m²· s⁻¹) in microgravity conditions using a 10 m drop tower (10⁻³ g, 1.4 s), to investigate if any potential natural convection in the liquid at normal gravity condition is present, influencing the results. However, no such influence was observed. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Motion of particles through the interface of different-density metal specimens under the conditions of superdeep penetration

The parameters of motion of particles in a thin layer of material adjacent to the plane boundary of two semi-infinite specimens of different densities under the conditions of superdeep penetration are calculated on the basis of the hydrodynamic model. Results of the calculations are checked experimentally. The efficiency of superdeep penetration for different-density materials (aluminum, steel, copper) and their combinations is determined. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 5, pp. 1050–1055, September–October, 2000.     

Nanohybrid scratch resistant coatings for teeth and bone viscoelasticity manifested in tribology

We cover teeth surfaces with nanohybrid coatings containing an inorganic ceramic and an organic copolymer constituents. We report the first ever values of scratch penetration depth and scratch recovery for bare and coated teeth. We find that uncoated teeth undergo viscoelastic recovery (healing) after microscratching – the first manifestation of bone viscoelasticity in tribology. The coatings fill "valleys" in teeth surfaces. In each case a large improvement in the scratch resistance as compared to uncoated teeth is seen. The extent of the improvement depends on the inorganic/organic component ratios in the nanohybrids. Electronic Publication     

Propagation characteristics of plane waves of defects in a viscoplastic medium

It is shown that dispersion is not observed in the propagation of a weakly damped wave, and dissipation is frequency-dependent. For strongly damped waves, dispersion and dissipation are observed. However, a wave in a viscoplastic medium decays over very short distances and the penetration depth of strongly damped waves of defects is bounded by the skinlayer thickness. Pis’ma Zh. Tekh. Fiz. 25, 91–94 (September 26, 1999)     

Some features of the kinetics of high-speed penetration in brittle media

The kinetics of the high-speed penetration of deformable rods into ceramics has been investigated. It is established that penetration takes place by a two-stage process. In the first stage the penetration velocity increases with increasing damage to the ceramic. The second stage corresponds to quasisteady penetration into a medium devoid of strength. It is shown that the first stage determines the high level of resistance of ceramics to high-intensity impact loading. Pis’ma Zh. Tekh. Fiz. 23, 68–73 (February 12, 1997)